Dsdv

DSDV
Destination-Sequenced Distance-Vector
Routing Protocol

Outline
 Introduction
 Distance-Vector
 DSDV Protocol
 Summary

Introduction
 The property of ad-hoc networks
 Topology may be quite dynamic
 No administrative host
 Hosts with finite power

Introduction
 The properties of the ad-hoc network routing
protocol
 Simple
 Less storage space
 Loop free
 Short control message (Low overhead)
 Less power consumption
 Multiple disjoint routes
 Fast rerouting mechanism

Introduction
 Routing Protocol:
 Table-driven (proactive)
 Source-initiated on-demand (reactive)
 Hybrid
 Routing Algorithm
 Link-State algorithm:
 Each node maintains a view of the network topology
 Distance-Vector algorithm:
 Every node maintains the distance of each destination

Link-State
 Like the shortest-path computation
method
 Each node maintains a view of the
network topology with a cost for each link
 Periodically broadcast link costs to its
outgoing links to all other nodes such as
flooding

Link-State
E
B
D
G
H
F
A
C
link costs

Distance-Vector
 known also as Distributed Bellman-Ford
or RIP (Routing Information Protocol)
 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 send table to all neighbors to
maintain topology

Distance Vector (Tables)
C
Dest. Next Metric …
A A 1
B B 0
C C 2
A A 0
B B 1
C B 3
1 2
A B 3
B B 2
C C 0
BA

(A, 1)
(B, 0)
(C, 1)
(A, 1)
(B, 0)
(C, 1)
Distance Vector (Update)
C
A A 1
B B 0
C C 1
A A 0
B B 1
C B 3 2
1 1
A B 3 2
B B 1
C C 0
BA
B broadcasts the new routing
information to his neighbors
Routing table
is updated

(D, 0)
(A, 2)
(B, 1)
(C, 0)
(D, 1)
(A, 1)
(B, 0)
(C, 1)
(D, 2)
Distance Vector (New Node)
C
1 1
BA D
1
broadcasts to update
tables of C, B, A with
new entry for D
A B 2
B B 1
C C 0
D D 1
A A 1
B B 0
C C 1
D C 2
A A 0
B B 1
C B 2
D B 3

Distance Vector (Broken Link)
C
1 1
BA D
1
Dest.c Next Metric …
… … …
D C 2
… … …
D B 3
… … …
D B 1
… … …
D D ∞

(D, 2)(D, 2)
Distance Vector (Loops)
C
1 1
BA D
1
… … …
D B 3
… … …
D C 2
… … …
D B 3

(D,2)
(D,4)
(D,3)
(D,5)
(D,2)
(D,4)
Distance Vector (Count to Infinity)
C
1 1
BA D
1
… … …
D B 3, 5, …
… … …
D B 3, 5, …
Dest.c Next Metric …
… … …
D C 2, 4, 6…

Distance Vector
 DV not suited for ad-hoc networks!
 Loops
 Count to Infinity
 New Solution -> DSDV Protocol

DSDV Protocol
 DSDV is Destination Based
 No global view of topology

DSDV Protocol
 DSDV is Proactive (Table Driven)
 Each node maintains routing information for
all known destinations
 Routing information must be updated
periodically
 Traffic overhead even if there is no change in
network topology
 Maintains routes which are never used

DSDV Protocol
 Keep the simplicity of Distance Vector
 Guarantee Loop Freeness
 New Table Entry for Destination Sequence Number
 Allow fast reaction to topology changes
 Make immediate route advertisement on significant
changes in routing table
 but wait with advertising of unstable routes
(damping fluctuations)

DSDV (Table Entries)
 Sequence number originated from destination. Ensures
loop freeness.
 Install Time when entry was made (used to delete stale
entries from table)
 Stable Data Pointer to a table holding information on
how stable a route is. Used to damp fluctuations in
network.
Destination Next Metric Seq. Nr Install Time Stable Data
A A 0 A-550 001000 Ptr_A
B B 1 B-102 001200 Ptr_B
C B 3 C-588 001200 Ptr_C
D B 4 D-312 001200 Ptr_D

DSDV (Route Advertisements)
 Advertise to each neighbor own routing information
 Destination Address
 Metric = Number of Hops to Destination
 Destination Sequence Number
 Rules to set sequence number information
 On each advertisement increase own destination
sequence number (use only even numbers)
 If a node is no more reachable (timeout) increase
sequence number of this node by 1 (odd sequence
number) and set metric = ∞

DSDV (Route Selection)
 Update information is compared to own routing
table
 1. Select route with higher destination sequence
number (This ensure to use always newest information
from destination)
 2. Select the route with better metric when sequence
numbers are equal.

DSDV (Tables)
C
Dest. Next Metric Seq
A A 1 A-550
B B 0 B-100
C C 2 C-588
A A 0 A-550
B B 1 B-100
C B 3 C-586
Dest. Next Metric Seq.
A B 1 A-550
B B 2 B-100
C C 0 C-588
BA 1 2

(A, 1, A-500)
(B, 0, B-102)
(C, 1, C-588)
(A, 1, A-500)
(B, 0, B-102)
(C, 1, C-588)
DSDV (Route Advertisement)
CBA
B increases Seq.Nr from 100 -> 102
B broadcasts routing information
to Neighbors A, C including
destination sequence numbers
A A 0 A-550
B B 1 B-102
C B 2 C-588
A A 1 A-550
B B 0 B-102
C C 1 C-588
A B 2 A-550
B B 1 B-102
C C 0 C-588
1 1

DSDV (Respond to Topology Changes)
 Immediate advertisements
 Information on new Routes, broken Links, metric
change is immediately propagated to neighbors.
 Full/Incremental Update:
 Full Update: Send all routing information from own
table.
 Incremental Update: Send only entries that has
changed. (Make it fit into one single packet)

(D, 0, D-000)
DSDV (New Node)
CBA D
A A 0 A-550
B B 1 B-104
C B 2 C-590
A A 1 A-550
B B 0 B-104
C C 1 C-590
A B 2 A-550
B B 1 B-104
C C 0 C-590
D D 1 D-000
1. D broadcast for first time
Send Sequence number D-000
2. Insert entry for D with
sequence number D-000
Then 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)
DSDV (New Node cont.)
CBA D
A A 1 A-550
B B 0 B-102
C C 1 C-592
D C 2 D-000
A A 0 A-550
B B 1 B-104
C B 2 C-590
A B 2 A-550
B B 1 B-102
C C 0 C-592
D 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…….

(D, 2, D-100)(D, 2, D-100)
DSDV (no loops, no count to infinity)
CBA D
Dest.c Next Metric Seq.
… … …
D C 2 D-100
… … …
D B 3 D-100
… … …
D D ∞ D-101
1. Node C detects broken Link:
-> Increase Seq. Nr. by 1
(only case where not the destination
sets the sequence number -> odd
number)
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

(D, ∞, D-101)(D, ∞, D-101)
DSDV (Immediate Advertisement)
CBA D
… … …
D C 3 D-100
… … …
D B 4 D-100
… … …
D B 1 D-100
… … …
D D 1 D-100
D D ∞ D-101
1. Node C detects broken Link:
-> Increase Seq. Nr. by 1
(only case where not the destination
sets the sequence number -> odd
number)
3. Immediate propagation
B to A:
(update information has higher
Seq. Nr. -> replace table entry)
2. Immediate propagation
C to B:
(update information has higher
Seq. Nr. -> replace table entry)
… … … ...
D C 2 D-100
D C ∞ D-101
… … … ...
D B 3 D-100
D B ∞ D-101

DSDV (Problem of Fluctuations)
What are Fluctuations
 Entry for D in A: [D, Q, 14, D-100]
 D makes Broadcast with Seq. Nr. D-102
 A receives from P Update (D, 15, D-102)
-> Entry for D in A: [D, P, 15, D-102]
A must propagate this route immediately.
 A receives from Q Update (D, 14, D-102)
-> Entry for D in A: [D, Q, 14, D-102]
A must propagate this route immediately.
This can happen every time D or any other node does its
broadcast and lead to unnecessary route advertisements
in the network, so called fluctuations.
A
D
QP
10 Hops11 Hops
(D,0,D-102)

DSDV (Damping Fluctuations)
A
D
QP
10 Hops11 Hops
How to damp fluctuations
 Record last and avg. Settling Time of every Route in
a separate table. (Stable Data)
Settling Time = Time between arrival of first route
and the best route with a given seq. nr.
 A still must update his routing table on the first
arrival of a route with a newer seq. nr., but he can
wait to advertising it. Time to wait is proposed to be
2*(avg. Settling Time).
 Like this fluctuations in larger networks can be
damped to avoid unececarry adverdisment, thus
saving bandwith.

Summery
 Advantages
 Simple (almost like Distance Vector)
 Loop free through destination seq. numbers
 No latency caused by route discovery
 Disadvantages
 No sleeping nodes
 Overhead: most routing information never
used

Dsdv

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