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CS254 Network Technologies

Lecture 5: Ethernet networks & devices

Dr Nikos AntonopoulosDepartment of Computing

University of SurreyAutumn 2006

Figure 14.1 Three generations of Ethernet

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14.1 Traditional Ethernet

MAC Sublayer

Physical Layer

Switched Ethernet

Full-Duplex Ethernet

Figure 14.2 802.3 MAC frame

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Figure 14.3 Minimum and maximum length

Figure 14.4 Ethernet addresses in hexadecimal notation

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Figure 14.5 Unicast and multicast addresses

Figure 14.6 Physical layer

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Figure 14.10 Categories of traditional Ethernet

Figure 14.13 Connection of stations to the medium using 10Base-T

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Figure 14.18 Switched Ethernet

Figure 14.19 Full-duplex switched Ethernet

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16.1 Connecting Devices

Repeaters

Hubs

Bridges

Two-Layer Switches

Figure 16.1 Connecting devices

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Figure 16.2 Repeater

A repeater connects segments of a LAN.

Note:

A repeater is a regenerator, not an amplifier.

A repeater forwards every frame; it has no filtering capability.

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Figure 16.3 Function of a repeater

Figure 16.4 Hubs

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A bridge has a table used in filtering decisions.

Note:

Bridge functionality

� Every bridge has a routing table which is used for routing frames from one network to another

� There are two main algorithms:��������� ��������� ��������� �������������� �!�"�#��$�%�������&��

� A bridge which implements the learning algo rithm o nly is called learning o r t rans p arent b rid ge

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Figure 16.5 Bridge

Learning algorithm

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Figure 16.6 Learning bridge

A Bridge problem

� If two or more transparent bridges are connected with each other forming a loop then there is the problem of livelock

� Livelock: A frame propagates infinitely through the bridges without ever reaching its destination

� Solution: Each bridge implements the spanning tree algorithm on start-up

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Figure 16.7 Loop problem

Spanning tree algorithm concepts� Each bridge is given a unique ID� Aim: Remove any loops among bridges by

transforming the logical organization of the bridges into a tree

� Concept 1: Each bridge exchanges messages with the other bridges to determine the shortest path from itself to the root bridge

� Concept 2: The bridge with the smallest ID number becomes the root bridge of the network

� Concept 3: Initially each bridge assumes to be the root bridge (selfish bridges)

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Figure 16.8 Prior to spanning tree application

Figure 16.10 Forwarding ports and blocking ports

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16.2 Backbone Networks

Bus Backbone

Star Backbone

Connecting Remote LANs

Figure 16.11 Bus backbone

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Figure 16.12 Star backbone

Figure 16.13 Connecting remote LANs

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16.3 Virtual LANs

Membership

Configuration

IEEE Standard

Advantages

Figure 16.14 A switch connecting three LANs

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Figure 16.15 A switch using VLAN software