highly dynamic destination- sequenced distance-vector routing protocol (dsdv) for mobile computers...
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Highly Dynamic Destination-Sequenced Distance-Vector Routing
Protocol (DSDV) for Mobile Computers
Charles E. PerkinsPravin Bhagwat
Mobile Computing, 1996
Outline Introduction of ad hoc network Overview of routing methods Goal of this paper DSDV protocol Property of the DSDV protocol Summary
Introduction of Ad Hoc Network Properties of ad-hoc networks
Dynamic and self-starting network No administrative intervention
required Battery-powered
Distance-Vector Every node maintains a routing
table all available destinations the next node to reach to destination the number of hops to reach the
destination Periodically exchanges route table
with all neighbors to keep routing data up to date
Problems of Distance Vector Loops
C1 1
BA D1
Dest.
NextMetri
c…
… … …D B 3
Dest.
NextMetri
c…
… … …D C 2
Dest.
NextMetri
c…
… … …D B 3
Dest.
NextMetri
c…
… … …D D ∞
Dest.
NextMetri
c…
… … …D D 1
Problems of Distance Vector Counting-to-infinity
(D,2)
(D,4)
(D,3)
(D,5)
(D,2)
(D,4)
1 1D
1
CBA
Dest.
Next Metric …… … …D B 3, 5, …
Dest.
Next Metric …… … …D C 2, 4, 6…
Dest.
Next Metric …… … …D B 3, 5, …
DSDV Protocol DV-based routing protocol Sequence number attached route
table Route advertisement Route updates Problem of fluctuations
DSDV Protocol DV-based routing protocol Sequence number attached route
table Route advertisement Responding to topology change Route selection criteria Problem of fluctuations
Route Table Entry Structure Forwarding table (for routing)
Advertised table (for update)
DestinationNextHop Metric
SequenceNumber
Install Time
Stable Data
A A 0 S550_A T001_A Ptr_AB B 1 S102_B T001_A Ptr_BC B 3 S588_C T002 _A Ptr_CD B 4 S312_D T001_A Ptr_D
Destination MetricSequenceNumber
A 0 S550_AB 1 S102_BC 3 S588_CD 4 S312_D
Route Advertisement Advertise to each neighbor own
routing information Advertised table
Rules to set sequence number Advertisement
increase own destination sequence number (use only even numbers)
Broken link increase sequence number of this node by 1
(odd sequence number) set metric =
Route Advertisement
(A, 1, A-500)(B, 0, B-102)(C, 1, C-588)
(A, 1, A-500)(B, 0, B-102)(C, 1, C-588)
CBA
B increases Seq. from 100 -> 102B broadcasts routing information to Neighbors A, C including destination sequence numbers
1 1
Dest.
NextMetri
cSeq
A A 0 A-550B B 1 B-102C B 2 C-588
Dest.
NextMetri
cSeq
A A 1 A-550B B 0 B-102C C 1 C-588
Dest. NextMetri
cSeq.
A B 2 A-550B B 1 B-102C C 0 C-588
Responding to Topology Change
Immediate advertisements New routes, broken links, metric
changes Full/Incremental Update
Full Update: Send all routing information from own table.
Incremental Update: Send only entries that has changed.
1.New Node
CBA
Dest.
NextMetri
cSeq.
A A 0 A-550B B 1 B-104C B 2 C-590
Dest.
NextMetri
cSeq.
A A 1 A-550B B 0 B-104C C 1 C-590
Dest.
NextMetri
cSeq.
A B 2 A-550B B 1 B-104C C 0 C-590D D 1 D-000
D
(D, 0, D-000)
1. D broadcast for first timeSend Sequence number D-000
2. Insert entry for D with sequence number D-000Then immediately broadcast own table
(A, 2, A-550)(B, 1, B-102)(C, 0, C-592)(D, 1, D-000)
(A, 2, A-550)(B, 1, B-102)(C, 0, C-592)(D, 1, D-000)
3. C increases its sequence number to C-592 then broadcasts its new table.
………………
4. B gets this new information and updates its table…….
Dest.
NextMetri
cSeq.
A B 2 A-550B B 1 B-104C C 0 C-590
2.Broken Link
CBA D
(D, 2, D-100)(D, 2, D-100)
2. B does its broadcast-> no affect on C (C knows that B has stale information because C has higher seq. number for destination D) -> no loop -> no count to infinity 1. Node C detects broken Link:
-> Increase Seq. Nr. by 1(only case where not the destination sets the sequence number -> odd number)
Dest.
NextMetri
cSeq.
… … …D B 3 D-
100
Dest.
NextMetri
cSeq.
… … …D C 2 D-
100
Dest.
NextMetri
cSeq.
… … …D D D-
101
3.Broken Link - Immediate Advertisement
Dest.
NextMetri
cSeq.
… … … ...
D B 3D-
100
D B D-101
Dest.
NextMetri
cSeq.
… … … ...
D C 2D-
100
D C D-101
Dest.
NextMetri
cSeq.
… … …D D 1
D-100
D D D-101
CBA D
(D, , D-101)
3. Immediate propagation B to A:(update information has higher Seq. Nr. -> replace table entry)
(D, , D-101)
2. Immediate propagationC to B:(update information has higher Seq. Nr. -> replace table entry)
1. Node C detects broken Link:-> Increase Seq. Nr. by 1(only case where not the destination sets the sequence number -> odd number)
Route Selection Criteria Update information is compared to
own routing table 1. Higher destination sequence
number 2. Better metric when sequence
numbers are equal.
Problem of Fluctuations Two routes with identical sequence
numbers are received in the wrong order Leads to unnecessary route
advertisements
Problem of Fluctuations
Dest. Metric
D 12
A
BC
D
Mobile Host Collection 1
Mobile Host Collection 2
Dest. Metric
D 11
Damping Fluctuations Settling time: time between arrival
of first route and the best route with a given sequence number Last settling time Average settling time
Delay: Average_Settling_Time × 2