Introduction to IT and Communications Technology

Justin ChampionC208 – 3292

Ethernet SwitchingCE00378-1

Content Looking at

SwitchingBridgesCollision Domains

Switch operation A switch works with the inspection of the MAC

address If the switch has a particular device attached the data

will be forwarded to that machine

Bridge operation

Bridges

Full duplex

Transmit and receive concurrently due to separate cables for each

Network latency This is the measure of the transfer time of a

Ethernet frameThe latency of the network is an important issue

Particularly with Multimedia low Latency is needed

Cut-through These switches

Will start to forward the frame as soon as the destination MAC address has been read

Reduces latency in the network Reduces reliability of the switch

Store-and-forward The frames will be stored in the switch

They are then forwarded to the destination When stored the frames can be checked for errors This increases latency on the network Does increase reliability

Prevents corrupted packets being forwarded

Spanning-tree-operation This is a protocol used between routers

It is responsible for generating routes between points Ensuring that looping does not take place Storing alternative routes, in the event of failure

STP states Each port which uses Spanning Tree Protocol (STP)

Will always be in one of the following 5 states Blocking

The port will only receive bridge protocol data unit (BDPU) frames These are used to exchange information with already operating ports on the

network When a switch is first turned on it will be in this state

Listening Building an active knowledge of the topology connected

Learning The port is preparing to transfer Ethernet frames Building a bridging table

Forwarding Sending or receiving Ethernet frames

Disabled This port will not be involved with the use of STP

Collision domains A collision domain

Is the part of the cable where multiple devices may potentially communicate at once

A good network will have small collision domains and therefore less likely to have collisions corrupting data

Collision domain segmentation Network devices which operate at different layers effect the

collision domain Layer 1 devices – repeaters, Hubs

Will extend the domain Layer 2 devices – Switches, Bridges

Will break up the domain Layer 3 devices – routers

Will break up the domain

Increasing a collision domain

Repeaters extendthe size of the collision domain

If a computer anywhere in this network communicates every device will receive the frame!

Four repeaters (part of 5-4-3-2-1 rule)

5 segments of network media

4 repeaters or hubs 3 host segments of the

network 2 link sections with no

hosts 1 large collision domain

Round-trip delay calculation

Extension of a collision domain Layer 1 devices just repeat the signal with NO

interpretationThis extends the collision domain, by forwarding all

traffic

Limiting the collision domain The following items will limit the collision domain

These devices processes the data before forwarding Bridge Router Switch

A bridge can segment a collision domain

A bridge can segment a collision domain

Bridge

A bridge can segment a collision domain

Broadcasts in a bridged environment Level 2 devices

These will segment the collision domain However they will have no effect on the broadcast domain A broadcast packet will be sent on all ports to all devices

Effect of broadcast radiation on hosts in an IP network

Average number of broadcasts and multicasts for IP

Broadcast domain segmentation

Data flow through a network

Segments

Summary Looked at Ethernet devices

Operations of switchesTypes of switches

Store and forward Cut through

Network latencyCollision domainsBroadcast domains