DSR Protocol 2 DSR Dynamic Source Routing q

DSR

Protocol 2: DSR (Dynamic Source Routing) q “Dynamic Source Routing in Ad-Hoc Wireless Networks”, D. B. Johnson and D. A. Maltz, Mobile Computing, 1996, pp. 153 -181. q on-demand q Each host maintains a route cache which contains all routes it has learnt. q Source Routing: l routes are denoted with complete information (each hop is registered) q Two major parts: l route discovery l route maintenance

Route Discovery Route Reply

Route Discovery of DSR q When a host has a packet to send, it first consults its route cache. l If there is an unexpired route, then it will use it. l Otherwise, a route discovery will be performed. q Route Discovery: l There is a “route record” field in the packet. Ø The source node will add its address to the record. Ø On receipt of the packet, a host will add its address to the “route record” and rebroadcast the packet. l To limit the number of ROUTE_REQUEST packets: Ø Each node only rebroadcasts the packet at most once. Ø Each node will consult its route cache to see if a route is already known.

ROUTE_REPLY of DSR q A ROUTE_REPLY packet is generated when l the route request packet reaches the destination l an intermediate host has an unexpired route to the destination q The ROUTE_REPLY packet will contain a route generated in two manner: l from destination: Ø the route that was traversed by the ROUTE_REQUEST packet l from intermediate host: Ø the route that was traversed by the ROUTE_REQUEST packet concatenated with the route in the intermediate host’s route cache

Stale Route Cache Problem q Definition: l A route may become broken (i. e. , stale), but is unaware by a host X. l With route cache, host X may keep on distributing erroneous information to other hosts.

Route Maintenance of DSR q When the data link layer encounters a link breakage, a ROUTE_ERROR packet will be initiated. l The packet will traverse in the backward direction to the source. l The source will then initiate another ROUTE_REQUEST. l Example: (next page) q Maintenance of route cache: l All routes which contain the breakage hop have to be removed from the route cache.

Route_Error x

Packet Type: Route Request (RREQ)

Packet Type: Route Reply (RREP)

Packet Type: Data Packet

Packet Type: Route_Error

Route Concentration Problem q With route cache, hosts are likely to share the same links (routes). (1) (2) (3) (4)