Presentation Routing algorithm

PRESENTATIONTOPIC
ROUTING ALGORITHM
Link State
DistanceVector

Group Member
BASIT HUSSAIN | 2017-CS-126
HAMZA KHAN | 2017-CS-105
IRTEZA HASSAN | 2017-CS-50

Router
• A router has two processes inside it.
• One of them handles each packet as it arrives, looking up the outgoing line
to use for it in the router tables.This process is forwarding.
• The other process is responsible for filling in and updating the routing
tables.That is where the routing algorithm comes into play.

Router
Router
Router 3
Router 1
Router 2

Routing Algorithm
• Part of the network layer responsible for deciding which output line an
incoming packet should be transmitted on.
• If the network uses datagrams internally, this decision must be made a new
path for every arriving data packet.
• If the network uses virtual circuits internally, routing decisions are made
only when a new virtual circuit is being set up.This case sometimes called
session routing.

Routing Example
• Routing = building maps and giving directions

Desired Properties of Routing Algorithm
• Correctness
• Simplicity
• Robustness
• Stability
• Fairness and Efficiency

Types of Routing Algorithms
• Non-Adaptive or Static Algorithm
Routing paths are computed in advance, offline, and downloaded to the routers when the
network is booted. It does not respond to failures.
• Adaptive or Dynamic Algorithm
Change their routing decisions to reflect changes in the topology, and sometimes
changes in the traffic.

Routing Algorithms
• Shortest Path Algorithm
• Flooding
• DistanceVector Routing
• Link State Routing
• Hierarchical Routing
• Broadcast Routing
• Multicast Routing
• Anycast Routing

DistanceVector Routing
• It’s a Adaptive or Dynamic Algorithm.
• Each Router Maintains a table called “Vector”.
• Table has the Best Known Distance for Each Routers.
• Tables are Updated by exchanging Information with neighbors(Router).
• Each Router knows the Best Distance to Reach another Router.
• Also Known as Bellman-Ford Routing Algorithm.

DistanceVector Routing
• Each Router’sTable has one entry for one router.
• This entry has two parts.
• Preferred out going Line for each Router.
• Estimated distance to destination Router.
• Distance is basically considered by no’s of Hops.
• Delays basically measured by sending ECHO packets to another Router.

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A I H K J Line
JA Delay is 8
JI Delay is 10
JH Delay is 12
JK Delay is 6
NewRoutingTableforRouterJ

Advantages & Disadvantages
• Advantages of DistanceVector routing –
• It is simpler to configure and maintain than link state routing.
• Disadvantages of DistanceVector routing –
• 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 onWAN links.

Link State Routing Algorithm
Why?
• DistanceVector Routing algorithm often took too long converge after the
network topology changed (due to the count-to-infinity problem).

Idea Behind Link State Routing
• This has five parts
1. Discovery its neighbors and learn their network addresses.
2. Set the distance or cost metric to each of its neighbors.
3. Construct a packet telling all it has just learned.
4. Send this packet to and receive packets from all other routers.
5. Compute the shortest path to every other router.

Learning About Neighbors
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Broadcast LAN
Graph Model

Setting Link Cost
• Each link to have a distance or cost metric for finding shortest paths.
• For example, 1-Gbps Ethernet may have a cost of 1 and 100-Mbps Ethernet a cost of 10.
• Higher capacity paths are the better choices.
• The most direct way to determine this delay is to send over the line a special ECHO packet
that the other side is required to send back immediately.
• The round-trip time and driving it by two, the sending router can get a reasonable estimate
of the delay.

Advantages and disadvantages of link-state
routing
• Advantage:
1. Routers have direct knowledge of all links in the network and how they are connected.
2. Link-state protocols require less router processor power than distance vector protocols.
3. The topology database eliminates the need for a routing table
• Disadvantage:
1. The necessary databases require more memory than a distance vector protocol requires.
2. The complex algorithm requires more CPU time than a distance vector protocol requires.

Building Link State Packet
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• Sequence Packet: Each packet contains a sequence no., this keep tracks
how many times this packet has sent.
• Age Packet: Show the life of a packet in Network, after passing by one Hop
it is decremented by one.
• When to build Link State packets?
 Build them periodically at regular intervals.
 Build them when some significant event occurs.

Link State Protocols
• IS-IS(Intermediate System – Intermediate System)
• OSPF(Open Shortest Path First)

Presentation Routing algorithm

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