Introduction to IT and Communications Technology Justin Champion C208 – 3292 Ethernet Switching CE

Content Looking at  Switching  Bridges  Collision 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 frame  The 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 extend the size of the collision domain If a computer anywhere in this network communicates every device will receive the frame!

Four repeaters (part of 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 interpretation  This 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

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 switches  Types of switches Store and forward Cut through  Network latency  Collision domains  Broadcast domains