McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Integrated ServicesDigital Network

(ISDN)

Developed by ITU-T in 1976

Set of protocols that combines digital telephony and data transport services. The whole idea is to digitize the telephone network to permit the transmission of audio, video and text over existing telephone lines.

The goal is to form a WAN that provides universal end-to-end connectivity over digital media.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-1

ISDN Services

Bearer services – provide the means to transfer information (voice, data, video) between users without the network manipulating the content of that information. Belongs to the first 3 layers of the OSI model.

Teleservices – the network my change or process the contents of the data.

- correspond to layers 4-7 of the OSI model- rely on the facilities of bearer services

Supplementary services – provide additional functionality to the bearer services and teleservices.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-1

ISDN Services

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-2

Voice Communication over an Analog Telephone Network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-3

Voice and Data Communication over an Analog Telephone Network

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-4

Analog and Digital Services over the Telephone Network

3 types of customers – the first one is the most prominent

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-5

Integrated Digital Network (IDN)

A combination of networks available for different purposes.

Access to these networks is by digital pipes

digital pipes – time-multiplexed channels sharing very-high-speed paths.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-6

Integrated Services Digital Network(ISDN)

ISDN incorporates all communication connections in a home or building into a single interface

With ISDN all customer services will become digital rather than analog.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Subscriber Access to the ISDN

• Subscriber loops – organized into multiple channels of different sizes

• B channel– basic user channel– Can carry any type of digital info

in Full-duplex mode– Carries transmissions end-to-end

• D channel– Primary function is to carry control

signaling for the B channel– Acts like an operator between the

user and the network at the network layer

Channel Data Rates (Kbps)

Bearer (B) 64

Data (D) 16, 64

Hybrid (H) 384 (H0), 1536(H11), 1920(H12)

H Channels- For high data rate applications such as video, teleconferencing and so on

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Two Types of Digital Subscriber Loops

• Basic rate interface (BRI)

• Primary rate interface (PRI)

– Each type is suited to a different level of customer needs

– Both include one D channel and some number of either B or H channels

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-7

Basic Rate Interface (BRI)

Designed to meet the needs of residential and small-office customers

The same twisted pair local loop that delivers analog transmission can be used to handle digital transmission

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-8

Primary Rate Interface (PRI)

PRI was designed to be compatible with existing T-1 lines

In Europe, the PRI includes 30 B channels and 2 D channels = capacity of 2.048 Mbps – the capacity of E-1 line

Other channel combinations:– 3H0 + D – 4H0 + D – H12 + D

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-9

Functional Grouping

NT – network terminationTE – terminal equipment

NT1• Controls the physical & electrical termination of the ISDN at the user’s premises

• Connects the user’s internal system to the digital subscriber loop

• Organizes the data stream s from a connected subscriber into frames that can be sent over the digital pipe

• Translates the frames received from the network into a format usable by the subscriber’s devices.

Defines the function of each type of equipment

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

NT2 ( ex. Digital PBX, LAN)• Performs functions at the physical (multiplexing), data link (flow control), network layers (packetizing) of the OSI model

• Provides intermediate signal processing between the data-generating devices and an NT1

• Used primarily to interface between a multiuser system and an NT1 in a PRI.

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

TE1 – same thing as DTE• Any device that supports the ISDN standards

• Ex. Digital telephones,integrated voice/data terminals

TE2• Any non-ISDN device• Ex. Terminal workstation, regular telephone• Can be used with the help of Terminal Adapter (TA)

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-10

Reference Points

Label used to identify individual interfaces between two elements of an ISDN installation

Defines the functions of the connections

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-11

ISDN Layers

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-12 Simplified Layers of ISDN

Mechanical and electrical specs of interfaces R, S, T, U

Encoding

Multiplexing

Power supply

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-13

BRI Interfaces

R interface – not defined by ISDN, it can be any EIA standards or V or X series

S interface – ISO standard, ISO 8887, four-, six-, or eight-wire connections.

U interface - Single-pair twisted-pair cable in each direction- Two binary, one quaternary (2B1Q) encoding

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-14

S Interface

Name TE NT

a Power source 3

Power sink 3

b Power source 3

Power sink 3

c Transmit Receive

d Receive Transmit

e Receive Transmit

f Transmit Receive

g Power sink 2 Power source 2

h Power sink 2 Power source 2

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-15

2B/1Q Encoding

00 01 10 11

-3 -1 +3 +1

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-16

BRI Frame

overhead

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

BRITopology

Point-to-point

Multipoint-limited distance to ensure frame

synchronization

As many as 8 devices can be connected to NT1, two can access the B-channels at 1 time

D channels use a mechanism like CSMA

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-18

PRI Interfaces

R and S – same as those defined for the BRI

T – identical to S standard- B8ZS Encoding

U – same for both, different rates

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-19

PRI Frame

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-20

LAPD Address Field

SAPI – Service Access Point Identifier- identifies the type of upper-layer service (network layer)

C/R – Command (0) / Response (1)

TEI – Terminal Equipment Identifier

000000 – call control for network layer (signaling use of D-channel)

000001 – call control for upper layer (ene-to-end signaling), not yet in use

010000 – packet communication ( data use of D channel)

111111 - management

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-21

Network Layer Packet Format

Protocol discriminator – identifies the protocol in use, for Q.931 = 0000 1000

Call Reference – sequence number of the call

Message Type – identifies the purpose of the message- call establishment- call information- call clearing - call miscellaneous

Reading assignment:Different messages under these four message types

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-22

Call Reference Field

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-23

Information Elements

Carries specific details about the connection that are required for call establishment:

- addresses of the sender and receiver- routing information- type of network that is desired for the B-channel exchange (X.25, ATM, Frame Relay)

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-24

Information Element Types

ID – identify the information being sentLength – length of the content in bytes

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-25

Addressing in ISDN

Addressing – important information element type in ISDN

NC – national Code

Subaddress – identify the device connected to NT1

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-26

Bit Rates for Different Applications

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-27

B-ISDN Services

Broadband ISDN – based on a change from metal cable to fiber optic cable at all levels of telecommunications

Interactive services – those that require two-way exchanges between either 2 subscribers or between a subscriber & a service provider

- conversational – real time exchanges such as telephone calls- messaging – store & forward exchanges such as voice mail- retrieval –retrieve info from a central office

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-27

B-ISDN Services

Distributive services – unidirectional services sent from a provider to subscribers, broadcast to the user

- without user control – user choice is limited to whether or not to receive the service at all

- with user control – allow the user a choice of times during which to receive them

McGraw-Hill ©The McGraw-Hill Companies, Inc., 2001

Figure 16-28

B-ISDN Accesses

155.520 Mbps – fill the needs of most residential and many business subscribers

155.520/622.080 Mbps – fill the needs of businesses that require the simultaneous receipt of multiple services and video conferencing