mcgraw-hill©the mcgraw-hill companies, inc., 2000 network operations & administration cs 4592...

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000

Network Operations & administration CS 4592Lecture 11

Instructor: Ibrahim Tariq

9.2

DIGITAL SUBSCRIBER LINEDIGITAL SUBSCRIBER LINE

After traditional modems reached their peak data rate, After traditional modems reached their peak data rate, telephone companies developed another technology, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. DSL, to provide higher-speed access to the Internet. Digital subscriber lineDigital subscriber line ( (DSLDSL) technology is one of the ) technology is one of the most promising for supporting high-speed digital most promising for supporting high-speed digital communication over the existing local loops. communication over the existing local loops.

ADSLADSL LiteHDSLSDSLVDSL

Topics discussed in this section:Topics discussed in this section:

9.3

ADSL is an asymmetric communication technology designed for residential users; it is not suitable for

businesses.

Note

9.4

ADSL is an adaptive technology. The system uses a data ratebased on the condition of

the local loop line.

Note

9.5

Discrete multitone technique(combination of QAM and FDM)

9.6

Bandwidth division in ADSL

9.7

ADSL modem

9.8

DSLAM Digital subscriber line access multiplexer

9.9

Summary of DSL technologies

9.10

CABLE TV NETWORKSCABLE TV NETWORKS

The The cable TV networkcable TV network started as a video service started as a video service provider, but it has moved to the business of Internet provider, but it has moved to the business of Internet access. In this section, we discuss cable TV networks access. In this section, we discuss cable TV networks per se; per se;

Traditional Cable NetworksHybrid Fiber-Coaxial (HFC) Network

Topics discussed in this section:Topics discussed in this section:

9.11

Traditional cable TV network

9.12

Communication in the traditional cable TV network is unidirectional.

Note

9.13

Hybrid fiber-coaxial (HFC) network

9.14

Communication in an HFC cable TV network can be bidirectional.

Note

9.15

CABLE TV FOR DATA TRANSFERCABLE TV FOR DATA TRANSFER

Cable companies are now competing with telephone Cable companies are now competing with telephone companies for the residential customer who wants companies for the residential customer who wants high-speed data transfer. In this section, we briefly high-speed data transfer. In this section, we briefly discuss this technology.discuss this technology.

9.16

Division of coaxial cable band by CATV

9.17

Downstream data are modulated using the 64-QAM modulation technique.

Note

9.18

The theoretical downstream data rateis 30 Mbps.

Note

9.19

Upstream data are modulated using the QPSK modulation technique.

Note

9.20

The theoretical upstream data rate is 12 Mbps.

Note

9.21

Cable modem (CM)

9.22

Cable modem transmission system (CMTS)

Packet Switching

Difference between circuit switching and packet switching: Packet Switching

Message is broken up into segments (packets). Each packet carries the identification of the intended

recipient, data used to assist in data correction and the position of the packet in the sequence.

Each packet is treated individually by the switching centre and may be sent to the destination by a totally different route to all the others.

Packet Switching

Packet Switching Advantages:

Security Bandwidth used to full potential Devices of different speeds can communicate Not affected by line failure (rediverts signal) Availability – do not have to wait for a direct

connection to become available During a crisis or disaster, when the public

telephone network might stop working, e-mails and texts can still be sent via packet switching

Packet Switching

Disadvantages Under heavy use there can be a delay Data packets can get lost or become

corrupted Protocols are needed for a reliable

transfer Not so good for some types data streams

e.g real-time video streams can lose frames due to the way packets arrive out of sequence.

Circuit Switching

There are three phases in circuit switching: Establish Transfer Disconnect

The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was originally sent.

Circuit Switching Circuit Switching

Advantages: Circuit is dedicated to the call – no

interference, no sharing Guaranteed the full bandwidth for

the duration of the call Guaranteed Quality of Service

Circuit Switching

Disadvantages: Inefficient – the equipment may be

unused for a lot of the call, if no data is being sent, the dedicated line still remains open

Takes a relatively long time to set up the circuit

During a crisis or disaster, the network may become unstable or unavailable.

It was primarily developed for voice traffic rather than data traffic.

Error Detection and

Correction

10.29

10.30

Data can be corrupted during transmission.

Some applications require that errors be detected and corrected.

Note

10.31

10-1 INTRODUCTION10-1 INTRODUCTION

Let us first discuss some issues related, directly or Let us first discuss some issues related, directly or indirectly, to error detection and correction.indirectly, to error detection and correction.

Types of ErrorsRedundancyDetection Versus CorrectionForward Error Correction Versus RetransmissionCodingModular Arithmetic

Topics discussed in this section:Topics discussed in this section:

10.32

In a single-bit error, only 1 bit in the data unit has changed.

Note

10.33

Figure 10.1 Single-bit error

10.34

A burst error means that 2 or more bits in the data unit have changed.

Note

10.35

Figure 10.2 Burst error of length 8

10.36

To detect or correct errors, we need to send extra (redundant) bits with data.

Note

10.37

The structure of encoder and decoder

10.38

In this book, we concentrate on block codes; we leave convolution codes

to advanced texts.

Note