CIS 725

Network Layer

Network Layer

• This layer provides communication between any two nodes

• Uniform addressing scheme independent of the network technology

Network layer

Data Link layer

Problems to be addressed

• Routing• Congestion control

Routing

• Processing nodes• Switches/routers• Communication links

Datagram routing

• Each packet is routed independently • Unordered• Unreliable

Virtual Circuit routing

• Set up a path for each connection• All messages are sent over this path• Ordered• Reliable

Routing Table

• Routing table contains the next hop information

• At each node i,

for each destination j,

what is the next hop

Bellman-Ford Algorithm

• Distance table:• Routing table

Distance Vector Algorithms

distance from i to j via k

• Protocol at node i:

On receiving routing table from k

update column k of the distance table as follows

For each destination j,

if k reports its distance to j as d then

update Dj,k = d + weight(i,k)

Routing table

• Recompute the routing table as follows:

For each destination k,

update next hop to j, where

Dj,k = min(Dx,k: for all x)

• Periodically or whenever the routing table changes, send routing table to all neighbors

Bellman-Ford Algorithm

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Bellman-Ford Algorithm

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Bellman-Ford Algorithm

• Distance vector algorithm– Best path criteria

• Latency• Jitter• bandwidth

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Link State Routing

• Each node maintains the state of every link• State of the link may contain several types

of information

Learning local information

• Exchange hello packets periodically• Measure the cost of adjacent links

Distributed link state information

• Link state packet:

* source id

* cost of incident edges

* sequence numbers

Building Link State Packets

(a) A subnet. (b) The link state packets for this subnet.

Distribution Algorithm

• Controlled flooding

- hop count

- sequence numbers

- age

• Receive LSP from nbr j

- compare sequence numbers

- update topology table

- propagate LSP to all nbrs except j

Hierarchical Routing

• Divide area into regions• Maintain accurate information about nodes

in the same region

Hierarchical Routing

Hierarchical routing.

Source-routing

• Message contains the entire path• Routing table lookup is avoided at each

node

Broadcasting/Multicasting

• To send a message to all nodes:

- make a separate message to each destination

- route each message independently

Multi-destination routing

• Include all destination address in message• Each node decides which links to forward

so that it reaches all destinations

Multicast trees

• Create a spanning tree• Prune the spanning tree: Steiner tree