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Ad hoc On-demand Multipath Distance Vector (AOMDV) Routing. Mahesh Marina Samir Das University of Cincinnati. On-demand Multipath Routing. In each route discovery, find multiple routes between source and destination. Use alternate routes on a route failure.

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ad hoc on demand multipath distance vector aomdv routing

Ad hoc On-demand Multipath Distance Vector (AOMDV) Routing

Mahesh Marina Samir Das

University of Cincinnati

on demand multipath routing
On-demand Multipath Routing
  • In each route discovery, find multiple routes between source and destination.
  • Use alternate routes on a route failure.
  • New route discovery needed only when all routes fail.
  • Fewer number of route discoveries.
  • Reduction in delay and routing overhead.
main question
Main Question
  • In the AODV framework, how to compute multiple paths between source and destination during route discovery?
  • With minimal additional overhead.
basic aodv route discovery
Basic AODV Route Discovery

RREQ (broadcast)

  • When a route is needed, source floods a route request for the destination.

A

E

D

S

B

C

basic aodv route discovery1
Basic AODV Route Discovery

RREQ (broadcast)

Reverse Path

  • Reverse path is formed when a node hears a non-duplicate route request.
  • Each node forwards the request at most once (pure flooding).

A

E

D

S

B

C

basic aodv route discovery2
Basic AODV Route Discovery

RREQ (broadcast)

Reverse Path

  • Reverse path is formed when a node hears a non-duplicate route request.
  • Each node forwards the request at most once (pure flooding).

A

E

D

S

B

C

basic aodv route discovery3
Basic AODV Route Discovery

Reverse Path

  • Observation: Duplicate RREQ copies completely ignored. Therefore, potentially useful alternate reverse path info lost.

A

E

D

S

B

C

alternate reverse paths a na ve approach
Alternate Reverse Paths: A Naïve Approach

Reverse Path

  • Form reverse paths using all duplicate RREQ copies.
  • Causes routing loops.

A

E

D

S

B

C

alternate reverse paths a na ve approach1
Alternate Reverse Paths: A Naïve Approach

Reverse Path

  • Question: how to form alternate “loop-free” reverse paths using some duplicate RREQ copies? Which some?

A

E

D

S

B

C

loop freedom
Loop Freedom
  • Key idea: Impose ordering among nodes in every path.
  • Notion of upstream/downstream nodes.

i

j

d

j is downstream to i w.r.t d

  • General loop-freedom rule: Never form a route at a downstream node via an upstream node.
aodv loop freedom
AODV Loop Freedom
  • Destination sequence numbers to order routing events in time.
  • Ordering among <seqno, hop count> tuples at different nodes on a path.
    • higher seqno has precedence
    • if same seqno, lower hop count has precedence
  • Can’t we use the same idea in AOMDV?
  • No. Because “hop count rule” restricts us to a single path.
  • But can use a similar idea though!
aomdv loop freedom
AOMDV Loop Freedom
  • Sequence number rule: Keep only routes for the highest dest seqno (like in AODV).
  • For the same dest seqno,

Route advertisement rule: Keep multiple routes but always advertise only one of them to others. Hop count of that path is the “advertised hop count”

    • Which one? Longest path at the time of first advertisement.
    • Why? Maximize chances of forming more paths.

Route acceptance rule: Accept a route from a neighbor only if it has a smaller or equal advertised hop count. Break ties using node ids.

    • No need for coordination with upstream nodes.
aomdv loop freedom1
AOMDV Loop Freedom
  • Sequence number rule: Keep only routes for the highest dest seqno (like in AODV).
  • For the same dest seqno,

Route advertisement rule: Keep multiple routes but always advertise only one of them to others. Hop count of that path is the “advertised hop count”

    • Which one? Longest path at the time of first advertisement.
    • Why? Maximize chances of forming more paths.

Route acceptance rule: Accept a route from a neighbor only if it has a smaller or equal advertised hop count. Break ties using node ids.

    • No need for coordination with upstream nodes.
aomdv loop freedom2
AOMDV Loop Freedom
  • Sequence number rule: Keep only routes for the highest dest seqno (like in AODV).
  • For the same dest seqno,

Route advertisement rule: Keep multiple routes but always advertise only one of them to others. Hop count of that path is the “advertised hop count”

    • Which one? Longest path at the time of first advertisement.
    • Why? Maximize chances of forming more paths.

Route acceptance rule: Accept a route from a neighbor only if it has a smaller or equal advertised hop count. Break ties using node ids.

    • No need for coordination with upstream nodes.
aomdv routing table entry
AOMDV Routing Table Entry

Dest

Seqno

Advertised hop count

Hop count 1

Next hop 1

Hop count 2

Next hop 2

aomdv loop freedom3
AOMDV Loop Freedom
  • Sequence number rule: Keep only routes for the highest dest seqno (like in AODV).
  • For the same dest seqno,

Route advertisement rule: Keep multiple routes but always advertise only one of them to others. Hop count of that path is the “advertised hop count”

    • Which one? Longest path at the time of first advertisement.
    • Why? Maximize chances of forming more paths.

Route acceptance rule: Accept a route from a neighbor only if it has a smaller or equal advertised hop count. Break ties using node ids.

    • No need for coordination with upstream nodes.
multiple loop free reverse paths
Multiple Loop-free Reverse Paths

RREQ (broadcast)

  • Suppose RREQ from S includes highest seqno for itself.

A

E

D

S

0

B

C

multiple loop free reverse paths1
Multiple Loop-free Reverse Paths

1

RREQ (broadcast)

Reverse Path

A

E

D

S

0

B

C

1

multiple loop free reverse paths2
Multiple Loop-free Reverse Paths

2

1

RREQ (broadcast)

Reverse Path

A

E

D

S

0

B

C

1

2

multiple loop free reverse paths3
Multiple Loop-free Reverse Paths

2

1

Reverse Path

A

E

D

S

0

B

C

1

2

multiple loop free forward paths
Multiple Loop-free Forward Paths

1

2

Forward Path

  • Another modification to basic AODV route discovery: multiple replies from destination.

A

E

D

S

0

B

C

2

1

how many paths
How Many Paths?
  • Too many paths are not useful.
    • Overhead proportional to # paths.
    • Diminishing utility with larger # paths. Analytical study in [Nasipuri-Das IC3N-99, ACM MONET J. 01]
  • Solution: Disjoint paths.
    • Automatically fewer paths.
    • Paths fail independently. Better utility.
    • Node or link disjoint?
    • Too few node disjoint paths in dense networks using flooding.
finding link disjoint paths

dest seq. next last hop

no hop hop count

D … N1 L1 …

D … N2 L2 …

Finding Link-disjoint Paths

Examples

How?

  • Maintain last hop info in routing table.
  • Ensure that next hops and last hops before destination are unique.
  • This requires route request and replies to carry first hop info.

D

S

D

S

D

S

performance evaluation
Performance Evaluation
  • Ns-2 with CMU wireless extensions.
  • 100 nodes in a 1000m x 1000m field.
  • Random way point mobility model
  • 25 CBR/UDP sources each sending 512 byte packets @ 2 packets/s.
summary
Summary
  • AOMDV - a multipath extension to AODV
    • multiple loop-free and link-disjoint paths.
  • AOMDV performance relative to AODV
    • more than factor of two improvement in delay.
    • about 25% reduction in routing load.