1. Vinay Singh Graduate school of Software Dongseo University
A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks
Vinay Singh
Graduate school of Software
Dongseo University

2. Contents Classifications of Routing Protocols.
Ad-hoc On Demand Distance vector Routing (AODV).
Path Setup in AODV.
Summary.
Alternative Versions of AODV.

3. Classification of routing protocols
Table-driven (proactive)
Up-to-date routing information maintained
Routing overhead independent of route usage
Source-initiated (demand-driven / reactive)
Routes maintained only for routes in use
Explicit route discovery mechanism
Hybrid Protocols
Combination of proactive and reactive

4. Classification (cont.)
Ad Hoc Routing Protocols
Reactive
Proactive
Hybrid
Source-initiated
on-demand
Table driven
Hybrid
DSDV
OLSR
WRP
ZRP
CGSR
AODV
DSR
TORA
ABR
SSR

5. Source-Initiated On-Demand Routing
Create routes only when needed
Routes found using a “route discovery” process
Route maintenance procedure used to repair routes

6. Ad Hoc On-Demand Distance Vector Routing
Primary Objectives
Minimize broadcasts
To separate local connectivity management & topology maintenance
Disseminate local connectivity changes to active mobile nodes

7. Ad Hoc On-Demand Distance Vector Routing
Uses a broadcast route discovery mechanism as in DSR
Dynamic route table entry establishment at intermediate nodes
Most current routing information through destination sequence numbers
Now RFC 3561, based on DSDV
Destination sequence numbers provide loop freedom
Source sends Route Request Packet (RREQ) when a route has to be found
Route Reply Packet (RREP) is sent back by destination
Route Error messages update routes

8. Route Requests in AODV S E F B C D A G H I
Represents a node that has received RREQ for D from S

9. Broadcast transmission
Route Requests in AODV
Broadcast transmission S E F B C D A G H I
Represents transmission of RREQ

10. Route Requests in AODV S E F B C D A G H I
Represents links on Reverse Path

11. Reverse Path Setup in AODVF B C D A G H I
Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once

12. Route Reply in AODV S E F B C D A G H I
Represents links on path taken by RREP

13. Route Request and Route Reply
Route Request (RREQ) includes the last known sequence number for the destination
An intermediate node may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender
Intermediate nodes that forward the RREP, also record the next hop to destination
A routing table entry maintaining a reverse path is purged after a timeout interval
A routing table entry maintaining a forward path is purged if not used for a active_route_timeout interval

14. Link Failure
A neighbor of node X is considered active for a routing table entry if the neighbor sent a packet within active_route_timeout interval which was forwarded using that entry
Neighboring nodes periodically exchange hello message
When the next hop link in a routing table entry breaks, all active neighbors are informed
Link failures are propagated by means of Route Error (RERR) messages, which also update destination sequence numbers

15. Route Error
When node X is unable to forward packet P (from node S to node D) on link (X,Y), it generates a RERR message
Node X increments the destination sequence number for D cached at node X
The incremented sequence number N is included in the RERR.
When node S receives the RERR, it initiates a new route discovery for D using destination sequence number at least as large as N.
When node D receives the route request with destination sequence number N, node D will set its sequence number to N, unless it is already larger than N.

16. AODV: Summary Routes need not be included in packet headers
Nodes maintain routing tables containing entries only for routes that are in active use
At most one next-hop per destination maintained at each node
DSR may maintain several routes for a single destination
Sequence numbers are used to avoid old/broken routes
Sequence numbers prevent formation of routing loops
Unused routes expire even if topology does not change

17. Modified version of AODV
AODVM:- Maintain multiple paths at the source .
AODVM-R:- Maintain multiple routes at the intermediate nodes.
AODVjr:- Simple, only destinations reply to RREQ and uses end-to-end hello messages to maintain routes.