A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks

1. A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks IEEE Personal Communications, April 1999, pp. 46-55 E. Royer and C.-K. Toh

2. Introduction • Two types of wireless networks: • infrastructured network: • base stations are the bridges • a mobile host will communicate with the nearest base station • handoff is taken when a host roams from one base to another • ad hoc network: • infrastructureless: no fixed base stations • without the assistance of base stations for communication • Due to transmission range constraint, • two MHs need multi-hop routing for communication • quickly and unpredictably changing topology

3. MANET • MANET = Mobile Ad Hoc Networks • a set of mobile hosts, each with a transceiver • no base stations; no fixed network infrastructure • multi-hop communication • needs a routing protocol which can handle changing topology

4. Applications of MANET • battlefields • nature disaster areas • fleet in oceans • historical cites • festival ground

5. Related Research • IEEE 802.11 for Wireless LANs • MAC • PHY • IETF manet group • to stimulate research and discuss possible standards in this area • Routing Protocols: • unicast – AODV, DSR, ZRP, TORA, CBRP, CEDAR • multicast – MAODV, AMRoute, ODMRP, AMRIS

6. Resources and Applications • NS-2: • AODV, DSR, DSDV, TORA • Telcordia: Intelligent Transportation System • AODV • MAODV: to distributed emergency information

7. Challenge of Ad Hoc Networks • No centralized entity • Mobile host is no longer just an end system • Acting as an intermediate system • Changing network topology over time • Every node can be mobile

8. Routing in MANET

9. Can Existing Internet Routing Protocols Be Used for MANET? • Link-state Routing • Distance-vector Routing

10. Link State Routing: Dijkstra’s Algorithm • Each node keeps its link state to its neighbors. • From each node, we gradually expand a spanning tree, until all nodes are scanned.

11. Link State Routing: Dijkstra’s Algorithm Initial State: each host only knows its direct neighbors

12. Evolution of States in C

13. Evolution of States in C (cont.)

14. Evolution of States in C (cont.) • Comments: This is a centralized algorithm, not appropriate.

15. Overview of Current Routing Protocols

16. On-demand vs. Table-driven • Table-Driven Routing Protocol: • proactive!! • continuously evaluate the routes • attempt to maintain consistent, up-to-date routing information • when a route is needed, one may be ready immediately • when the network topology changes • the protocol responds by propagating updates throughout the network to maintain a consistent view

17. Source-Initiated On-Demand Routing Protocol: • reactive!! • on-demand style: create routes only when it is desired by the source node • route discovery: invoke a route-determination procedure • the procedure is terminated when • a route has been found • no route is found after all route permutations are examined • longer delay: sometimes a route may not be ready for use immediately when data packets come

18. Table-Driven Routing Protocols Protocol 1: DSDV: Destination Sequence Distance Vector Protocol 2: CGSR: Clustered Gateway Switch Routing

19. Protocol 1: DSDV (Destination Sequence Distance Vector) • “Highly Dynamic Destination-Sequence Distance-Vector Routing (DSDV) for Mobile Computers” • Charles E. Perkins & Pravin Bhagwat • Dated: 1994 • Computer Communications Review, ‘94 • pp. 234-244

20. DSDV Outline • Each node keeps a routing table to all other nodes. • based on next-hop routing • Once its routing table changes, a node broadcasts its table to other nodes.

21. DSDV(cont.)

22. DSDV(cont.)

23. Protocol 2: CGSR (Clusterhead Gateway Switch Routing) • “Routing in Clustered Multihop, Mobile Wireless Networks with Fading Channel”, C.-C. Chiang, 1996, Proc. IEEE SICON ’97, pp. 197-211.

24. CGSR: Cluster Head and Gateway • The arrangement of cluster head is similar to dominating set in graph theory. • Definition: each node is either in the dominating set or is neighboring to a node in the dominating set.

25. CGSR(cont.) (5 hops) (3 hops)

26. CGSR (cont.) • A routing table among cluster heads are maintained. • also based on the DSDV manner • Data forwarding steps: • from cluster head to cluster head • in a hierarchical manner • then from cluster head to cluster members • between two cluster heads, gateways are used to forward the packets • Adv: less routing information to be kept • Disadv: longer route

27. Source-Initiated On-DemandRouting Protocols AODV DSR TORA ABR SSR ZRP

28. Protocol 1:AODV • AODV: Ad hoc On-demand Distance Vector routing protocol • On track to become an IETF Experimental RFC • References • C. E. Perkins, E. M. Belding-Royer, and S. R. Das, “Ad hoc On-Demand Distance Vector (AODV) Routing,” IETF Internet Draft, draft-ietf-manet-aodv-13.txt, Feb. 17, 2003 (work in progress). • C. E. Perkins and E. M. Royer, “Ad hoc On-Demand Distance Vector Routing,”Proceedings 2nd IEEE Workshop on Mobile Computing Systems and Applications, February 1999, pp. 90-100.

29. AODV Concepts (1) • Pure on-demand routing protocol • A node does not perform route discovery or maintenance until it needs a route to another node or it offers its services as an intermediate node • Nodes that are not on active paths do not maintain routing information and do not participate in routing table exchanges • Uses a broadcast route discovery mechanism • Uses hop-by-hoprouting • Routes are based on dynamic table entries maintained at intermediate nodes • Comparison: Dynamic Source Routing (DSR) uses source routing

30. AODV Concepts (2) • Local HELLO messages are used to determine local connectivity • Can reduce response time to routing requests • Can trigger updates when necessary • Sequence numbers are assigned to routes and routing table entries • to supersede stale cached routing entries • Every node maintains two counters • Node sequence number • Broadcast ID

31. type flags resvd hopcnt broadcast_id dest_addr dest_sequence_# source_addr source_sequence_# AODV Route Request (1) • Initiated when a node wants to communicate with another node, but does not have a route to that node • Source node broadcasts a route request (RREQ) packet to its neighbors

32. AODV Route Request (2) • Sequence numbers • Source sequence indicates “freshness” of reverse route to the source • Destination sequence number indicates freshness of route to the destination • Every neighbor receives the RREQ and either … • Returns a route reply (RREP) packet, or • Forwards the RREQ to its neighbors • (source_addr, broadcast_id) uniquely identifies the RREQ • broadcast_id is incremented for every RREQ packet sent • Receivers can identify and discard duplicate RREQ packets

33. AODV Route Request (3) • If a node cannot respond to the RREQ • The node increments the hop count • The node saves the following information to set up a reverse path (AODV assumes symmetrical links) • Neighbor that sent this RREQ packet • Destination IP address • Source IP address • Broadcast ID • Source node’s sequence number • Expiration time for reverse path entry (to enable garbage collection)

34. AODV Example (1) • Node 1 needs to send a data packet to Node 7 • Assume Node 6 knows a current route to Node 7 • Assume that no other route information exists in the network (related to Node 7) 4 6 1 7 5 3 2

35. AODV Example (2) • Node 1 sends a RREQ packet to its neighbors • source_addr = 1 • dest_addr = 7 • broadcast_id = broadcast_id + 1 • source_sequence_# = source_sequence_# + 1 • dest_sequence_# = last dest_sequence_# for Node 7 4 6 1 7 5 3 2

36. AODV Example (3) • Nodes 2 and 4 verify that this is a new RREQ and that the source_sequence_# is not stale with respect to the reverse route to Node 1 • Nodes 2 and 4 forward the RREQ • Update source_sequence_# for Node 1 • Increment hop_cnt in the RREQ packet 4 6 1 7 5 3 2

37. AODV Example (4) • RREQ reaches Node 6, which knows a route to 7 • Node 6 must verify that the destination sequence number is less than or equal to the destination sequence number it has recorded for Node 7 • Nodes 3 and 5 will forward the RREQ packet, but the receivers recognize the packets as duplicates 4 6 1 7 5 3 2

38. AODV Route Reply (1) • If a node receives an RREQ packet and it has a current route to the target destination, then it unicasts a route reply packet (RREP) to the neighbor that sent the RREQ packet type flags rsvd prsz hopcnt dest_addr dest_sequence_# source_addr lifetime

39. AODV Route Reply (2) • Intermediate nodes propagate the first RREP for the source towards the source using cached reverse route entries • Other RREP packets are discarded unless… • dest_sequence_# number is higher than the previous, or • destination_sequence_# is the same, but hop_cnt is smaller (i.e., there’s a better path) • RREP eventually makes it to the source, which can use the neighbor sending the RREP as its next hop for sending to the destination • Cached reverse routes will timeout in nodes not seeing a RREP packet

40. AODV Example (5) • Node 6 knows a route to Node 7 and sends an RREP to Node 4 • source_addr = 1 • dest_addr = 7 • dest_sequence_# = maximum(own sequence number, dest_sequence_# in RREQ) • hop_cnt = 1 4 6 1 7 5 3 2

41. AODV Example (6) • Node 4 verifies that this is a new route reply (the case here) or one that has a lower hop count and, if so, propagates the RREP packet to Node 1 • Increments hop_cnt in the RREP packet 4 6 1 7 5 3 2

42. Dest Next Hops 7 4 3 AODV Example (7) • Node 1 now has a route to Node 7 in three hops and can use it immediately to send data packets • Note that the first data packet that prompted path discovery has been delayed until the first RREP was returned 4 6 1 7 5 3 2

43. AODV Route Maintenance • Route changes can be detected by… • Failure of periodic HELLO packets • Failure or disconnect indication from the link level • Failure of transmission of a packet to the next hop (can detect by listening for the retransmission if it is not the final destination) • The upstream (toward the source) node detecting a failure propagates an route error (RERR) packet to the source node with a new destination sequence number and a hop count of infinity (unreachable) • The source (or another node on the path) can rebuild a path by sending a RREQ packet

44. AODV Example (8) 4 • Assume that Node 7 moves and link 6-7 breaks • Node 6 issues an RERR packet indicating the broken path • The RERR propagates back to Node 1 • Node 1 can discover a new route 6 1 7 5 3 2 7

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

46. Route Discovery Route Reply

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

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

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

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