1. Introduction   The Dynamic Source Routing protocol (DSR) [15, 16] 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.   In designing DSR, we sought to create a routing protocol that had   very low overhead yet was able to react very quickly to changes in   the network.  The DSR protocol provides highly reactive service in   order 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 main 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.       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 layer 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 wayJohnson, et al             Expires 19 January 2005              [Page 1]INTERNET-DRAFT     The Dynamic Source Routing Protocol      19 July 2004   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.   All state maintained by DSR is "soft state" [6], in that the loss   of any state will not interfere with the correct operation of the   protocol; all state is discovered as needed and can easily and   quickly be rediscovered if needed after a failure without significant   impact on the protocol.  This use of only soft state allows the   routing protocol to be very robust to problems such as dropped or   delayed routing packets or node failures.  In particular, a node in   DSR that fails and reboots can easily rejoin the network immediately   after rebooting; if the failed node was involved in forwarding   packets for other nodes as an intermediate hop along one or more   routes, it can also resume this forwarding quickly after rebooting,   with no or minimal interruption to the routing 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 support for multiple   routes 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 sender of   a packet selects and controls the route used for its own packets,   which together with support for multiple routes also allows features   such as load balancing to be defined.  In addition, all routes used   are easily guaranteed to be loop-free, since the sender can avoid   duplicate hops in the routes selected.   The operation of both Route Discovery and Route Maintenance in DSR   are designed to allow unidirectional links and asymmetric routes to   be 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.   This document specifies the operation of the DSR protocol for   routing unicast IPv4 packets in multi-hop wireless ad hoc networks.   Advanced, optional features, such as Quality of Service (QoS) support   and efficient multicast routing, and operation of DSR with IPv6 [7],   are covered in other documents.  The specification of DSR in this   document provides a compatible base on which such features can beJohnson, et al             Expires 19 January 2005              [Page 2]INTERNET-DRAFT     The Dynamic Source Routing Protocol      19 July 2004   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 19 January 2005              [Page 3]INTERNET-DRAFT     The Dynamic Source Routing Protocol      19 July 20042. Assumptions   The DSR protocol as described here is designed mainly for mobile   ad hoc networks of up to about two hundred nodes, and is designed   to work well with even very high rates of mobility.  Other protocol   features and enhancements that may allow DSR to scale to larger   networks are outside the scope of this document.   We assume in this document 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 ad hoc 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 [16].  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 theJohnson, et al             Expires 19 January 2005              [Page 4]INTERNET-DRAFT     The Dynamic Source Routing Protocol      19 July 2004   interface into promiscuous mode.  Use of promiscuous receive mode is   entirely optional.   Wireless communication ability between any pair of nodes may at   times not work equally well in both directions, due for example to   differing antenna or propagation patterns or sources of interference   around the two nodes [1, 20].  That is, wireless communications   between each pair of nodes will in many cases be able to operate   bidirectionally, but at times the wireless link between two nodes   may be only unidirectional, allowing one node to successfully   send packets to the other while no communication is possible   in the reverse direction.  Some MAC protocols, however, such as   MACA [19], MACAW [2], or IEEE 802.11 [13], limit unicast data   packet transmission to bidirectional links, due to the required   bidirectional exchange of RTS and CTS packets in these protocols and   due to the link-layer 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 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.   A routing protocol such as DSR chooses a next-hop for each packet   and provides the IP address of that next-hop.  When the packet   is transmitted, however, the lower-layer protocol often has a   separate, MAC-layer address for the next-hop node.  DSR uses the   Address Resolution Protocol (ARP) [30] to translate from next-hop IP   addresses to next-hop MAC addresses.  In addition, a node MAY add   an entry to its ARP cache based on any received packet, when the IP   address and MAC address of the transmitting node are available in   the packet; for example, the IP address of the transmitting node   is present in a Route Request option (in the Address list being   accumulated) and any packets containing a source route.  Adding   entries to the ARP cache in this way avoids the overhead of ARP in   most cases.Johnson, et al             Expires 19 January 2005              [Page 5]INTERNET-DRAFT     The Dynamic Source Routing Protocol      19 July 2004