Business data communications 4e chapter 15

Business Data Communic ations, 4e 3 Traditional Ethernet ✘ Ethernet and CSMA/CD IEEE 802.3 ✘ Carrier sense multiple access with collision detection ✘ Four step procedure ✘ If medium is i

Chapter 15:

LAN Systems

Business Data Communications, 4e

High-Speed LANs

✘ Why?

✘ Extraordinary growth in speed, power, and storage

capacity of PCs

✘ Increasing use of LANs as computing platforms

✘ Examples

✘ Server farms

✘ Workgroups with “power” requirements

✘ High-speed backbones

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Traditional Ethernet

✘ Ethernet and CSMA/CD (IEEE 802.3)

✘ Carrier sense multiple access with collision detection

✘ Four step procedure

✘ If medium is idle, transmit

✘ If medium is busy, listen until idle and then transmit

✘ If collision is detected, cease transmitting

✘ After a collision, wait a random amount of time before

retransmitting

802.3 Medium Notation

✘ Notation format:

<data rate in Mbps><signaling method><maximum segment length in hundreds of meters>

✘ e.g 10Base5 provides 10Mbps baseband, up to 500 meters

✘ T and F are used in place of segment length for

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802.3 10BaseX Media Options

Fast Ethernet (100Mbps)

✘ Easy to integrate with existing systems

✘ Can use UTP (-TX) or fiber (-FX)

✘ Uses star-wired topology, using a central multiport repeater (broadcast method)

✘ If NICs support full-duplex mode, switched hub

must be used

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802.3 100Base-T Options

802.3 100BaseX Media Options

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Gigabit Ethernet

✘ Still under development

✘ Retains CSMA/CD protocol and Ethernet format, ensuring smooth upgrade path

✘ Uses optical fiber over short distances

✘ 1-gbps switching hub provides backbone

connectivity

Gigabit Ethernet Media Options

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Example 100-Mbps Ethernet

Backbone Strategy

Token Ring LANs (802.5):

Medium Access Control

✘ Token “seized” by changing a bit on the circulating

frame to indicate start of frame rather than token

✘ Default configuration requires sender to complete

transmission and begin receiving transmitted frame

before releasing the token

✘ “Early token release” allows release of token after

transmission but before receipt of frame

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802.5 Transmission Media

✘ Original specified shielded twisted pair with data

rates of 4 and 16mbps

✘ New addition to standard allows use of UTP for

4mbps

✘ Utilizes differential Manchester encoding

✘ 1997 update to IEEE 802.5 introduced dedicated

token ring (DTR).

Fibre Channel

✘ combine the best features of channel and

protocol-based technologies

✘ the simplicity and speed of channel communications

✘ the flexibility and inter-connectivity that characterize

protocol-based network communications.

✘ more like a traditional circuit-switched or

packet-switched network, in contrast to the typical

shared-Business Data Communic ations, 4e

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Fibre Channel Goals

✘ Full-duplex links with two fibers

per link

✘ Performance from 100 Mbps to

800 Mbps on a single link (200

Mbps to1600 Mbps per link)

✘ Support for distances up to 10

km

✘ Small connectors

✘ High-capacity utilization with

distance insensitivity

✘ Greater connectivity than existing multidrop channels

✘ Broad availability (i.e., standard components)

✘ Support for multiple cost/performance levels, from small systems to supercomputers

✘ Ability to carry multiple existing interface command sets for

existing channel and network protocols

Fibre Channel Elements

✘ The end systems

✘ Includes one or more N_ ports for interconnection

✘ Fabric

✘ Collection of switching elements s between systems

✘ Each element includes multiple F_ ports

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Fibre Channel Protocol Architecture

✘ FC-0 Physical Media: Includes optical fiber, coaxial cable, and shielded twisted pair, based on distance requirements

✘ FC-1 Transmission Protocol: Defines the signal encoding scheme

✘ FC-2 Framing Protocol: Defines topologies, frame format,

flow/error control, and grouping of frames

✘ FC-3 Common Services: Includes multicasting

✘ FC-4 Mapping: Defines the mapping of various channel and

network protocols to Fibre Channel

Wireless LANS

✘ LAN extension

✘ Wireless network connected to a main wire-based network

✘ Cross-building interconnect

✘ Point-to-point link between networks in separate buildings

✘ Nomadic access

✘ Wireless link between a LAN hub and a mobile data terminal

✘ Ad hoc networks

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Wireless LAN Requirements

✘ Throughput

✘ Number of nodes:

✘ Connection to backbone

LAN

✘ Service area

✘ Battery power consumption

✘ Transmission robustness and security

✘ Co-located network operation

✘ License-free operation

✘ Handoff/roaming

✘ Dynamic configuration

IEEE 802.11 Standards

✘ Association/Re-Association/Disassociation

✘ Authentication

✘ Privacy

✘ Physical Media

✘ Infrared at 1 or 2 Mbps at a wavelength of 850-950 nm

✘ Direct-sequence spread spectrum in the 2.4-GHz ISM band