Routing

12-NTU-1065 Mohsin Shoukat

12-NTU-1083 Shahmeer Ali

Table of Contents

• Routing

• Desirable properties of routing

• Design parameter of routing algorithms

• Fixed Routing

– Dijkstra Algorithm

• Flooding Routing

• Adaptive/Dynamic Routing

– Distance Vector Routing

– Link state Routing

• Multicast Routing

Router

• A routers networking hardware device which send and receive data packets to other networks.

Routing

• The routing is to chose the best cost effective

path, which is selected by routing algorithm

Desirable Properties of Routing

Correctness and simplicity

Robustness

Stability

Fairness and Optimality

Efficiency

Design Parameter of Routing Algorithms

Performance criteria :Number of hops , Cost , Delay, Throughput

Decision time : Datagram , Virtual circuit

Decision plane :EACH NODE (Distributed), Central Node (Centralized) , Originated

Node (Source).

Network Information source: None , Adjacent node , Nodes Along Route , All

Nodes.

Network information updating time: continuous, periodic , major load change ,

topology change.

Fixed Routing

A route is selected for each source-destination pair of nodes in network.

The routes are fixed they only may change if there is change in topology in network.

Fixed Routing :Example

• SUCH a big routing directory is created in network control center.

• This has a big drawbacks. If this NC center fail everything fail, so it is not very reliable.

From

Node

To Node

1 2 3 4 5 6

1 - 2 3 2 2 2

2 1 - 1 6 6 6

3 1 1 - 4 5 1

4 6 6 3 - 5 6

5 4 4 3 4 - 4

6 2 2 2 4 4 -

Fixed Routing

As directory is packet receive and send it to its next node.Question is how these directory created?

Node 1 Directory

Destinatio

n

Next Node

2 2

3 3

4 2

5 2

6 2

Node 2 Directory

Destination Next Node

1 1

3 1

4 6

5 6

6 6

Node 3 Directory

Destination Next Node

1 1

2 1

4 4

5 5

6 1

Node 4 Directory

Destinatio

n

Next Node

1 6

2 6

3 3

5 5

6 6

Node 5 Directory

Destination Next Node

1 4

2 4

3 3

4 4

6 4

Node 6 Directory

Destination Next Node

1 2

2 2

3 2

4 4

5 4

Dijkstra algorithm

It find the least cost paths from given node to all other nodes .

It work on static condition when topology and cost fix.

• These are basic steps:

• -initialization; M= {s} , Dn =dSN for n!=s

• -find neighboring nodes not in M has least-cost path from s

include in M.

• -update the least cost path.

Dijkstra Algorithm

Iteration M C(2) path C(3) path C(4) path C(5) path C(6) path

1 (1) 2, 1-2 2, 1-3 ------- ------- -------

2 (1,2) 2, 1-2 2, 1-3 6,1-2-4 ------- 3, 1-2-6

3 (1,2,3) 2, 1-2 2, 1-3 5,1-2-6-4 7, 1-2-6-4-5 3, 1-2-6

Dijkstra Algorithm

Iteration M C(2) path C(3) path C(4) path C(5) path C(6) path

4 (1,2,3,6) 2, 1-2 2, 1-3 5, 1-2-6-4 7, 1-2-6-4-5 3, 1-2-6

5 (1,2,3,4,6) 2,1-2 2, 1-3 5, 1-2-6-4 7, 1-2-6-4-5 3, 1-2-6

6 (1,2,3,4,5,6) 2, 1-2 2, 1-3 5, 1-2-6-4 7,1-2-6-4-5 3,1-2-6

Fixed routing

Advantages:

• Simple, cost given, least cost path given you can use it simple.

• Works well for stable load network.

• Same for virtual-circuit or datagram.

Problems:

• Lack of flexibility, if network condition change it fail

• Does not react to failure network, or congestion condition

Flooding Routing

• Require no network any information whatsoever

• Every incoming packet is send to all node except from which it come.

Flooding Routing

Advantages:

• Reliable.

• All routes are tried, so at least one packet goes to shortest route.

• All nodes direct or indirectly visited.

Problems:

• Generate large number copies are generate which make congestion.

• Suitable if use damping mechanism so that larges number of packets are not make.

Technique To Use

• Hop-Count: a hop counter is contain in header of packet and it decrease each one time when pass through the node and discard when it reach to zero.

• Sequence Number: Keep track of packets which are responsible for flooding using a sequence number .Avoid sending them out second time.

Flooding

Utilities Of Flooding:

Flooding is robustness: in case of war or load or topology change under such

case this is very useful

May be used in virtual circuit like when packet reach to D from least cost path

it send acknowledgment and it save.

Flooding always uses shortest path since it explore every possible path to D.

Some time to messages all nodes so it’s good. To upgrade info this helpful

Rather its disadvantages it’s also have imp utilities.

Selective Flooding

• A variation which is slightly more practical is Selective Flooding.

• The router don’t send packets to in all direction but in the direction to the

destination. Give weightage to check whether it is going to D or moving away

to D.

Random Routing

• This has the simplicity and robustness of flooding with far

less traffic load.

• A node only selective one outgoing path for retransmission of incoming packet.

Random Routing

Don’t need the info of the network like how many packets are in Queue bandwidth etc.

Round Robin fashion in which you chose random and choose a link and next time you choose other link etc.

Random Routing

A refinement is to assign a Probability to each outgoing link and to select the link based on that probability

So here the Data Rate is used as network information use higher data rate path so packet shall be deliver to the destination but it also has a limitation like it don’t select cost effective path

Adaptive routing

Adaptive routing use networking information for it’s routing

Routing decision change as condition on the network change.

Two principal that affecting routing decision.

– Failure: when a node, link fail it can’t longer use as a route.

– Congestion: when a particular area of the network congested it is desirable

to move the route packets around the congestion area.

So adaptive routing changes dynamically with the networking condition.

Adapting Routing

• For Adaptive Routing, there must be exchange network information among

the nodes.

• Number Of Hops (simplest one but the not use i.e. for particular ‘S’ TO ‘D’ how

many hops packets use)

• Time Delay in msec (for a particular S to D , queue length is know we can call

the time delay)

• Total Packets : Total number of packets queued in network.

Adapting Routing

More Information Exchange, Better Routing, More Overhead

More Frequent, Better Routing, More Overhead

So there is trade off.

Adaptive Routing

Problems

• Routing is done dynamically changing condition so it put Burdon on

switching nodes.

• More processing power required for Routing Decisions

• It may react too quickly to change network state, thus produces

Congestion.

Adaptive Routing

Advantages

• Improve performance

• Can aid in congestion control

• Widely used

Distance Vector Routing

• Key characteristic:

Knowledge about Entire Network.

Routing only to Neighbor.

Information sharing at Regular Interval.

Network ID Cost Next Router

Link State Routing

• Basic steps:

• Identify the neighboring nodes.

• Measure the delay or cost to each of its neighbor.

• Form a packet contain all the information.

• Send the packets to all other nodes (flooding)

• Compute the shortest path to every other node (Dijkstra algorithm)

• Here in link state information gather is only from its neighboring nodes rather entire network like distance routing.

• So the basic idea is it gather information to its neighboring node and route to all like flooding.

• And information sharing gather is done after regular interval.

Advertise ID NetworkID

(destination)

Cost Next Router

Link State Routing

Problems

Information is gather at regular interval

More complex

It’s make some kind of database.

Computational power and memory

Expensive

Multicast Routing

• Sending information from S to D. but in some case we have to send some message to a group of peoples.

• Uses for Broadcasting

Technique

-Find The Spanning Tree

-Flooding

Review

• Routing

• Desirable properties of routing

• Design parameter of routing algorithms

• Fixed Routing

• Dijkstra Algorithm

• Flooding routing

• Adaptive/dynamic routing

• Adaptive Routing

• Distance vector routing

• Link state routing

• Multicast routing