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Building Routing Table

There are 2 methods of building routing tables. 1. Manually 2. Software

There are then further 2 methods of computing these.

Static Routing

It is not flexible.
It is done at boot time
It has small network overhead.

Dynamic Routing

It can work around network failures automatically.
It allows automatic updates by the programmers.

Computing Shortest Path in a Graph

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We use Djikstra's [^1] algorithm to compute the shortest path.

Distributed Route Computation

If a node fails then the switch updates its routing table information to avoid the failed hardware.

Distance Vector Routing

The switches periodically broadcast topology information throughout the network.
Then other switches update their routing tables according to the information received.

Vector - Distance Algorithm

Link-State Routing

The network topology is separated from route computations.
switches send link-state information about local connections and then they build their routing tables

Comparison

Distance Vector Routing

  • Simple to implement
  • switch updates its own routing table first
  • It is used in RIP.
  • Complex to implement
  • switch performs independent computations.
  • it is used in OSPF.

Example of WAN Technologies

ARPANET

Began in 1960s, it was funded by Advanced Research Project Agency, which is an organization of US defense department.

X.25

This was standard for connection-oriented networking.
It began from IFU which was originally CCITT.

Frame Relay

It is used for Telco service for delivering blocks of data.
It is connection based service and requests Telco to establish the circuit between 2 end points.
Its speeds are following: - 56 Kbps - 1.5 Mbps - 100 Mbps

SMDS

Switched Multi megabit Data Service is also a Telco service.
This one is connection less and speed ranges from 1.5 Mbps to 1000 Mbps.

ATM

Asynchronous transfer mode was designed for lower jitter, high capacity, audio, video and data.
It uses fixed size 48 octets data and 5 octets header.

  1. Read more about Djikstra's Algorithm. ↩