Unit 1 - Part BNetwork Examples

Using Telephone & Cable Networksfor

Data Transmission

9-1 TELEPHONE NETWORK

Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s.

The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice.

~ Major Components ~ LATAs’ ~ Signaling ~ Services Provided by Telephone Networks

Topics discussed in this section:

a) Major Components of a telephone system

Endoffices

Local loop

Trunk

Tandemoffices Regional offices

Trunk• •

•

The major components of Telephone system are : 1. Local Loop it is the twisted-pair cable that connects the subscriber

telephone to the nearest end office or local central office. 2. Trunks

they are the transmission media that handle the communication between offices.

3. Switching Offices A switching office consists of switches, in that each switch

connects several local loops or trunks and allows a connection between different subscribers. [ three types – End, Tandem and Regional ]

LATA stands for Local Access Transport Areas’

Intra-LATA services. (i.e. services within a LATA )

Inter-LATA services. (i.e. services between LATAs’ )

b) LATA stands for Local Access Transport Areas’

Typical Structure of a LATA involving different switching offices

Point of presences (POPs)

Inter-LATA Services

Intra-LATA Services

c) Signalling

The details involved in communication between two ends on a telephone network can be broadly divided into two :

~ Data Transfer

~ Signalling

Data transfer and Signaling networks

Layers in SS7 [ SS7 – Signaling System Seven ]

SS7 is a layered architecture similar to Internet model that is used in Signaling network of Telephone System.

9-2 DIAL-UP MODEMS

Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz.

But for realizing data communication the telephone lines make use of only a signal bandwidth of 2400Hz ( ranging from 600 to 3000 Hz. )

Telephone line bandwidth

Modulation / demodulation

Modemstands for modulator/demodulator.

Note

Modem Standards [ The V – Series ]

The V – Series :

V.32

V.32bis

V.34bis

V.90

V.92

The V.32 and V.32bis constellation and bandwidth

Uploading and downloading in 56K modems

The downward stream data rate is higher since there is no quantization error while downloading.

9-3 DIGITAL SUBSCRIBER LINE

After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet.

Digital subscriber line (DSL) technology is one of the most promising for supporting high-speed digital communication over the existing local loops.

i) ADSL ii) ADSL Lite iii) HDSL iv) SDSL v) VDSL

Topics discussed in this section:

Discrete Multitone Technique [ DMT ]

Discrete Multitone Technique [ DMT ] combines FDM & QAM.

Bandwidth division in ADSL

ADSL modem

DSLAM [ DSL Access Multiplexer ]

Summary of DSL technologies

9-4 CABLE TV NETWORKS

The cable TV network originally started as a video service provider, but now it has moved to the business of Internet access.

1. Traditional Cable Networks2. Hybrid Fiber-Coaxial (HFC) Network

Topics discussed in this section:

1. Traditional cable TV network

Communication in the traditional cable TV network is unidirectional.

Note

2. Hybrid Fiber-Coaxial ( HFC ) Network

Communication in an HFC cable TV network can be bidirectional.

Note

Fiber Cable

9-5 CABLE TV FOR DATA TRANSFER

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

BandwidthSharingCM and CMTSData Transmission Schemes: DOCSIS

Topics discussed in this section:

Bandwidth division of coaxial cable by CATV

Sharing

Both upstream and downstream bands are shared by the subscribers.

Upstream Data bandwidth is 37 MHz. This means that there are only six channels (of 6MHz each ) available in the upstream direction.

Downstream data bandwidth is 200MHz. This means that there are thirty-three channels (of 6 MHz each ) available in the downstream direction.

Cable modem (CM) [ at Subscriber Premises ]

Cable modem transmission system (CMTS) [ at Company Premises ]