Networking Chapter 4

Ethernet BasicsEthernet Basics

Chapter 4

ObjectivesObjectives• Define and describe Ethernet• Explain early Ethernet implementations• Describe ways to extend and enhance

Ethernet networks

OverviewOverview

Three Parts to Chapter 4Three Parts to Chapter 4

• Ethernet• Early Ethernet Networks• Extending and Enhancing Ethernet Networks

EthernetEthernet

• First Ethernet implementation– Develop by Xerox in 1973– Based on bus topology– Transferred data at 3Mbps max– Evolved into today’s Ethernet standards

Ethernet is a standard for a family of network technologies that share the same basic bus topology, frame type, and network access method.

• Next iteration of Ethernet– DIX standard (ca 1979)– DIX = Digital Equipment (DEC)+Intel+Xerox– Transferred data at 10Mbps max

• Standardization– DIX transferred control to IEEE– IEEE created the 802.3 (Ethernet) subcommittee

• 10BaseT– Earliest version of Ethernet to use UTP cabling– Used data frames and CSMA/CD

• Topology– Hybrid star-bus– Hub at center

• Electronic repeater• Each connection on hub is a port• Each Ethernet NIC on network is a node.• Does not send signal back down the originating port

Figure 4.1 Ethernet hub

• Organizing the Data: Ethernet Frames– All networking technologies use frames

– Ethernet frames contain seven pieces of information

• Preamble• Destination MAC address• Source MAC address• Length

• Data• Pad• Frame Check Sequence

Figure 4.2 Ethernet frame

Figure 4.3 Frames propagating on a network

• Ethernet Security Vulnerability– Sniffers can order a NIC to run in promiscuous mode

– In promiscuous mode, the NIC processes all frames

– There are programs, such as AntiSniff, which network administrators can use to detect sniffers on an Ethernet network.

CSMA/CD

Carrier SenseEach NIC on the network examines the wire before sending a frame. If the node detects traffic, it will back off a random amount of time and try again.

Collision DetectionIf two NICs transmit at the same time, a colli-sion results. NICs may listen to detect a collision.

Multiple AccessAll machines have equal access to the wire. Access to the wire is on a first-come, first-served basis

Figure 4.4 No one else is talking – send the frame!

Figure 4.5 Collision!

Figure 4.6 Rolling for timing

Early Ethernet NetworksEarly Ethernet Networks

• 10BaseT – Created in 1990

– Over 99% of all networks use this or its newer versions

– Two or more computers connected to a central hub

– NICs connect with wires per 802.3 standards

– Hubs for 10BaseT• Vary in size, shape, and number of ports

• Need electrical power

10BaseTSpeed

10 MbpsSignal TypeBaseband

A single signalon the cable

Type of cableTwisted Pair

Figure 4.7 Two 10BaseT hubs

• 10BaseT (Continued)– UTP

• Uses CAT3 or better with RJ-45 connectors

• Two pairs of wires required (four-pair cable commonly used)

• One pair of wires sends data to the hub

• The other pair receives data from the hub

– RJ-45 connector• Introduced with 10BaseT

• Each pin connects to a single wire in cable

• Devices put voltage on the individual wires

• Pins numbered from 1 to 8

Figure 4.8 A typical four-pair CAT 5e unshielded twisted-pair cable

Figure 4.9 Two views of an RJ-45 connector

• RJ-45 Pin Assignments– 1 and 2 send data

– 3 and 6 receive data

• RJ-45 Connector called a crimp– Crimping is the act of installing an RJ-45 connector

– Crimper is the tool used

Figure 4.10 The pins on an RJ-45 connector are numbered 1 through 8.

Figure 4.11 Color-coded pairs

• TIA/EIA 568A and TIA/EIA 568B– Color-coded schemes for installing a crimp

– TIA/EIA 568A• Green/white, green, orange/white, blue, blue/white, orange,

brown/white, brown

– TIA/EIA 568B• orange/white, orange, green/white, blue, blue/white, green,

brown/white, brown

Figure 4.12 The TIA/EIA 568A and 568B standards

• 10BaseT Limits and Specifications– Distance between hub and computer = 100 meters

– No more than 1024 computers connected to one hub• Such a high number too expensive and not practical

• Too many collisions would occur

• 10BaseT Summary– Speed: 10 Mbps

– Signal type: Baseband

– Distance: 100 meters between the hub and the node

– Node limit: No more than 1,024 nodes per hub

– Topology: Star bus topology: physical star, logical bus

– Cable type: Uses CAT3 or better UTP cabling with RJ-45 connectors

• 10BaseFL– Distance: two kilometers (2,000 meters) between the

hub and the node

– Immune to EMI – ideal for high-interference environments

– More secure because difficult to tap into

– Multimode fiber-optic cables with ST or SC connectors

Figure 4.13 Typical 10BaseFL card

• 10BaseFL Summary– Speed: 10Mbps

– Signal type: Baseband

– Distance: 2000 meters between hub and node

– Node limit: No more than 1,024 nodes per hub

– Topology: Star bus topology: physical star, logical bus

– Cable type: Uses multimode fiber-optic cabling with ST or SC connectors

• Connecting different types of Ethernet networks– Same Ethernet packets, although different cabling and

hubs

– Media converter will connect differently-cabled Ethernet networks

Figure 4.14 Typical copper-to-fiber Ethernet media converter (photo courtesy of TRENDnet)

Extending & Enhancing Extending & Enhancing Ethernet NetworksEthernet Networks

• Connecting Ethernet Segments– Uplink Ports

• Connect two hubs using a straight-through cable

• Marked on hub

• One end of cable to the uplink in one hub, other end in regular port of second hub

• Daisy chain no more than four hubs

• Uplink port may have a button to switch between regular or uplink mode, electronically reversing the wires inside the hub for that port

• When connecting hubs

– Only daisy-chain hubs– Take time to figure out the uplink ports– If incorrectly connected, they simply will not work

Figure 4.15 Typical uplink port

Figure 4.16 Daisy-chained hubs

Figure 4.17 Hierarchical hub configuration. This will not work!

Figure 4.18 Press-button port

• Connecting Ethernet Segments (Continued)– Crossover Cables

• Another way to connect two hubs without an uplink port

• Connect via two normal ports using one crossover cable

• Crossover cable reverses the sending and receiving pairs on one end

• One end crimped per TIA/EIA 568A

• Second end crimped per TIA/EIA 568B

Figure 4.19 A crossover cable reverses the sending and receiving pairs

• Switched Ethernet– The Trouble with Hubs

• A hub sends all packets out all ports

• Increased traffic will slow network

• Total bandwidth is 10 Mbps

• When two nodes attempt to use wire at the same time, CSMA reduces the effective speed to ~ 5 Mbps

• Add more conversations: network slows further

Figure 4.20 One conversation gets all the bandwidth

Switched

Figure 4.21 Two conversations must share the bandwidth

Hubs

• Switched Ethernet (Continued)– Switches to the Rescue

• Ethernet switch takes advantage of MAC addresses (OSI Data Link layer)

• Creates point-to-point connections between two conversing computers

• Effectively gives every conversation the full bandwidth of the network

• When first turned on, switch copies the source MAC addresses and builds a table of MAC addresses of each computer

• Uses the table to create point-to-point connections between each pair of communicating devices

Figure 4.22 A switch tracking MAC addresses

Figure 4.23 A switch making two separate connections

• Switched Ethernet (Continued)– Switches to the Rescue (Continued)

• Switch makes CSMA/CD insignificant

• Connect switches any way you wish

• Commonly connected in a tree organization

• No collisions

Figure 4.24 Switches are very commonly connected in a tree organization

Figure 4.25 Hub (top) and switch (bottom) comparison