IETF MANET Working Group David B. Johnson, Rice University INTERNET-DRAFT David A. Maltz, AON Networks 17 November 2000 Yih-Chun Hu, Carnegie Mellon University Jorjeta G. Jetcheva, Carnegie Mellon University The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026 except that the right to produce derivative works is not granted. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft is a submission to the IETF Mobile Ad Hoc Networks (MANET) Working Group. Comments on this draft may be sent to the Working Group at manet@itd.nrl.navy.mil, or may be sent directly to the authors. Johnson, et al Expires 17 May 2001 [Page i] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Abstract The Dynamic Source Routing protocol (DSR) is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes. DSR allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration. The protocol is composed of the two mechanisms of "Route Discovery" and "Route Maintenance", which work together to allow nodes to discover and maintain source routes to arbitrary destinations in the ad hoc network. The use of source routing allows packet routing to be trivially loop-free, avoids the need for up-to-date routing information in the intermediate nodes through which packets are forwarded, and allows nodes forwarding or overhearing packets to cache the routing information in them for their own future use. All aspects of the protocol operate entirely on-demand, allowing the routing packet overhead of DSR to scale automatically to only that needed to react to changes in the routes currently in use. This document specifies the operation of the DSR protocol for routing unicast IP packets in multi-hop wireless ad hoc networks. Johnson, et al Expires 17 May 2001 [Page ii] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Contents Status of This Memo i Abstract ii 1. Introduction 1 2. Assumptions 3 3. DSR Protocol Overview 5 3.1. Basic DSR Route Discovery . . . . . . . . . . . . . . . . 5 3.2. Basic DSR Route Maintenance . . . . . . . . . . . . . . . 7 3.3. Additional Route Discovery Features . . . . . . . . . . . 8 3.3.1. Caching Overheard Routing Information . . . . . . 8 3.3.2. Replying to Route Requests using Cached Routes . 9 3.3.3. Preventing Route Reply Storms . . . . . . . . . . 10 3.3.4. Route Request Hop Limits . . . . . . . . . . . . 12 3.4. Additional Route Maintenance Features . . . . . . . . . . 12 3.4.1. Packet Salvaging . . . . . . . . . . . . . . . . 12 3.4.2. Automatic Route Shortening . . . . . . . . . . . 13 3.4.3. Increased Spreading of Route Error Messages . . . 14 4. Conceptual Data Structures 15 4.1. Route Cache . . . . . . . . . . . . . . . . . . . . . . . 15 4.2. Route Request Table . . . . . . . . . . . . . . . . . . . 17 4.3. Send Buffer . . . . . . . . . . . . . . . . . . . . . . . 18 4.4. Retransmission Buffer . . . . . . . . . . . . . . . . . . 19 5. Packet Formats 20 5.1. Destination Options Header . . . . . . . . . . . . . . . 21 5.1.1. DSR Route Request Option . . . . . . . . . . . . 22 5.2. Hop-by-Hop Options Header . . . . . . . . . . . . . . . . 24 5.2.1. DSR Route Reply Option . . . . . . . . . . . . . 25 5.2.2. DSR Route Error Option . . . . . . . . . . . . . 27 5.2.3. DSR Acknowledgment Option . . . . . . . . . . . . 29 5.3. DSR Routing Header . . . . . . . . . . . . . . . . . . . 30 6. Detailed Operation 33 6.1. General Packet Processing . . . . . . . . . . . . . . . . 33 6.1.1. Originating a Packet . . . . . . . . . . . . . . 33 6.1.2. Adding a DSR Routing Header to a Packet . . . . . 34 6.1.3. Receiving a Packet . . . . . . . . . . . . . . . 36 6.1.4. Processing a Routing Header in a Received Packet 38 6.2. Route Discovery Processing . . . . . . . . . . . . . . . 40 6.2.1. Originating a Route Request . . . . . . . . . . . 40 Johnson, et al Expires 17 May 2001 [Page iii] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.2.2. Processing a Received Route Request Option . . . 42 6.2.3. Generating Route Replies using the Route Cache . 43 6.2.4. Originating a Route Reply . . . . . . . . . . . . 45 6.2.5. Processing a Route Reply Option . . . . . . . . . 46 6.3. Route Maintenance Processing . . . . . . . . . . . . . . 47 6.3.1. Using Network-Layer Acknowledgments . . . . . . . 47 6.3.2. Using Link Layer Acknowledgments . . . . . . . . 48 6.3.3. Originating a Route Error . . . . . . . . . . . . 48 6.3.4. Processing a Route Error Option . . . . . . . . . 49 6.3.5. Salvaging a Packet . . . . . . . . . . . . . . . 49 7. Constants 50 8. IANA Considerations 51 9. Security Considerations 52 Appendix A. Location of DSR in the ISO Network Reference Model 53 Appendix B. Implementation and Evaluation Status 54 Acknowledgements 55 References 56 Chair's Address 59 Authors' Addresses 60 Johnson, et al Expires 17 May 2001 [Page iv] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 1. Introduction The Dynamic Source Routing protocol (DSR) [12, 13] is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes. Using DSR, the network is completely self-organizing and self-configuring, requiring no existing network infrastructure or administration. Network nodes cooperate to forward packets for each other to allow communication over multiple "hops" between nodes not directly within wireless transmission range of one another. As nodes in the network move about or join or leave the network, and as wireless transmission conditions such as sources of interference change, all routing is automatically determined and maintained by the DSR routing protocol. Since the number or sequence of intermediate hops needed to reach any destination may change at any time, the resulting network topology may be quite rich and rapidly changing. The DSR protocol allows nodes to dynamically discover a source route across multiple network hops to any destination in the ad hoc network. Each data packet sent then carries in its header the complete, ordered list of nodes through which the packet will pass, allowing packet routing to be trivially loop-free and avoiding the need for up-to-date routing information in the intermediate nodes through which the packet is forwarded. By including this source route in the header of each data packet, other nodes forwarding or overhearing any of these packets may also easily cache this routing information for future use. In designing DSR, we sought to create a routing protocol that had very low overhead yet was able to react quickly to changes in the network. The DSR protocol provides highly reactive service to help ensure successful delivery of data packets in spite of node movement or other changes in network conditions. The DSR protocol is composed of two mechanisms that work together to allow the discovery and maintenance of source routes in the ad hoc network: - Route Discovery is the mechanism by which a node S wishing to send a packet to a destination node D obtains a source route to D. Route Discovery is used only when S attempts to send a packet to D and does not already know a route to D. - Route Maintenance is the mechanism by which node S is able to detect, while using a source route to D, if the network topology has changed such that it can no longer use its route to D because a link along the route no longer works. When Route Maintenance indicates a source route is broken, S can attempt to use any other route it happens to know to D, or can invoke Route Discovery again to find a new route for subsequent packets to D. Johnson, et al Expires 17 May 2001 [Page 1] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Route Maintenance for this route is used only when S is actually sending packets to D. In DSR, Route Discovery and Route Maintenance each operate entirely "on demand". In particular, unlike other protocols, DSR requires no periodic packets of any kind at any level within the network. For example, DSR does not use any periodic routing advertisement, link status sensing, or neighbor detection packets, and does not rely on these functions from any underlying protocols in the network. This entirely on-demand behavior and lack of periodic activity allows the number of overhead packets caused by DSR to scale all the way down to zero, when all nodes are approximately stationary with respect to each other and all routes needed for current communication have already been discovered. As nodes begin to move more or as communication patterns change, the routing packet overhead of DSR automatically scales to only that needed to track the routes currently in use. Network topology changes not affecting routes currently in use are ignored and do not cause reaction from the protocol. In response to a single Route Discovery (as well as through routing information from other packets overheard), a node may learn and cache multiple routes to any destination. This allows the reaction to routing changes to be much more rapid, since a node with multiple routes to a destination can try another cached route if the one it has been using should fail. This caching of multiple routes also avoids the overhead of needing to perform a new Route Discovery each time a route in use breaks. The operation of both Route Discovery and Route Maintenance in DSR are designed to allow uni-directional links and asymmetric routes to be easily supported. In particular, as noted in Section 2, in wireless networks, it is possible that a link between two nodes may not work equally well in both directions, due to differing antenna or propagation patterns or sources of interference. DSR allows such uni-directional links to be used when necessary, improving overall performance and network connectivity in the system. This document specifies the operation of the DSR protocol for routing unicast IP packets in multi-hop wireless ad hoc networks. Advanced, optional features, such as Quality of Service (QoS) support and efficient multicast routing, are covered in other documents. The specification of DSR in this document provides a compatible base on which such features can be added, either independently or by integration with the DSR operation specified here. The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [4]. Johnson, et al Expires 17 May 2001 [Page 2] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 2. Assumptions We assume that all nodes wishing to communicate with other nodes within the ad hoc network are willing to participate fully in the protocols of the network. In particular, each node participating in the network SHOULD also be willing to forward packets for other nodes in the network. The diameter of an ad hoc network is the minimum number of hops necessary for a packet to reach from any node located at one extreme edge of the ad hoc network to another node located at the opposite extreme. We assume that this diameter will often be small (e.g., perhaps 5 or 10 hops), but may often be greater than 1. Packets may be lost or corrupted in transmission on the wireless network. We assume that a node receiving a corrupted packet can detect the error and discard the packet. Nodes within the ad hoc network MAY move at any time without notice, and MAY even move continuously, but we assume that the speed with which nodes move is moderate with respect to the packet transmission latency and wireless transmission range of the particular underlying network hardware in use. In particular, DSR can support very rapid rates of arbitrary node mobility, but we assume that nodes do not continuously move so rapidly as to make the flooding of every individual data packet the only possible routing protocol. A common feature of many network interfaces, including most current LAN hardware for broadcast media such as wireless, is the ability to operate the network interface in "promiscuous" receive mode. This mode causes the hardware to deliver every received packet to the network driver software without filtering based on link-layer destination address. Although we do not require this facility, some of our optimizations can take advantage of its availability. Use of promiscuous mode does increase the software overhead on the CPU, but we believe that wireless network speeds are more the inherent limiting factor to performance in current and future systems; we also believe that portions of the protocol are suitable for implementation directly within a programmable network interface unit to avoid this overhead on the CPU [13]. Use of promiscuous mode may also increase the power consumption of the network interface hardware, depending on the design of the receiver hardware, and in such cases, DSR can easily be used without the optimizations that depend on promiscuous receive mode, or can be programmed to only periodically switch the interface into promiscuous mode. Use of promiscuous receive mode is entirely optional. Wireless communication ability between any pair of nodes can at times not work equally well in both directions, due for example to differing antenna or propagation patterns or sources of interference Johnson, et al Expires 17 May 2001 [Page 3] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 around the two nodes [1, 17]. That is, wireless communications between each pair of nodes will in many cases be able to operate bi-directionally, but at times the wireless link between two nodes may be only uni-directional, allowing one node to successfully send packets to the other while no communication is possible in the reverse direction. Although many routing protocols operate correctly only over bi-directional links, DSR can successfully discover and forward packets over paths that contain uni-directional links. Some MAC protocols, however, such as MACA [16], MACAW [2], or IEEE 802.11 [10], limit unicast data packet transmission to bi-directional links, due to the required bi-directional exchange of RTS and CTS packets in these protocols and due to the link-level acknowledgement feature in IEEE 802.11; when used on top of MAC protocols such as these, DSR can take advantage of additional optimizations, such as the easy ability to reverse a source route to obtain a route back to the origin of the original route. The IP address used by a node using the DSR protocol MAY be assigned by any mechanism (e.g., static assignment or use of DHCP for dynamic assignment [8]), although the method of such assignment is outside the scope of this specification. Johnson, et al Expires 17 May 2001 [Page 4] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 3. DSR Protocol Overview 3.1. Basic DSR Route Discovery When some node S originates a new packet destined to some other node D, it places in the header of the packet a source route giving the sequence of hops that the packet is to follow on its way to D. Normally, S will obtain a suitable source route by searching its "Route Cache" of routes previously learned, but if no route is found in its cache, it will initiate the Route Discovery protocol to dynamically find a new route to D. In this case, we call S the "initiator" and D the "target" of the Route Discovery. For example, suppose a node A is attempting to discover a route to node E. The Route Discovery initiated by node A in this example would proceed as follows: ^ "A" ^ "A,B" ^ "A,B,C" ^ "A,B,C,D" | id=2 | id=2 | id=2 | id=2 +-----+ +-----+ +-----+ +-----+ +-----+ | A |---->| B |---->| C |---->| D |---->| E | +-----+ +-----+ +-----+ +-----+ +-----+ | | | | v v v v To initiate the Route Discovery, node A transmits a "Route Request" message as a single local broadcast packet, which is received by (approximately) all nodes currently within wireless transmission range of A, including node B in this example. Each Route Request message identifies the initiator and target of the Route Discovery, and also contains a unique request identification (2, in this example), determined by the initiator of the Request. Each Route Request also contains a record listing the address of each intermediate node through which this particular copy of the Route Request message has been forwarded. This route record is initialized to an empty list by the initiator of the Route Discovery. In this example, the route record initially lists only node A. When another node receives a Route Request (such as node B in this example), if it is the target of the Route Discovery, it returns a "Route Reply" message to the initiator of the Route Discovery, giving a copy of the accumulated route record from the Route Request; when the initiator receives this Route Reply, it caches this route in its Route Cache for use in sending subsequent packets to this destination. Otherwise, if this node receiving the Route Request has recently seen another Route Request message from this initiator bearing this same request identification and target address, or if it finds that its own address is already listed in the route record in the Route Request message, it discards the Request. Otherwise, this node appends its own address to the route record in the Route Request Johnson, et al Expires 17 May 2001 [Page 5] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 message and propagates it by transmitting it as a local broadcast packet (with the same request identification). In this example, node B broadcast the Route Request, which is received by node C; nodes C and D each also broadcast the Request in turn, resulting in a copy of the Request being received by node E. In returning the Route Reply to the initiator of the Route Discovery, such as node E replying back to A in this example, node E will typically examine its own Route Cache for a route back to A, and if found, will use it for the source route for delivery of the packet containing the Route Reply. Otherwise, E SHOULD perform its own Route Discovery for target node A, but to avoid possible infinite recursion of Route Discoveries, it MUST piggyback this Route Reply on its own Route Request message for A. It is also possible to piggyback other small data packets, such as a TCP SYN packet [26], on a Route Request using this same mechanism. Node E could also simply reverse the sequence of hops in the route record that it is trying to send in the Route Reply, and use this as the source route on the packet carrying the Route Reply itself. For MAC protocols such as IEEE 802.11 that require a bi-directional frame exchange as part of the MAC protocol [10], this route reversal is preferred as it avoids the overhead of a possible second Route Discovery, and it tests the discovered route to ensure it is bi-directional before the Route Discovery initiator begins using the route. However, this technique will prevent the discovery of routes using uni-directional links. In wireless environments where the use of uni-directional links is permitted, such routes may in some cases be more efficient than those with only bi-directional links, or they may be the only way to achieve connectivity to the target node. When initiating a Route Discovery, the sending node saves a copy of the original packet in a local buffer called the "Send Buffer". The Send Buffer contains a copy of each packet that cannot be transmitted by this node because it does not yet have a source route to the packet's destination. Each packet in the Send Buffer is stamped with the time that it was placed into the Buffer and is discarded after residing in the Send Buffer for some timeout period; if necessary for preventing the Send Buffer from overflowing, a FIFO or other replacement strategy MAY also be used to evict packets before they expire. While a packet remains in the Send Buffer, the node SHOULD occasionally initiate a new Route Discovery for the packet's destination address. However, the node MUST limit the rate at which such new Route Discoveries for the same address are initiated, since it is possible that the destination node is not currently reachable. In particular, due to the limited wireless transmission range and the movement of the nodes in the network, the network may at times become partitioned, meaning that there is currently no sequence of nodes Johnson, et al Expires 17 May 2001 [Page 6] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 through which a packet could be forwarded to reach the destination. Depending on the movement pattern and the density of nodes in the network, such network partitions may be rare or may be common. If a new Route Discovery was initiated for each packet sent by a node in such a situation, a large number of unproductive Route Request packets would be propagated throughout the subset of the ad hoc network reachable from this node. In order to reduce the overhead from such Route Discoveries, a node MUST use an exponential back-off algorithm to limit the rate at which it initiates new Route Discoveries for the same target. If the node attempts to send additional data packets to this same node more frequently than this limit, the subsequent packets SHOULD be buffered in the Send Buffer until a Route Reply is received giving a route to this destination, but the node MUST NOT initiate a new Route Discovery until the minimum allowable interval between new Route Discoveries for this target has been reached. This limitation on the maximum rate of Route Discoveries for the same target is similar to the mechanism required by Internet nodes to limit the rate at which ARP Requests are sent for any single target IP address [3]. 3.2. Basic DSR Route Maintenance When originating or forwarding a packet using a source route, each node transmitting the packet is responsible for confirming that the packet has been received by the next hop along the source route; the packet SHOULD be retransmitted (up to a maximum number of attempts) until this confirmation of receipt is received. For example, in the situation shown below, node A has originated a packet for node E using a source route through intermediate nodes B, C, and D: +-----+ +-----+ +-----+ +-----+ +-----+ | A |---->| B |---->| C |-- | D | | E | +-----+ +-----+ +-----+ +-----+ +-----+ In this case, node A is responsible for receipt of the packet at B, node B is responsible for receipt at C, node C is responsible for receipt at D, and node D is responsible for receipt finally at the destination E. This confirmation of receipt in many cases may be provided at no cost to DSR, either as an existing standard part of the MAC protocol in use (such as the link-level acknowledgement frame defined by IEEE 802.11 [10]), or by a "passive acknowledgement" [15] (in which, for example, B confirms receipt at C by overhearing C transmit the packet to forward it on to D). If neither of these confirmation mechanisms are available, the node transmitting the packet can explicitly request a DSR-specific software acknowledgement be returned by the next hop; this software acknowledgement will normally be transmitted Johnson, et al Expires 17 May 2001 [Page 7] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 directly to the sending node, but if the link between these two nodes is uni-directional, this software acknowledgement may travel over a different, multi-hop path. If no receipt confirmation is received after the packet has been retransmitted the maximum number of attempts by some hop, this node SHOULD return a "Route Error" message to the original sender of the packet, identifying the link over which the packet could not be forwarded. For example, in the example shown above, if C is unable to deliver the packet to the next hop D, then C returns a Route Error to A, stating that the link from C to D is currently "broken". Node A then removes this broken link from its cache; any retransmission of the original packet can be performed by upper layer protocols such as TCP, if necessary. For sending such a retransmission or other packets to this same destination E, if A has in its Route Cache another route to E (for example, from additional Route Replys from its earlier Route Discovery, or from having overheard sufficient routing information from other packets), it can send the packet using the new route immediately. Otherwise, it SHOULD perform a new Route Discovery for this target (subject to the exponential back-off described in Section 3.1). 3.3. Additional Route Discovery Features 3.3.1. Caching Overheard Routing Information A node forwarding or otherwise overhearing any packet MAY add the routing information from that packet to its own Route Cache. In particular, the source route used in a data packet, the accumulated route record in a Route Request, or the route being returned in a Route Reply MAY all be cached by any node. Routing information from any of these packets received can be cached, whether the packet was addressed to this node, sent to a broadcast (or multicast) MAC address, or received while the node's network interface is in promiscuous mode. One limitation, however, on caching of such overheard routing information is the possible presence of uni-directional links in the ad hoc network (Section 2). For example, in the situation shown below, node A is using a source route to communicate with node E: +-----+ +-----+ +-----+ +-----+ +-----+ | A |---->| B |---->| C |---->| D |---->| E | +-----+ +-----+ +-----+ +-----+ +-----+ ^ | +-----+ +-----+ +-----+ +-----+ +-----+ | V |---->| W |---->| X |---->| Y |---->| Z | +-----+ +-----+ +-----+ +-----+ +-----+ Johnson, et al Expires 17 May 2001 [Page 8] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 As node C forwards a data packet along the route from A to E, it can always add to its cache the presence of the "forward" direction links that it learns from the headers of these packets, from itself to D and from D to E. However, the "reverse" direction of the links identified in the packet headers, from itself back to B and from B to A, may not work for it since these links might be uni-directional. If C knows that the links are in fact bi-directional, for example due to the MAC protocol in use, it could cache them but otherwise SHOULD not. Likewise, node V in the example above is using a different source route to communicate with node Z. If node C overhears node X transmitting a data packet to forward it to Y (from V), node C SHOULD consider whether the links involved can be known to be bi-directional or not before caching them. If the link from X to C (over which this data packet was received) can be known to be bi-directional, then C could cache the link from itself to X, the link from X to Y, and the link from Y to Z. If all links can be assumed to be bi-directional, C could also cache the links from X to W and from W to V. Similar considerations apply to the routing information that might be learned from forwarded or otherwise overheard Route Request or Route Reply packets. 3.3.2. Replying to Route Requests using Cached Routes A node receiving a Route Request for which it is not the target, searches its own Route Cache for a route to the target of the Request. If found, the node generally returns a Route Reply to the initiator itself rather than forwarding the Route Request. In the Route Reply, it sets the route record to list the sequence of hops over which this copy of the Route Request was forwarded to it, concatenated with its own idea of the route from itself to the target from its Route Cache. However, before transmitting a Route Reply packet that was generated using information from its Route Cache in this way, a node MUST verify that the resulting route being returned in the Route Reply, after this concatenation, contains no duplicate nodes listed in the route record. For example, the figure below illustrates a case in which a Route Request for target E has been received by node F, and node F already has in its Route Cache a route from itself to E: Johnson, et al Expires 17 May 2001 [Page 9] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 +-----+ +-----+ +-----+ +-----+ | A |---->| B |- >| D |---->| E | +-----+ +-----+ \ / +-----+ +-----+ \ / \ +-----+ / >| C |- +-----+ | ^ v | Route Request +-----+ Route: A - B - C - F | F | Cache: C - D - E +-----+ The concatenation of the accumulated route from the Route Request and the cached route from F's Route Cache would include a duplicate node in passing from C to F and back to C. Node F in this case could attempt to edit the route to eliminate the duplication, resulting in a route from A to B to C to D and on to E, but in this case, node F would not be on the route that it returned in its own Route Reply. DSR Route Discovery prohibits node F from returning such a Route Reply from its cache for two reasons. First, this limitation increases the probability that the resulting route is valid, since F in this case should have received a Route Error if the route had previously stopped working. Second, this limitation means that a Route Error traversing the route is very likely to pass through any node that sent the Route Reply for the route (including F), which helps to ensure that stale data is removed from caches (such as at F) in a timely manner. Otherwise, the next Route Discovery initiated by A might also be contaminated by a Route Reply from F containing the same stale route. If the Route Request does not meet these restrictions, the node (node F in this example) discards the Route Request rather than replying to it or propagating it. 3.3.3. Preventing Route Reply Storms The ability for nodes to reply to a Route Request based on information in their Route Caches, as described in Section 3.3.2, could result in a possible Route Reply "storm" in some cases. In particular, if a node broadcasts a Route Request for a target node for which the node's neighbors have a route in their Route Caches, each neighbor may attempt to send a Route Reply, thereby wasting bandwidth and possibly increasing the number of network collisions in the area. Johnson, et al Expires 17 May 2001 [Page 10] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 For example, the figure below shows a situation in which nodes B, C, D, E, and F all receive A's Route Request for target G, and each have the indicated route cached for this target: +-----+ +-----+ | D |< >| C | +-----+ \ / +-----+ Cache: C - B - G \ / Cache: B - G \ +-----+ / -| A |- +-----+\ +-----+ +-----+ | | \--->| B | | G | / \ +-----+ +-----+ / \ Cache: G v v +-----+ +-----+ | E | | F | +-----+ +-----+ Cache: F - B - G Cache: B - G Normally, they would all attempt to reply from their own Route Caches, and would all send their Replys at about the same time since they all received the broadcast Route Request at about the same time. Such simultaneous replies from different nodes all receiving the Route Request may create packet collisions among some or all of these Replies and may cause local congestion in the wireless network. In addition, it will often be the case that the different replies will indicate routes of different lengths, as shown in this example. If a node can put its network interface into promiscuous receive mode, it SHOULD delay sending its own Route Reply for a short period, while listening to see if the initiating node begins using a shorter route first. That is, this node SHOULD delay sending its own Route Reply for a random period d = H * (h - 1 + r), where h is the length in number of network hops for the route to be returned in this node's Route Reply, r is a random number between 0 and 1, and H is a small constant delay (at least twice the maximum wireless link propagation delay) to be introduced per hop. This delay effectively randomizes the time at which each node sends its Route Reply, with all nodes sending Route Replys giving routes of length less than h sending their Replys before this node, and all nodes sending Route Replys giving routes of length greater than h sending their Replys after this node. Within the delay period, this node promiscuously receives all packets, looking for data packets from the initiator of this Route Discovery destined for the target of the Discovery. If such a data packet received by this node during the delay period uses a source route of length less than or equal to h, this node may infer that the initiator of the Route Discovery has already received a Route Reply giving an equally good or better route. In this case, Johnson, et al Expires 17 May 2001 [Page 11] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 this node SHOULD cancel its delay timer and SHOULD NOT send its Route Reply for this Route Discovery. 3.3.4. Route Request Hop Limits Each Route Request message contains a "hop limit" that may be used to limit the number of intermediate nodes allowed to forward that copy of the Route Request. This hop limit is implemented using the Time-to-Live (TTL) field in the IP header of the packet carrying the Route Request. As the Request is forwarded, this limit is decremented, and the Request packet is discarded if the limit reaches zero before finding the target. This Route Request hop limit can be used to implement a variety of algorithms for controlling the spread of a Route Request during a Route Discovery attempt. For example, a node MAY send its first Route Request attempt for some target node using a hop limit of 1, such that any node receiving the initial transmission of the Route Request will not forward it to other nodes by rebroadcasting it. This form of Route Request is called a "non-propagating" Route Request. It provides an inexpensive method for determining if the target is currently a neighbor of the initiator or if a neighbor node has a route to the target cached (effectively using the neighbors' Route Caches as an extension of the initiator's own Route Cache). If no Route Reply is received after a short timeout, then a "propagating" Route Request (i.e., with no hop limit) MAY be sent. Another possible use of the hop limit in a Route Request is to implement an "expanding ring" search for the target [13]. For example, a node could send an initial non-propagating Route Request as described above; if no Route Reply is received for it, the node could initiate another Route Request with a hop limit of 2. For each Route Request initiated, if no Route Reply is received for it, the node could double the hop limit used on the previous attempt, to progressively explore for the target node without allowing the Route Request to propagate over the entire network. However, this expanding ring search approach could have the effect of increasing the average latency of Route Discovery, since multiple Discovery attempts and timeouts may be needed before discovering a route to the target node. 3.4. Additional Route Maintenance Features 3.4.1. Packet Salvaging After sending a Route Error message as part of Route Maintenance as described in Section 3.2, a node may attempt to "salvage" the data packet that caused the Route Error rather than discarding it. To Johnson, et al Expires 17 May 2001 [Page 12] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 attempt to salvage a packet, the node sending a Route Error searches its own Route Cache for a route from itself to the destination of the packet causing the Error. If such a route is found, the node may salvage the packet after returning the Route Error by replacing the original source route on the packet with the route from its Route Cache. The node then forwards the packet to the next node indicated along this source route. For example, in the situation shown in the example of Section 3.2, if node C has another route cached to node E, it can salvage the packet by applying this route to the packet rather than discarding the packet. When salvaging a packet in this way, a count is maintained in the packet of the number of times that it has been salvaged, to prevent a single packet from being salvaged endlessly. Otherwise, it could be possible for the packet to enter a routing loop, as different nodes repeatedly salvage the packet and replace the source route on the packet with routes to each other. 3.4.2. Automatic Route Shortening Source routes in use may be automatically shortened if one or more intermediate hops in the route become no longer necessary. This mechanism of automatically shortening routes in use is somewhat similar to the use of passive acknowledgements. In particular, if a node is able to overhear a packet carrying a source route (e.g., by operating its network interface in promiscuous receive mode), then this node examines the unused portion of that source route. If this node is not the intended next hop for the packet but is named in the later unused portion of the packet's source route, then it can infer that the intermediate nodes before itself in the source route are no longer needed in the route. For example, the figure below illustrates an example in which node D has overheard a data packet being transmitted from B to C, for later forwarding to D and to E: +-----+ +-----+ +-----+ +-----+ +-----+ | A |---->| B |---->| C | | D | | E | +-----+ +-----+ +-----+ +-----+ +-----+ \ ^ \ / --------------------- In this case, this node (node D) returns a "gratuitous" Route Reply message to the original sender of the packet (node A). The Route Reply gives the shorter route as the concatenation of the portion of the original source route up through the node that transmitted the overheard packet (node B), plus the suffix of the original source route beginning with the node returning the gratuitous Route Reply (node D). In this example, the route returned in the gratuitous Route Johnson, et al Expires 17 May 2001 [Page 13] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Reply message sent from D to A gives the new route as the sequence of hops from A to B to D to E. 3.4.3. Increased Spreading of Route Error Messages When a source node receives a Route Error for a data packet that it originated, this source node propagates this Route Error to its neighbors by piggybacking it on its next Route Request. In this way, stale information in the caches of nodes around this source node will not generate Route Replys that contain the same invalid link for which this source node received the Route Error. For example, in the situation shown in the example of Section 3.2, node A learns from the Route Error message from C, that the link from C to D is currently broken. It thus removes this link from its own Route Cache and initiates a new Route Discovery (if it doesn't have another route to E in its Route Cache). On the Route Request packet initiating this Route Discovery, node A piggybacks a copy of this Route Error message, ensuring that the Route Error message spreads well to other nodes, and guaranteeing that any Route Reply that it receives (including those from other node's Route Caches) in response to this Route Request does not contain a route that assumes the existence of this broken link. Johnson, et al Expires 17 May 2001 [Page 14] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 4. Conceptual Data Structures This document describes the DSR protocol in terms of a number of conceptual data structures. This section describes each of these data structures and provides an overview of its use in the protocol. In an implementation of the protocol, these data structures MAY be implemented in any manner consistent with the external behavior described in this document. 4.1. Route Cache All routing information needed by a node participating in an ad hoc network using DSR is stored in a Route Cache. Each node in the network maintains its own Route Cache. A node adds information to its Route Cache as it learns of new links between nodes in the ad hoc network; for example, a node may learn of new links when it receives a packet carrying either a Route Reply or a DSR Routing header. Likewise, a node removes information from its Route Cache as it learns that existing links in the ad hoc network have broken; for example, a node may learn of a broken link when it receives a packet carrying a Route Error or through the link-layer retransmission mechanism reporting a failure in forwarding a packet to its next-hop destination. It is possible to interface a DSR network with other networks, external to this DSR network. Such external networks may, for example, be the Internet, or may be other ad hoc networks routed with a routing protocol other than DSR. Such external networks may also be other DSR networks that are treated as external networks in order to improve scalability. The complete handling of such external networks is beyond the scope of this document. However, this document specifies a minimal set of requirements and features necessary to allow nodes only implementing this specification to interoperate correctly with nodes implementing interfaces to such external networks. This minimal set of requirements and features involve the First Hop External (F) and Last Hop External (L) bits in a DSR Routing Header and a DSR Route Reply option, and the addition of an External flag bit tagging each node in the Route Cache, copied from the First Hop External (F) and Last Hop External (L) bits in the Routing header or Route Reply from which the link to this node was learned. The Route Cache SHOULD support storing more than one route to each destination. In searching the Route Cache for a route to some destination node, the Route Cache is indexed by destination node address. - Each implementation of DSR at any node MAY choose any appropriate strategy and algorithm for searching its Route Cache and Johnson, et al Expires 17 May 2001 [Page 15] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 selecting a "best" route to the destination from among those found. For example, a node MAY choose to select the shortest route to the destination (the shortest sequence of hops), or it MAY use an alternate metric to select the route from the Cache. - However, if there are multiple cached routes to a destination, the selection of routes when searching the Route Cache SHOULD prefer routes that do not have the External flag set on any node. This will prefer routes that lead directly to the target node instead of routes that attempt to reach the target via any external networks connected to the DSR ad hoc network. - In addition, any route selected when searching the Route Cache MUST NOT have the External bit set for any nodes other than possibly the first node, the last node, or both; the External bit MUST NOT be set for any intermediate hops in the route selected. An implementation of a Route Cache MAY provide a fixed capacity for the cache, or the cache size MAY be variable. - Each implementation of DSR at each node MAY choose any appropriate policy for managing the entries in its Route Cache, such as when limited cache capacity requires a choice of which entries to retain in the cache. For example, a node MAY chose a "least recently used" (LRU) cache replacement policy, in which the entry last used longest ago is discarded from the cache if a decision needs to be made to allow space in the cache for some new entry being added. - However, the Route Cache replacement policy SHOULD allow routes to be categorized based upon "preference", where routes with a higher preferences are less likely to be removed from the cache. For example, a node could prefer routes for which it initiated a Route Discovery over routes that it learned as the result of promiscuous snooping on other packets. In particular, a node SHOULD prefer routes that it is presently using over those that it is not. Any suitable data structure organization, consistent with this specification, MAY be used to implement the Route Cache in any node. For example, the following two types of organization are possible: - In DSR, the route returned in each Route Reply that is received by the initiator of a Route Discovery (or that is learned from the header of overhead packets, as described in Section 6.1.3) represents a complete path (a sequence of links) leading to the destination node. By caching each of these paths separately, a "path cache" organization for the Route Cache can be formed. A path cache is very simple to implement and easily guarantees that all routes are loop-free, since each individual route from Johnson, et al Expires 17 May 2001 [Page 16] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 a Route Reply or Route Request or used in a packet is loop-free. To search for a route in a path cache data structure, the sending node can simply search its Route Cache for any path (or prefix of a path) that leads to the intended destination node. This type of organization for the Route Cache in DSR has been extensively studied through simulation [5, 11, 19] and through implementation of DSR in a mobile outdoor testbed under significant workload [20, 21]. - Alternatively, a "link cache" organization could be used for the Route Cache, in which each individual link in the routes returned in Route Reply packets (or otherwise learned from the header of overhead packets) is added to a unified graph data structure of this node's current view of the network topology. To search for a route in link cache, the sending node must use a more complex graph search algorithm, such as the well-known Dijkstra's shortest-path algorithm, to find the current best path through the graph to the destination node. Such an algorithm is more difficult to implement and may require significantly more CPU time to execute. However, a link cache organization is more powerful than a path cache organization, in its ability to effectively utilize all of the potential information that a node might learn about the state of the network: links learned from different Route Discoveries or from the header of any overheard packets can be merged together to form new routes in the network, but this is not possible in a path cache due to the separation of each individual path in the cache. This type of organization for the Route Cache in DSR, including the effect of a range of implementation choices, has been studied through detailed simulation [9]. The choice of data structure organization to use for the Route Cache in any DSR implementation is a local matter for each node and affects only performance; any reasonable choice of organization for the Route Cache does not affect either correctness or interoperability. 4.2. Route Request Table The Route Request Table records information about Route Requests that were recently originated or forwarded by this node. The table is indexed by IP address. The Route Request Table on a node records the following information about nodes to which this node has initiated a Route Request: Johnson, et al Expires 17 May 2001 [Page 17] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 - The time that this node last originated a Route Discovery for that target node. - The number of consecutive Route Requests initiated for this target since receiving a valid Route Reply giving a route to that target node. - The remaining amount of time before which this node MAY next attempt at a Route Discovery for that target node. - The Time-to-Live (TTL) field used in the IP header of last Route Request initiated by this node for that target node. In addition, the Route Request Table on a node also records the following information about initiator nodes from which this node has received a Route Request: - A FIFO cache of size REQUEST_TABLE_IDS entries containing the Identification value and target address from the most recent Route Requests received by this node from that initiator node. Nodes SHOULD use an LRU policy to manage the entries in their Route Request Table. The number of Identification values to retain in each Route Request Table entry, REQUEST_TABLE_IDS, MUST NOT be unlimited, since, in the worst case, when a node crashes and reboots, the first REQUEST_TABLE_IDS Route Requests it initiates could appear to be duplicates to the other nodes in the network. 4.3. Send Buffer The Send Buffer of some node is a queue of packets that cannot be transmitted by that node because it does not yet have a source route to each respective packet's destination. Each packet in the Send Buffer is stamped with the time that it is placed into the Buffer, and SHOULD be removed from the Send Buffer and discarded SEND_BUFFER_TIMEOUT seconds after initially being placed in the Buffer. If necessary, a FIFO strategy SHOULD be used to evict packets before they timeout to prevent the buffer from overflowing. Subject to the rate limiting defined in Section 6.2, a Route Discovery SHOULD be initiated as often as possible for the destination address of any packets residing in the Send Buffer. Johnson, et al Expires 17 May 2001 [Page 18] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 4.4. Retransmission Buffer The Retransmission Buffer of a node is a queue of packets sent by this node that are awaiting the receipt of an acknowledgment from the next hop in the source route (Section 5.3). For each packet in the Retransmission Buffer, a node maintains (1) a count of the number of retransmissions and (2) the time of the last retransmission. Packets are removed from the buffer when an acknowledgment is received, or when the number of retransmissions exceeds DSR_MAXRXTSHIFT. In the later case, the removal of the packet from the Retransmission Buffer SHOULD result in a Route Error being returned to the original source of the packet (Section 6.3). Johnson, et al Expires 17 May 2001 [Page 19] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5. Packet Formats Dynamic Source Routing makes use of four options carrying control information that can be piggybacked in any existing IP packet. The mechanism used to represent these options in a packet is based on the design of the Hop-by-Hop and Destination Options mechanisms in IPv6 [7]. The ability to generate and process such options must be added to an IPv4 protocol stack. Specifically, the Protocol field in the IP header is used to indicate that a Hop-by-Hop Options extension header or Destination Options extension header follows the IP header, and the Next Header field in the extension header is used to indicate the type of protocol header (such as a transport layer header) following the extension header. In addition, DSR makes use of one additional header type, to carry the source route for a packet. This DSR Routing header is based on the design of the Routing header defined for IPv6 [7]. DSR defines a new value for the Routing Type field to distinguish a DSR Routing header from other types of Routing headers. For IPv6, all extension headers are a multiple of 8 bytes in length. However, for use in IPv4 packets, all extension headers only MUST be a multiple of 4 bytes long. This requirement preserves the alignment of any following extension headers and of any additional header (e.g., a TCP header [26]) following the last extension header. Johnson, et al Expires 17 May 2001 [Page 20] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.1. Destination Options Header The Destination Options extension header is used to carry optional information that needs to be examined only by a packet's destination node(s). The Destination Options extension header is identified by a Next Header (or Protocol) value of 60 in the immediately preceding header [7], and has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Destination Options header. Uses the same values as the IPv4 Protocol field [27]. Hdr Ext Len 8-bit unsigned integer. Length of the Destination Options header in 4-octet units, not including the first 8 octets. Options Variable-length field, of length such that the complete Destination Options header is an integer multiple of 4 octets long. Contains one or more TLV-encoded options. The following destination option type is used by the DSR protocol: - DSR Route Request option (Section 5.1.1) Johnson, et al Expires 17 May 2001 [Page 21] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.1.1. DSR Route Request Option The DSR Route Request destination option is encoded in type-length-value (TLV) format as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Target Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[2] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[n] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IP fields: Source Address MUST be set to the address of the node originating this packet. Intermediate nodes that repropagate the Route Request MUST not change this field. Destination Address MUST be set to the limited broadcast address (255.255.255.255). Hop Limit (TTL) Can be varied from 1 to 255, for example to implement non-propagating Route Requests and Route Request expanding-ring searches (Section 3.3.4). Route Request fields: Option Type ???. The top three bits of this Option Type value are equal to 011, meaning that a node that does not understand this option MUST discard the packet, and that the Option Data may change en-route [7]. Johnson, et al Expires 17 May 2001 [Page 22] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Option Length 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Option Length fields. Identification A unique value generated by the initiator (original sender) of the Route Request. Nodes initiating a Route Request generate a new Identification value for each Route Request, for example based on a sequence number counter of all Route Requests initiated by the node. This value allows a receiving node to determine whether it has recently seen a copy of this Route Request: if this Identification value is found by this receiving node in its Route Request Table (in the cache of Identification values in the entry there for this initiating node), this receiving node MUST discard the Route Request. When propagating a Route Request, this field MUST be copied from the received copy of the Route Request being forwarded. Target Address The address of the node that is the target of the Route Request. Address[1..n] Address[i] is the address of the i-th hop recorded in the Route Request option. The number of addresses present in this field is indicated by the Option Length field in the option (n = (Option Length - 6) / 4). Each node repropagating the Route Request adds its own address to this list, increasing the Option Length value by 4. The DSR Route Request destination option MUST NOT appear more than once within any single Destination Options extension header. Johnson, et al Expires 17 May 2001 [Page 23] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.2. Hop-by-Hop Options Header The Hop-by-Hop Options extension header is used to carry optional information that must be examined by every node along a packet's delivery path. The Hop-by-Hop Options extension header is identified by a Protocol value of 0 in the IP header [7], and has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | . . . Options . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Next Header 8-bit selector. Identifies the type of header immediately following the Hop-by-Hop Options header. Uses the same values as the IPv4 Protocol field [27]. Hdr Ext Len 8-bit unsigned integer. Length of the Hop-by-Hop Options header in 4-octet units, not including the first 8 octets. Options Variable-length field, of length such that the complete Hop-by-Hop Options header is an integer multiple of 4 octets long. Contains one or more TLV-encoded options. If present in an IP packet, the Hop-by-Hop Options extension header MUST appear in the packet immediately following the IP header. The following hop-by-hop option types are used by the DSR protocol: - DSR Route Reply option (Section 5.2.1) - DSR Route Error option (Section 5.2.2) - DSR Acknowledgment option (Section 5.2.3) Johnson, et al Expires 17 May 2001 [Page 24] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.2.1. DSR Route Reply Option The DSR Route Reply hop-by-hop option is encoded in type-length-value (TLV) format as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length |L| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[2] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[n] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Type ???. The top three bits of this Option Type value are equal to 000, meaning that a node that does not understand this option SHOULD ignore this option and continue processing the packet, and that the Option Data does not change en-route [7]. Option Length 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Option Length fields. Last Hop External (L) Set to indicate that the last node indicated by the Route Reply is actually in a network external to the DSR network; the exact sequence of hops leading to it outside the DSR network are not represented in the Route Reply. Nodes caching this hop in their Route Cache MUST flag the cached hop with the External flag. Such hops MUST NOT be returned in a cached Route Reply generated from this Route Cache entry, and selection of routes from the Route Cache to route a packet being sent SHOULD prefer routes that contain no nodes flagged as External. Reserved Sent as 0; ignored on reception. Johnson, et al Expires 17 May 2001 [Page 25] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Address[1..n] The source route being returned by the Route Reply, indicating a route from the node with address Address[1] to the node with address Address[n]. The number of addresses present in this field is indicated by the Option Length field in the option (n = (Option Length - 1) / 4). A DSR Route Reply destination option MAY appear one or more times within a single Hop-by-Hop Options extension header. Johnson, et al Expires 17 May 2001 [Page 26] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.2.2. DSR Route Error Option The DSR Route Error hop-by-hop option is encoded in type-length-value (TLV) format as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | Error Type |Reservd|Salvage| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Unreachable Node Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Type ???. The top three bits of this Option Type value are equal to 000, meaning that a node that does not understand this option SHOULD ignore this option and continue processing the packet, and that the Option Data does not change en-route [7]. Option Length 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Option Length fields. For the current definition of the DSR Route Error option, this field MUST be set to 13. Extensions to the DSR Route Error option format may be included after the fixed portion of the DSR Route Error option specified above. The presence of such extensions will be indicated by the Option Length field. When the Option Length is greater than 13 octets, the remaining octets are interpreted as extensions. Currently, no extensions have been defined. Error Type The type of error encountered. Currently, the following type value is defined: NODE_UNREACHABLE 1 Other values of the Error Type field are reserved for future use. Johnson, et al Expires 17 May 2001 [Page 27] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Reservd Reserved. Sent as 0; ignored on reception. Salvage A 4-bit unsigned integer. Copied from the Salvage field in the DSR Routing header of the packet triggering the Route Error, incremented by the node returning the Route Error. Error Source Address The address of the node originating the Route Error (e.g., the node that attempted to forward a packet and discovered the link failure). Error Destination Address The address of the node to which the Route Error must be delivered (e.g., the node that generated the routing information claiming that the hop Error Source Address to Unreachable Node Address was a valid hop). Unreachable Node Address The address of the node that was found to be unreachable (the next hop neighbor to which the node with address Error Source Address was attempting to transmit the packet). A DSR Route Error destination option MAY appear one or more times within a single Hop-by-Hop Options extension header. Johnson, et al Expires 17 May 2001 [Page 28] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.2.3. DSR Acknowledgment Option The DSR Acknowledgment hop-by-hop option is encoded in type-length-value (TLV) format as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Option Type | Option Length | Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ACK Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ACK Destination Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option Type ???. The top three bits of this Option Type value are equal to 000, meaning that a node that does not understand this option SHOULD ignore this option and continue processing the packet, and that the Option Data does not change en-route [7]. Option Length 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Option Length fields. Identification Copied from the Identification field of the DSR Routing header of the packet being acknowledged. ACK Source Address The address of the node originating the DSR Acknowledgment. ACK Destination Address The address of the node to which the DSR Acknowledgment is to be delivered. A DSR Acknowledgement destination option MAY appear one or more times within a single Hop-by-Hop Options extension header. Johnson, et al Expires 17 May 2001 [Page 29] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 5.3. DSR Routing Header As specified for IPv6 [7], a Routing header is used by a source to list one or more intermediate nodes to be "visited" on the way to a packet's destination. This function is similar to IPv4's Loose Source and Record Route option, but the Routing header does not record the route taken as the packet is forwarded. The specific processing steps required to implement the Routing header must be added to an IPv4 protocol stack. The Routing header is identified by a Next Header value of 43 in the immediately preceding header, and has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . type-specific data . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The type-specific data for a Routing Header carrying a DSR Source Route is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F|L| Reserved |Salvage| Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[2] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address[n] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Johnson, et al Expires 17 May 2001 [Page 30] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Routing header fields: Next Header 8-bit selector. Identifies the type of header immediately following the Routing header. Hdr Ext Len 8-bit unsigned integer. Length of the Routing header in 4-octet units, not including the first 8 octets. Routing Type ??? Segments Left Number of route segments remaining, i.e., number of explicitly listed intermediate nodes still to be visited before reaching the final destination. Type-specific fields: First Hop External (F) Set to indicate that the first node indicated by the Routing header is actually in a network external to the DSR network; the exact sequence of hops leading from it outside the DSR network are not represented in the Routing header. Nodes caching this hop in their Route Cache MUST flag the cached hop with the External flag. Such hops MUST NOT be returned in a Route Reply generated from this Route Cache entry, and selection of routes from the Route Cache to route a packet being sent SHOULD prefer routes that contain no hops flagged as External. Last Hop External (L) Set to indicate that the last hop indicated by the Routing header is actually in a network external to the DSR network; the exact sequence of hops leading to it outside the DSR network are not represented in the Routing header. Nodes caching this hop in their Route Cache MUST flag the cached hop with the External flag. Such hops MUST NOT be returned in a Route Reply generated from this Route Cache entry, and selection of routes from the Route Cache to route a packet being sent SHOULD prefer routes that contain no hops flagged as External. Johnson, et al Expires 17 May 2001 [Page 31] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Reserved Sent as 0; ignored on reception. Salvage A 4-bit unsigned integer. Count of number of times that this packet has been salvaged as a part of DSR routing (Section 3.4.1). Identification Used to request that a DSR Acknowledgement option be returned to this transmitting node for this hop. The special value of 0 indicates that no DSR Acknowledgement is requested. Otherwise, the Identification field is set to a unique nonzero number by this node transmitting the packet and is copied into the Identification field of the DSR Acknowledgement option when returned by the node receiving the packet over this hop. Address[1..n] The sequence of addresses of the source route. In routing and forwarding the packet, the source route is processed as described in Sections 6.1.2 and 6.1.4. Johnson, et al Expires 17 May 2001 [Page 32] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6. Detailed Operation 6.1. General Packet Processing 6.1.1. Originating a Packet When originating any packet, a node using DSR routing MUST perform the following sequence of steps: - Search the node's Route Cache for a route to the address given in the IP Destination Address field in the packet's header. - If no such route is found in the Route Cache, then perform Route Discovery for the Destination Address, as described in Section 6.2. - If the packet contains a Route Request option, then replace the IP Destination Address field with the IP "limited broadcast" address (255.255.255.255) [3]. - Else, this node must have a route to the Destination Address of the packet (since otherwise a Route Request would have been added to the packet). If the length of this route is greater than 1 hop, or if the node determines to request a DSR network-layer acknowledgement from the first hop of the route, then insert a DSR Routing header into the packet, as described in Section 6.1.2. The source route in the packet is initialized from the route to the Destination Address found in the Route Cache. - Transmit the packet to the address given in the IP Destination Address, using Route Maintenance to retransmit the packet if necessary, as described in Section 6.3. Johnson, et al Expires 17 May 2001 [Page 33] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.1.2. Adding a DSR Routing Header to a Packet The design of the DSR Routing header is based on the design of a Routing header in IPv6 [7]. A node originating a packet adds a DSR Routing header to the packet, if necessary, in order to carry the source route of hops from this originating node to the final destination address of the packet. Specifically, the node adding the DSR Routing header constructs the Routing header and modifies the IP packet according to the following sequence of steps: - A DSR Routing header, as described in Section 5.3, is created and added to the packet after the IP header and any Hop-by-Hop Options header that may already be in the packet, but before any Destination Options header (e.g., containing a DSR Route Reply option) that may be present. - The number of Address fields to include in the DSR Routing header (n) is the number of intermediate nodes in the source route for the packet (i.e., excluding address of the originating node and the final destination address of the packet). The Segments Left field in the DSR Routing header is initialized equal to n. - The Source Address from the IP header is copied into Address[n] in the DSR Routing header. - The first hop of the source route for the packet is copied into the Source Address field in the IP header. - The remaining hops of the source route for the packet are copied into sequential Address[i] fields in the DSR routing header, for i = 1, 2, ..., n-1. - The First Hop External (F) bit in the Routing header is copied from the External bit flagging the first hop node in the source route for the packet, as indicated in the Route Cache. - The Last Hop External (L) bit in the Routing header is copied from the External bit flagging the last hop node in the source route for the packet, as indicated in the Route Cache. - All other fields in the type-specific data in the DSR Routing header are initialized to 0. - The Routing Type field in the DSR Routing header is initialized to ???. - The Hdr Ext Len field in the DSR Routing header is initialized to 4. Johnson, et al Expires 17 May 2001 [Page 34] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 - Next Header field in the DSR Routing header is set equal to the current value in the Protocol field in the IP header (or the Next Header field in the preceding extension header), and the Protocol field (or preceding Next Header field) is set equal to 43 to indicate a Routing header extension header [7]. Johnson, et al Expires 17 May 2001 [Page 35] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.1.3. Receiving a Packet When a node receives any packet, it MUST process the packet according to the following sequence of steps: - If the Destination Address in the packet's IP header does not match any of this receiving node's own IP address(s), then the processing of this packet depends on whether the packet contains a DSR Routing header: * If the packet contains a DSR Routing header, then discard the packet. * Else, if the packet contains a Hop-by-Hop Options extension header (if present, this MUST immediately follow the packet's IP header), then process the options contained in the Hop-by-Hop Options extension header. Forward the packet using normal IP forwarding proceedures and do not process the packet further. - Examine and process each of the extension headers (if any) in the packet in the order in which they occur in the packet. By dispatching on the Protocol field in the packet's IP header, and subsequently dispatching on the Next Header field of each encountered extension header, the appropriate protocol module is executed by the receiving node for each extension header. - If a Hop-by-Hop Options extension header or Destination Options extension headers is encountered in processing the packet, the receiving node MUST process any options given in this header in the order in which they occur in the Options field within the option. Any DSR routing information carried in a packet SHOULD be examined and reflected in the node's Route Cache, even if the options in the packet are not otherwise processed as described above. In particular, the following routing information SHOULD be handled in this way: - In a DSR Route Request option, the accumulated route record, represented by the IP Source Address of the packet and by the sequence of Address[i] entries in the Route Request option SHOULD be added to the node's Route Cache. - In a DSR Route Reply option, the route record being returned, represented by the sequence of Address[i] entries in the Route Request option and by the Destination Address in the packet's IP header SHOULD be added to the node's Route Cache. Johnson, et al Expires 17 May 2001 [Page 36] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 - In a DSR Acknowledgement option, the single link from the ACK Source Address to the ACK Destination Address SHOULD be added to the node's Route Cache. - In a DSR Route Error option, the single link from the Error Source Address to the Unreachable Node Address MUST be removed from the node's Route Cache. - In a DSR Routing header, the indicated source route SHOULD be added to the node's Route Cache, subject to the conditions identified in Section 3.3.1. The full sequence of hops in the DSR Routing header is as follows: * The Source Address in the packet's IP header is the first hop (the sender of the packet). * Let n equal Hdr Ext Len. This is the number of addresses in the Routing header. Let i equal n minus Segments Left. * The sequence of hops Address[1], Address[2], ..., Address[i] follow immediately after the IP Source Address in the source route. * The Destination Address in the packet's IP header follows immediately next in the source route. * The sequence of hops Address[i+1], Address[i+2], ..., Address[n] follow next in the source route. The address Address[n] above is the final hop in the source route. In addition to the processing of received packets described above, a node SHOULD examine the packet to determine if the receipt of this packet indicates an opportunity for automatic route shortening, as described in Section 3.4.2. If the received packet satisfies the tests described there, then this node SHOULD perform the following sequence of steps: - Return a gratuitous Route Reply to the IP Source Address of the packet, as described in Section 3.4.2. - Discard the received packet, since the packet has been received before its normal traversal of the packet's source route would have caused it to reach this receiving node. Another copy of the packet will normally arrive at this node as indicated in Johnson, et al Expires 17 May 2001 [Page 37] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 the packet's source route; discarding this initial copy of the packet, which triggered the gratuitous Route Reply, will prevent the duplication of this packet that would otherwise occur. 6.1.4. Processing a Routing Header in a Received Packet A Routing header in a packet is not examined or processed until the packet reaches the node identified in the Destination Address field in the packet's IP header. In that node, dispatching on the Protocol field in the packet's IP header (or the Next Header field in the preceding extension header) causes the Routing header module in that node's IP implementation to be invoked. The node then examines the Routing Type field in the Routing header to determine the specific type of processing for that type of Routing header. The processing for a Routing header here in general follows the procedures specified for IPv6 Routing headers, and the processing specifically for a DSR Routing header in general follows the general procedures specified for a Type 0 Routing header in IPv6 [7]. If, while processing a received packet, a node encounters a Routing header with an unrecognized Routing Type value, the required behavior of the node depends on the value of the Segments Left field, as follows: - If Segments Left is 0, the node MUST ignore the Routing header and proceed to process the next header in the packet, whose type is identified by the Next Header field in the Routing header. - If Segments Left is non-zero, the node MUST discard the packet and send an ICMP Parameter Problem, Code 0, message [24] to the packet's Source Address, pointing to the unrecognized Routing Type. If, after processing a Routing header in a received packet, an intermediate node determines that the packet is to be forwarded onto a link whose link MTU is less than the size of the packet, the node MUST discard the packet and send an ICMP Packet Too Big message to the packet's Source Address [24]. A DSR Routing header is identified by a Routing Type value of ??? in the Routing header. A DSR Routing header for IPv4 is processed according to the following sequence of steps: - If the value of the Segments Left field in the Routing header equals 0, then proceed to process the next header in the packet, whose type is identified by the Next Header field in the Routing header. Do not process the Routing header further. Johnson, et al Expires 17 May 2001 [Page 38] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 - Else, let n equal Hdr Ext Len. This is the number of addresses in the Routing header. - If the value of the Segments Left field is greater than n, then send an ICMP Parameter Problem, Code 0, message [24] to the IP Source Address, pointing to the Segments Left field, and discard the packet. Do not process the Routing header further. - Else, decrement the value of the Segments Left field by 1. Let i equal n minus Segments Left. This is the index of the next address to be visited in the Address vector. - If Address[i] or the IP Destination Address is a multicast address, then discard the packet. Do not process the Routing header further. - Else, swap the IP Destination Address and Address[i]. - Forward the packet to the IP address specified in the Destination Address field of the IP header, following normal IP forwarding procedures, including checking and decrementing the Time-to-Live (TTL) field in the packet's IP header [25, 3]. In this forwarding of the packet, the next hop node (identified by the Destination Address) MUST be treated as a direct neighbor node; the transmission to that next node MUST be done in a single IP forwarding hop, without Route Discovery and without searching the Route Cache. - In forwarding the packet, perform Route Maintenance for the next hop of the packet, by verifying that the packet was received by that next hop, as described in Section 6.3. Multicast addresses must not appear in a DSR Routing header or in the IP Destination Address field of a packet carrying a DSR Routing header. Johnson, et al Expires 17 May 2001 [Page 39] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.2. Route Discovery Processing Route Discovery is the mechanism by which a node S wishing to send a packet to a destination node D obtains a source route to D. Route Discovery is used only when S attempts to send a packet to D and does not already know a route to D. The node initiating a Route Discovery is known as the "initiator" of the Route Discovery, and the destination node for which the Route Discovery is initiated is known as the "target" of the Route Discovery. Route Discovery operates entirely on demand, with a node initiating Route Discovery based on its own origination of new packets for some destination address to which it does not currently know a route. Route Discovery does not depend on any periodic or background exchange of routing information or neighbor node detection at any layer in the network protocol stack at any node. The Route Discovery procedure utilizes two types of messages, a DSR Route Request (Section 5.1.1) and a DSR Route Reply (Section 5.2.1), to actively search the ad hoc network for a route to the desired destination. These DSR messages MAY be carried in any type of IP packet, through use of extension headers as described in Section 5: a Route Request is carried in a Destination options extension header, and a Route Reply is carried in a Hop-by-Hop options extension header. A Route Discovery for a destination SHOULD NOT be initiated unless the initiating node has a packet in the Send Buffer requiring delivery to that destination. A Route Discovery for a given target node MUST NOT be initiated unless permitted by the rate-limiting information contained in the Route Request Table. After each Route Discovery attempt, the interval between successive Route Discoveries for this target must be doubled, up to a maximum of MAX_REQUEST_PERIOD. 6.2.1. Originating a Route Request A node initiating a Route Discovery for some target creates and initializes a DSR Route Request option in some IP packet. This MAY be a separate IP packet, used only to carry this Route Request option, or the node MAY include the Route Request option in some existing packet it needs to send to the target node (e.g., the IP packet originated by this node, that caused the node to attempt Route Discovery for the destination address of the packet). The Route Request option MUST be included in a Destination Options extension header in the packet. To initialize the Route Request option, the node performs the following sequence of steps: Johnson, et al Expires 17 May 2001 [Page 40] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 - The Option Type in the option MUST be set to the value ???. - The Option Length field in the option MUST be set to the value 6. The total size of the Route Request option when initiated is 8 octets; the Option Length field excludes the size of the Option Type and Option Length fields themselves. - The Identification field in the option MUST be set to a new value, different from that used for other Route Requests recently initiated by this node. For example, each node MAY maintain a single counter value for generating a new Identification value for each Route Request it initiates. - The Target Address field in the option MUST be set to the IP address that is the target of this Route Discovery. The Source Address in the IP header of this packet MUST be the node's own IP address. The Destination Address in the IP header of this packet MUST be the IP "limited broadcast" address (255.255.255.255). A node MUST maintain in its Route Request Table, information about Route Requests that it initiates. When initiating a new Route Request, the node MUST use the information recorded in the Route Request Table entry for the target of that Route Request, and it MUST update that information in the table entry for use in the next Route Request initiated for this target. In particular: - The Route Request Table entry for a target node records the Time-to-Live (TTL) field used in the IP header of the last Route Request initiated by this node for that target node. This value allows the node to implement a variety of algorithms for controlling the spread of its Route Request on each Route Discovery initiated for a target. As examples, two possible algorithms for this use of the TTL field are described in Section 3.3.4. - The Route Request Table entry for a target node records the number of consecutive Route Requests initiated for this target since receiving a valid Route Reply giving a route to that target node, and the remaining amount of time before which this node MAY next attempt at a Route Discovery for that target node. These values MUST be used to implement an exponential back-off algorithm to limit the rate at which this node initiates new Route Discoveries for the same target address. Until a valid Route Reply is received for this target node address, the timeout between consecutive Route Discovery initiations for this target node SHOULD increase by doubling the timeout value on each new initiation. Johnson, et al Expires 17 May 2001 [Page 41] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 The behavior of a node processing a packet containing both a Routing Header and a Route Request Destination option is unspecified. Packets SHOULD NOT contain both a Routing Header and a Route Request Destination option. [This is not exactly true: A Route Request option appearing in the second Destination Options header that IPv6 allows after the Routing Header would probably do-what-you-mean, though we have not triple-checked it yet. Namely, it would allow the originator of a route discovery to unicast the request to some other node, where it would be released and begin the flood fill. We call this a Route Request Blossom since the unicast portion of the path looks like a stem on the blossoming flood-fill of the request.] Packets containing a Route Request Destination option SHOULD NOT be retransmitted, SHOULD NOT request an explicit DSR Acknowledgment by setting the R bit, SHOULD NOT expect a passive acknowledgment, and SHOULD NOT be placed in the Retransmission Buffer. The repeated transmission of packets containing a Route Request Destination option is controlled solely by the logic described in this section. 6.2.2. Processing a Received Route Request Option When a node receives a packet containing a Route Request option, the node MUST process the option according to the following sequence of steps: - If the Target Address field in the Route Request matches this node's own IP address, then the node SHOULD return a Route Reply to the initiator of this Route Request (the Source Address in the IP header of the packet), as described in Section 6.2.4. The source route for this reply is the sequence of hops initiator, Address[1], Address[2], ..., Address[n], target where initiator is the address of the initiator of this Route Request, each Address[i] is an address from the Route Request, and target is the target of the Route Request (the Target Address field in the Route Request). The node MUST then continue processing the packet normally, including any following options or extension headers in the packet. The node MUST NOT retransmit the Route Request to propagate it to other nodes. Do not process the Route Request option further. - Else, the node MUST examine the route recorded in the Route Request option (the IP Source Address field and the sequence of Address[i] fields) to determine if this node's own IP address already appears in this list of addresses. If so, the node MUST discard the entire packet carrying the Route Request option. Johnson, et al Expires 17 May 2001 [Page 42] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 - Else, the node MUST search its Route Request Table for an entry for the initiator of this Route Request (the IP Source Address field). If such an entry is found in the table, the node MUST search the cache of Identification values of recently received Route Requests in that table entry, to determine if an entry is present in the cache matching the Identification value and target node address in this Route Request. If such an (Identification, target address) entry is found in this cache in this entry in the Route Request Table, then the node MUST discard the entire packet carrying the Route Request option. - Else, this node SHOULD repropagate this Route Request. If it does so, the node MUST do so according to the following sequence of steps: * Add an entry for this Route Request in its cache of (Identification, target address) values of recently received Route Requests. * Create a copy of this entire packet and perform the following steps on the copy of the packet. * Append this node's own IP address to the list of Address[i] values in the Route Request, and increase the value of the Option Length field in the Route Request by 4 (the size of an IP address). * This node SHOULD search its own Route Cache for a route (from itself, as if it were the source of a packet) to the target of this Route Request. If such a route is found in its Route Cache, then this node SHOULD follow the procedure outlined in Section 6.2.3 to return a "cached Route Reply" to the initiator of this Route Request, if permitted by the restrictions specified there. * If the node does not return a cached Route Reply, then this node SHOULD link-layer re-broadcast this copy of the packet, with a short jitter delay before the broadcast is sent. The jitter period SHOULD be chosen as a random period, uniformly distributed between 0 and BROADCAST_JITTER. 6.2.3. Generating Route Replies using the Route Cache As described in Section 3.3.2, it is possible for a node processing a received Route Request to avoid propagating the Route Request further toward the target of the Request, if this node has in its Route Cache a route from itself to this target. Such a Route Reply generated by a node from its own cached route to the target of a Route Request is called a "cached Route Reply", and this mechanism can greatly reduce Johnson, et al Expires 17 May 2001 [Page 43] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 the overall overhead of Route Discovery on the network by reducing the flood of Route Requests. The general processing of a received Route Request is described in Section 6.2.2; this section specifies the additional requirements that MUST be met before a cached Route Reply may be generated and returned and specifies the procedure for returning such a cached Route Reply. While processing a received Route Request, for a node to possibly return a cached Route Reply, it MUST have in its Route Cache a route from itself to the target of this Route Request. However, before generating a cached Route Reply for this Route Request, the node MUST verify that there are no duplicate addresses listed in the route accumulated in the Route Request together with the route from this node's Route Cache. Specifically, there MUST be no duplicates among the following addresses: - The IP Source Address of the packet containing the Route Request, - The Address[i] fields in the Route Request, and - The nodes listed in the route obtained from this node's Route Cache, excluding the address of this node itself (this node itself is the common point between the route accumulated in the Route Request and the route obtained from the Route Cache). If any duplicates exist among these addresses, then the node MUST NOT send a cached Route Reply. The node SHOULD continue to process the Route Request as described in Section 6.2.2. If the Route Request and the route from the Route Cache meet the restriction above, then the node SHOULD construct and return a cached Route Reply as follows: - The source route for this reply is the sequence of hops initiator, Address[1], Address[2], ..., Address[n], c-route where initiator is the address of the initiator of this Route Request, each Address[i] is an address from the Route Request, and c-route is the sequence of hops in the source route to this target node, obtained from the node's Route Cache. In appending this cached route to the source route for the reply, the address of this node itself MUST be excluded, since it is already listed as Address[n]. - Send a Route Reply to the initiator of the Route Request, using the procedure defined in Section 6.2.4. The initiator of the Route Request is indicated in the Source Address field in the packet's IP header. Johnson, et al Expires 17 May 2001 [Page 44] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.2.4. Originating a Route Reply A node originates a Route Reply in order to reply to a received and processed Route Request, according to the procedures described in Sections 6.2.2 and 6.2.3. The Route Reply is returned in a DSR Route Reply option (Section 5.2.1). The Route Reply option MAY be returned to the initiator of the Route Request in a separate IP packet, used only to carry this Route Reply option, or it MAY be included in any other IP packet being sent to this address. The Route Reply option MUST be included in a Hop-by-Hop Options extension header in the packet returned to the initiator. To initialize the Route Reply option, the node performs the following sequence of steps: - The Option Type in the option MUST be set to the value ???. - The Option Length field in the option MUST be set to the value (n * 4) + 1, where n is the number of addresses in the source route being returned (excluding the Route Discovery initiator node's address). - The Last Hop External (L) bit in the option MUST be initialized to 0. - The Reserved field in the option MUST be initialized to 0. - The sequence of addresses of the source route are copied into the Address[i] fields of the option. Address[1] MUST be set to the first hop of the route after the initiator of the Route Discovery, Address[n] MUST be set to the last hop of the source route (the address of the target node), and each other Address[i] MUST be set to the next address in sequence in the source route being returned. The Destination Address field in the IP header of the packet carrying the Route Reply option MUST be set to the address of the initiator of the Route Discovery (i.e., for a Route Reply being returned in response to some Route Request, the IP Source Address of the Route Request). After creating and initializing the DSR Route Reply option and the IP packet containing it, send the Route Reply, jittered by T milliseconds, where T is a uniformly distributed random number between 0 and BROADCAST_JITTER. If sending a Route Reply to the originator of the Route Request requires performing a Route Discovery, the Route Reply hop-by-hop option MUST be piggybacked on the packet that contains the Route Request. This piggybacking prevents a loop wherein the target of the Johnson, et al Expires 17 May 2001 [Page 45] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 new Route Request (which was itself the originator of the original Route Request) must do another Route Request in order to return its Route Reply. If sending the Route Reply to the originator of the Route Request does not require performing Route Discovery, a node SHOULD send a unicast Route Reply in response to every received Route Request targeted at it. 6.2.5. Processing a Route Reply Option Upon receiving a Route Reply, a node SHOULD extract the source route from the Route Reply and add this routing information to its Route Cache. The source route from the Route Reply is the sequence of hops initiator, Address[1], Address[2], ..., Address[n] where initiator is the value of the Destination Address field in the IP header of the packet carrying the Route Reply (the address of the initiator of the Route Discovery), and each Address[i] is a node through which the source route passes, in turn, on the route to the target of the Route Discovery. Address[n] is the address of the target. If the Last Hop External (L) bit is set in the Route Reply, the node MUST flag the hop Address[n] in its Route Cache as External. Each packet in the Send Buffer SHOULD then be checked to see whether the information in the Route Reply and now in the Route Cache allows it to be sent immediately. Johnson, et al Expires 17 May 2001 [Page 46] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.3. Route Maintenance Processing Route Maintenance is the mechanism by which node S is able to detect, while using a source route to D, if the network topology has changed such that it can no longer use its route to D because a link along the route no longer works. When Route Maintenance indicates a source route is broken, S can attempt to use any other route it happens to know to D, or can invoke Route Discovery again to find a new route for subsequent packets to D. Route Maintenance for this route is used only when S is actually sending packets to D. When forwarding a packet, a node MUST attempt to receive an acknowledgement for the packet from the next hop. If no acknowledgement is received, the node SHOULD return a Route Error to the IP Source Address of the packet, as described in Section 6.3.3 6.3.1. Using Network-Layer Acknowledgments When a node retransmits a packet or has no other way to ensure successful delivery of a packet to the next hop, it SHOULD request a network-layer acknowledgement by placing a non-zero value in the Identification field of the DSR Routing header. Such a value MUST be unique over all packets delivered to the same next hop which are either unacknowledged or recently acknowledged. A node receiving a DSR Routing header with a non-zero value in the Identification field MUST send an acknowledgement to the previous hop by performing the following sequence of steps: - Create a packet and set the IP Source Address to the address of this node, the IP Destination Address to the address of the previous hop, and the IP Protocol field to the protocol number reserved for Hop-by-Hop Options extension headers. - Set the Hop-by-Hop Options extension header's Next Header field to be the "No Next Header" value. Set the Header Extension Length to the size of a DSR Acknowledgement Option. - Set the DSR Acknowledgement option's Option Type field to the Option Type reserved for DSR Acknowledgements, and the Option Length field to 10. - Copy the Identification field from the Routing Header into the Identification field in the DSR Acknowledgement Option. Set the ACK Source Address field in the option to be the IP Source Address and the ACK Destination Address field to the IP Destination Address. - Send the packet as described in Section 6.1.1. Johnson, et al Expires 17 May 2001 [Page 47] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.3.2. Using Link Layer Acknowledgments If explicit failure notifications are provided by the link layer, then all packets are assumed to be correctly received by the next hop, and a Route Error is sent only when an explicit failure notification is made from the link layer. Nodes receiving a packet without a Routing Header do not need to send an explicit Acknowledgment to the packet's originator, since the link layer will notify the originator if the packet was not received properly. 6.3.3. Originating a Route Error When a node is unable to verify successful delivery of a packet to the next hop after a maximum number of retransmission attempts, a node SHOULD send a Route Error to the IP Source Address of the packet. When sending a Route Error for a packet containing either a DSR Route Error option or a DSR Acknowledgement option, a node SHOULD add these options to it's Route Error, subject to some limit on lifetime. Specifically, we define the "salvage count" of an option to be the sum of one plus the salvage count recorded in the DSR Routing header plus the sum of the salvage counts of any DSR Route Errors preceding that option. A node transmitting a Route Error MUST follow the following steps: - Create a packet and set the IP Source Address to the address of this node, the IP Destination Address to the address IP Source Address of the packet experiencing the error. - Insert a Hop-by-Hop Options Header into the packet. - Add a Route Error Option, setting the Error Type to NODE_UNREACHABLE, the Reserved bits to 0, the Salvage value to one plus the Salvage value from the DSR Routing header, and the Unreachable Node Address to the address of the next hop. Set the Error Source Address to the IP Source Address and the Error Destination to the IP Destination Address. - The node MAY append each DSR Route Error and DSR Acknowledgement, in order, from the packet experiencing the error, though it MUST exclude options with salvage counts greater than 15. - Send the packet as described in Section 6.1.1. Johnson, et al Expires 17 May 2001 [Page 48] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 6.3.4. Processing a Route Error Option A node receiving a Route Error MUST process it as follows: - Delete all routes from the Route Cache that have a link from the Route Error Source Address to the Unreachable Node Address. - If the Hop-by-Hop option following the Route Error is a DSR Acknowledgement or DSR Route Error option sent by this node (that is, with Acknowledgement or Error Source Address equal to this node's address), copy the Hop-by-Hop options following the current Route Error into a new packet with IP Source Address equal to this node's own IP address and IP Destination Address equal to the Acknowledgement or Error Destination Address. Transmit this packet as described in Section 6.1.1, with the salvage count in the DSR Routing header set to the Salvage value of the Route Error. 6.3.5. Salvaging a Packet When a node is unable to verify successful delivery of a packet to the next hop after a maximum number of retransmission attempts and has transmitted a Route Error to the sender, it MAY attempt to salvage the packet by examining its route cache. If the node can find a route to the packet's IP Destination Address in its own Route Cache, then this node replaces the packet's Routing header with a new Routing Header in the same way as described in Section 6.1.2, except that Address[1] MUST be set to the address of this node and the Salvage field MUST be set to 1 plus the value of the Salvage field in the Routing Header that caused the error. Johnson, et al Expires 17 May 2001 [Page 49] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 7. Constants BROADCAST_JITTER 10 milliseconds MAX_ROUTE_LEN 15 nodes Route Cache ROUTE_CACHE_TIMEOUT 300 seconds Send Buffer SEND_BUFFER_TIMEOUT 30 seconds Route Request Table REQUEST_TABLE_SIZE 64 nodes REQUEST_TABLE_IDS 16 identifiers MAX_REQUEST_REXMT 16 retransmissions MAX_REQUEST_PERIOD 10 seconds REQUEST_PERIOD 500 milliseconds NONPROP_REQUEST_TIMEOUT 30 milliseconds Retransmission Buffer DSR_RXMT_BUFFER_SIZE 50 packets Retransmission Timer DSR_MAXRXTSHIFT 2 Johnson, et al Expires 17 May 2001 [Page 50] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 8. IANA Considerations This document proposes the use in IPv4 of the Destination Options extension header, the Hop-by-Hop Options extension header, and Routing header, which were originally defined for IPv6 [7]. The Next Header values indicating these three extension header types (60, 0, and 43, respectively) must therefore be reserved within the IPv4 Protocol number space. In addition, the "No Next Header" type value of 69, defined for IPv6, must also be defined for use in IPv4. Other protocols in IPv4 wishing to use these IPv6-style extension headers can also make use of these Protocol number assignments. For use within a Destination Options extension header, this document defines one new type of destination option, which must be assigned an Option Type value: - DSR Route Request option, described in Section 5.1.1. The top three bits of this Option Type value MUST be 011. For use within a Hop-by-Hop Options extension header, this document defines three new types of hop-by-hop options, each of which must be assigned an Option Type value: - DSR Route Reply option, described in Section 5.2.1. The top three bits of this Option Type value MUST be 000. - DSR Route Error option, described in Section 5.2.2. The top three bits of this Option Type value MUST be 000. - DSR Acknowledgment option, described in Section 5.2.3. The top three bits of this Option Type value MUST be 000. For use within a Routing header, this document defines one new type of routing header, which must be assigned an Routing Type value: - DSR Routing Header, defined in Section 5.3. Johnson, et al Expires 17 May 2001 [Page 51] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 9. Security Considerations This document does not specifically address security concerns. This document does assume that all nodes participating in the DSR protocol do so in good faith and without malicious intent to corrupt the routing ability of the network. In mission-oriented environments where all the nodes participating in the DSR protocol share a common goal that motivates their participation in the protocol, the communications between the nodes can be encrypted at the physical channel or link layer to prevent attack by outsiders. Johnson, et al Expires 17 May 2001 [Page 52] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Appendix A. Location of DSR in the ISO Network Reference Model When designing DSR, we had to determine at what layer within the protocol hierarchy to implement ad hoc network routing. We considered two different options: routing at the link layer (ISO layer 2) and routing at the network layer (ISO layer 3). Originally, we opted to route at the link layer for several reasons: - Pragmatically, running the DSR protocol at the link layer maximizes the number of mobile nodes that can participate in ad hoc networks. For example, the protocol can route equally well between IPv4 [25], IPv6 [7], and IPX [28] nodes. - Historically [12, 13], DSR grew from our contemplation of a multi-hop propagating version of the Internet's Address Resolution Protocol (ARP) [23], as well as from the routing mechanism used in IEEE 802 source routing bridges [22]. These are layer 2 protocols. - Technically, we designed DSR to be simple enough that it could be implemented directly in the firmware inside wireless network interface cards [12, 13], well below the layer 3 software within a mobile node. We see great potential in this for DSR running inside a cloud of mobile nodes around a fixed base station, where DSR would act to transparently extend the coverage range to these nodes. Mobile nodes that would otherwise be unable to communicate with the base station due to factors such as distance, fading, or local interference sources could then reach the base station through their peers. Ultimately, however, we decided to specify and to implement [20] DSR as a layer 3 protocol, since this is the only layer at which we could realistically support nodes with multiple network interfaces of different types forming an ad hoc network. Johnson, et al Expires 17 May 2001 [Page 53] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Appendix B. Implementation and Evaluation Status The DSR protocol has been implemented under the FreeBSD 2.2.7 operating system running on Intel x86 platforms. FreeBSD is based on a variety of free software, including 4.4 BSD Lite from the University of California, Berkeley. For the environments in which we used it, this implementation is functionally equivalent to the protocol specified in this draft. During the 7 months from August 1998 to February 1999, we designed and implemented a full-scale physical testbed to enable the evaluation of ad hoc network performance in the field, in a actively mobile ad hoc network under realistic communication workloads. The last week of February and the first week of March included demonstrations of this testbed to a number of our sponsors and partners, including Lucent Technologies, Bell Atlantic, and DARPA. A complete description of the testbed is available as a Technical Report [20]. The software was ported to FreeBSD 3.3, and a preliminary version of Quality of Service (QoS) support was added. A demonstration of this modified version of DSR was presented in July 2000. Those QoS features are not included in this draft, and will be added later in a seprate draft on top of the base protocol specified here. The DSR protocol has been extensively studied using simulation; we have implemented DSR in the ns-2 simulator [5, 19] and conducted evaluations of different caching strategies documented in this draft [9]. Several independant groups have also used DSR as a platform for their own research, or and as a basis of comparison between ad hoc network routing protocols. Johnson, et al Expires 17 May 2001 [Page 54] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Acknowledgements The protocol described in this draft has been designed and developed within the Monarch Project, a research project at Rice University and Carnegie Mellon University which is developing adaptive networking protocols and protocol interfaces to allow truly seamless wireless and mobile node networking [14, 6]. The authors would like to acknowledge the substantial contributions of Josh Broch in helping to design, simulate, and implement the DSR protocol. Josh is currently on leave of absence from Carnegie Mellon University at AON Networks. We thank him for his contributions to earlier versions of this draft. We would also like to acknowledge the assistance of Robert V. Barron at Carnegie Mellon University. Bob ported our DSR implementation from FreeBSD 2.2.7 into FreeBSD 3.3. Johnson, et al Expires 17 May 2001 [Page 55] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 References [1] David F. Bantz and Frederic J. Bauchot. Wireless LAN design alternatives. IEEE Network, 8(2):43--53, March/April 1994. [2] Vaduvur Bharghavan, Alan Demers, Scott Shenker, and Lixia Zhang. MACAW: A media access protocol for wireless LAN's. In Proceedings of the ACM SIGCOMM '94 Conference, pages 212--225, August 1994. [3] Robert T. Braden, editor. Requirements for Internet hosts---communication layers. RFC 1122, October 1989. [4] Scott Bradner. Key words for use in RFCs to indicate requirement levels. RFC 2119, March 1997. [5] Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, and Jorjeta Jetcheva. A performance comparison of multi-hop wireless ad hoc network routing protocols. In Proceedings of the Fourth Annual ACM/IEEE International Conference on Mobile Computing and Networking, pages 85--97, October 1998. [6] Carnegie Mellon University Monarch Project. CMU Monarch Project Home Page. Available at http://www.monarch.cs.cmu.edu/. [7] Stephen E. Deering and Robert M. Hinden. Internet Protocol version 6 (IPv6) specification. RFC 2460, December 1998. [8] Ralph Droms. Dynamic Host Configuration Protocol. RFC 2131, March 1997. [9] Yih-Chun Hu and David B. Johnson. Caching strategies in on-demand routing protocols for wireless ad hoc networks. In Proceedings of the Sixth Annual ACM International Conference on Mobile Computing and Networking, August 2000. [10] IEEE Computer Society LAN MAN Standards Committee. Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, IEEE Std 802.11-1997. The Institute of Electrical and Electronics Engineers, New York, New York, 1997. [11] Per Johansson, Tony Larsson, Nicklas Hedman, Bartosz Mielczarek, and Mikael Degermark. Scenario-based performance analysis of routing protocols for mobile ad-hoc networks. In Proceedings of the Fifth Annual ACM/IEEE International Conference on Mobile Computing and Networking, pages 195--206, August 1999. [12] David B. Johnson. Routing in ad hoc networks of mobile hosts. In Proceedings of the IEEE Workshop on Mobile Computing Systems and Applications, pages 158--163, December 1994. Johnson, et al Expires 17 May 2001 [Page 56] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 [13] David B. Johnson and David A. Maltz. Dynamic Source Routing in ad hoc wireless networks. In Mobile Computing, edited by Tomasz Imielinski and Hank Korth, chapter 5, pages 153--181. Kluwer Academic Publishers, 1996. [14] David B. Johnson and David A. Maltz. Protocols for adaptive wireless and mobile networking. IEEE Personal Communications, 3(1):34--42, February 1996. [15] John Jubin and Janet D. Tornow. The DARPA Packet Radio Network Protocols. Proceedings of the IEEE, 75(1):21--32, January 1987. [16] Phil Karn. MACA---A new channel access method for packet radio. In ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pages 134--140, September 1990. [17] Gregory S. Lauer. Packet-radio routing. In Routing in Communications Networks, edited by Martha E. Steenstrup, chapter 11, pages 351--396. Prentice-Hall, Englewood Cliffs, New Jersey, 1995. [18] S.B. Lee, A. Gahng-Seop, X. Zhang, and A.T. Campbell. INSIGNIA: An IP-Based Quality of Service Framework for Mobile Ad Hoc Networks. Journal of Parallel and Distributed Computing, 60(4):374--406, April 2000. [19] David A. Maltz, Josh Broch, Jorjeta Jetcheva, and David B. Johnson. The effects of on-demand behavior in routing protocols for multi-hop wireless ad hoc networks. IEEE Journal on Selected Areas of Communications, 17(8):1439--1453, August 1999. [20] David A. Maltz, Josh Broch, and David B. Johnson. Experiences designing and building a multi-hop wireless ad hoc network testbed. Technical Report CMU-CS-99-116, School of Computer Science, Carnegie Mellon University, Pittsburgh, Pennsylvania, March 1999. [21] David A. Maltz, Josh Broch, and David B. Johnson. Quantitative lessons from a full-scale multi-hop wireless ad hoc network testbed. In Proceedings of the IEEE Wireless Communications and Networking Conference, September 2000. [22] Radia Perlman. Interconnections: Bridges and Routers. Addison-Wesley, Reading, Massachusetts, 1992. [23] David C. Plummer. An Ethernet address resolution protocol: Or converting network protocol addresses to 48.bit Ethernet addresses for transmission on Ethernet hardware. RFC 826, November 1982. Johnson, et al Expires 17 May 2001 [Page 57] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 [24] J. B. Postel, editor. Internet Control Message Protocol. RFC 792, September 1981. [25] J. B. Postel, editor. Internet Protocol. RFC 791, September 1981. [26] J. B. Postel, editor. Transmission Control Protocol. RFC 793, September 1981. [27] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700, October 1994. See also http://www.iana.org/numbers.html. [28] Paul Turner. NetWare communications processes. NetWare Application Notes, Novell Research, pages 25--91, September 1990. Johnson, et al Expires 17 May 2001 [Page 58] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Chair's Address The MANET Working Group can be contacted via its current chairs: M. Scott Corson Phone: +1 301 405-6630 Institute for Systems Research Email: corson@isr.umd.edu University of Maryland College Park, MD 20742 USA Joseph Macker Phone: +1 202 767-2001 Information Technology Division Email: macker@itd.nrl.navy.mil Naval Research Laboratory Washington, DC 20375 USA Johnson, et al Expires 17 May 2001 [Page 59] INTERNET-DRAFT The Dynamic Source Routing Protocol 17 November 2000 Authors' Addresses Questions about this document can also be directed to the authors: David B. Johnson Phone: +1 713 348-3063 Rice University Fax: +1 713 348-5930 Computer Science Department, MS 132 Email: dbj@cs.rice.edu 6100 Main Street Houston, TX 77005-1892 USA David A. Maltz Phone: +1 650 688-3128 AON Networks Fax: +1 650 688-3119 3045 Park Blvd. Email: dmaltz@cs.cmu.com Palo Alto, CA 94306 USA Yih-Chun Hu Phone: +1 412 268-3075 Carnegie Mellon University Fax: +1 412 268-5576 Computer Science Department Email: yihchun@cs.cmu.edu 5000 Forbes Avenue Pittsburgh, PA 15213-3891 USA Jorjeta G. Jetcheva Phone: +1 412 268-3053 Carnegie Mellon University Fax: +1 412 268-5576 Computer Science Department Email: jorjeta@cs.cmu.edu 5000 Forbes Avenue Pittsburgh, PA 15213-3891 USA Johnson, et al Expires 17 May 2001 [Page 60]