1

Networking and LAN

Cut through, Store and forward and adaptive switch mechanism

9EC606A.36 2

Recap

In the previous class, you have learnt about

– Ethernet frame format

9EC606A.36 3

Objectives

On completion of this period, you would be able to know about

• Network Hub• Network Switch• Store and Forward switch• Cut through switch• Adaptive switching mechanism

4

Network Hub

9EC606A.36

• Hubs, switches, and routers are all devices used to connect one or more computers to other computers, networked devices, or to other networks

• Each has two or more sockets called ports into which one can plug in the cables to make the connection

• A hub is typically the least expensive, least intelligent, and least complicated of the three

• Hub takes the signal from one port and sends out to the other ports after due amplification and pulse shaping

• Hub is a physical layer device

• Hub is a multi-port repeater

Hub

6

Network Switch

9EC606A.36

• A switch does essentially what a hub does but more efficiently

• Switch also performs amplification, pulse reshaping functions like hub

• Switch learns about the configuration of the network

• By observing the traffic, it learns which physical address computer is to which port

• From the observation it prepares a forward table

• When it receives a packet from a port, it reads the MAC address from the frame header and looks into forward table. Then forwards the packet only to the port to which the machine with the destination MAC address is attached

• Therefore Switch works both on physical layer and MAC layer

Network Switch

Network Switch

9

Various Switch Architectures

• Store and Forward

• Cut through

• Adaptive

9EC606A.36

10

Store and Forward Switch

• A switch performing store-and-forward will wait to

forward a frame until it has received the entire frame

• Store-and-forward is most often used in environments

supporting reliable physical or data link protocols

• A received frame is often checked for errors before being

forwarded

9EC606A.36

11

• This type of switch is inherently slower in environments

where upper layer protocols already provide reliable

services

• The tip off that you are dealing with a store and forward

style switch is whether the switch has buffers

9EC606A.36

Store and Forward Switch Contd..

12

• Cut-through switches begin forwarding the frame as soon as the switch has read the destination address

• A cut through switch will forward the data before it has completed receiving the frame

• These switches will function at wire speed, forwarding traffic as fast as it receives it

• Nearly all cut-through switches have no RAM buffers for storing frames

9EC606A.36

Cut Through Switch

13

• Adaptive switch is an advanced switching architecture

• It provides the communications infrastructure with unprecedented high availability, scalability

• It enables Peripheral Component Interconnect (PCI)-based

telecommunications, data communications and embedded

systems to incorporate 224 PCI bus segments

9EC606A.36

Adaptive Switch

9EC606A.36 14

Summary

In this class, you have learnt about

• Hub is a physical layer device

• Switch is a layer-2 device

• Store and Forward switch stores the entire frame in a buffer then it reads the header then forwards the frame to the concerned port

• Cut through switch waits until it receives the frame header, then it forwards the frame to the concerned port without actually waiting for the arrival of the complete frame

9EC606A.36 15

Quiz

1. Hub is a _________ device

Ans: Physical layer

9EC606A.36 16

2. Switch works on _________ and

____________layers

Ans : Physical and MAC

Quiz

9EC606A.36 17

Frequently Asked Questions

1. What are the differences between hub and switch?

2. What are the differences between switch and router?

3. What are the differences between store and forward switch and cut

through switch?

4. Explain Store and forward cut through switch mechanism