Tuesday, December 23, 2014

Data Networks: Integrated Services Digital Network (ISDN), Digital Subscribers Line (DSL), Asynchronous Transfer Mode (ATM), etc. P- 04. Information Communication Technology for Libraries

इस ब्लॉग्स को सृजन करने में आप सभी से सादर सुझाव आमंत्रित हैं , कृपया अपने सुझाव और प्रविष्टियाँ प्रेषित करे , इसका संपूर्ण कार्य क्षेत्र विश्व ज्ञान समुदाय हैं , जो सभी प्रतियोगियों के कॅरिअर निर्माण महत्त्वपूर्ण योगदान देगा ,आप अपने सुझाव इस मेल पत्ते पर भेज सकते हैं - chandrashekhar.malav@yahoo.com

Data Networks: Integrated Services Digital Network (ISDN), Digital Subscribers Line (DSL), Asynchronous Transfer Mode (ATM), etc.

P- 04. Information Communication Technology for Libraries *

By :Usha Munshi,Paper Coordinator

Multiple Choice Questions

0 / 1 Points

Question 1: Multiple Choice

Applications such as High Definition Television, voice over IP, Internet access requires _________
  • Wrong Answer Checked ADSL
  • Wrong Answer Un-checked SDSL
  • Wrong Answer Un-checked HDSL
  •  Un-checked VDSL
0 / 1 Points

Question 2: Multiple Choice

ATM AAL-2 uses .............. for MPEG videos
  •  Un-checked VBR
  • Wrong Answer Un-checked CBR
  • Wrong Answer Checked VPI
  • Wrong Answer Un-checked None of the above
0 / 1 Points

Question 3: Multiple Choice

ATM Adaptation layer is similar to .... layer in OSI model
  • Wrong Answer Un-checked Physical
  • Wrong Answer Un-checked Data Link
  •  Un-checked Transport
  • Wrong Answer Checked all of the above
0 / 1 Points

Question 4: Multiple Choice

ATM fixed cell has ......................... bytes
  • Wrong Answer Un-checked 32 bytes
  • Wrong Answer Un-checked 64 bytes
  • Wrong Answer Checked 48 bytes
  •  Un-checked 53 Bytes
1 / 1 Points

Question 5: Multiple Choice

ATM stand for
  • Wrong Answer Un-checked All time Money
  • Correct Answer Checked Asynchronous Transfer Mode
  • Wrong Answer Un-checked Asynchronous Transferable Machine
  • Wrong Answer Un-checked Asynchronous Transfer Machine
0 / 1 Points

Question 6: Multiple Choice

BRI (Basic Rate Interface) consist of
  • Wrong Answer Un-checked Four B channel and Two D channel
  •  Un-checked Two B channel and one D channel
  • Wrong Answer Checked Twenty Three B channel and one D channel
  • Wrong Answer Un-checked Thirty B channel and one D channel
0 / 1 Points

Question 7: Multiple Choice

Broadband Integrated Services Data Networks(B-ISDN's) can provide bandwidth
  • Wrong Answer Un-checked not more than 28.8 Kbits/sec
  • Wrong Answer Checked Ranging from 28-64 Kbits/sec
  • Wrong Answer Un-checked Around 2Mbits/sec at the most
  •  Un-checked Upto 155Mbits/s
1 / 1 Points

Question 8: Multiple Choice

Following is a teleservice
  • Wrong Answer Un-checked Telex
  • Wrong Answer Un-checked Telephony
  • Wrong Answer Un-checked Teleconferencing
  • Correct Answer Checked All of the above
0 / 1 Points

Question 9: Multiple Choice

ISDN provides following services
  • Wrong Answer Checked Data
  • Wrong Answer Un-checked Video
  • Wrong Answer Un-checked Voice
  •  Un-checked All of the above
1 / 1 Points

Question 10: Multiple Choice

ISDN stands for
  • Correct Answer Checked Integrated Service Digital Network
  • Wrong Answer Un-checked Interaction System Digital Network
  • Wrong Answer Un-checked Inexpensive System Digital Network
  • Wrong Answer Un-checked None of these
0 / 1 Points

Question 11: Multiple Choice

Old telephone system (POTS), was ________ system.
  • Wrong Answer Un-checked Digital
  •  Un-checked Analog
  • Wrong Answer Checked Digital as well as Analog
  • Wrong Answer Un-checked None of the above
0 / 1 Points

Question 12: Multiple Choice

Ordinary telephone lines use ________
  •  Un-checked Copper Wires
  • Wrong Answer Un-checked Aluminium
  • Wrong Answer Checked Fibre
  • Wrong Answer Un-checked None of the above
0 / 1 Points

Question 13: Multiple Choice

POTS provides following services
  •  Un-checked Voice
  • Wrong Answer Un-checked Data
  • Wrong Answer Un-checked Video
  • Wrong Answer Checked All of the above
0 / 1 Points

Question 14: Multiple Choice

PRI (Primary Rate Interface) has a capacity of _______ bandwidth
  • Wrong Answer Un-checked 66 Kbps
  • Wrong Answer Checked 64 Kbps
  •  Un-checked 1.544 Mbps
  • Wrong Answer Un-checked None of the above
1 / 1 Points

Question 15: Multiple Choice

PSTN stands for ________
  • Wrong Answer Un-checked Private Switched Telephone Network
  • Correct Answer Checked Public Switched Telephone Network
  • Wrong Answer Un-checked Public Serial Telephone Network
  • Wrong Answer Un-checked Private Serial Telephone Network
0 / 1 Points

Question 16: Multiple Choice

Voice and data service cannot co-exist on some wire in_____
  • Wrong Answer Un-checked ADSL
  •  Un-checked HDSL
  • Wrong Answer Un-checked SDSL
  • Wrong Answer Checked VDSL
0 / 1 Points

Question 17: Multiple Choice

______ is suitable for businesses that require comparable upstream and downstream data rates.
  • Wrong Answer Un-checked VDSL
  •  Un-checked SDSL
  • Wrong Answer Un-checked ADSL
  • Wrong Answer Checked Both (a) and (b)
0 / 1 Points

Question 18: Multiple Choice

________ is the supplementary service in ISDN
  • Wrong Answer Checked Telephony
  • Wrong Answer Un-checked Telefax
  •  Un-checked Call waiting
  • Wrong Answer Un-checked None of the above
4 / 18 PointsFinal Score:

1. Objectives

Objective of this module is to introduce how normal telephone lines are used for data communication.  Telephone lines can be used with various equipment to provide data services in addition to voice. The digital technologies used for such integrated services will be discussed in details which include ISDN, ATM, DSL etc. At the end of the module, a student will be able to understand the basic  knowledge about the technologies behind various data network solutions and its public use. 

2. Introduction

Alexander Graham Bell invented telephone in 1876, which is used for long distance telephone calls later over a pair of copper wires. The plain old telephone service (POTS) is based on analogue signal transmission. Based on this technology, the advanced forms of telephony services such as Integrated Services Digital Network (ISDN), cellular telephone systems, and voice over Internet Protocol (VoIP) etc. were introduced. The advantage of POTS is that a simple connection in its basic form is used in residence as well as small business. The technology of POTS is characterized by bi-directional communications, frequency range of the human voice, signalling using call-progress tones, such as dial tone and ringing signal, subscriber dialling etc. The pair of wires  from the central switch office to a subscriber's home is used for service which is called a subscriber loop. The communication circuits of the public switched telephone network could be modernized by advances in digital communications. The basic telephone network is working based on the principle of circuit switching, which is called circuit switched networks. There could be dedicated circuit between two points. Instead of copper wires, same circuit can be established with the optical fibre cable also, based on the distance and architecture required. Advanced technology can be introduced in the same line to make it as packet switched networks. These technological solutions can enable the ordinary telephone links for data communication also. Such advanced technological solutions like ISDN, ATM, DSL for data networks are discussed in this module. 

3.0 Integrated Services Digital Network (ISDN)

Public telephone networks (PSTN) and carriers can incorporate circuit switched and packet switched networks. Telephone and other service equipment can be connected to the cloud network through the public carriers using respective equipments. Analogue phones, facsimile, modem and other devices can be connected to the nearest LEC (Local Exchange Carrier) which is connected to the public carriers. Depending upon the technologies used, the transmission will use the carrier which is specified with each transmission. Analogue phone calls can be made available through  circuit switched networks and data transmission can be done through packet switched networks which use same carrier channels. 

3.1 ISDN Principle

ISDN is a WAN (Wide Area Network) technology combining best features of circuit-switching and packet-switching technologies.   Voice, data and video services can be integrated on this technology by using the same public carriers. ISDN is such a solution for integrating all digital services on the normal telephone carriers.  It uses PSTN with a cloud architecture, meaning that users connect to a network and what happens inside of the network “cloud” is hidden from the user. A user using a computer and a modem dials the number of a another computer and creates a temporary circuit between the two. When the communications session is completed, the circuit is disconnected.
The key feature of the ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. It offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 Kbit/s. Development of ISDN is governed by a set of recommendations issued by  ITU-T, called I-series recommendations, which are based on services offered to users, user-network interfaces (UNI), ISDN capabilities etc.
The principle of ISDN according to ITU –T is as stated below:
  • The ISDN is supported by a wide range of voice and non-voice applications of the same network. It provides a range of services· using a limited set of connections and multipurpose user-network interface arrangements.
  • ISDN supports a variety of applications that include both switched and non-switched connections. The switched connections. Include both circuit and packet switched connections.
  • As far as possible, new services introduced into an ISDN should be arranged to be compatible with the 64 Kbps switched digital connections.
  • A layered protocol structure should be used for the specification of access to an ISDN.
This is the same as the OSI reference model. The standards which have already been developed for OSI applications such as X.25 can be used for ISDN. (Please refer Module M-11 ISO-OSI and TCP/IP module). ISDNs may be implemented in a variety of configurations.

3.2 ISDN Services

The purpose of the ISDN is to provide fully integrated digital services to users. These services fall into categories- better services, teleservices and supplementary services.
3.2.1 Bearer Services: Bearer services provide the means to transfer information (voice, data and video) between users without the network manipulating the content of that information. The network does not need to process the information and therefore does not change the content.
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Bearer services belong to the first three layers of the OSI model and are well defined in the ISDN standard. They can be provided using circuit-switched, packet-switched, frame-switched, or cell-switched networks (ATM).
3.2.2 Teleservices: In teleservices, the network may change  the contents of the data. These services correspond to layers 4-7 of the OSI model. Teleservices relay on the facilities of the bearer services and are designed to accommodate complex user needs, without the user having to be aware of the details of the process. Teleservices include telephony, teletex, telefax, videotex, telex and teleconferencing.    
 Alternate Text

3.2.3 Supplementary Service: Supplementary services are those services that provide additional functionality to the bearer services and teleservices. Examples of these services are reverse charging, call waiting, and message handling, all familiar from today's telephone company services.
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3.3 ISDN Interfaces

There are several kinds of access interfaces to the ISDN
Basic Rate Interface (BRl)
Primary Rate Interface (PRl)
Broadband-ISDN (B-ISDN)
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                                       *Photo : Self

3.3.1 Basic Rate Interface (BRI): Basic Rate Interface service consists of two data-bearing channels ('B' channels) and one signalling channel ('D' channel) to initiate connections. The B channels operate at 64 Kbps maximum.  
The D channel operates at a maximum of 16 Kbps. The two channels can operate independently. For example, one channel can be used to send a fax to a remote location, while the other channel is used as a TCP/IP connection to a different location.
The basic rate interface (BRl) specifies a digital pipe consisting of two B channels and 16 Kbps D channel. Two B channels of 64 Kbps each, plus one D channel of 16 Kbps, equal 144 Kbps. In addition, the BRl service itself requires 48 Kbps of operating overhead. BRl therefore requires a digital pipe of 192 Kbps. Conceptually, the BRl service is like a large pipe that contains three smaller pipes, two for the B channels and one for the D channel.
3.3. 2 Primary Rate Interface (PRI): Primary Rate Interface service consists of a D channel and either 23 (depending on the country).  The usual Primary Rate Interface (PRI) specifies a digital pipe with 23 B channels and one 64 Kbps D channel. Twenty-three B channels of 64 Kbps each, plus one D channel of 64 Kbps equals 1.536 Mbps. In addition, the PRI service itself uses 8 Kbps of overhead.
PRI therefore requires a digital pipe of 1.544 Mbps. Conceptually; the PRI service is like a large pipe containing 24 smaller pipes, 23 for the B channels and 1 for the D channel. The rest of the pipe carries the overhead bits required for its operation.
3.3.3 Broadband-ISDN (B-ISDN) and ATM: Narrowband ISDN has been designed to operate over the current communications infrastructure, which is heavily dependent on the copper cable. B-ISDN however, relies mainly on the evolution of fiber optics.  B-ISDN would be able to provide end users with increased transmission rate,up to 155.54Mbits/s on a switching basis
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Photo: Self

One of the fundamental principles of the B-ISDN is to offer subscribers a large variety of services such as video telephony, video surveillance, high volume file transfer, High Definition Television (HDTV) and many more services not offered by N-ISDN. 

3.4 ISDN Architecture

Alternate Text

3.5 ATM (Asynchronous Transfer Mode)

Page Contents3.5.1 ATM Architecture

ATM stands for  Asynchronous Transfer Mode which is a high speed networking ITU standard, similar to technologies discussed above, which support  voice, video and data communications. ATM networks are connection-oriented. ATM technology design to improve utilization and Quality of Service (QoS) on high traffic network. ATM operates at a data link layer (layer 2 in the OSI model ) . Ethernet and other technologies uses variable-length packets and use routing techniques in network for data transmission but ATM uses fixed -sized  cells (53 bytes)  for data transfer  and no routing techniques. 53 bytes ATM cells includes 48 bytes of data and 5 bytes of header information as shown a figure below. Performance of ATM is expressed in the form of OC (Optical Carrier) levels, written as 'OC-xx' and 'DS-xx' for normal links.  Common levels for ATM are 155 Mbps (OC-3) and 622 Mbps (OC-12), but 10 Gbps performance level is also feasible. The scalable speeds of 1.544 Mbps (DS-1) and 6.312 Mbps (DS-3) are also common. ATM provides scalable bandwidth from Mbps to Gbps due to its asynchronous nature and times slots are available on demand.
          The technology integrate data, voice and video  with fixed packets length (called cells). This technology is combined circuit and packet switching networks. Best features like fixed path, known delay and guaranteed quality of service  (QoS) is borrowed from circuit switching. The concept of using bandwidth when needed is borrowed from packet switching. The benefits of ATM are the following.
◦     High performance wire hardware switching
◦     Dynamic bandwidth for burst traffic
◦     Class-of-service support for multimedia
◦     Scalable speed and network size
◦     Common LAN/WAN architecture
◦     Opportunities for simplification via VC architecture
◦     International standards compliance

3.5.1 ATM Architecture

          ATM architecture consist of three layers such as Physical layer, ATM layer and Adaptation Layer. ATM layer is analogous to the data link layer of the OSI model. ATM layer is responsible for the simultaneous sharing of virtual circuit (VC) over physical link and passing cell through ATM network to do this, it uses VPI and VCI information in the header of each ATM cell. ATM define a path before transmission starts and path is called virtual circuits (VC). The technology supports and combines voice with real time and low delay, video with high bandwidth, low delay and jitter and data transfer for internet services. ATM allows multiple traffic stream to share the same physical path.
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          Adaptation layer is only at the edge of ATM network for data segmentation and reassembly of data. ATM Adaptation Layer (AAL) form upper layers to ATM layer below. This is not available in ATM switch, but only in end systems. Different versions of AAL layers are available depending on ATM service class. AAL-1 uses constant bit rate (CBR) for services for e.g. circuit emulation. AAL-2 uses variable bit rate (VBR) for services like MPEG videos. Low overhead AAL is used carry IP datagrams, which is called AAL-5. Forming of 48 bytes data packets is the job of AAL-5. 
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4.0 Digital Subscribers Line (DSL)

Telephonic services are provided to home users through copper wires. DSL is a medium for transferring data over normal telephone copper lines. This can be used to connect to the Internet. Therefore, DSL is family of technologies that provides Internet access by transmitting digital data over the wires of a local telephonic network. Generally, modems are used for getting Internet connection. Modem is an equipment which convert analog signal to digital  signal and vice-versal. DSL circuit is much faster than regular phone lines even though it uses normal copper wire. The same phone jacket can be used for DSL modem with a splitter. To get a connection one need to contact an local ISP ( Internet Service Provider) who provides Internet services. Phone line splitter can be connected to phone line wall jack. The splitter will have two RJ-11 sockets, ie. one for DSL modem and another for telephone. A phone line filter is used to connect to telephone from the splitter. One connection will go to the DSL modem and modem will be connected to the computer through an Internet cable. The sample connection is shown in the diagram. Generally, DSL connection are called Broad band connection. There are different technologies of DSL, such as ADSL ( Asymmetric) , SDSL (Symmetric), HDSL (High-bit-rate ), VDSL (Very high bit-rate)
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4.1 Asymmetric DSL (ADSL)

ADSL type of Broad Band communication technology used for connecting to the Internet as mention above. ADSL allows more data to be send to over existing copper line when compared to traditional modem line. As special filter is to be installed on subscriber telephonic line to allow voice and Internet services at the same time. subscriber must be geographically close to the ISP preferably within a radius of 2 to 2.5 miles. Radius are support data rates from 1.5 to 9 Mbps when receiving data (downstream) and 16 to 640 Kbps when sending data ( Upstream). It is called asymmetric because the download and upload speeds are not symmetric. For voice service, the frequency reach 0KHz and 4KHz and 20KHz to 2.2 MHz for DSL service in some cases data rates can go up to 52Mbps .

4.2 Symmetric DSL (SDSL)

SDSL is technology developed in Europe and functions by transmitting digital pulses in the high frequency area of telephone wire. This can not provide voice service on same wires. SDSL needs a special modem and allows equal bandwidth downstream from ISP to customer premises and upstream from the subscriber to the ISP. SDSL can transmit up to 1.54 Mbps. Due to the symmetric speed, this can be used as WAN technology for small and medium businesses. Application such as web costing, file transfer and distance learning can be deployed with SDSL.

4.3 High-bit-rate DSL (HDSL)

HDSL is communication protocol standardizing in 1994. This is the first DSL technology to use a  high frequency of copper cables. HDSL gives 1.544 Mbps for DS1 services in America and 2.048 Mbps over telephone without a need for repeaters. Unlike ADSL, HDSL operates in the baseband and does not allow both services to coexist on the same wires

4.4 Very high bit-rate DSL (VDSL)

VDSL line lengths are generally between 150 mts and 2000 mts. VDSL provides high amount of bandwidth with speeds up to 52 Mbps while ADSL can give maximum of 8 to 10 Mbps. In India, MTNL as well as BSNL provides high speed combo broadband plans on VDSL technology. It uses frequency band from 25 KHz to 12 MHz. Second generation VDSL provides data rates exceeding 100 Mbps with frequency up to 30 MHz. VDSL is capable of supporting applications such as High Definition television, Voice over IP, Internet access etc. 


    1.     http://portal.BSNL.in
    2.     DSL Advances by Thomas Starr, Massimo Sorbara, John M. Cioffi, Peter J. Silverman from          Prentice Hall  Proffessional.
Additional References


1.  ISDN and Broadband ISDN with Frame Relay and ATM, 4/E By William Stallings
2.  ISDN: How to Get a High-Speed Connection to the Internet By Charles Summers (Author), Bryant Dunetz (Author)
3.  ISDN: concepts, facilities, and services By Gary C. Kessler
4.  ISDN By Raj Jain, Professor of CIS, The Ohio State University, Columbus, OH 43210
5.  ISDN protocol reference model By International Telecommunication Union (CH)

Integrated Services Digital Network is a telephone system network. It is a wide area network becoming widely available. Prior to the ISDN, the phone system was viewed as a way to transport voice, with some special services available for data. The key feature of the ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system.
A communications device that multiplexes (combines) several signals for transmission over a single medium. A demultiplexer completes the process by separating multiplexed signals from a transmission line. Frequently a multiplexer and demultiplexer are combined into a single device capable of processing both outgoing and incoming signals. A multiplexer is sometimes called a mux.
Client/Server Architecture The client/server architecture significantly decreased network traffic by providing a query response rather than total file transfer. It allows multi-user updating through a GUI front end to a shared database. Remote Procedure Calls (RPCs) or standard query language (SQL) statements are typically used to communicate between the client and server.
1. TDM is the digital multiplexing technique.
2. In TDM, the channel/link is not divided on the basis of frequency but on the basis of time.
3. Total time available in the channel is divided between several users.
4. Each user is allotted a particular a time interval called time slot or time slice during which the data is transmitted by that user.
In Computer network, a proxy server is a server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server.

Frequency-Division Multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. It is analog technique. Each signal is assigned a different frequency (sub channel) within the main channel.
Server : A server is a computer in network that provides services to the client computers such as logon requests processing, files access and storage, internet accessprinting access and many other types of services. Servers are mostly equipped with extra hardware such as plenty of external memory (RAM), more data store capacity (hard disks), high processing speed and other features.

The Token-Passing Protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.
Frame relay has evolved from X.25 packet switching and objective is to reduce network delays, protocol overheads and equipment cost. Error correction is done on an end-to-end basis rather than a link -to-link basis as in X.25 switching. Frame relay can support multiple users over the same line and can establish a permanent virtual circuit or a switched virtual circuit.

A server process (program) fulfills the client request by performing the task requested. Server programs generally receive requests from client programs, execute database retrieval and updates, manage data integrity and dispatch responses to client requests.
• X.25 is a standard used by many older public networks specially outside the U.S.
• This was developed in 1970s by CCITT for providing an interface between public packet-switched network and their customers.
The earliest electronic network is the telephone system. This telephone network commonly uses analog technology that was quite different from digital technology used in the computer-based networks. The advantages of digital technology over the analog technology in terms of economics and services forced the telephone industry to move rapidly to install fiber and digital networks.
ISDN structure includes a central ISDN office. All the users are linked to this office through a digital pipe. This digital pipe may be of different capacities and may have different data transfer rates. These digital pipes between the customers and central office are organized into multiple channels of different size.
The client is a process that sends a message to a server process requesting that the server perform a task. Client programs usually manage the user-interface portion of the application, validate data entered by the user, dispatch requests to server programs, and sometimes execute business logic.
Integrated Services Digital Network (ISDN) is a set of CCITT /ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. This technology uses ISDN adapters in place of modems and provides very fast speed up. ISDN requires adapters at both ends of the transmission.
BBS (Bulletin Board System): A single computer running special communications software that acts as a kind of electronic bulletin board. That allows remote users to dial in via a public telephone line to exchange messages and chat with one another. which is a service usually set up by an organization or a club to provide or exchange informationA BBS allows multiple people to use it at the same time in order to exchange ideas, offer help with software problems, and converse (through typed conversations) with other users currently connected to the BBS. You access the BBS through your modem , a device that transmits data through ordinary telephone lines. While connected to a BBS, a user can share information with other computer users, leave messages, and upload and download programs. One popular BBS is the Boston Computer Exchange, a place where members can buy, sell, or trade computers. Pay-for-use information services, such as CompuServe, Prodigy, and Internet are like BBS, but much larger. There are thousands of other BBSs across the globe offering a variety of topics and interests ranging from software support to dating services. To communicate with other computers, a modem is necessary.

• Session Initiation Protocol (SIP) was designed by IETF and is described in RFC 3261.
Divides Application Processing across multiple machines.Non-critical data and functions are processed on the client Critical functions are processed on the server
ISDN provides two basic types of interfaces to users.

  1. Basic Rate Interface (BRI)
  2. Primary Rate Interface (PRI)
Products for ISDN technology from different vendors even with similar features and options may create some compatibility issues. CCITT after good deliberations over the years published the first significant ISDN standards in a number of red binders in 1984 and they were simply known as the Red Book standards. The group subsequently met four years later which culminated in the publication of the 1988 Blue Book standards. These international publications were the foundation for the evolving ISDN national standards. The CCITT eventually was reformed into the group, which is now called the ITU- T. The standards used to define ISDN make use of the OSI reference model with the first three layers of this OSI reference model.
The broadcast systems generally allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted then it is received and processed by every machine on the network. This mode is called broadcasting.
When data is sent to the receiver, flow control should be carried out so that the flow of data does not overwhelm the receiver. Any receiving device has a limited speed at which it can process the incoming data and a limited amount ofmemory to store the incoming data. The receiving device should be able to inform the sending device before these limits are reached so that the transmission is stopped or reduced, temporarily.

Asynchronous Transfer Mode (ATM) Also called cell relay, a high-speed switched network technology developed by the telecommunications industry to implement the next, BROADBAND generation of ISDN.ATM was designed for use in WANS such as the public telephone system and corporate data networks, though it has also been applied to create super-fast LANS. It can carry all kinds of traffic - voice, video and data – simultaneously at speeds up to 155megabits per second.
A software layer that accepts user data, such as digitized voice, video or computer data, and converts to and from cells for transmission over an ASYNCHRONOUS TRANSFER MODE network. AAL software mostly runs at the end-points of a connection, though in a few circumstances AAL software is run inside an ATM switch. AAL includes facilities to carry traffic that uses other network protocols, such as TCP/IP, over ATM.

The application of methods derived from INFORMATION THEORY to the detection and correcting of errors in DIGITAL data streams. Error correction is of the utmost importance in most areas of computing and communications technology. For example: Internet's TCP protocol provides error detection, CD-ROMS devote around 14% of their total data capacity to redundant error correction information (and music CDS only a little less), and modem speeds above 28 kilobits per second would be impossible over public telephone lines without error correcting PROTOCOLS such as v.90.

(xDSL) A whole class of digital telecommunication technologies that can offer BROADBAND data rates, up to 50 megabits per second (Mbps), over the existing copper wires of the analogue public telephone system. By employing advanced modulation schemes, xDSL technologies support Internet or other data access simultaneously with voice telephone calls. In the meta-acronym xDSL, the x stands for the first letter of any of the individual acronyms used for these technologies: ADSL, HDSL, SDSL and VDSL.
In the world of asynchronous communication (over Mac or PC serial ports), CTS stands for clear to send. When acomputer needs to communicate with an outside device physically connected to it (peripheral), the two of them have to go through this preamble of making sure each of them is ready to hear what the other has to say, and confirm that they are going to be speaking the same language. Somewhere near the beginning of this preamble, one device will send an RTS (Request To Send) message. The receiving device will then reply with a CTS message "Yes, I'm now ready for anything you want to send me." I know, the whole thing sounds like you may be sitting there drumming your fingers on your desk, waiting for these flipping machines to get done with their senseless checklist. Relax. Like most processes done by a computer, this one takes less than a millisecond.



During the last few years,the desire for broadband communication has been moving closer to reality.Exceeding the bandwidth limitations of the installed switching system is an ongoing challenge,driven by the users' demand and brought closer to reality by new technology.Broadband Integrated Services Digital Network or B-ISDN is a broadband communication network developed by International Telegraph And Telephone Consultative Committee(CCITT) that enables the transmission of design simulations and other multimedia transmission that include text,voice, video and graphics in one network.This B-ISDN would be able to provide end users with increased transmission rate,up to 155.54Mbits/s on a switching basis.This is a great improvement as compared to the earlier rate of 64kbits/s employed in theISDN which is not suitable for high definition moving pictures.

Evolution of B-ISDN

When 'integrated' digital switching and transmission systems were first considered in the 1960's,one of the selling points was that digital operation would pave the way for a truly multi-service network that would carry data and facimile as well as voice service.At that time non-voice services were very much in the minority,and consequently the standard of the integrated digital network(IDN) were geared to the transmission of speech The choice of a 64kbit/s(European standard) channel was conditioned by the expected need for several changes between the analogue and digital transmission modes as calls pass through the network.As advances in micro-electronic technology made it possible to extend digital techniques to the subscriber's link with the local exchange and thence to the subscriber's terminal,over old copper wire,standards for an 'Integrated Service Digital Network' or ISDN were established.This was still based on the 64kbits/s circuit network channel. This was quite reasonable as apart from voice ,typescript could be sent fairly fast and large software could be downloaded within minutes.However users still were not satisfied with this speed as in this competitive world,information is expected to reach end users within the blink of an eye.The only service that didn't seem possible within the 64kbits/s channels were those based on high definition moving pictures.
Within the International Telegraph And Telephone Consultative Committee(CCITT), there has been the desire to explore at an early stage the possibility of producing recommendation for networks that would carry broadband services meaning network that enables the transmission of bits at a very high rate to accomodate high definition moving pictures,as well as all those services offered by the ISDN.
The first requirement was that the new type of network should be able to carry not only existing services but also those that might be needed well in the future such as mixed media services,High Definition Television(HDTV) as well as holographic images.The change from anologue to digital operation on an international scale is proving costly enough.Hence it is desirable that the new network should be capable of evolution from ISDN,rather than requiring a complete replacement of existing network.After much debate, the CCITT decided to provide a new network fitting all the criterions mentioned above called Broadband Integrated Service Digital Network(B-ISDN).This network was also decided to be based on a switching technique known as Asynchronous Transfer Mode(ATM). The term ATM network is sometimes used as a synonym for this B-ISDN network.

What is ATM ?

ATM is a general class of digital packet switching technology that relay and route traffic by means of an address contained within the header.Unlike more familiar packet technology,such as X.25 or frame relay,ATM uses fixed length packets called cells.A cell is 53 bytes long comprising of a 5-byte header containing the address and a 48-byte information field.The switching of the ATM circuit is statistically natured and switching is done purely on hardware level without the need for software interface.Hence enabling a high switching rate.

Atm in B-ISDN

One of the fundamental principles of the B-ISDN is to offer subscribers a large variety of services such as video telephony,video surveillance,high volume file transfer,High Definition Television(HDTV) and many more services not offered by ISDN.These services would require the transmission of data at different bit rates .Thus a technique was needed to switch information flows that have time constrain relating to video or voice as well as information flows that are more sporadic and have widely variable bit rate.In this context,it is critical that the multiplexing and switching technology used to support these B-ISDNservices and the needed bandwidth management be extremely flexible.Traditional time division multiplexing which devide bandwidth into a number of fixed capacity channels,simply do not have the needed flexibility.Packet switching technology which allow variable length packets,may not meet the stringent delay requirements needed for some real time services such as voice and video.Since ATM cells are only 53 bytes long,real time services when given priority, need not wait longer than 53-byte cell time(3 microseconds for a 155Mbits/s ) before being given access to the communication channel.The variable bit rate offered by B-ISDN is due to the ATM technology used.The fixed length cells allows the prediction of the size of the buffers to be used and hence the bits could be transmitted at any convenient rate unlike the fixed rate(64Kbits/s) specified by ISDN

Using fiber optic cables

There are also plans for B-ISDN to provide fiber optic cables to replace existing twisted pair copper wires.This may be costly but it could certainly bring much improvement.For example,The fiber optic offers such a large bandwidth that it could accomodate 100Gbits/s data rate.This would certainly reduce delay caused by the limited bandwidth offered by the conventional twisted pair wire, to within a blink of an eye.Furthermore the fiber optic medium is designed to produce a bit error rate orders of magnitude lower than that provided by twisted pair copper wires(10^-12 versus 10^-6 for example) Hence the requirements for error detection/correction protocols might be relaxed by the elimination of the need for extensive layers of protection. The size of the 5-byte header could be reduced by reducing the number of bits required for error correction,making room for a larger information field.


The full implementation of B-ISDN is certainly something worth looking forward to.With the usage of ATM technology as well as the laying of fiber optic cables,the B-ISDN would certainly revolutionise the transmission of information.With the extremely high and flexible bit rate, users could be assured of a negligible delay between the sender and recipient.
  • "Packet Power" by C.J.Hughes(F) and A.(Gill)Waters.IEE Review,October 1991 ,pp 357-360
  • "Broadband ISDN ATM Layer Management:Operations,Administration, and Maintenance Consideration" by Susumu Yoneda,IEEE Network Magazine,May 1991, pp 31-35
  • An Introduction to Broadband Networks by Anthony S. Acampora

  • ISDN

    ISDN protocols described here include:
    International Variants of ISDN 
    ISDN Frame Structure 
    ISDN Terminology  
    ISDN (Integrated Services Digital Network) is an all digital communications line that allows for the transmission of voice, data, video and graphics, at very high speeds, over standard communication lines. ISDN provides a single, common interface with which to access digital communications services that are required by varying devices, while remaining transparent to the user. Due to the large amounts of information that ISDN lines can carry, ISDN applications are revolutionizing the way businesses communicate.ISDN is not restricted to public telephone networks alone; it may be transmitted via packet switched networks, telex, CATV networks, etc.
    The ISDN is illustrated here in relation to the OSI model:

    ISDN applications
    For more information on ISDN testing 

    The LAPD (Link Access Protocol - Channel D) is a layer 2 protocol which is defined in CCITT Q.920/921. LAPD works in the Asynchronous Balanced Mode (ABM). This mode is totally balanced (i.e., no master/slave relationship). Each station may initialize, supervise, recover from errors, and send frames at any time. The protocol treats the DTE and DCE as equals.
    The format of a standard LAPD frame is as follows:
    Address field
    Control field
    LAPD frame structure
    The value of the flag is always (0x7E). In order to ensure that the bit pattern of the frame delimiter flag does not appear in the data field of the frame (and therefore cause frame misalignment), a technique known as Bit Stuffing is used by both the transmitter and the receiver.
    Address field
    The first two bytes of the frame after the header flag is known as the address field. The format of the address field is as follows:
    LAPD address field
    EA1First Address Extension bit which is always set to 0.
    C/RCommand/Response bit. Frames from the user with this bit set to 0 are command frames, as are frames from the network with this bit set to 1. Other values indicate a response frame.
    EA2Second Address Extension bit which is always set to 1.
    TEITerminal Endpoint Identifier. Valid values are as follows:
     0-63Used by non-automatic TEI assignment user equipment.
     64-126Used by automatic TEI assignment equipment.
     127Used for a broadcast connection meant for all Terminal Endpoints.
    Control field
    The field following the Address Field is called the Control Field and serves to identify the type of the frame. In addition, it includes sequence numbers, control features and error tracking according to the frame type.
    The Frame Check Sequence (FCS) enables a high level of physical error control by allowing the integrity of the transmitted frame data to be checked. The sequence is first calculated by the transmitter using an algorithm based on the values of all the bits in the frame. The receiver then performs the same calculation on the received frame and compares its value to the CRC.
    Window size
    LAPD supports an extended window size (modulo 128) where the number of possible outstanding frames for acknowledgement is raised from 8 to 128. This extension is generally used for satellite transmissions where the acknowledgement delay is significantly greater than the frame transmission times. The type of the link initialization frame determines the modulo of the session and an "E" is added to the basic frame type name (e.g., SABM becomes SABME).
    Frame types
    The following are the Supervisory Frame Types in LAPD:
    RRInformation frame acknowledgement and indication to receive more.
    REJRequest for retransmission of all frames after a given sequence number.
    RNRIndicates a state of temporary occupation of station (e.g., window full).
    The following are the Unnumbered Frame Types in LAPD:
    DISCRequest disconnection
    UAAcknowledgement frame.
    DMResponse to DISC indicating disconnected mode.
    FRMRFrame reject.
    SABMInitiator for asynchronous balanced mode. No master/slave relationship.
    SABMESABM in extended mode.
    UIUnnumbered Information.
    XIDExchange Information.
    There is one Information Frame Type in LAPD:
    Info  Information transfer frame.

    ISDN decode
    Interested in more details about testing this protocol? click here

    International Variants of ISDN
    The organization primarily responsible for producing the ISDN standards is the CCITT. The CCITT study group responsible for ISDN first published a set of ISDN recommendations in 1984 (Red Books). Prior to this publication, various geographical areas had developed different versions of ISDN. This resulted in the CCITT recommendation of a common ISDN standard for all countries, in addition to allocated variants definable for each country.
    The use of nation-specific information elements is enabled by using the Codeset mechanism which allows different areas to use their own information elements within the data frames.
    Following is a description of most ISDN variants:
    National ISDN1 (Bellcore)
    This variant is used in the USA by Bellcore. It has four network-specific message types. It does not have any single octet information elements. In addition to Codeset 0 elements it has four Codeset 5 and five Codeset 6 information elements.
    National ISDN-2 (Bellcore)
    The main difference between National ISDN-1 and ISDN-2 is parameter downloading via components (a component being a sub-element of the Extended Facility information element). These components are used to communicate parameter information between ISDN user equipment, such as an ISDN telephone, and the ISDN switch.
    Other changes are the addition of the SEGMENT, FACILITY and REGISTER message types and the Segmented Message and Extended Facility information elements. Also, some meanings of field values have changed and some new accepted field values have been added.
    5ESS (AT&T)
    This variant is used in the USA by AT&T. It is the most widely used of the ISDN protocols and contains 19 network-specific message types. It has no Codeset 5, but does have 18 Codeset 6 elements and an extensive information management element.
    Euro ISDN (ETSI)
    This variant is to be adopted by all of the European countries. Presently, it contains single octet message types and has five single octet information elements. Within the framework of the protocol there are no Codeset 5 and Codeset 6 elements, however each country is permitted to define its own individual elements.
    VN3, VN4 (France)
    These variants are prevalent in France. The VN3 decoding and some of its error messages are translated into French. It is a sub-set of the CCITT document and only has single octet message types. The more recent VN4 is not fully backward compatible but closely follows the CCITT recommendations. As with VN3, some translation has taken place. It has only single octet message types, five single octet information elements, and two Codeset 6 elements.
    1TR6 (Germany)
    This variant is prevalent in Germany. It is a sub-set of the CCITT version, with minor amendments. The protocol is part English and part German.
    ISDN 30 [DASS-2] (England)
    This variant is used by British Telecom in addition to ETSI (see above). At layers 2 and 3 this standard does not conform to CCITT structure. Frames are headed by one octet and optionally followed by information. However most of the information is IA5 coded, and therefore ASCII decoded.
    In 1989 Australian ISDN was introduced.  This used Telecom Australia specified protocols TPH 1856 for PRI and TPH 1962 for BAI.  These were adopted by the Regulator Austel as Australian Technical Standards in 1990 - TS 014 and TS013 respectively.  These protocols were developed from CCITT Red Book ISDN recommendations.In 1996, a new ISDN was established using EuroISDN protocols.  The Regulator (Austel) issued new Standards, these being TS031 for BAI and TS 038 for PRI.  These were replaced by new industry Standards in 2001, these being AS/ACIF S.031 and AS/ACIF S.038 for BAI and PRI respectively.There are currently no Australian ISDN BAI (TS 013) services in operation, while there are a small and declining number of Australian ISDN PRI (TS 014) in service.All Australian carrier networks are EuroISDN capable, but there may be some differences in Supplementary Services offered.  Some smaller carrier networks are also Australian ISDN (TS 014) capable.  The major carrier only provides EuroISDN based services.
    The Japanese ISDN service provided by NTT is known as INS-Net and its main features are as follows:
    • Provides a user-network interface that conforms to the CCITT Recommendation Blue Book.
    • Provides both basic and primary rate interfaces.
    • Provides a packet-mode using Case B.
    • Supported by Signalling System No. 7 ISDN User Part with the network.
    • Offered as a public network service.
    ARINC 746
    In passenger airplanes today there are phones in front of each passenger. These telephones are connected in a T1 network and the conversation is transferred via a satellite. The signalling protocol used is based on Q.931, but with a few modifications and is known as ARINC 746. The leading companies in this area are GTE and AT&T. In order to analyze ARINC, the LAPD variant should also be specified as ARINC.
    ARINC 746 Attachment 11 
    ARINC (Aeronautical Radio, INC.) Attachment 11 describes the Network Layer (layer 3) message transfer necessary for equipment control and circuit switched call control procedures between the Cabin Telecommunications Unit (CTU) and SATCOM system, North American Telephone System (NATS), and Terrestrial Flight Telephone System (TFTS). The interface described in this attachment is derived from the CCITT recommendations Q.930, Q.931 and Q.932 for call control and the ISO/OSI standards DIS 9595 and DIS 9596 for equipment control. These Network Layer messages should be transported in the information field of the Data Link Layer frame.
    ARINC 746 Attachment 17
    ARINC (Aeronautical Radio, INC.) Attachment 17 represents a system which provides passenger and cabin crew access to services provided by the CTU and intelligent cabin equipment. The distribution portion of the CDS transports the signalling and voice channels from headend units to the individual seat units. Each zone within the aircraft has a zone unit that controls and services seat units within that zone.
    Northern Telecom - DMS 100
    This variant represents Northern Telecom’s implementation of National ISDN-1. It provides ISDN BRI user-network interfaces between the Northern Telecom ISDN DMS-100 switch and terminals designed for the BRI DSL. It is based on CCITT ISDN-1 and Q Series Recommendations and the ISDN Basic Interface Call Control Switching and Signalling Requirements and supplementary service Technical References published by Bellcore.
    DPNSS1 (Digital Private Network Signalling System No. 1) is a common-channel signalling system used in Great Britain. It extends facilities normally only available between extensions on a single PBX to all extensions on PBXs that are connected together in a private network. It is primarily intended for use between PBXs in private networks via time-slot 16 of a 2048 kbit/s digital transmission system. Similarly it may be used in time-slot 24 of a 1.544 kbit/s digital transmission system. Note that the LAPD variant should also be selected to be DPNSS1.
    Swiss Telecom
    The ISDN variant operated by the Swiss Telecom PTT is called SwissNet. The DSS1 protocol for SwissNet is fully based on ETS. Amendments to this standard for SwissNet fall into the category of definitions of various options in the standard and of missing requirements. They also address SwissNet-specific conditions, e.g., assuring compatibility between user equipment and SwissNet exchanges of different evolution steps.
    QSIG is a modern, powerful and intelligent inter-private PABX signalling system. QSIG standards specify a signalling system at the Q reference point which is primarily intended for use on a common channel; e.g. a G.703 interface. However, QSIG will work on any suitable method of connecting the PINX equipment. The QSIG protocol stack is identical in structure to the DSSI protocol stack. Both follow the ISO reference model. Both can have an identical layer 1 and layer 2 (LAPD), however, at layer 3 QSIG and DSS1 differ.
    Interested in more details about testing this protocol? click here

    ISDN Frame Structure
    Shown below is the general structure of the ISDN frame.
    Protocol discriminator
    Length of reference call value
    Call reference value
    Message type
    Other information elements as required
    ISDN frame structure
    Protocol discriminator
    The protocol used to encode the remainder of the Layer.
    Length of call reference value
    Defines the length of the next field. The Call reference may be one or two octets long depending on the size of the value being encoded.
    Set to zero for messages sent by the party that allocated the call reference value; otherwise set to one.
    Call reference value
    An arbitrary value that is allocated for the duration of the specific session, which identifies the call between the device maintaining the call and the ISDN switch.
    Message type
    Defines the primary purpose of the frame. The message type may be one octet or two octets (for network specific messages). When there is more than one octet, the first octet is coded as eight zeros. A complete list of message types is given in ISDN Message Types below.
    ISDN Information Elements
    There are two types of information elements: single octet and variable length.
    Single octet information elements
    The single octet information element appears as follows:
    Information element identifier
    Information element
    Single octet information element
    Following are the available single octet information elements:
    1 000 ----Reserved
    1 001 ----Shift
    1 010 0000More data
    1 010 0001Sending Complete
    1 011 ----Congestion Level
    1 101 ----Repeat indicator
    Variable length information elements
    The following is the format of the variable length information element:
    Information element identifier
    Length of information elements
    Information elements (multiple bytes)
    Variable length information element
    The information element identifier identifies the chosen element and is unique only within the given Codeset. The length of the information element informs the receiver as to the amount of the following octets belonging to each information element. Following are possible variable length information elements:
    0 0000000Segmented Message
    0 0000100Bearer Capability
    0 0001000Cause
    0 0010100Call identify
    0 0010100Call state
    0 0011000Channel identification
    0 0011100Facility
    0 0011110Progress indicator
    0 0100000Network-specific facilities
    0 0100111Notification indicator
    0 0101000Display
    0 0101001Date/time
    0 0101100Keypad facility
    0 0110100Signal
    0 0110110Switchhook
    0 0111000Feature activation
    0 0111001Feature indication
    0 1000000Information rate
    0 1000010End-to-end transit delay
    0 1000011Transit delay selection and indication
    0 1000100Packet layer binary parameters
    0 1000101Packet layer window size
    0 1000110Packet size
    0 1101100Calling party number
    0 1101101Calling party subaddress
    0 1110000Called party number
    0 1110001Called Party subaddress
    0 1110100Redirecting number
    0 1111000Transit network selection
    0 1111001Restart indicator
    0 1111100Low layer compatibility
    0 1111101High layer compatibility
    0 1111110User-user
    0 1111111Escape for ex
    Other valuesReserved
    ISDN Message Types
    Following are possible ISDN message types:
    Call Establishment
    000 00001Alerting
    000 00010Call Proceeding
    000 00011Progress
    000 00101Setup
    000 00111Connect
    000 01101Setup Acknowledge
    000 01111Connect Acknowledge
    Call Information Phase
    001 00000User Information
    001 00001Suspend Reject
    001 00010Resume Reject
    001 00100Hold
    001 00101Suspend
    001 00110Resume
    001 01000Hold Acknowledge
    001 01101Suspend Acknowledge
    001 01110Resume Acknowledge
    001 10000Hold Reject
    001 10001Retrieve
    001 10011Retrieve Acknowledge
    001 10111Retrieve Reject
    Call Clearing
    010 00101Disconnect
    010 00110Restart
    010 01101Release
    010 01110Restart Acknowledge
    010 11010Release Complete
    011 00000Segment
    011 00010Facility
    011 00100Register
    011 01110Notify
    011 10101Status inquiry
    011 11001Congestion Control
    011 11011Information
    011 11101Status
    Interested in more details about testing this protocol? click here

    ISDN Terminology
    The Basic Rate Interface is one of the two services provided by ISDN. BRI is comprised of two B-channels and one D-channel (2B+D). The B-channels each operate at 64 Kbps and the D-channel operates at 16 Kbps. It is used by single line business customers for typical desk-top type applications.
    C/R refers to Command or Response. The C/R bit in the address field defines the frame as either a command frame or a response frame to the previous command.
    Three main Codesets are defined. In each Codeset, a section of the information elements are defined by the associated variant of the protocol:
    Codeset 0The default code, referring to the CCITT set of information elements.
    Codeset 5The national specific Codeset.
    Codeset 6The network specific Codeset.
    The same value may have different meanings in various Codesets. Most elements usually appear only once in each frame.
    In order to change Codesets two methods are defined:
    Shift  This method enables a temporary change to another Codeset. Also termed as non-locking shift, the shift only applies to the next information element.
    Shift Lock  This method implements a permanent change until indicated otherwise. Shift-Lock may only change to a higher Codeset.
    Customer Premises Equipment - refers to all ISDN compatible equipment connected at the user sight. Examples of devices are telephone, PC, Telex, Facsimile, etc. The exception is the FCC definition of NT1. The FCC views the NT1 as a CPE because it is on the customer sight, but the CCITT views NT1 as part of the network. Consequently the network reference point of the network boundary is dependent on the variant in use.
    ISDN Channels B, D and H
    The three logical digital communication channels of ISDN perform the following functions:
    B-ChannelCarries user service information including: digital data, video, and voice.
    D-ChannelCarries signals and data packets between the user and the network
    H-ChannelPerforms the same function as B-Channels, but operates at rates exceeding DS-0 (64 Kbps).
    ISDN Devices
    Devices connecting a CPE and a network. In addition to facsimile, telex, PC, telephone, ISDN devices may include the following:
    TATerminal Adapters - devices that are used to portray non-ISDN equipment as ISDN compatible.
    LELocal Exchange - ISDN central office (CO). The LE implements the ISDN protocol and is part of the network.
      Local Termination - used to express the LE responsible for the functions associated with the end of the Local Loop.
      ETExchange Termination - used to express the LE responsible for the switching functions.
      NTNetwork Termination equipment exists in two forms and is referred to accordingly. The two forms are each responsible for different operations and functions.
        • NT1 - Is the termination of the connection between the user sight and the LE. NT1 is responsible for performance, monitoring, power transfer, and multiplexing of the channels.
        • NT2 - May be any device that is responsible for providing user sight switching, multiplexing, and concentration: LANs, mainframe computers, terminal controllers, etc. In ISDN residential environments there is no NT2
          Terminal Equipment - any user device e.g.: telephone or facsimile. There are two forms of terminal equipment:
          • TE1 - Equipment is ISDN compatible.
          • TE2 - Equipment is not ISDN compatible
          ISDN Reference Points
          Reference points define the communication points between different devices and suggest that different protocols may be used at each side of the point. The main points are as follows:

          RA communication reference point between a non-ISDN compatible TE and a TA.
          SA communication reference link between the TE or TA and the NT equipment.
          TA communication reference point between user switching equipment and a Local Loop Terminator.
          UA communication reference point between the NT equipment and the LE. This reference point may be referred to as the network boundary when the FCC definition of the Network terminal is used.
          The following diagram illustrates the ISDN Functional Devices and Reference Points:
          The Link Access Protocol on the D-channel. LAPD is a bit orientated protocol on the data link layer of the OSI reference model. Its prime function is ensuring the error free transmission of bits on the physical layer (layer 1).
          The Primary Rate Interface is one of the two services provided by ISDN. PRI is standard dependent and thus varies according to country. In North America, PRI has twenty-three B-channels and one D-channel (23B+D). In Europe, PRI has thirty B-channels and one D-channel (30B+D).
          The American B- and D-channels operate at an equal rate of 64 Kbps. Consequently, the D-channel is sometimes not activated on certain interfaces, thus allowing the time slot to be used as another B-channel. The 23B+D PRI operates at the CCITT designated rate of 1544 Kbps.
          The European PRI is comprised of thirty B-channels and one D-channel (30B+D). As in the American PRI all the channels operate at 64 Kbps. However, the 30B+D PRI operates at the CCITT designated rate of 2048 Kbps.
          Service Access Point Identifier -the first part of the address of each frame.
          Terminal End Point Identifier - the second part of the address of each frame.
          Interested in more details about testing this protocol? click here
          Additional Information

        • Wireless/Networking - By Category

          Networking Basics - Key Concepts in Computer Networking
          Start learning about computer networking basics by exploring this guide to the important concepts and technologies. The A-Z terms and Frequently Asked Questions (FAQ) lists span many essential topics, while other sections of this guide each focus on one core area of networks.
          Wi-Fi Wireless Networks and Technology
          Most agree that wireless networking represent the future of computer and Internet connectivity worldwide. Wi-Fi continues to be the pre-eminent technology for building general-purpose wireless networks.
          TCP/IP - Transmission Control Protocol / Internet Protocol
          TCP/IP is arguably the single most important computer networking technology. The Internet and most home networks support TCP/IP as the "language" computers use to find and connect with each other.
          Internet Access and Services
          Get on the Internet, share broadband Internet or other connections among network devices, and take advantage of all the Web has to offer.
          Proxy Servers and Proxy Lists
          On the Internet, proxy servers provide a way to visit sites anonymously. Proxy servers also provide network firewall, connection sharing, and caching technology for private networks.
          Home Networking - Setting Up a Home Network
          Home networks can be set up with or without Internet access, using various combinations of computer hardware and software.
          VPN - Virtual Private Networking
          VPN solutions support remote access and private data communications over public networks as a cheaper alternative to leased lines. VPN clients communicate with VPN servers utilizing a number of specialized protocols.
          Peer to Peer File Sharing - P2P Networking
          Peer-to-peer (P2P) networking eliminates the need for central servers, allowing all computers to communicate and share resources as equals. Music file sharing, instant messaging and other popular network applications rely on P2P technology.
          Hardware - Network Gear
          Computer networks may utilize hubs, switches, routers, adapters, cables and several other types of hardware equipment. Become savvy in how network gear works and how to use it.
          Windows Networking
          The Microsoft Windows family of operating systems support numerous networking technologies and features.
          Networking With Apple Devices
          Apple devices including Macs, iPhones, iPods and iPad support standard wired and wireless networking technologies, but they also utilize custom applications and some special techniques for networking with each other and with non-Apple devices.
          Network Design for Homes and Businesses
          Design considerations for computer networks cover a wide range of topics including layout, capacity planning, and security.
          Bluetooth Wireless Technology
          Bluetooth is a specification for using low-power radio technology to link phones and computers over short distances without wires. Learn about Bluetooth technology to network cell phones, PDAs, and computer peripherals.
          VoIP - Voice Over IP - Internet Telephony
          With VoIP - voice over IP - service, consumers enjoy the convenience of a cell phone with the benefits of full Internet connectivity for telephony. The same Internet Protocol (IP) technology used in conventional data networks can be used to transmit voice and fax.
          Practice Exams in Computer Networking
          Learn about computer networking the fun and easy way, by taking this series of interactive question-and-answer quizzes / practice tests. These tests offer excellent practice for certifica

        • tion exams.

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