23-02-2013, 04:28 PM
Comparison between DSR and AODV
Comparison between DSR.ppt (Size: 61 KB / Downloads: 79)
DSR Overview
Source routing: routes are stored in a route cache, data packets carry the source route in the packet header
Route discovery
Condition: a node sends data to a destination for which it does not know the route
Actions: source floods the network with RREQ. Each node receiving RREQ rebroadcasts it unless it is destination or it has the route to the destination in its cache.
Route reply
A destination node or a node knowing the route to the destination in its cache replies with RREP. RREQ and RREP are also source routed.
Route carried back by RREP is cached at the source
AODV Overview
Discovers routes on an “on-demand” basis via a similar route discovery process, but uses a different mechanism to maintain routing info.
AODV uses routing table, one entry per destination. It relies on routing table entries to propagate a RREP back to the source, and route data packets to the destination.
AODV uses sequence # maintained at each destination to determine freshness of routing info. And to prevent routing loops. These sequence # are carried by all routing packets.
Common features of DSR and AODV
Both discover routes only in the presence of data packets in the need for a route to the destination
Route discovery is based on query and rely cycles and route information is stored in all intermediate nodes on the route
Route table entires (AODV), route caches (DSR)
High level difference
DSR uses source routing, but AODV uses a table-driven routing framework and destination sequence # to prevent loops and determine route freshness.
DSR does not rely on any timer-based activities, but AODV does.
DSR uses routing cache aggressively, and maintains multiple routes per dest. AODV uses one route per destination.
Differences between DSR and AODV (I)
DSR has access to greater amount of routing information than AODV by the virtual of SR. AODV can gather limited information.
DSR: in a single query-reply cycle, source learns route to each intermediate node in the route in addition to the dest. Each intermediate node also learns route to other nodes on the route. Promiscuous listening also helps to learn the route to every node on the route
AODV: no source routing or promiscuous listening. It causes AODV to rely on a route discovery flood more often, generating more network overhead
Consequence
For application-oriented metris --- delay and throughput, DSR outperforms AODV in less stressful situations (smaller # of nodes and lower load and/or mobility).
AODV outperforms DSR in more stress situations (more load, higher mobility)
DSR: Aggressive use of caching, lack of mechanism to expire stale cache
DSR consistently generates less routing load than AODV.
Solution Space
Where you are allowed to modify/add the design, what is the information you can get
Scenario 1: no change at any intermediate node (e.g. base station), change is only allowed at both the sender & receiver sides; however, wireless link may provide information regarding whether it is wireless-related loss or not
Scenario 2: no change at any intermediate node, no change at the receiver side, only sender side is allowed to be modified; no addition information feedback other than loss
Link-Layer Solutions
Play with different link-layer recovery schemes by recovering loss locally:
ARQ, FEC, channel-swapping, hybrid
suppress DUP_ACKs from TCP to some degree
how much you can shield from the standard TCP ?