1. Reactive Routing Protocols for Ad hoc Mobile Wireless Networks

2. Ad Hoc Routing Protocols
Overview
Ad Hoc Routing Protocols
Reactive
Proactive
Table-Driven
Demand-Driven
DSDV
WRP
AODV
LMR
DSR
ABR
CGSR
TORA
SSR
Elizabeth Royer and Chai Keong Toh, “A review of Current Routing Protocols for Ah Hoc Mobile Wireless Networks”, IEEE personal Communications April 1999

3. Proactive vs Reactive Proactive Reactive
Route from each node to every other node in the network
Routes from Source to Destination only
Routes are ready to use instantaneously
Routes constructed when needed, higher connection setup delay
Periodic route-update packets
Route update when necessary
Large routing tables
Small or No routing tables

4. On-Demand Routing Protocols
Source Routing
Hop-by-Hop Routing
ABR
DSR
AODV
LMR
LAR
RDMAR
SSA
TORA
Elizabeth Royer and Chai Keong Toh, “A review of Current Routing Protocols for Ah Hoc Mobile Wireless Networks”, IEEE personal Communications April 1999

5. Source Routing vs Hop-by-Hop Routing
Data packets carry the complete addresses from source to destination
Data packets carry the address of the destination and the next hop
No routing table in intermediate nodes
All nodes maintain localized routing tables
Not Scalable
Scalable

6. General Properties Loop Free Routing Two Operation Phases
Route Establishment
Route Request  RouteRequest Packet, flooded by the Source node
Route Reply  RouteReply Packet, returned to source node by Destination or Intermediate node
Route Maintenance
Route Reconstruction
Route Deletion
These protocols have two phase of operations Route establishment and Route Maintenance. During route establishment, the source flood the network with a routerequest packet, the destination node of receiving this request sends back a routereply packet which carry the route traversed by the routerequest packet.

7. Protocols DSR: Dynamic Source Routing ABR: Associativity-Based Routing
SSA: Signal Stability-Based Adaptive Routing Algorithm
AODV: Ad Hoc On-Demand Distance Vector
LAR : Location Aided Routing Protocol
RDMAR: Relative Distance Micro-Discovery Ad Hoc Routing
LMR: Light-weight Mobile Routing
TORA: Temporally Ordered Routing Algorithm
ARA: Ant-colony-based Routing Algorithm

8. On-Demand Routing Protocols
Source Routing
Hop-by-Hop Routing
ABR
DSR
AODV
LMR
LAR
RDMAR
SSA
TORA
Elizabeth Royer and Chai Keong Toh, “A review of Current Routing Protocols for Ah Hoc Mobile Wireless Networks”, IEEE personal Communications April 1999

9. Dynamic Source Routing (DSR)
Full source-route is aggregated in RouteRequest, and sent back in RouteReply
Each data packet carry the full address for all nodes along the path
Can store Multiple routes to destination
Good for Small/ Low mobility networks

10. DSR– Route Discovery Source Node broadcast RouteRequest packet
Each Intermediate node do the following steps:
If request received before  discard
If node ID is listed in request  discard
If Route to the destination is available send RouteReply to the source node with full path
Otherwise  append node ID and rebroadcast
When destination is reached  return RouteReply with full path
Intermediate nodes cache all paths they overhear
Source node caches all paths received and choose Shortest Path

11. DSR - Route Request E B D C S F A G S-B S-B-E S S-B-C S-B S-A-G-F
Source Node broadcast RouteRequest packets. Each neighbor will check if it received this request before or if its ID is in the list. If yes it will drop the packet. If not it will append its ID to the packet and rebroadcast the packet again. As you can see here the packet coming from Node C to E and from C to F will be dropped at E and F respectively because E and F already got a RouteRequest from the same source. A G
S-A-G
S-A
RouteRequest Dropped

12. DSR - Route Reply E B D C S F A G B-E-D E-D S-B-E-D S-B-E-D S-B-E-D
S-A-G-F-D S
S-A-G-F-D F
When D gets the RouteRequest, it will append its ID and transmit RouteReply to the source using the same path that it gets it from.
In this case Node D will send RouteReply to S through S-B-E-D and S-A-G-F-D. Node S will add the whole route in the cache for Data packet usage. It will select the shortest path first which is S-B-E-D.
All node along the path will cache these routes towards the destination D
F-D
S-A-G-F-D A
S-A-G-F-D G
A-G-F-D
S-A-G-F-D
G-F-D

13. DSR– Route Maintenance
Triggered when a link breaks between two nodes along the path from the Source to the destination
Node who discover the break send a RouteError to inform the source node about the broken link
Source Node
erase the route from the cache, and
Use another cached routes, Or
Request a new Route
if two nodes along the path from the source to the destination move away from each other and the link between them is broken
A node can not communicate to the other node  when it retransmit packets and don’t hear any response

14. DSR – Route Maintenance
RouteError E B
RouteError D C S
S-B-E-D
S-A-G-F-D F
When a link is broken  due to movement of nodes or any other reason
The node that discover the failure link will send RouteError to the Source
When the source gets the RouteError Packet it will delete the path from the cache
And will find another route in its cache, if it didn’t find any route it will run RouteRequest again A G

15. DSR Promiscuous mode, intermediate nodes learns about routes breaks
During network partition, if the destination is in different partition a backoff algorithm is used to prevent frequent RouteRequest broadcast

16. DSR -- Concerns Scalability Large overhead in each data packet
No Local repair of the broken link
Stale cache information could result to inconsistence during route reconstruction
Poor Performance as Mobility increases
Some concerns about DSR:
Scalability, since the source need to add the IDs of all nodes along the path to the destination which increase the overhead in every data packet sent
When a link is broken RouteError packets need to go all the way to the source to inform it about the problem
Intermediate node can use outdated routes stored in their cache
As mobility increases more links are broken hence more route reconstructions is needed

17. Associativity-Based Routing (ABR)
Select Longer-Lived routes
Beacon based protocol
Defining the Location Stability between nodes
Used as a metric instead of shortest hop
Determined by beacon counting
Links between nodes classified into Stable and Unstable link according to beacons counts
This is another protocol that uses a different metrics than shortest path. It also uses the same mechanism as DSR which is aggregating the node IDs along the path to the final destination. The objective is to select a longer lived routes which will help in reducing the cost of reconstructing routes. The metric used instead of the shortest hop count is the Location Stability or the Associatvity between nodes. Moving nodes tend to break the associativity with their neighbors and hence they are not a good candidates to carry routes.
Nodes periodically broadcast beacons to signify their existence with their neighbors, Location Stability is determined by counting the periodic beacons that a node receives from its neighbors. Links between nodes are classified into Stable and Unstable links based on the count of beacons.

18. ABR– Route Discovery Source Node broadcast RouteRequest packet
Each intermediate node do the following steps:
If request received before  discard
If node ID is listed in request  discard
If route to the destination is available  send RouteReply
Otherwise  append node ID and Beacon Count and rebroadcast

19. ABR– Route Discovery Destination node
Once get the first RouteRequest, it waits for certain period to receive multiple RouteRequests
From multiple routes, it selects the route with maximum proportion of stable links
If more than one route has the maximum proportion of stable links, the shortest path is selected
Only single route is selected by the destination

20. ABR - Route Request E B D C S F A G S-B S-B-E S S-B S-B-C S-B-C-F
S-B-E-D
S-B-C-F-D S D
S-B C
S-B-C S
S-B-C-F F
S-B-C S
Source Node broadcast RouteRequest packets. Each neighbor will check if it received this request before or if its ID is in the list. If yes it will drop the packet. If not it will append its ID and the status of the link weather it is stable or not to the packet and rebroadcast the packet again.
The destination node will get the routes S-B-E-D and S-A-G-F-D, it will select the latter one due to less unstable links in the route although it is not the shortest one. A G
S-A-G
RouteRequest Dropped
S-A
Unstable Link

21. ABR - Route Reply E B
S-B-C-F-D D C
S-B-C-F-D S
S-B-C-F-D F A G

22. ABR – Route Maintenance
Try to bypass the broken link without flooding the RouteRequest globally
Downstream node, sends RouteError to the destination, deleting cache entries along the path
Upstream node broadcasts a RouteRepair with limited time to live
If failed, next upstream node broadcast RouteRepair
Is successful, new route is used
If the process traverse near source node, a new RouteRequest is initiated

23. ABR – Concerns Chosen path may not be shortest path
May lead to higher delay in route repairs
Single path selection
High cost of periodic beaconing
Power
Bandwidth

24. Signal Stability-based adaptive routing algorithm (SSA)
Derivative of ABR
Adds Signal Strength as a prime metric
In addition to beacon count, each node keep record of the signal strength of other neighbors
Links are classified as Strong/Stable links vs Weak/unstable links

25. SSA– Route Discovery
RouteRequests are forwarded through strong/stable links only
RouteRequest received through weak/unstable links are dropped
Failed RouteRequest  flood route discovery without Signal strength metric
Destination node,once get the first RouteRequest over stable links, it sends RouteReply
If the attempt to forward the routerequest through the final destination failed, the protocol ignores the Signal stability metric at all

26. SSA - Route Request E B D C S F A G S-B S-B-C-E S S-B-C S-B S-B-C-F
S-B-C-F-D
S-B-C
S-B C S
S-B-C-F F
S-B-C S
Source Node broadcast RouteRequest packets. Each neighbor will check if it received this request before or if its ID is in the list. If yes it will drop the packet. If not it will append its ID and the status of the link weather it is stable or not to the packet and rebroadcast the packet again.
The destination node will get the routes S-B-E-D and S-A-G-F-D, it will select the latter one due to less unstable links in the route although it is not the shortest one. A G
S-A-G
S-A
RouteRequest Dropped
Unstable Link

27. SSA - Route Reply E B D C
S-B-C-F-D S
S-B-C-F-D F A G

28. SSR – Route Maintenance
End nodes of the broken links notify source and destination
Erasing cache entries along the path
Source broadcast a new RouteRequest to find Stable link

29. SSA – Concerns
Restrict condition on forwarding RouteRequest  large setup time in case no stable links are found
Bandwidth consumption because will send RouteRequest many times
Hop count increase  because shortest hop paths may have unstable links

30. On-Demand Routing Protocols
Source Routing
Hop-by-Hop Routing
ABR
DSR
AODV
LMR
LAR
RDMAR
SSA
TORA
Elizabeth Royer and Chai Keong Toh, “A review of Current Routing Protocols for Ah Hoc Mobile Wireless Networks”, IEEE personal Communications April 1999

31. Ad Hoc On-Demand Distance Vector Routing (AODV)
Source Routing (DSR, ABR and SSA) is good for smaller networks due to large data packet overhead
AODV:
Hop by Hop basis
No need to include the full path in the data packet
Update Neighborhood information through periodic beacons

32. AODV– Route Discovery Source Node broadcast RouteRequest packet
Each intermediate node gets a RouteRequest do the following steps:
Establish a reverse link to node it received the RouteRequest from
If request received before  discard
If route to destination is available and up-to-date  return RouteReply using the reverse link
Otherwise  rebroadcast the RouteRequest
Destination node respond with RouteReply using the reverse link

33. AODV - Route Discovery E B D C S F A G
RouteRequest

34. AODV - Route Discovery E B D C S F A G
Reverse Path Setup
RouteRequest

35. AODV - Route Discovery E B D C S F A G RouteRequest Dropped
Reverse Path Setup
RouteRequest

36. AODV - Route Discovery E B D C S F A G RouteReply Reverse Path Setup
RouteRequest

37. AODV - Route Discovery E B D C S F A G Forward Route Setup RouteReply
Reverse Path Setup

38. AODV - Route Discovery E B D C S F A G Forward Route Setup RouteReply
Reverse Path Setup

39. AODV - Route Discovery E B D C S F A G Forward Route Setup RouteReply
Reverse Path Setup

40. AODV – Route Maintenance
When a node detects a link failure, it sends special RouteReply with infinity distance
RouteReply is propagated to source node
Source node initiates a new RouteRequest

41. AODV – Route Maintenance
RouteReply E B
RouteReply D C S F
When a link is broken  due to movement of nodes or any other reason
The node that discover the failure link will send RouteError to the Source
When the source gets the RouteError Packet it will delete the path from the cache
And will find another route in its cache, if it didn’t find any route it will run RouteRequest again A G

42. AODV Concerns
Route Reply from intermediate nodes can lead to inconstant routes  Stale Cache
Periodic beaconing cost
Let talk about the details of the protocol. When a node need to send something to another node. It initiates the route request procedure by sending a Route Request Packet RREQ. Each Intermediate node will setup a reverse destination vector back towards the source.

43. Location Aided Routing (LAR)
Reduce the routing overhead in the network
Source node flood the request to certain area where it last heard from the destination
For the first time, it uses normal flood mechanism broadcast to all locations
GPS is required

44. LAR
Expected Zone: The region that may contain the destination based on its previous location, speed and time.
Request Zone: The region that RouteRequest packet are allowed to propagate to reach the destination

45. LAR
Two Scheme:
Flood the RouteRequest into the request zone only to reach the destination in the expected zone
Stores the coordinates in the route request packets, the packets can only travel in the direction where the relative distance to the destination becomes smaller

46. LAR
Destination: once receive RouteRequest from the source, it sends RouteReply with its location and time stamp

47. Relative Distance Micro-Discovery ad hoc routing(RDMAR)
Reduce the routing overhead in the network
Minimize the flooding effect by limiting route request to certain number of hops
Used in Route Construction and Maintenance
No need for GPS
At the first time it works like normal flooding operation Route discovery will have global effect

48. Light Wight Mobile Routing (LMR)
Destination rooted Directed Acyclic Graph  Based of link reversals protocol
Multiple route to the destination
no need to initiate another RouteRequest unless all routes failed
Less Overhead
Good for routing in moderate mobile network
This is another protocol that uses a different metrics than shortest path. It also uses the same mechanism as DSR which is aggregating the node IDs along the path to the final destination. The objective is to select a longer lived routes which will help in reducing the cost of reconstructing routes. The metric used instead of the shortest hop count is the Location Stability or the Associatvity between nodes. Moving nodes tend to break the associativity with their neighbors and hence they are not a good candidates to carry routes.
Nodes periodically broadcast beacons to signify their existence with their neighbors, Location Stability is determined by counting the periodic beacons that a node receives from its neighbors. Links between nodes are classified into Stable and Unstable links based on the count of beacons.

49. LMR– Route Discovery Every node is aware of its neighbors
Once RouteRequest received by one of the destinstion neighbors it sends RouteReply
As the RouteReply packet traverse back to the source node, DAG is constructed
every packet is
only sent once by every node. The node remembers the
packet IDs of the packets it has received or sent
The unsigned links, through which the RPY packet
passes, are converted to directed links. The direction is
from the receiving node to the node that sent the RPY.

50. LMR - Route Request E B D C S F A G
Nevertheless, if a node does not receive the response
within a reasonable time, a timer expires and the node
can send a new QRY. This can be repeated until the node
finally gets a response or it does not need the route
anymore. A G

51. LMR - Route Reply E B D C S F A G
As the RouteReply Packet traverse to the source the unsigned links become directed towards the destination
S has many routes to D

52. LMR – Route Maintenance
Triggered, when the last route to the destination is lost
Node around the broken links inform its upstream neighbor using RouteError packet
The packet informs the neighbors that no valid route exists anymore through the node to the destination
If the upstream neighbor has a route to the destination it sends Routeply packet, the links adjusted

53. LMR - Route MaintenanceB D C S F A G
Route Error

54. LMR - Route MaintenanceB D C S F A G
Route Reply

55. LMR – Concerns
Unlimited time to recover from network partitioning  proposal for TORA

56. Temporally Ordered Routing Algorithm (TORA)
Like LMR based on Link Reversal Algorithms
Solve LMR problem in case of Network partitions by limiting the route maintenance packets to a small region
Adopt the height metrics
Requires time synchronization

57. TORA – Route Discovery
Source broadcast RouteRequest to the destination
Destination sets it height to zero and transmit an RouteReply packet
Each node along the way to the source increase its height by one and rebroadcasts the RouteReply Packet with its updated heights

58. TORA - Route Request E B D C S F A G
Nevertheless, if a node does not receive the response
within a reasonable time, a timer expires and the node
can send a new QRY. This can be repeated until the node
finally gets a response or it does not need the route
anymore. A G

59. TORA - Route Reply E B D C S F A G Height = 2 Height = 1 Height = 0

60. TORA – Route Maintenance
Triggered when the last link towards the destination is lost
Adjust Height Level and propagate through the network
Links are reversed to reflect the change
Route Deletion is flooded to delete invalid routes

61. Ant Colony Based Routing Protocols (ARA)
Adopt natural example
When ants look for food, they leave transient trail on the path for others to follow
Forwarding ANT (RouteRequest) calculates a pheromone value at each hop
Once destination is reached, Backward ANT (RouteReply) traverse back to the source
Data packet traverse along the path increase pheromone value
Pheromone value of other unused path will decrease until path is expired

62. Comparison Protocol Routes Route Selection Beacon DSR Multiple
Shortest Path No
ARB
Single
Link Stability
Yes
SSA
Signal Strength
AODV
Shortest Path, Freshness
LAR
RDMAR
LMR-TORA
Link reversal
ARA

63. Comparison Protocol DSR Global ARB SSA AODV LAR GPS Localized RDMAR
Maintenance
Special Needs
Route Discovery
DSR
Global, notify source
Global
ARB
Local, bypass broken link
SSA
AODV
LAR
GPS
Localized
RDMAR
LMR-TORA
Link reversal
Time Sync
ARA
Back track until route is found