Classification of routing protocols
- 2. Introduction Classification Table Driven Routing Protocols – Destination Sequenced Distance Vector (DSDV) On–Demand Routing protocols –Ad hoc On–Demand Distance Vector Routing (AODV) Hybrid routing protocols
- 3. The environment of Ad hoc acomplished with the following terms: ◦ Changing topology dynamically ◦ Absence of fixed infrastructure ◦ No Centralized administration(No Access point) ◦ Bandwidth constrained wireless links ◦ Energy-constrained nodes ◦ Link loss issues
- 4. Routing protocols for ad-hoc wireless networks can be broadly classified into four categories based on: 1. Routing information update mechanism; 2. Usage of temporal information for routing(e.g. cached routes); 3. Routing topology information; 4. Utilization of specific resources (e.g. GPS).
- 5. Based on routing information update mechanism ◦ Proactive (table-driven) routing protocols: -Every node maintain the network topology (routing tables) -Periodically exchange to all nodes in the network using flooding ◦ Reactive (on-demand) routing protocols: - Path is acquired by connection establishment process ◦ Hybrid protocols: - Combined of above two methods. Based on usage of temporal information ◦ Based on past temporal information: -Make decision based on the past status of the links. ◦ Based on future temporal information. -Make decision based on the expected future status of the links.
- 6. Based on the routing topology ◦ Flat topology routing protocols – use of flat addressing scheme ◦ Hierarchial topology routing protocols- use of logical hierarchy in the network Routing based on utilization of specific resources: ◦ Power-aware routing-Aims at minimizing the consumption power ◦ Geographical information assisted routing. -Improve performnce of routing and control overhead
- 10. These are proactive routing protocols. – They maintain the global topology information in the form of tables at every node. We consider: • Destination Sequenced Distance Vector Routing Protocol (DSDV) • Wireless Routing Protocol (WRP) • Cluster Head Gateway Routing Protocol (CGCR) • Source-tree Adaptive Routing Protocol (STAR) Common advantages and shortcoming of these protocols: • Low delay of route setup process: all routes are immediately available; • High bandwidth requirements: updates due to link loss leads to high control overhead; • Low scalability: control overhead is proportional to the number of nodes; • High storage requirements: whole table must be in memory.
- 11. Destination sequenced distance vector routing protocol (DSDV) Modification of the Bellman-Ford algorithm where each node maintains: • the shortest path to destination; • the first node on this shortest path. This protocol is characterized by the following: • routes to destination are readily available at each node in the routing table (RT); • RTs are exchanged between neighbors at regular intervals; • RTs are also exchanged when significant changes in local topology are observed by a node. RT updates can be of two types: • incremental updates: – take place when a node does not observe significant changes in a local topology. • full dumps: – take place when significant changes of local topology are observed.
- 13. The reconfiguration of path (used for ongoing data transfer) is done as follows: • the end node of the broken link sends a table update message with: - broken link’s weight assigned to infinity; – sequence number greater than the stored sequence number for that destination. • each node resends this message to its neighbors to propagate the broken link to the network; • even sequence number is generated by end node, odd – by all other nodes. Note: single link break leads to the propagation of RT updates through the whole network
- 15. Route maintenance in DSDV is performed as follows: when a neighbor node perceives a link break (node 3): it sets all routes through broken link to ∞; broadcasts its routing table. node 5 receives update message, it informs neighbors about the shortest distance to node 6; this information is propagated through the network and all node updates their RTs; node 1 may now sends their packets through route 1 − 3 − 5 − 6 instead of 1 − 3 − 6.
- 16. These protocols find paths to destination only when needed (on-demand) to transmit a packet. We consider: ◦ Dynamic source routing protocol (DSR) ◦ Ad hoc on-demand distance vector routing protocol (AODV) ◦ Location aided routing (LAR) ◦ Associativity-based routing (ABR) ◦ Signal stability-based adaptive routing protocol (SSA) These protocols have the following advantages and shortcomings: ◦ - high delay of route setup process: routes are established on-demand; ◦ - small control overhead: no route updates; ◦ - low scalability: no route updates; ◦ - low storage requirements: only needed routes are in cache.
- 17. This is a source-based routing protocol. The difference between DSR and other on-demand routing protocols is: on-demand protocols periodically exchange the so-called beacon (hello) packets: hello packets are used to inform neighbors about existence of the node. DSR does not use hello packets. The basic approach of this protocol is as follows: during route contraction DSR floods a RouteRequest packets in the network; intermediate nodes forward RouteRequest if it is not redundant; destination node replies with RouteReply; the RouteReply packet contains the path traversed by RouteRequest packet; the receiver responds only if this is a first RouteRequest (not duplicate).
- 18. The DSR protocol uses the sequence numbers: RouteRequest packet carries the path traversed and the sequence number; the sequence numbers are used to prevent loop formation and nodes check it. The DSR also uses route cache in each node: if node has a route in the cache, this route is used.
- 19. Refinements of DSR: to avoid over-flooding the network, exponential back-off is used between RouteRequest sending; intermediate node is allowed to reply with RouteReply if it has a route to destination in cache: if the link is broken the RouteError is sent to the sender by node adjacent to a broken link.
- 20. The major differences between AODV and DSR are as follows: in DSR a data packet carries the complete path to be traversed; in AODV nodes store the next hop information (hop-by-hop routing) for each data flow. The RouteRequest packet in AODV carries the following information: the source identifier (SrcID): this identifies the source; the destination identifier (DestID): this identifies the destination to which the route is required; the source sequence number (SrcSeqNum); the destination sequence number (DestSeqNum): indicates the freshness of the route. the broadcast identifier (BcastID): is used to discard multiple copies of the same RouteRequest. the time to live (TTL): this is used to not allow loops.
- 21. The AODV protocol performs as follows: when a node does not have a valid route to destination a RouteRequest is forwarded; when intermediate node receives a Route Request packet two cases are possible: -if it does not have a valid route to destination, the node forwards it; -if it has a valid route, the node prepares a Route Reply message if the RouteRequest is received multiple times, the duplicate copies are discarded:are determined comparing BcastID-SrcID pairs. when RouteRequest is forwarded, the address of previous node and its BcastID are stored; -are needed to forward packets to the source. if RouteReply is not received before a time expires, this entry is deleted; either destination node or intermediate node responses with valid route; when RouteRequest is forwarded back, the address of previous node and its BcastID are stored; -are needed to forward packets to the destination.
- 23. In case of the link break: end-node are notified by unsolicited RouteReply with hop count set to ∞. end-node deletes entries and establishes a new path using new BcastID. link status is observed using the link-level beacons or link-level ACKs.
- 24. -connection setup delay is less -having stale entries -heavy control overhead -more bandwidth consumption