Wireless Ad Hoc Network Routing Protocols CSE 802.11 Maya Rodrig.
CSE 802.11 University of Washington
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Transcript of CSE 802.11 University of Washington
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CSE 802.11University of Washington
Multipath Routing Protocols in AdHoc Networks
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First Question
Why another lecture on ad-hoc routing protocols?
Keyword: multipath Ability to provide multiple routing options from a
source to a destination Have “enough redundancy” to handle the ad-hoc nature
of these networks
Today, the multipath property of routing protocols will take center stage
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But … before we begin….
Why do we need different protocols than in the Internet?
The attributes of the problem have changed: Infrastructureless
Nodes’ availabilities are very low…
Must provide incentives to cooperate
Adequate security story Cooperation-induced trust
Mobility: topology changes frequently
Power consumption: communication and computation consume energy
Network environment: More complex (subject to more factors)
Factors change frequently and in unpredictable ways
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But … before we begin….
Why do we need different protocols than in the Internet?
The attributes of the problem have changed: Infrastructureless
Nodes’ availabilities are very low…
Must provide incentives to cooperate
Adequate security story Cooperation-induced trust
Mobility: topology changes frequently
Power consumption: communication and computation consume energy
Network environment: More complex (subject to more factors)
Factors change frequently and in unpredictable ways
P2P!!!
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90% of sessions last less than 1 hour
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90% of sessions last less than 10 mins
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50% of sessions last less than 1 hour
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The Availability Story Revealed
Consider a path P of 4 hops and 5 nodes Assuming independent behavior What is the probability that P will change within the
next 10 minutes? Ad-Hoc: 89% P2P: 77%
Can’t afford to propagate every change throughout the network (like Internet protocols) Although you might need node discovery
Need on-demand routing protocols
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Desirable Characteristics of Ad-Hoc Routing Protocols
Adapt to rapid changes Multipath On-demand
Low communication overhead Low computation overhead Provides incentive to cooperate Secure Loop-free Maintains node connectivity
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Desirable Characteristics of Ad-Hoc Routing Protocols
Adapt to rapid changes Multipath On-demand
Low communication overhead Low computation overhead Provides incentive to cooperate Secure Loop-free Maintains node connectivity
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Multi-path Ad-Hoc Routing Protocols
Multipath DSR 2 versions in today’s paper
AOMDV AODV-BR ROAM MDVA
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Multi-path Ad-Hoc Routing Protocols
Multipath DSR 2 versions in today’s paper
AOMDV AODV-BR ROAM MDVA
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DSR - Route Discovery Example
Route Request
Message
1
2
3
5
4
7
6
8
9
101
1
1, 2
1, 2
1, 3
1, 3
1, 2, 5
1, 2, 5
1, 2, 5
1, 3, 4
1, 2, 5, 6
1, 3, 4, 7
1, 3, 4, 7
1, 3, 4, 7, 9
1, 2, 5, 6, 8
1, 2, 5, 6, 8
Route Reply
1, 3, 4, 7, 9, 10
From: Stefan Dulman([email protected])
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How it works: S broadcasts a Route Request message to D Each node forwards request by adding its own address
and re-broadcasting Requests propagate until:
The target is found
A node that knows a route to D is found
DSR Route Discovery
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Route Maintenance
If a node does not receive a confirmation from the next node that the packet was successfully forwarded, initiates a Route Error message back to the source
The data packet will be transmitted over another existing path (if multipath) or a new route discovery could be initiated
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DSR – With Multipath (1st Version)
Route Request
Message
1
2
3
5
4
7
6
8
9
101
1
1, 2
1, 2
1, 3
1, 3
1, 2, 5
1, 2, 5
1, 2, 5
1, 3, 4
1, 2, 5, 6
1, 3, 4, 7
1, 3, 4, 7
1, 3, 4, 7, 9
1, 2, 5, 6, 8
1, 2, 5, 6, 8
Route Reply
1, 3, 4, 7, 9, 10
1, 2, 5, 6, 8, 10
Remember link-wise disjoint paths between source and destination
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Multipath Behavior
When primary route breaks, pick the best alternate route to forward data
When no alternate routes left, re-initiate route discovery
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DSR – With Multipath (2nd Version)
Route Request
Message
1
2
3
5
4
7
6
8
9
101
1
1, 2
1, 2
1, 3
1, 3
1, 2, 5
1, 2, 5
1, 2, 5
1, 3, 4
1, 2, 5, 6
1, 3, 4, 7
1, 3, 4, 7
1, 3, 4, 7, 9
1, 2, 5, 6, 8
1, 2, 5, 6, 8
Route Reply
1, 3, 4, 7, 9, 10
1, 2, 5, 6, 8, 10
Remember one link-wise disjoint path between each intermediate node and destination
3, 5, 6, 8, 10
4, 5, 6, 8, 10
7, 8, 10 9, 8, 10
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Multipath Behavior
When a node detects a link is broken, the node replaces the unused path in the data packet with its alternate path
When alternate path breaks, the node transmits an error packet backward
Route discovery restarts only after all alternate paths between all intermediate nodes and destination have failed
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DSR Properties
Multipath On-demand Loop-free (source routing) Maintains connectivity
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Performance Enhancements
Full use of route cache Nodes operate in promiscuous mode to overhear route
discoveries Intermediary nodes must check for loop-free
Piggy-backing data on route discoveries
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DSR Issues
Scalability issues: Source routing means each packet carries the full path MD5 - 16bytes per nodeID
10 nodes means 160bytes
11% of 1500 bytes packet
4X the size of TCP/IP header
IP - 4bytes per nodeID 10 nodes means 40bytes
3% of 1500 bytes packet
As big as the TCP/IP header
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Basic AODV Route Discovery
When a route is needed, source floods a route request for the destination.
S
A
B
E
C
D
RREQ (broadcast)
From: U. of CincinattiMarina & Das
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Basic AODV Route Discovery
Reverse path is formed when a node hears a non-duplicate route request.
Each node forwards the request at most once (pure flooding).
S
A
B
E
C
D
RREQ (broadcast)Reverse Path
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Basic AODV Route Discovery
Reverse path is formed when a node hears a non-duplicate route request.
Each node forwards the request at most once (pure flooding).
S
A
B
E
C
D
RREQ (broadcast)Reverse Path
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Basic AODV Route Discovery
Observation: Duplicate RREQ copies completely ignored. Therefore, potentially useful alternate reverse path info lost.
S
A
B
E
C
D
Reverse Path
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Alternate Reverse Paths: A Naïve Approach
Form reverse paths using all duplicate RREQ copies.
Causes routing loops.
S
A
B
E
C
D
Reverse Path
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Alternate Reverse Paths: A Naïve Approach
Question: how to form alternate “loop-free” reverse paths using some duplicate RREQ copies?
S
A
B
E
C
D
Reverse Path
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Loop Freedom
Key idea: Impose ordering among nodes in every path.
Notion of upstream/downstream nodes.
General loop-freedom rule: Never form a route at a downstream node via an upstream node.
dji
j is downstream to i w.r.t d
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Multiple Loop-free Reverse Paths
Suppose RREQ from S includes highest seqno for itself.
S
A
B
E
C
D
RREQ (broadcast)
0
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S
A
B
E
C
D
RREQ (broadcast)Reverse Path
0
1
1
Multiple Loop-free Reverse Paths
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S
A
B
E
C
D
RREQ (broadcast)Reverse Path
0
1
1
2
2
Multiple Loop-free Reverse Paths
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S
A
B
E
C
D
Reverse Path
0
1
1
2
2
Multiple Loop-free Reverse Paths
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Alternate Paths
Keep multiple routes but always advertise only one hop count to others. Hop count of that path is the “advertised hop count”
Which one? Longest path at the time of first advertisement.
Or.. Keep only the disjoint alternate paths The set of copy packets received at any node defines a set
of disjoint paths To ensure link-wise disjoint paths:
Exchange the first and last hops in packet
A different first and last hop ensures link-wise disjoint
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AOMDV Properties
Multipath: Can support local policies for choosing alternate paths
On-demand Loop-free
Sequence numbers
Maintains connectivity
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Final thoughts…
Unexplored trade-offs: Reliability vs. energy consumption vs. benefit Disjoint paths vs. braided paths
Bad interaction between TCP and on-demand adhoc protocols The perennial problem of not being able to distinguish
between congestion and broken link When will TCP be using ECNs?
Crazy idea: use cell infrastructure to compute routing tables