Communication Systems (2) CT 1401

Lecture-7: Integrated Services for Digital Network (ISDN)

By : Ashwaq fahadSupervision : Dr.Ouiem Bchir

Outline Definition Integrated Services for Digital Network

(ISDN) Types interface ISDN ISDN Components and Reference Points ISDN Benefits Advantages and disadvantages of ISDN ISDN Uses ISDN Protocols ISDN Protocol Operating OSI Layers ISDN Encapsulation

Integrated Services for Digital Network (ISDN)

Definition Integrated Services for Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. It was first defined in 1988 in the CCITT red book Prior to ISDN, the telephone system was viewed as a way to transport voice [1]

Integrated Services for Digital Network (ISDN)

What Is ISDN?

Cisco supports the following two ISDN interface types, which combine the channel types in the preceding list: Basic Rate Interface (BRI)— One 16-kbps D

channel + two B channels Primary Rate Interface (PRI)— 1 64-kbps D

channel + 23 B channels in North America and Japan, for a total capacity of 1536 kbps. 1 64-kbps D channel + 30 B channels in Europe and other parts of the world, for a total capacity of 1984 kbps.[2]

Types interface ISDN

ISDN Components and Reference Points

Terminal Adapter (TA) - Converter device that converts standard electrical signals into the form used by ISDN - allows non-ISDN devices to operate on an ISDN network.

Terminal Equipment Type 1 (TE1) - Compatible with the ISDN network. Example: Telephones, personal computers, fax machine or videoconferencing machine.

Terminal Equipment Type 2 (TE2) - Not compatible with the ISDN network. Example: Analog phone or modem, requires a TA (TE2 connects to TA).

Network termination type 1 & 2 (NT1 and NT2) - A small connection box that physically connects the customer site to the Telco local loop, provides a four-wire connection to the customer site and a two-wire connection to the network (PRI – CSU/DSU). [2]

ISDN Components and Reference Points

Carries a variety of user traffic, such as digital video, data, and telephone network services, using the normal phone circuit-switched network

Offers much faster call setup than modems by using out-of-band signaling (D channel)◦ Often less than one second

Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel)◦ Can combine multiple B channels to bandwidth of 128

kbps Can negotiate PPP links [3]

ISDN Benefits

Advantages1. The basic advantage of ISDN is to facilitate the user with

multiple digital channels. These channels can operate concurrently through the same one copper wire pair.

2. The digital signals broadcasting transversely the telephone lines.

3. ISDN provides high data rate because of digital scheme which is 56kbps.

4. ISDN network lines are able to switch manifold devices on the single line such as faxes, computers, cash registers credit cards readers, and many other devices. These all devices can work together and directly be connected to a single line

5. ISDN takes only 2 seconds to launch a connection while other modems take 30 to 60 second for establishment [4]

Advantages and disadvantages of ISDN

Disadvantages1. The disadvantage of ISDN lines is that it is

very costly than the other typical telephone system.

2. ISDN requires specialized digital devices just like Telephone Company [4]

Advantages and disadvantages of ISDN

Remote Access (Telecommuters) Remote Nodes (Voice and Data) SOHO Connectivity (Small Branches) [5]

ISDN Uses

Remote Access (Telecommuters)

ISDN Uses

Remote Nodes (Voice and Data)

ISDN Uses

SOHO Connectivity (Small Branches)

ISDN Uses

E-series protocols—Telephone network standards for ISDN.

I-series protocols—Specify ISDN concepts and interfaces.

Q-series protocols—Standards for ISDN switching and signaling.

Operate at the physical, data link, and network layers of the OSI reference model [6]

ISDN Protocols

Physical layer ISDN protocols◦BRI (ITU-T I.430) / PRI (ITU-T I.431)

Defines two ISDN physical layer frame formats Inbound (local exchange to ISDN customer)

Outbound (ISDN customer to local exchange ) [6]

ISDN Protocol Operating OSI Layers

Physical layer ISDN protocols

Data link layer ISDN protocols◦LAPD signaling protocol (ITU-T Q.920 for

BRI and Q.921 for PRI) for transmitting control and signaling information over the D channel • LAPD frame format similar to ISO HDLC

frame format [6]

ISDN Protocol Operating OSI Layers

Data link layer ISDN protocols

Network layer ISDN protocols◦ITU-T I.930 and ITU-T Q.931 defines

switching and signaling methods using the D channel.

ISDN Protocol Operating OSI Layers

Two Layer 3 specifications are used for ISDN signaling: ◦ITU-T I.450 (also known as ITU-T Q.930)◦ITU-T I.451 (also known as ITU-T Q.931)◦Together, these protocols support: User-to-user circuit-switched connections User-to-user packet-switched connections A variety of standards for:

Call establishment Call termination [6]

Network layer ISDN protocols

NoteWith Q.921/Q.931 the second digit indicates

the OSI layer.

The two most common encapsulations:◦ PPP◦ HDLC

ISDN defaults to HDLC. PPP is much more robust.

◦ Open standard specified by RFC 1661 ◦ Supported by most vendors [7]

ISDN Encapsulation

[1] http://en.wikipedia.org/wiki/Integrated_Services_Digital_Network[2]https://www.informit.com/library/content.aspx?b=CCIE_Practical_Studies_I&seqNum=84[3]http://www.telecom.co.nz/business/ourproducts/phonesystems/isdn/featuresandbenefits/[4] http://freewimaxinfo.com/isdn.html[5] http://www.jet.net/isdn/isdnintro.html [6] http://www.firewall.cx/networking-topics/wan-technologies/238-isdn-layers-protocols-components.html[7] http://netcert.tripod.com/ccna/wan/isdn.html

References