Routing Algorithms. Distance Vector routing Algorithm. link state routing algorithm. path vector routing algorithm

1. Routing Algorithms
N.G.S.Parameswaran.
Assistant Professor,
Department of Computer Applications,
V.H.N.S.N. College (Autonomous)
Virudhunagar.

2. Routing
• The process of moving a packet of data
from source to destination.
• Routing is usually performed by a
dedicated device called a Router.
• It is the key feature of Internet because
it enables messages to pass from one
computer to another and eventually
reach the target machine

3. Classification of Routing Algorithms
Adaptive Algorithms
• These are the algorithms which change their
routing decisions whenever network topology or
traffic load changes.
• The changes in routing decisions are reflected in
the topology as well as traffic of the network.
• Also known as Dynamic routing, these make
use of dynamic information such as current
topology, load, delay, etc. to select routes.
• Optimization parameters are distance, number
of hops and estimated transit time.

4. Classification of Adaptive Algorithms
• (a) Isolated – In this method each, node makes its routing
decisions using the information it has without seeking
information from other nodes. The sending nodes doesn’t
have information about status of particular link.
Disadvantage is that packet may be sent through a
congested network which may result in delay. Examples:
Hot potato routing, backward learning.
• (b) Centralized – In this method, a centralized node has
entire information about the network and makes all the
routing decisions. Advantage of this is only one node is
required to keep the information of entire network and
disadvantage is that if central node goes down the entire
network is done.
• (c) Distributed – In this method, the node receives
information from its neighbors and then takes the decision
about routing the packets. Disadvantage is that the packet
may be delayed if there is change in between interval in
which it receives information and sends packet.

5. Non-Adaptive Algorithms
• These are the algorithms which do not change their routing
decisions once they have been selected. This is also known
as static routing as route to be taken is computed in advance
and downloaded to routers when router is booted.
• (a) Flooding – This adapts the technique in which every
incoming packet is sent on every outgoing line except from
which it arrived. One problem with this is that packets may
go in loop and as a result of which a node may receive
duplicate packets. These problems can be overcome with the
help of sequence numbers, hop count and spanning tree.
• (b) Random walk – In this method, packets are sent host by
host or node by node to one of its neighbors randomly. This
is highly robust method which is usually implemented by
sending packets onto the link which is least queued.

6. Types of Routing Algorithms
• Distance Vector
• Link State
• Path Vector

7. Distance Vector Routing Algorithm
• Historically known as the old ARPANET
routing algorithm (or known as Bellman-
Ford algorithm).
• Each router maintains a Distance Vector
table containing the distance between
itself and ALL possible destination nodes.
• Distances based on a chosen metric, are
computed using information from the
neighbors’ distance vectors.

8. • A router transmits its distance vector to
each of its neighbors in a routing packet.
• Each router receives and saves the most
recently received distance vector from each
of its neighbors.
• A router recalculates its distance vector
when:
– It receives a distance vector from a neighbor
containing different information than before.
– It discovers that a link to a neighbor has gone
down.
Algorithm

9. The DV calculation is based on minimizing the cost to
each destination.
Dx(y) = Estimate of least cost from x to y
C(x,v) = Node x knows cost to each neighbor v
Dx = [Dx(y): y ∈ N ] = Node x maintains distance vector
Node x also maintains its neighbors' distance vectors
– For each neighbor v, x maintains Dv = [Dv(y): y ∈ N ]
• From time-to-time, each node sends its own distance
vector estimate to neighbors.
• When a node x receives new DV estimate from any
neighbor v, it saves v’s distance vector and it updates
its own DV using B-F equation:
Dx(y) = min { C(x,v) + Dv(y)} for each node y ∈ N

10. • Advantages
– It is simpler to configure and maintain than link
state routing.
• Disadvantages
– It is slower to converge than link state.
– It is at risk from the count-to-infinity problem.
– It creates more traffic than link state since a hop
count change must be propagated to all routers and
processed on each router. Hop count updates take
place on a periodic basis, even if there are no
changes in the network topology, so bandwidth-
wasting broadcasts still occur.
– For larger networks, distance vector routing results
in larger routing tables than link state since each
router must know about all other routers. This can
also lead to congestion on WAN links.

11. Link State Routing Algorithm
• Also known as Shortest path Routing algorithm.
• Information about the state of (Router
interfaces) links is known as link-states
• This information includes:
• The interface's IP address and subnet mask.
• The type of network, such as Ethernet
(broadcast) or Serial point-to-point link.
• The cost of that link.
• Any neighbor routers on that link.

12. • It is a dynamic routing algorithm in which each
router shares knowledge of its neighbors with
every other router in the network.
• A router sends its information about its
neighbors only to all the routers through
flooding.
• Information sharing takes place only whenever
there is a change.
• It makes use of Dijkastra’s Algorithm for
making routing tables.
Link State Routing Algorithm

13. Two Phases
Reliable flooding
» Tell all routers what you know about your
local topology
Path calculation (Dijkstraʼs algorithm)
» Each router computes best path over
complete network

20. Path Vector Routing
• Path Vector Routing is a routing algorithm in unicast
routing protocol of network layer, and it is useful for
interdomain routing.
• The principle of path vector routing is similar to that of
distance vector routing.
• It assumes that there is one node in each autonomous
system that acts on behalf of the entire autonomous
system is called Speaker node.
• The speaker node in an AS creates a routing cable and
advertises to the speaker node in the neighbouring ASs.
• A speaker node advertises the path, not the metrics of
the nodes, in its autonomous system or other
autonomous systems.

22. • It is the initial table for each speaker node in a
system made four ASs.
• Here Node A1 is the speaker node for AS1, B1 for
AS2, C1 for AS3 and D1 for AS4, Node A1 creates
an initial table that shows A1 to A5 and these are
located in AS1, it can be reached through it
• A speaker in an autonomous system shares its
table with immediate neighbours.
• Here Node A1 share its table with nodes B1 and
C1 , Node C1 share its table with nodes A1,B1
and D1 , Node B1 share its table with nodes A1
and C1 , Node D1 share its table with node C1

23. • If router A1 receives a packet for nodes
A3 , it knows that the path is in AS1.
• If it receives a packet for D1,it knows that
the packet should go from AS1,to AS2
and then to AS3 ,then the routing table
shows that path completely.
• If the node D1 in AS4 receives a packet
for node A2,it knows it should go through
AS4,AS3,and AS1.
Working Principle

24. Functions of Path vector Routing
• PREVENTION OF LOOP
• POLICY ROUTING
• OPTIMUM PATH

25. Any Probes?

26. Thank You