1. Adhoc Networks Routing Tutorial - Part II -
Internet Computing KUT (
Youn-Hee Han
It is licensed under a Creative Commons Attribution 2.5 License

2. Reactive Routing Protocols
Computer Network

3. Reactive Approach - Principle
On-Demand
Re-active, become active only when needed
The routes are created when required
The source has to discover a route to the destination.
The source and intermediate nodes have to maintain a route as long as it is used.
Routes have to be repaired in case of topology changes.
Normally 3 Phases
Route Discovery
Route Maintain
Route Delete
More Scalable than Table Drive (Proactive) Protocols
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4. Reactive Approach - Principle
Representative Protocols
DSR – Dynamic Source Routing
AODV – Ad Hoc On-demand Distance Vector Routing
TORA – Temporally Ordered Routing Algorithm
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5. Dynamic Source Routing (DSR)
Full Routes are kept in each data packet
Sender of a packet determines the complete sequence of nodes to forward the packet
Reaction to topology changes more rapid
node caches multiple routes to destination
Avoids need to perform Route Discovery each time a route breaks
Each host participating in the ad hoc network maintains a route cache in which it caches source routes for destination nodes
Computer Network

6. Dynamic Source Routing (DSR)
Route Discovery:
allows any host to dynamically discover a route to any other host in the ad hoc network.
a host initiating a route discovery broadcasts a route request packet, Route Request (RREQ)
each route request packet contains a route record, request ID
If a host saw the packet (with the same request ID) before, discards it.
Otherwise, the host looks up its route caches to look for a route to destination, If not find, appends its address into the packet, rebroadcast,
If finds a route in its route cache, sends a route reply packet, which is sent to the source by route cache, RREQ’s info. or the route discovery.
if successful, initiating host receives a route reply packet, Route Reply (RREP)
Any node which has a route to the destination replies with a route reply
the route is saved in the cache for future use
Any route that is seen through a node is cached
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7. Dynamic Source Routing (DSR)
Route maintenance:
A host monitors the correct operation of routes in use
A host is able to detect that the network topology has changed such that it can no longer use its route to D because a link along the route no longer works
A Route ERROR is sent to the Source
All nodes along the path remove that route
예를 들어 S – E – F – J – D
임의의 노드 이동 (if F)
E와 J는 Route cache에 저장된 경로중 F가 포함된 경로는 모두 삭제
E와 J는 각각 S와 D에게 Route ERROR를 보냄
S와 D도 Route cache에 저장된 경로중 F가 포함된 경로는 모두 삭제
If receives a Route ERROR, the source uses a cached alternate route to destination or sends out request packets for a new route
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8. DSR – Route Discovery Y Z S E F B C M L J A G H D K I N
When node S wants to send a packet to node D, but does
not know a route to D, node S initiates a route discovery
Source node S floods Route Request (RREQ)
Each node appends its own address when forwarding RREQ Y Z S E F B C M L J A G H D K I N
Represents a node that has received RREQ for D from S
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9. Broadcast transmission (ACKed)
DSR – Route Discovery
Originating a RREQ
RREQ Y
Source
Destination
Route Record S D
Broadcast transmission (ACKed) Z
[S] S E F B C M L J A G H D K I N
ACKs:
Link-layer ACK or
Passive ACKs or
App-level software-initiated ACKs
Represents transmission of RREQ
Represents a node that has received RREQ for D from S
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10. DSR – Route Discovery Forwarding RREQ Y RREQ Z S [S,E] E F B C M L J A
Source
Destination
Route Record S D
S, E
RREQ Z
Path Accumulation S
[S,E] E F B C M L J A G
[S,C] H D K I N
Forwarding RREQ
A request is forwarded by a node if
the node is not destination
the node has not seen RREQ with the same Request Id (from the same source)
When forwarding RREQ, use a random delay to avoid collision
Node H receives packet RREQ from two neighbors B and C
Node C and E send RREQ to each other
Duplicate RREQ are discarded
[X,Y] Represents list of Node ID appended to RREQ
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11. DSR – Route Discovery Forwarding RREQ Y Z S E F B [S,E,F] C M L J A G
Route cache
S – E – F Z S E F B
[S,E,F] C M L J A G H D K
[S,B,A]
[S,C,G] I N
[S,C,H]
Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once
Duplicate RREQ are discarded
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12. DSR – Route Discovery Forwarding RREQ Y Z S E F [S,E,F,J] B C M L J AH D
[S,C,H,I] K I N
[S,C,G,K]
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13. DSR – Route Reply
Destination D on receiving the first RREQ, sends a Route Reply (RREP)
RREP includes the route from S to D on which RREQ was received by node D
Route Reply is sent by reversing the route in Route Request (RREQ)
this requires bi-directional link
to ensure this, RREQ should be forwarded only if it received on a link that is known to be bi-directional
If IEEE MAC is used to send data, then links have to be bi-directional (since ACK is used)
If unidirectional (asymmetric) links are used, then RREP may need a route discovery for S from node D
Piggyback RREP on RREQ to S
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14. DSR – Route Reply RREP delivery Y RREP [S,E,F,J,D] Z S E F B C M L J A
Route cache
S – E – F – J – D
RREP [S,E,F,J,D] Z S E F B C M L J A G H D K I N
RREP control message
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15. DSR Optimization - Route Caching
Each node caches a new route it learns
When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F
When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S
When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route [F,J,D] to node D
When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D
Other optimisations:
Piggybacking on route discoveries
data on route requests
RREP on Route Discovery from D to S
RREP Hop Limit
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16. DSR - Summary Advantages Disadvantages
Reactive: routes maintained only between nodes who need to communicate
Route caching can further reduce route discovery overhead
a single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches
Disadvantages
Packet header size grows with route length due to source routing
Flood of route requests may potentially reach all nodes in the network
Care must be taken to avoid collisions between route requests and route reply propagated by neighboring nodes
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17. DSR - Summary
Increased contention if too many route replies come back due to nodes replying using their local cache
Route Reply Storm problem
Reply storm may be eased by preventing a node from sending RREP if it hears another RREP with a shorter route
Route reply storms also prevented by randomising delay time before sending route replies
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18. DSR – one more example (1,4) (1,3) (1,4,7) (1,2) (1,3,5,6) (1,3,5)
source broadcasts a packet containing address of source and destination
source
(1,4) 1 4
The destination sends a reply packet to source. 8
(1,3)
destination 3 7
(1,4,7) 2
The node discards the packets having been seen
(1,2) 6 5
(1,3,5,6)
(1,3,5)
The route looks up its route caches to look for a route to destination
If not find, appends its address into the packet
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19. AODV AODV: Ad hoc On-demand Distance Vector routing protocol
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 RFC 3561, July, 2003.
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
Computer Network

20. Adhoc On-demand Distance Vector (AODV)
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-hop routing
Routes are based on dynamic table entries maintained at intermediate nodes
Similar to Dynamic Source Routing (DSR), but DSR uses source routing
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21. Adhoc On-demand Distance Vector (AODV)
Designed for MANETs with 10,000 to 100,000 nodes
Uses a broadcast route discovery mechanism as in DSR
Each node only keeps next-hop information
Improves scalability and performance
Reduces dissemination of control traffic
Eliminates overhead on data traffic
From DSR
Route discovery
Route maintenance
From DSDV
Hop-by-hop routing
Sequence numbers
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22. AODV – overview Route Table Entry Destination IP Address (KEY)
Destination Sequence Number
it is used to determine the freshness of the information contained from the originating node.
crucial to avoiding routing loops
Valid Destination Sequence Number flag
Other state and routing flags
valid, invalid, repairable, being repaired
Network Interface
Hop Count
number of hops needed to reach destination
Next Hop
List of Precursors
Neighboring nodes to which a RREP was forwarded.
Lifetime (expiration or deletion time of the route)
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23. AODV – overview Route Table Entry 4 2 5 3 1 6 Node 1 에서의 routing table
DstIP
DstSeq
State
Hop
Next
Lifetime
Precursor 2 3
Valid 1 10 5 7 4
valid 4 2 5 3 1 6
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24. AODV – overview Route Table Entry 4 2 5 3 1 6 Node 1 에서의 routing table
DstIP
DstSeq
State
Hop
Next
Lifetime
Precursor 2 3
Valid 1 10 5 7 4
Unvalid 4 2 5 3 1 6
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25. AODV – overview Basic Message Set RREQ – Route request
RREP – Route reply
RERR – Route error
HELLO – For link status monitoring
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26. AODV – overview RREQ Messages
While communication routes between nodes are valid, AODV does not play any role.
A RREQ message is broadcasted when a node needs to discover a route to a destination.
As a RREQ propagates through the network, intermediate nodes use it to update their routing tables (in the direction of the source node)
Setup Reverse Path to Source Node
DSN is set to the value in the originator sequence number field of the RREQ, if it is greater than the stored DSN.
The RREQ also contains the most recent sequence number for the destination (DSN).
If the source node don’t know it, DSN is zero
A valid destination route must have a sequence number at least as great as that contained in the RREQ.
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27. AODV – overview RREQ Message Format 1 J: Join Flag, R: Repair Flag
G: Gratuitous RREP flag
indicates whether a gratuitous RREP should be unicast to the node specified in the Destination IP Address field
D: Destination only flag
indicates only the destination may respond to this RREQ
U: Unknown sequence number
indicates the destination sequence number is unknown
Hop Count
The number of hops from the Originator IP Address to the node handling the request.
RREQ ID
A sequence number uniquely identifying the particular RREQ when taken in conjunction with the originating node's IP address.
Destination Sequence Number
The latest sequence number received in the past by the originator for any route towards the destination.
Originator Sequence Number
The current sequence number to be used in the route entry pointing towards the originator of the route request. 1
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28. AODV Route Discovery (1/7)B A S E F H J D C G I K Z Y M N L
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29. AODV Route Discovery (2/7)B A S E F H J D C G I K Z Y M N L
Source
Destination
Hop count S D 1
RREQ 전송
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30. AODV Route Discovery (3/7)B A S E F H J D C G I K Z Y M N L
Source
Destination
Hop count S D 2
Reverse Path
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31. AODV Route Discovery (4/7)B A S E F H J D C G I K Z Y M N L
Source
Destination
Hop count S D 3
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32. AODV Route Discovery (5/7)B A S E F H J D C G I K Z Y M N L
Source
Destination
Hop count S D 4
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33. AODV Route Discovery (6/7)
Route Table B A S E F H J D C G I K Z Y M N L
Destination
Next hop
Expire time S E 10
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34. AODV – overview RREP Messages
When a RREQ reaches a destination node, the destination route is made available by unicasting a RREP back to the source route.
A node generates a RREP if:
It is itself the destination.
It has an active route to the destination.
Ex: an intermediate node may also respond with an RREP if it has a “fresh enough” route to the destination.
As the RREP propagates back to the source node, intermediate nodes update their routing tables (in the direction of the destination node).
Setup Forward Path to Source Node
You should point out that the RREQ/RREP mechanism depends on the assumption that links are symmetrical, or bidirectional.
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35. AODV – overview RREP Message Format 2 R: Repair Flag
A: Acknowledgment required
receiver of the RREP is expected to return a RREP-ACK message
Prefix Size
If nonzero, the 5-bit Prefix Size specifies that the indicated next hop may be used for any nodes with the same routing prefix (as defined by the Prefix Size) as the requested destination
Hop Count
The number of hops from the RREP generator to the Destination IP Address.
Destination Sequence Number
The destination sequence number associated to the route.
Lifetime
The time in milliseconds for which nodes receiving the RREP consider the route to be valid.
Destination IP Address
The IP address of the destination for which a route is supplied.
Originator IP Address
The IP address of the node which originated the RREQ for which the route is supplied. 2
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36. AODV Route Discovery (7/7)
Route Table
RREP 전송
Forward Path Y
Destination
Next hop
Expire time S E 9 D J 10 Z S E F B C M L J A G H D K I N
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37. AODV – overview RERR Messages RERR Message is broadcasted when:
This message is broadcast for broken links
Generated directly by a node or passed on when received from another node
RERR Message is broadcasted when:
A node detects that a link with adjacent neighbor is broken (destination no longer reachable).
If it gets a data packet destined to a node for which it does not have an active route and is not repairing.
If it receives a RERR from a neighbor for one or more active routes.
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38. AODV – overview RERR Message Format N: No delete flag 3 DestCount
set when a node has performed a local repair of a link, and upstream nodes should not delete the route.
DestCount
The number of unreachable destinations included in the message; MUST be at least 1.
Unreachable Destination IP Address
The IP address of the destination that has become unreachable due to a link break.
Unreachable Destination Sequence Number
The sequence number in the route table entry for the destination listed in the previous Unreachable Destination IP Address field.
RREP-ACK Message Format 3 4
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39. AODV – overview Hello Messages
HELLO messages are used to determine local connectivity
HELLO Message = RREP with TTL = 1
If a node does not receive any packets (HELLO messages or otherwise) from a neighbor for more than ALLOWED_HELLO_LOSS * HELLO_INTERVAL, the node will assume that the link to this neighbor is currently lost.
A node should use HELLO messages only if it is part of an active route.
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40. AODV – overview Basic Messaging Routing G A B D F C E Source RREQ RREQ
RREP
RREQ B D
RREQ
RREP
RREQ
RREQ
RREP F
Destination C
RREQ
RREQ
Charles, you may not want to include this slide, and leave coverage of the topic to whomever is covering either message types (Visal) or route discovery (Fahd?). My intention was just to introduce the basic message flow, and not get into details. In the example shown, the basic flow is clear, but some explanation is required to show how nodes B and F handle duplicates of the RREQ, i.e., how do they decide to throw away the RREQs from C, E and G? I think the Hop Count field in the message is the key, but describing this starts to encroach on later parts of the presentation. E
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41. AODV – overview Why Sequence Numbers in AODV A B C D E A B C D E
To avoid using old/broken routes
To determine which route is newer
To prevent formation of loops
Assume that A does not know about failure of link C-D because RERR sent by C is lost
Now C performs a route discovery for D. Node A receives the RREQ (say, via path C-E-A)
Node A will reply since A knows a route to D via node B
Results in a loop (for instance, C-E-A-B-C ) A B C D E A B C D E
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42. AODV – overview destination sequence number (DSN) used as timestamps.
DSN is updated whenever a node receives new (i.e., not stale) information about the sequence number from RREQ, RREP, or RERR messages
Source sequence number in RREQ indicates “freshness” of reverse route to the source
Destination sequence number in RREQ indicates the latest sequence number received in the past by the originator towards the destination.
Destination sequence number in RREP or RERR indicates “freshness” of route to the destination
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43. AODV – overview Sequence Numbers Rule
A sender node MUST increment it before it sends a RREQ
An intermediate node in RREQ path determines whether Received DSN < Stored DSN. If it is, the RREQ message MUST be discarded and the sender is notified of the new information.
Ensures RREQs not forwarded unnecessarily
Before a node sends a RREP in response to a RREQ, it MUST update its own sequence number to MAX {its current stored DSN : DSN in the RREQ packet}.
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44. AODV – overview
When does an intermediate node sends RREP to the RREQ originator?
“an intermediate node has a more fresh information”
It means
Seq(A) < Seq(B)
Intermediate node (B) either has a newer route to endpoint than the start node (A)
If a node receives a RREQ, when does a node updates its routing table entry?
1. Received Number > Stored Number
2. Received Number == Stored Number, and (The number in hop count field of the message + 1) < Stored hop count number
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45. AODV – Flowchart Generate RREQ packet
Control Messages sent of Port 654 UDP
When need to send data.
Have a route
to destination? No
Generate RREQ packet (Hop Count = 0)
Yes
Broadcast RREQ packet
NET_TRAVERSAL_TIME Timer set
Retry ++
Start to transmit
data packet
NET_TRAVERSAL_TIME= 2 * NET_TRAVERSAL_TIME
Yes
RREP received within NET_TRAVERSAL_TIME?
Retry < RREQ_RETRIES? No
Yes No
Packet Sending is not allowed
End

46. AODV – Flowchart Receive RREQ packet Receive RREQ packet
Already Process RREQ ID?
Yes No
Discard it
Set the Reverse path
Destination ? No
Fresh Route Information
to destination ? No
Yes
Yes
Rebroadcast
RREQ packet
Reply RREP packet
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47. AODV – Flowchart Receive RREP packet Receive RREP packet
Set Forward path
Source node? No
Update next hop
information
Yes
Start to transmit
data packet
Unicast RREP
via Reverse path
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48. AODV – Flowchart Detecting broken link Detecting Broken Link
Generate RERR packet
Precursor count = 1? No
Yes
Multiple unicast RERR
Unicast RERR
via Reverse path
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49. Timeouts
A routing table entry maintaining a reverse path is purged after a timeout interval
timeout should be long enough to allow RREP to come back
A routing table entry maintaining a forward path is purged if not used for a active_route_timeout interval
if no is data being sent using a particular routing table entry, that entry will be deleted from the routing table (even if the route may actually still be valid)
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50. Link Failure Detection
Hello messages
Absence of hello message is used as an indication of link failure
When it is sent?
Every HELLO_INTERVAL, a node checks whether it has sent a broadcast (a RREQ or an layer 2 message) within the HELLO_INTERVAL
If it has not, it broadcasts HELLO
Alternatively, failure to receive several MAC-level acknowledgement may be used as an indication of link failure
A neighbor of node X is still considered active for if the neighbor sent a packet within active_route_timeout interval which was forwarded using an entry in the routing table
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51. AODV Route Maintenance
Link failures are propagated by means of RERR messages
When node X detects a link failure to its Neighbor Y, which is a node on the path node S to node D, 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
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52. 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 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
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53. AODV Route Maintenance
Route reconstruction ( = route recovery)
If a route is broken due to the movement of a node 3’ 3’ 3 1 2 1 2 R R s 4 s 4
Node 3 moves to mew location 3’
Node 2 notices loss of link, sends link failure (RERR) to node 1
Node 1 forward link failure (RERR) to source
Source reinitiate rote discovery, finds new route through nodes
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54. Route Maintenance 경로 손실시 자신의 Precursor 노드에게 알린다 S – E – F – J – D S 이동
E부터 D까지 Forward path 유지
모든 Reverse path 손실
F 이동
S부터 E까지 Reverse path, J부터 D까지 Forward path 유지
S부터 F까지 Forward path, F부터 D까지 Reverse path 손실
D 이동
S부터 J까지 Reverse path 유지
모든 Forward path 손실
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55. AODV - Route Discovery (1/10)B D C A
1. Node S needs a route to D in order to send data packets to D
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56. AODV - Route Discovery (2/10)B D C A
1. Node S needs a route to D in order to send data packet to D
2. Creates a Route Request (RREQ)
Enters D’s IP addr, seq#,
S’s IP addr, seq#
hopcount (=1)
- Destination Sequence Number
. The latest sequence number received in the past by the originator for any route towards the destination.
- Originator Sequence Number
. The current sequence number to be used in the route entry pointing towards the originator of the route request.
- Hop Count
. The number of hops from the Originator IP Address to the node handling the request.
- RREQ ID
. A sequence number uniquely identifying the particular RREQ when taken in conjunction with the originating node’s IP address.
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57. AODV - Route Discovery (3/10)B
RREQ S A C D
2. Creates a Route Request (RREQ)
Enters D’s IP addr, seq#,
S’s IP addr, seq#
hopcnt (=1)
3. Node S broadcasts RREQ to neighbors
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58. AODV - Route Discovery (4/10)B
RREQ S A C D
4. Node A receives RREQ
Makes reverse route entry for S dest = S, nexthop = S, hopcnt = 1
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59. AODV - Route Discovery (5/10)B
RREQ S A C D
4. Node A receives RREQ
Makes reverse route entry for S dest = S, nexthop = S, hopcnt = 1
It has no route to D, so it rebroadcasts RREQ
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60. AODV - Route Discovery (6/10)B
RREQ S A C D
5. Node C receives RREQ
Makes reverse route entry for S dest = S, nexthop = A, hopcnt = 2
It has a route to D, and the seq# for route for D is >=D’s seq# in RREQ
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61. AODV - Route Discovery (7/10)B S A
RREP C D
6. Node C sends RREP
C creates a Route Reply (RREP) Enters D’s IP addr, seq # S’s IP addr, hopcnt to D (=1) Lifetime
Unicasts RREP towards A
- Destination Sequence Number
. The destination sequence number associated to the route.
- Hop Count
. The number of hops from the Originator IP Address to the Destination IP Addresses For multicast route requests this indicates the number of hops to the multicast tree member sending the RREP.
- Lifetime . The time in milliseconds for which nodes receiving the RREP consider the route to be valid.
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62. AODV - Route Discovery (8/10)B
RREP S A
RREP C D
7. Node A receives RREP
Makes forward route entry to D dest = D, nexthop = C, hopnt = 2, Lifetime
Unicasts RREP to S
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63. AODV - Route Discovery (9/10)B
RREP S A C D
8. Node S receives RREP
Makes forward route entry to D dest = D, nexthop = A, hopcnt = 3, Lifetime
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64. AODV - Route Discovery (10/10)B S A C D
9. Node S sends data packets on route to D
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65. Route Maintenance (1/5) 1. Link between C and D breaks down
RERR C D
1. Link between C and D breaks down
C can perform local repair for the route to D
The RERR message is sent whenever a link break causes one or more destinations to become unreachable from some of the node’s neighbors.
- N flag
. No delete flag
. set when a node has performed a local repair of a link, and upstream nodes should not delete the route.
- Destcount
. the number of unreachable destinations included in the RERR message.
. Must be at least 1.
- Unreachable Destination IP Address
. The IP address of the destination that has became unreachable due to a link break.
- Unreachable Destination Sequence Number
. The sequence number in the route table entry for the destination listed in the previous Unreachable Destination IP Address field.
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66. Route Maintenance (2/5) 1. Link between C and D breaks down
RERR C D
1. Link between C and D breaks down
C can perform local repair for the route to D
2. Node C invalidates route to D in route table
The RERR message is sent whenever a link break causes one or more destinations to become unreachable from some of the node’s neighbors.
- N flag
. No delete flag
. set when a node has performed a local repair of a link, and upstream nodes should not delete the route.
- Destcount
. the number of unreachable destinations included in the RERR message.
. Must be at least 1.
- Unreachable Destination IP Address
. The IP address of the destination that has became unreachable due to a link break.
- Unreachable Destination Sequence Number
. The sequence number in the route table entry for the destination listed in the previous Unreachable Destination IP Address field.
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67. Route Maintenance (3/5) 3. Node C creates Route Error (RERR) messageB S A
RERR C D
3. Node C creates Route Error (RERR) message
C creates a Route Error (RERR) Enters DestCount (=1), D’s IP addr, seq #
“DestCount” field indicates the number of unreachable destinations included in the RERR message.
Sends to upstream neighbors in precursor list
The RERR message is sent whenever a link break causes one or more destinations to become unreachable from some of the node’s neighbors.
- N flag
. No delete flag
. set when a node has performed a local repair of a link, and upstream nodes should not delete the route.
- Destcount
. the number of unreachable destinations included in the RERR message.
. Must be at least 1.
- Unreachable Destination IP Address
. The IP address of the destination that has became unreachable due to a link break.
- Unreachable Destination Sequence Number
. The sequence number in the route table entry for the destination listed in the previous Unreachable Destination IP Address field.
Computer Network

68. Route Maintenance (4/5) 4. Node A receives RERRB
RERR S A
RERR C D
4. Node A receives RERR
Checks whether C is its next hop on route to D
Deletes route to D or invalidates the route to D
Forwards RERR to S
If the hop count of the newly determined route to the destination is greater than the hop count of the previously known route
should issue a RERR message for the destination, with the ‘N’ bit set.
Computer Network

69. Route Maintenance (5/5) 5. Node S receives RERRB D C A
RERR
5. Node S receives RERR
Checks whether A is its next hop on route to D
Deletes route to D or invalidates the route to D
Rediscovers route if still needed
Computer Network

70. AODV Example (1/8) Node 1 needs to send a data packet to Node 74 6 1 7 5 3 2
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)
Computer Network

71. AODV Example (2/8) Node 1 sends a RREQ packet to its neighbors4 6 1 7 5 3 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
Computer Network

72. AODV Example (3/8) 4 6 1 7 5 3 2
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 in its routing table
Increment hop_cnt in the RREQ packet
Computer Network

73. AODV Example (4/8) RREQ reaches Node 6, which knows a route to 71 7 5 3 2
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
Computer Network

74. AODV Example (5/8) 4 6 1 7 5 3 2
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
Computer Network

75. AODV Example (6/8) 4 6 1 7 5 3 2
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
Computer Network

76. AODV Example (7/8) 4
Dest
Next
Hops 7 4 3 6 1 7 5 3 2
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
Computer Network

77. AODV Example (8/8) Assume that Node 7 moves and link 6-7 breaks4 6 1 7 5 3 2 7
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
Computer Network

78. AODV vs. DSR Common Processes of AODV and DSR Maintain Sequence Number
Routing Table operations
Create or update route table entry
Route Discovery
Route message creation (RREQ, RREP)
Route message processing at each node
Check route table for destination address route entry
Reverse route entry for originator and precursors
Route Management
Active Link Monitoring
link-layer feedback, Hello messages, neighbor discovery, route timeouts
Updating route lifetimes
Route Error Generation
Route Error Processing
Computer Network

79. AODV vs. DSR AODV is not source routed DSR is source routed
Nodes only choose the next hop
May lead to lower memory requirements, faster more compressed routing tables.
DSR is source routed
Nodes choose full route through network when sending a packet
Computer Network

80. AODV vs. DSR Different Processes of AODV and DSR
Path accumulation
DSR=> Source route accumulated in Request packet
AODV=> Route table entry does not contain list of precursors
Routing tables for AODV, after a route discovery process
Routing tables for DSR, after a route discovery process A B C D
Destination
Next A B C D
Destination
path
B-A
C-B-A
B-C
C-B
B-C-D
C-D
Computer Network

81. AODV vs. DSR Congestion Handling
One method that AODV handle congestion is:
If the source node receives no RREP from the destination, it may broadcast another RREQ, up to a maximum of RREQ_RETRIES.
For each additional attempt that a source node tried to broadcast RREQ, the waiting time for the RREP is multiplied by 2.
DSR is not capable of handling congestion.
Explain why DSR can’t handle congestion
Computer Network

82. AODV – one more example source destination
The source broadcasts a route packet
The neighbors in turn broadcast the packet till it reaches the destination
source
RREQ
destination
RREP
Reply packet follows the reverse path of route request packet recorded in broadcast packet
The node discards the packets having been seen
Computer Network

83. Various Ad Hoc Routing Projects
DSR (Dave Johnson, CMU)
WINGs (JJ Garcia/UCSC)
ROAM (JJ Garcia/UCSC)
WAMIS (Gerla/UCLA)
ODMRP (Gerla et.al/UCLA)
TRAVLR (Kleinrock/UCLA)
Tora/IMEP (Park, Corson/UMD)
Link Quality (Rohit Dube/UMD)
LAR (Texas A&M)
TBRPF (SRI)
OLSR (Inria: Clausen./Jacquet)
DSDV (Dest. Sequence #'s)
AODV (refinement of DSDV)
AOMDV (Multipath – Das/Marina)
Hierarchical (Akyildiz/Georgia Tech)
GPSR (Karp/Harvard)
CBRP (Singapore)
Terminodes (EPFL)
MMWN (Steenstrup/BBN)
ABR (C.K. Toh)
STAR (JJ Garcia/UCSC)
ZRP (Zygmunt Haas/Cornell)
Fisheye/Hierarchical (UCLA)
CEDAR (Urbana-Champaign)
Computer Network