“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.
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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