A Review of Current Routing Potocols for Ad-Hoc MobileWireless Networks

Yibo Sunsunyibo@gmail.com

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

Elizabeth M.Royer, C-K Toh Link: http://bingweb.binghamton.edu/~ysun6/review-current-routing-prot.

pdf

Ad-Hoc, Mobile, Wireless

Infrastructureless networks : no fixed routers

All nodes are capable of movement and can be connected dynamically

Interconnections between nodes are changing on a continual basis

E.G

Emergency search-and rescue operations

Meetings in which persons wish to quickly share information

Data acquisition operations in inhospitable terrains

A brief view of Ad-Hoc Routing Protocols

Table-Driven Routing Protocols

Basic idea: Maintain consistent, up-to-date routing information from each node to every other node in the network.

Each node:Maintains one or more tables to store

routing informationRespond to changes in network topology by

propagating updates throughout the network

Destintion-Sequenced Distance-Vector Routing (DSDV) Based on classical Bellman-Ford routing

mechanism Improvement : freedom from loops in

routing table Table Record Structure

All possible destinations and the hop count Each entry with a sequence number assigned

by the destination node (to distinguish stale routes from new ones, thereby avoiding the formation of routing loops)

Route update mechanism

“full dump” packet All available routing information and can require multiple

network protocol data units (NPDUs) Periodically, or on certain event

“incremental” packet Routes changed since last full dump Contains the address of the destination, the hop count to

reach it, the sequence number, and a new unique sequence number

Both packets are sent in broadcast way, and should fit into a standard size NPDU, to decrease traffic.

Route update mechanism (contd.)

Route labeled with the most recent sequence number is always used

Route with smaller metric is used to shorten the path, when two updates have the same sequence number

Drawback: cares 0 about power saving, link state changing, few on fault-tolerant, and lack of scalability (each node maintain a whole routing table)

Clusterhead Gateway Switch Routing (CGSR) CGSR uses DSDV as the underlying

routing scheme, but differed in type of addressing and network organization Layered infrastructure

“Cluster head” node: a node controlling a group of ad-hoc nodes

“Gateway” node: node within communication range of two or more cluster heads

LCC (Least Cluster Change) algorithm Cluster heads only change when two cluster heads

come into contact, or when a node moves out of contact of all other cluster heads.

Head-to-Gateway

Node cache A routing table Cluster member table

Routing procedureOn receiving a packet, a node First, consult its cluster member table and routing table

to determine the nearest cluster head along the route to destination.

Next, check its routing table to determine the node in order to reach the selected cluster head

Last, transmit

Wireless Routing Protocol (WRP)

Node Cache Distance table Routing table Link-cost table (cares about link-state) Message retransmission list (MRL) table

Sequence number of the update message Retransmission counter Acknowledgment-required flag vector List of updates sent to neighbor

Route update mechanism

When link changes, a node send its neighbors the update message contains:The destinationThe distance to the destinationThe predecessor of the destination

Send “Hello” message to ensure connectivity, if no packets to send

Source-Initiated On-demand Routing

Routes only when desired by the source node.

Include two parts: Route discoveryRoute maintenance

Ad-hoc On-Demand Distance Vector Routing (AODV)

AODV is built on DSDV, while improved by minimizing the number of required broadcasts, by creating routes on an on-demand basis.

The author of AODV classify it as a pure on-demand route acquisition system.

Node cache Broadcast ID Sequence number

Route discovery First, broadcast a route request (RREQ) packet to its

neighbor Then, it is forwarded to their neighbors, and so on Till the destination is found, or an inter node with a “fresh

enough” route to the destination is found During forwarding, the inter nodes record in their route

table the address of the neighbor, from which the first copy of the broadcast packet is received, thereby establishing a reverse path

Route maintenance Source move:

Reinitiate the route discovery protocol to find a new route to the destination

Inter node move: The upstream neighbor propagates a link failure

notification message to each of its active upstream neighbors to inform them of the erasure of that part of the route

And it is forwarded, and so on, till the source is reached The source then reinitiate the route discovery procedure

“Hello” message

Dynamic Source Routing (DSR)

Based on the concept of source routingMobile nodes are required to maintain

route caches that contain the source routes of which the mobile is aware

Temporally-ordered Routing Algorithm (TORA)

For highly dynamic mobile networking environment, hence the key design concept is: localization of control message to a small set of nodes near the occurrence of a topological change.

Based on link reversal TORA includes 3 parts

Route creation Route Maintenance Route erasure

Associativity-Based Routing (ABR)

ABR uses a totally new routing metric called: degree of association stability, defined by connection stability of one route, hence to derive longer-lived routes.

Each node periodically generates a beacon to signify its existence. The neighbors then update the associativity table, increase the corresponding entry’s associativity tick .

High associativity tick = low mobility

Route discovery Source broadcast query and await-reply (BQ-REPLY cycle) All nodes receiving query append their address, associativi

ty ticks with their neighbor with Qos information to the query packet

A successor node erases its upstream node neighbors’ associativity tick entries and retains only the entry concerned with itself and its upstream node

The destination can choose the best path (first consider overall degree, then the shortest path), then send a reply packet

Route re-construction (RRC) Source Move cause Route discovery again Destination Move:

Upstream node erases its route and determines if the node is still reachable by a localized query (LQ[H])

If destination receive LQ, replies the best partial path; or if timeout, then backtrack to upstream node, along with LN[0] message to inform erase the route

Route deletion

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