Integrated Services Digital Network

uPublic networks are used for a variety ofservices

–Public Switched Telephone Network

–Private Lines (leased)

–Packet Switched Data Networks

–Circuit Switched Data networks

ISDN

uUsers have a variety of equipment toconnect to public networks

–Telephones

–Private Branch Exchanges

–Computer Terminals or PCs

–Mainframe Computers

uA variety of physical interfaces and accessprocedures are required for connection

ISDN

uThe telephone network has evolved into adigital one with digital exchanges and links

uThe signalling system has become a digitalmessage-oriented common channelsignalling system (SS#7)

uThe term ‘Integrated Digital Network’ isused to describe these developments

ISDN

uThe Public Switched Telephone network isstill analogue from the subscriber to thelocal exchange

uThe need has arisen to extend the digitalnetwork out to subscribers and to provide asingle standardised interface to all differentusers of public networks

uISDN fulfils that need

Figure 15-1

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

ISDN Services

Integrated Services DigitalNetwork

Telephone

Data

terminal

PBX

Alarm

LAN

Customer

ISDN

Interface

ISDN

central

office

Packet

switched

network

Circuit

switched

network

Databases

Other

Networks

& services

‘Digital

pipe’

Figure 15-4

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Analog and Digital Services

Figure 15-5

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Integrated Digital Network

Figure 15-6

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Integrated Services Digital Network

ISDN

uIn Practice there are multiple networksproviding the service nationally

uThe user however, sees a single network

Benefits to Subscribers

uSingle access line for all services

uAbility to tailor service purchased to suitneeds

uCompetition among equipment vendors dueto standards

uAvailability of competitive serviceproviders

Architecture

Common

physical

interface

ISDN

central

office

Network-based

processing

services

Digital circuit-

switched backbone

Packet-switched network

Integrated Digital Network

ISDN subscriber loop

Basic 2B+D

Primary 30B+D

ISDN Channels

uThe Digital pipe is made up of channels -one of three types

uB channel, D channel or H channel

uChannels are grouped and offered as apackage to users

B Channel

u B channel-64 kbps

uB is basic user channel

–can carry digital data or PCM-encoded voice

–or mixture of lower rate traffic.

B Channel

uFour kinds of connection possible

uCircuit-switched

uPacket-switched - X.25

uFrame mode - frame relay (LAPF)

uSemipermanent - equivalent to a leased line

D Channel

uD Channel - 16 or 64 kbps

uCarries signalling information to controlcircuit-switched calls on B channels

uCan also be used for packet switching orlow-speed telemetry

H Channel

uCarry user information at higher bit rates384kbps or 1536kbps or 1920kbps

uCan be used as a high-speed trunk

uCan also be subdivided as per user’s ownTDM scheme

uUses include high speed data, fastfacsimile, video, high-quality audio

ISDN Channels and theirApplications

ISDN Channel Groupings

uBasic Access -

Õ two 64 kbps B channels

Õ plus one 16kbps D channel

uB channels can be used for voice and data

u simultaneous calls to separate destinationssupported

uD channel used for signalling and also fordata using X.25

ISDN Basic Access

uIntended for small business and residentialuse

uA single physical interface is provided

uData rate is 144kbps plus 48kbps overheadbits totalling 192 kbps

uMost existing subscriber loops can supportbasic access

Figure 15-7

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Basic Rate Interface

Figure 15-17

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

BRI Frame

ISDN Primary Access

uIntended for users with greater capacityrequirements

uExample would be a digital PBX

uTwo standards exist

–1.544 Mbps American

–2.048 Mbps European

Figure 15-20

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

PRI Frame

Figure 15-8

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Primary Rate Interface

ISDN Primary Access

uTypically it is structured as 30 B channelsplus one 64kbps D channel (Europe)

uCan also be structured as H channels

–5H0 +D for a 2.048 Mbps interface

– or 1H12 +D

ISDN Primary Interface

uMultiple channels multiplexed on singlemedium

uOnly point to point configuration is allowed

uTypically supports a digital PBX andprovides a synchronous TDM facility

User Access

uDefined using two concepts

–Functional groupings of equipment

–Reference points to separate functionalgroupings

Typical User Access Layout

ISDN

Tele -

phone

PC with

ISDN

Interface

Card

Integrated

Voice/data

Terminal

2-wire

Subscriber

Loop

User/network

Interface

4-wire

S-bus

Up to 8 devices

point to multi-point mode

Figure 15-9

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Functional Grouping

Figure 15-10

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

Reference Points

ISDN Protocol Architecture

Application

Presentation

Session

Transport

Network

Datalink

Physical

End-end

user

signalling

Physical

I.451/Q.931

call control

LAPD (Q921)

I.430 basic interface + I.431 primary interface

X.25

packet level

for further

study

LAPB

Frame

Relay

X.25

packet level

Figure 15-12

WCB/McGraw-Hill

 The McGraw-Hill Companies, Inc., 1998

ISDN Layers for B and D Channels

ISDN Data Link Layer

uLink Access Protocol for the D channel(LAPD) defined for ISDN

uThree applications are supported

–Control Signalling

–Packet Switching

–Telemetry

B-Channel

uUses

–Circuit Switching

–Semi-permanent circuits

–Packet switching

B-Channel

uCircuit Switching

–Circuit is set up on B-channel on demand

–D-channel call control protocol is used

–Transparent full-duplex digital data pathestablished between users

–Layers 2 to 7 are not visible to ISDN orspecified

B-Channel

uSemipermanent circuit can be set up byprior agreement between users and networkoperator

uCan be for indefinite time or at specifiedtimes during day or week

uAs with circuit switched connection, fullduplex digital data path is established

uLayers 2 to 7 are not visible to ISDN orspecified

D-Channel Packet Switching

uIntegrated X.25 service can be accessed byD-Channel in addition to B-Channel

uISDN provides a semi-permanentconnection to a packet switching nodewithin ISDN

uThe X.25 level 3 protocol is used for thepacket layer

uLAPD is used for the link layer