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Part I
Q1: What is ISDN?
Integrated Services Digital Network ( ISDN ) is a set of communications 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 phone system was viewed as a way to transport voice, with some special services available for data. The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. There are several kinds of access interfaces to ISDN defined as Basic Rate Interface (BRI), Primary Rate Interface (PRI) and Broadband ISDN (B-ISDN).
ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide. It offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 kilobit/s. A major market application for ISDN in some countries is Internet access, where ISDN typically provides a maximum of 128 kbit/s in both upstream and downstream directions. Channel bonding can achieve a greater data rate; typically the ISDN B-channels of 3 or 4 BRIs (6 to 8 64 kbit/s channels) are bonded.
ISDN has been developed to ease integration of all services, except full motion video. It is based on the 64-kbit/s channel, variously called DS0 or E0, depending on the standard followed (i.e., European or North American). Whereas 4 kHz was the basic building block of analog telephony, 64 kbits/s is the basic building block of the digital network and ISDN. The ISDN basic building block is designed to serve, among other services [1]:
- Digital voice
- 64-kbit/s data, both circuit- and packet-switched
- Telex/teletext
- Facsimile
- Slow-scan video
Q2: Draw a diagram showing ISDN Devices and Reference Points?
Figure Sample ISDN Configuration Illustrates Relationships Between Devices and Reference Points illustrates a sample ISDN configuration and shows three devices attached to an ISDN switch at the central office. Two of these devices are ISDN- compatible, so they can be attached through an S reference point to NT2 devices. The third device (a standard, non-ISDN telephone) attaches through the reference point to a TA. Any of these devices also could attach to an NT1/2 device, which would replace both the NT1 and the NT2. In addition, although they are not shown, similar user stations are attached to the far-right ISDN switch.
Q3: What are the standard interfaces, their data rates and channel
types in ISDN?
ISDN Interfaces (Standard Reference Points)
The ISDN standards specify four distinct interfaces in the customer's connection to the network: R, S, T, and U.
From the standards viewpoint, these are not "real" physical interfaces, but simply STANDARD REFERENCE POINTS where physical interfaces may be necessary. However, in common practice, the names of reference points are used to refer to physical interfaces.
ISDN CHANNELS
A CHANNEL is the basic unit of ISDN service. The ISDN Standards define three basic types of channels:
Bearer channels (B channels) Delta (or "Demand") channels (D channels) High-capacity channels (H channels)
B CHANNEL
A B channel is a 64-Kbps unit of clear digital bandwidth. Based on the data rate required to carry one digital voice conversation, a B channel can carry any type of digital information (voice, data, or video) with no restrictions on format or protocol imposed by the ISDN carrier.
D CHANNEL
A D channel is a signalling channel. It carries the information needed to connect or disconnect calls and to negotiate special calling parameters (i.e., automatic number ID, call waiting, data protocol). The D channel can also carry packet- switched data using the X.25 protocol.
The D channel is not a clear channel. It operates according to a well-defined pair of layered protocols:
Q.921 (LAPD) at the Data Link Layer (Layer 2) Q.931 at the upper layers (Layers 3 and above)
The data rate of a D channel varies according to the type of access it serves: a
Basic Rate Access D channel operates at 16 Kbps and a Primary Rate Access D
channel operates at 64 Kbps.
SIGNALLING ON THE D CHANNEL
The ISDN D channel carries all signalling between the customer's terminal device and the carrier's end switching office.
Signalling information with end-to-end significance (i.e., which must be received by the terminal device at a call's destination, such as Automatic Calling Number Identification information) travels between the carrier's switching offices on the carrier's common-channel signalling network and on to the destination terminal through the receiving user's D channel.
H CHANNEL
An H channel is a special, high-speed clear channel. H channels, designed primarily for full-motion color video, are not yet in common use. There are currently three kinds of H channel:
H0 ("H-zero") H11 ("H-one-one") H12 ("H-one-two")
An H0 channel operates at 384 Kbps (roughly one fourth of a North American
Primary Rate Access or one fifth of a European Primary Rate Access). An H
channel operates at 1.536 Mbps and occupies one whole North American Primary
Rate Access. An H12 channel occupies an entire European Primary Rate Access.
Q4: Describe in short on following topics?
1. Line coding used in ISDN
2. ISDN standards
3. ISDN applicatins
ANS: Line Coding in ISDN: North American systems transmit a full-
duplex signal of 1.544 MBPS. This includes 23 B-Channels (1472 KBPS), 1 B-Channel ( KBPS), and a framing/synchronization pattern (8 KBPS).
International ISDN systems transmit a full-duplex signal of 2.048 MBPS. This includes 30 B- Channels (1920 KBPS), 1 B-Channel (64 KBPS), and a framing/synchronization pattern ( KBPS).
North American T1 PRI Line Coding
In North American Primary Rate ISDN systems, transmission of T1 signals normally occurs over Twisted-Pair cable using one of two types of line coding - AMI or B8ZS. B8ZS is more
ISDN Standards: The international standard for the digital telephone network is
Signaling System 7 (SS-7), a protocol suite in its own right, roughly comparable to TCP/IP. End users never see SS-7, since it is only used between telephone switches. ISDN provides a fully digital user interface to the SS-7 network, capable of transporting either voice or data. BISDN (Broadband ISDN) uses ATM instead of SS-7 as the underlying networking technology.
An ISDN interface is time division multiplexed into channels. In accordance with SS- convention, control and data signals are seperated onto different channels. Contrast this to TCP/IP, where control packets are largely regarded as special cases of data packets and are transported over the same channel. In ISDN, the D channel is used for control, and the B channels are for data. B channels are always bi-directional 64 kbps, the standard data rate for transporting a single audio conversation; D channels vary in size.
A number of international standards define ISDN. I.430 describes the Physical layer and part of the Data Link layer for BRI. Q.921 documents the Data Link protocol used over the D channel. Q.931, one of the most important ISO standards, documents the Network layer user-to-network interface, providing call setup and breakdown, channel allocation, and a variety of optional
services. Varients of Q.931 are used in both ATM and voice-over-IP. G.711 documents the standard 64 kbps audio encoding used by telcos throughout the world.
ISDN Applications: It includes Caller Line Identification (CLIP), Callers
list, Internet, Fax, Answering Machine, Voice Recorder, Mailbox, File
Transfer, Cordless Phones, SMS, WAP, Video conferencing.
Q5: What is the difference between PRA (30B+2D) and E1?
PRA (30DB+2D)
PRA (Primary Rate Access) Telecom Definition
The user interface to an integrated services digital network (ISDN) intended for
large business applications in European countries and elsewhere outside of North
America and Japan. Also known as 30B+D, PRA offers 30 bearer (B) channels for
user payload, plus one data (D) channel for signaling and control, and is
backward-compatible with E-1 transmission. Primary rate interface (PRI), the
North American version, offers 23 bearer (B) channels, plus one data (D) channel,
and is backward-compatible with T1 and J-1 transmission systems. PRI and PRA
both provide a full-duplex (FDX) point-to-point connection through an NT2-type
intelligent CPE switching device, such as a PBX or router, for interfacing with the
central office (CO) switch.The B and D channels are clear channels of 64 kbps, as
signaling and control are out-of-band.The B channels can be used individually to
connect on demand to any other ISDN device, or multiple B channels can be
bonded and treated as a single fast connection for bandwidth-intensive
applications such as data file transfers, videoconferencing, and any multimedia
combination. Although the D channel is reserved exclusively for signaling and
control, those functions are fairly light. ISDN standards, therefore, provide for
non-facility associated signaling (NFAS), which allows a D channel to support up to
five PRA/PRI circuits.
E
Part II
Q1: What is ATM?
Asynchronous Transfer Mode (ATM) is a switching technique for
telecommunication networks. It uses asynchronous time-division multiplexing,
and it encodes data into small, fixed-sized cells_._ This differs from networks such as
the Internet or Ethernet LANs that use variable sized packets or frames_._ ATM
provides data link layer services that run over physical links. ATM has functional
similarity with both circuit switched networking and small packet switched
networking. This makes it a good choice for a network that must handle both
traditional high-throughput data traffic (e.g., file transfers), and real-time, low-
latency content such as voice and video. ATM uses a connection-oriented model
in which a virtual circuit must be established between two endpoints before the
actual data exchange begins. ATM is a core protocol used over the SONET/SDH
backbone of the ISDN.
Q2: Draw ATM network, show all the interfaces and devices?
ANS: ATM Devices
An ATM network consists of an ATM switch and ATM end systems.
The ATM switch handles transmission of cells through the ATM network. Its functions are: accepting the incoming cell from an ATM end station or another ATM switch; reading and updating the cell-header information and switching the cell toward its destination.
The ATM end system contains an ATM network interface adapter. Examples of such end systems are workstations, routers, and LAN switches.
Figure 3: An ATM network.
ATM Network Interfaces
An ATM network is maid of ATM switches connected by ATM interfaces.
There are two main types of interfaces: UNI and NNI.
The UNI connects ATM end systems to an ATM switch.
The NNI connects two ATM switches.
UNI and NNI are also subdivided into public and private UNIs and NNIs.
A private UNI connects an ATM end system and a private ATM switch.
A public UNI connects an ATM end system or private switch to a public switch.
A private NNI connects two private ATM switches.
A public NNI connects two public ATM switches.
Figure 4: ATM interfaces.
Payload and padding if necessary (48 bytes)
ATM protocol reference model:
7 4 3 0 VPI VPI VCI VCI VCI PT CLP HEC
Payload and padding if necessary (48 bytes)
Assignment# 3
Q1: Draw successful and unsuccessful call setup scenario using C-
ISUP signaling?
Signaling System #7 (SS7), also known as C7 in Europe, is a critical component of
modern telecommunications systems. Despite the upcoming migration to IP
networks and evolution to IP-centric architectures such as the IP Multimedia
Subsystem (IMS), it remains the glue that binds all telecommunication networks
together.
I S U P C A L L ( S u c c e s s f u l ) :
The call flow diagram in the example shows ISUP messages exchanged between two MSCs that are interconnected using a Signaling Transfer Point (STP). The only task of the STP is to route the SS#7 signaling messages. It does not setup or release any calls. However, due to its central position in the network the STP is an excellent connection point for databases that enable the network to offer intelligent services like number portability or prepaid calling card. Each ISUP call attempt starts with an Initial Address Message (IAM) containing the Called Party Number dialed by the originating user. The Address Complete Message (ACM) indicates that the SPC-B has received all dialing information that is necessary to reach the terminating exchange for this call. No additional dialing information can be sent by A-party after receiving this message.Answer Message (ANM) indicates that B-party (called party) is now connected and the call is active until Release(REL) message either from A- or B-party of the call is received. This message includes a cause value that indicates e.g. “normal call clearing”.The party that received the REL confirms call release with a Release Complete (RLC) message.
Q2: Describe Q.763 - Signaling System No. 7 – ISDN user part
formats and codes?
ANS: The Signalling Information Field (SIF) for all ISUP Message Signal Units (MSU) contain the
following components:
Routing Label Circuit Identification Code Message Type Mandatory Fixed Part Mandatory Variable Part Optional Part
An SS7 point code is similar to an IP address in an IP network. It is a unique address for a node (Signaling Point, or SP), used in MTP layer 3 to identify the destination of a message signal unit (MSU).
In such a message you will find an OPC (Originating Point Code) and a DPC (Destination Point Code); sometimes documents also refer to it as a signaling point code. Depending on the network, a point code can be 24 bits (North America, China), 16 bits (Japan), or 14 bits (ITU standard, International SS7 network and most countries) in length.
ANSI point codes use 24 bits, mostly in 8-8-8 format. ITU point codes use 14 bits and are written in 3-8-3 format.
Fourteen bit point codes can be written in a number of formats. The most common formats are decimal number, hexadecimal number, or 3-8-3 format (3 most significant bits, 8 middle bits, 3 least significant bits).
Twenty-four bit point codes are written in one of decimal, hexadecimal, or 8-8-8 format.
