Chapter 6

Data Link Control and Multiplexing

Data Link Control Module

Flow Control

Error ControlTwo types of errors

Lost frameA frame fails to arrive at the other side

Damaged frameA recognizable frame does arrive, but some of the bits are in error

Collectively referred to as automatic repeat request (ARQ), common techniques for error control are:

Error detectionPositive acknowledgmentRetransmission after timeoutNegative acknowledgment and retransmission

Motivations for Multiplexing

Multiplexing

Frequency-Division

Multiplexing (FDM)

Time-Division Multiplexing

(TDM)

FDM of

Three Voiceband

Signals

Transmitted TV Signal

Wavelength-Division Multiplexing (WDM)

ITU WDM Channel Spacing (G.692)

FDM Example: ADSL

ADSL Channel

Configuration

Echo Cancellation

Entire frequency band for the upstream channel overlaps the lower portion of the downstream channelAdvantages

The higher the frequency, the greater the attenuationMore flexible for changing upstream capacity

DisadvantagesNeed for echo cancellation logic on both ends of line

Discrete Multitone (DMT)

Synchronous Time-Division Multiplexing (TDM)

TDM Frame Structure

Digital Carrier Systems

North American and International TDM Carrier Standards

DS-1 Transmission Format

21

T-1 Facilities

Transmission facilities supporting DS-1Often used for leased dedicated transmission between customer premises

Private voice networksPrivate data networkVideo teleconferencingHigh-speed digital facsimileInternet access

Synchronous Optical Network SONET/

Synchronous Digital Hierarchy (SDH)

Sonet/SDH Signal Hierarchy

SONET/SDH Frame Formats

Cellular and Cordless Telephone Systems

Summary Flow control Error control Motivation for

multiplexing FDM WDM ADSL

Chapter 6: Data Link Control and Multiplexing

Synchronous TDM The TDM mechanism Digital carrier systems T-1 facilities SONET/SDH Cellular and cordless

phone systems