TELECOMMUNICATION(ISDN)

ISDN

(INTEGRATED SERVICES DIGITAL NETWORK)

ISDN is a set of standards which define an end to end Digital Network

Features of ISDN

• Uses Digital Signal

• Uses Existing telephone wiring

• Charges are generally based on the duration of

call (How long the WAN link was used)

• Alternate to using leased lines

• Can transport many types of Network traffic

(Voice, Data, Video, Text, Graphics etc)

• Faster Data transfer rate than modems

• Faster Call setup than Modems

ISDN Components

• Terminal Equipment type 1 (TE1)

* ISDN compatible device (Router with ISDN Interface)

* TE1s connect to the ISDN network through a four-wire,twisted-pair digital link

• Terminal Equipment type 2 (TE2)

* ISDN Non-compatible devices.

* Will require a terminal adapter.

• Terminal Adapter (TA)

* Converts standard electrical signals into the form used by ISDN

* Needed for connection with TE2 devices

* The ISDN TA can be either a standalone device or a board inside

the TE2

• Network termination type 1 (NT1)

* Network-termination devices that connect the four-wire

Subscriber wiring to the conventional two-wire local loop

* Is a customer premises equipment (CPE) device (North America)

• Network termination type 2 (NT2)

* Intelligent device that performs switching & concentrating.

* Provides multiple ISDN interfaces on an ISDN line. The NT2

may be as simple as a bridging device connected to an NT1 unit

or it may be as complicated as a PBX (Private Branch

exchanges)

ISDN Reference points

• R---The reference point between non-ISDN equipment and a TA.

• S---The reference point between user terminals and the NT2.

• T---The reference point between NT1 and NT2 devices.

• U---The reference point between NT1 devices and line-termination

equipment in the carrier network. The U reference point is

relevant only in North America, where the NT1 function is not

provided by the carrier network

INTERFACES OF ISDN

BRI (Basic Rate Interface)

• Connection from the ISDN office to the user location provides for

access to three channels. The channels are two 64Kb B-channels and

one 16Kb D-channel

• The B-channels and the D-channel provide the user with access to the

circuit switched network

PRI (Primary Rate Interface)

• ISDN Primary Rate Interface service provides digital access via a T1

line. A T1 line provides a 1.544 bandwidth. This bandwidth is divided

into 24 64Kb channels. The ISDN PRI service uses 23 B channel

access and uses the 24th (D) channel for signaling purposes

ISDN Protocols

• E - Protocols recommend telephone network standards for ISDN

(International Telephone Numbering Plans)

• I - Protocols for I.400=User-Network Interface & I.100=Concepts,

Structures & Terminology

• Q - Protocols, how switching and signaling should operate, call

setup etc. (Q.921=LAPD & Q.931=ISDN Network layer)

LAPD is used to deliver signaling messages to the switch (call setup)

Link Access Procedure on the D channel

(not between routers, only between router and ISDN switches)