Destination-Sequenced Distance Vector routing
Encyclopedia
Destination-Sequenced Distance-Vector Routing (DSDV) is a table-driven routing scheme for ad hoc mobile networks based on the Bellman-Ford algorithm
. It was developed by C. Perkins and P.Bhagwat in 1994. The main contribution of the algorithm was to solve the routing loop problem
. Each entry in the routing table contains a sequence number, the sequence numbers are generally even if a link is present; else, an odd number is used. The number is generated by the destination, and the emitter needs to send out the next update with this number. Routing information is distributed between nodes by sending full dumps infrequently and smaller incremental updates more frequently.
For example the routing table of Node A in this network is
Naturally the table contains description of all possible paths reachable by node A, along with the next hop, number of hops and sequence number.
Whenever the topology of the network changes, a new sequence number is necessary before the network re-converges; thus, DSDV is not suitable for highly dynamic networks. (As in all distance-vector protocols, this does not perturb traffic in regions of the network that are not concerned by the topology change.)
is an attempt at making DSDV more robust, more efficient and more widely applicable while staying within the framework of proactive protocols.
Bellman-Ford algorithm
The Bellman–Ford algorithm computes single-source shortest paths in a weighted digraph.For graphs with only non-negative edge weights, the faster Dijkstra's algorithm also solves the problem....
. It was developed by C. Perkins and P.Bhagwat in 1994. The main contribution of the algorithm was to solve the routing loop problem
Routing loop problem
A routing loop is a common problem with various types of networks, particularly computer networks. They are formed when an error occurs in the operation of the routing algorithm, and as a result, in a group of nodes, the path to a particular destination forms a loop.In the simplest version, a...
. Each entry in the routing table contains a sequence number, the sequence numbers are generally even if a link is present; else, an odd number is used. The number is generated by the destination, and the emitter needs to send out the next update with this number. Routing information is distributed between nodes by sending full dumps infrequently and smaller incremental updates more frequently.
| Destination | Next Hop | Number of Hops | Sequence Number | Install Time |
|---|---|---|---|---|
| A | A | 0 | A 46 | 001000 |
| B | B | 1 | B 36 | 001200 |
| C | B | 2 | C 28 | 001500 |
Naturally the table contains description of all possible paths reachable by node A, along with the next hop, number of hops and sequence number.
Selection of Route
If a router receives new information, then it uses the latest sequence number. If the sequence number is the same as the one already in the table, the route with the better metric is used. Stale entries are those entries that have not been updated for a while. Such entries as well as the routes using those nodes as next hops are deleted.Disadvantages
DSDV requires a regular update of its routing tables, which uses up battery power and a small amount of bandwidth even when the network is idle.Whenever the topology of the network changes, a new sequence number is necessary before the network re-converges; thus, DSDV is not suitable for highly dynamic networks. (As in all distance-vector protocols, this does not perturb traffic in regions of the network that are not concerned by the topology change.)
Influence
While DSDV itself does not appear to be much used today, other protocols have used similar techniques. The best-known sequenced distance vector protocol is AODV, which, by virtue of being a reactive protocol, can use simpler sequencing heuristics. BabelBabel (protocol)
The Babel routing protocol is a distance-vector routing protocol for Internet Protocol packet-switched networks that is designed to be robust and efficient on both wireless mesh networks and wired networks....
is an attempt at making DSDV more robust, more efficient and more widely applicable while staying within the framework of proactive protocols.