Integrated Services Digital Network (ISDN)

[mindreader]

Integrated Services Digital Network (ISDN)
INTRODUCTION

Spiraling demand for transparent, affordable, and dependable access to media-rich Web-based voice, data, and video services contributes to persistent usage of Integrated Services Digital Network (ISDN) applications in the present-day networking environment. Also known as Narrowband ISDN (N-ISDN), ISDN supports digital transmission over ordinary twisted copper wire pair traditionally used for telephone service. Distinguished by its projected ability to facilitate worldwide connectivity via the in-place twisted copper wireline infrastructure, ISDN technology was widely promoted by the communications industry as a universal global transport solution during the 1970s and 1980s. At that time, however, affordable, dependable, compatible, and easily implemented ISDN services for small business and residential networks were not readily available from telecommunications carriers, vendors, and equipment manufacturers. By the1990s, competitive residential and small business solutions based on DSL (Digital Subscriber Line) and wireline and wireless cable network technologies outpaced ISDN implementations at SOHO (Small Office/Home Office) venues and small-sized business establishments. In addition, ISDN implementations were also overshadowed by multiservice, high-capacity, high-performance broadband solutions based on ATM (Asynchronous Transfer Mode) technology. As a consequence, ISDN is not currently viewed as a worldwide platform for provisioning access to voice, video, and data services over the local loop. Nonetheless, commitment to ISDN utilization in residential venues and in sectors that include education, medicine, and business is reflected in continued ISDN deployments. The primary attraction of ISDN in the present-day marketplace is its ability to provision affordable video, audio, and data services and dependable throughput over the same twisted pair copper communications lines in place for the Public Switched Telephone Network (PSTN).


PURPOSE
Key ISDN concepts and recent research in the ISDN arena are introduced. Challenges associated with the incorporation of ISDN technology into the networking infrastructure for enabling reliable information transport are explored. Standards organizations and standards activities in the ISDN domain are reviewed. Guidelines for planning an ISDN implementation are described. Representative ISDN initiatives and applications in fields such as telemedicine, tele-education, and telebusiness are highlighted. The role of ISDN technology in enabling implementation of Web-based virtual communities is noted as well.


FOUNDATIONS
Developed in the 1970s to provision digital voice and data services over copper wire phonelines, ISDN technology was expected to replace conventional PSTN (Public Switched Telephone Network) technology. The Consultative Committee for International Telephone and Telegraph or CCITT (now known as the International Telecommunications Union or the ITU) completed the initial I.210 Recommendation for ISDN implementation in 1984.
ISDN was initially distinguished by its capabilities in enabling subscribers at SOHO (Small Office/Home Office) venues to access the Internet at faster rates than speeds supported by conventional analog voiceband modems. Despite ISDN capabilities in economically facilitating digital video, voice, and data delivery over the POTS (Plain Old Telephone System) infrastructure to the customer premise, ISDN services were not widely deployed or universally accepted.
The complexity of the ISDN ordering and service initialization process and poor technical support provisioned by communications carriers to ISDN subscribers adversely affected ISDN implementation. ISDN products from competitive communications carriers were not always interoperable and ISDN services were not universally obtainable. Moreover, ISDN subscribers encountered variations in vendor packages and were often frustrated in their efforts to determine the availability of ISDN services and applications at any given location.
Additional roadblocks to the realization of global ISDN included lack of uniform services and technical complexity in integrating ISDN into the existing telecommunications infrastructure. The relatively limited use of this technology contributed to cynical interpretations of the ISDN acronym that continue to circulate today. For disenchanted ISDN customers, the ISDN acronym translates to “It Sure Does Nothing,” and “It Sure Doesn’t Network.” By contrast, ISDN advocates maintain that the ISDN acronym stands for “It Sure Does Network” and “Information Services Delivered Now.” Despite the accelerating popularity of competitive residential access technologies, ISDN remains a viable solution for facilitating access to previously inaccessible teleservices, particularly for subscribers in isolated locations and remote communities.

[mindreader]

ISDN FEATURES AND FUNCTIONS

Depending on user needs and requirements, ISDN configurations enable diverse tele-applications and tele-activities. For example, ISDN deployments in metropolitan areas and rural locations facilitate LAN (Local Area Network) interconnectivity, teleworking, telemarketing, remote publishing, electronic commerce (E-commerce), videoconferencing, and voice telephony service. ISDN also fosters tele-instruction, telemedicine consultations, voicemail, and remote monitoring and surveillance services. In addition, ISDN enables connectivity to enterprisewide intranets and extranets, and serves as an effective backup solution for networks employing ATM, Frame Relay (FR), and T-1 (1.544 Mbps or Megabits per second) or E-1 (European-2.048 Mbps) leased-line connections.

A multiservice technology, ISDN enables transmission of delay-sensitive and bursty data traffic via virtual links that can be shared with other subscribers. For example, ISDN employs circuit-switched connections for establishing a virtual pathway between two ISDN subscribers that is virtually fixed for the duration of the phone call. In addition to basic telephony service, ISDN circuit-switched connections also support caller ID (Identification), call forwarding, call hold, and automatic callback. ISDN employs packet-switched connections to facilitate desktop publishing, compressed video transmission, and bulk file transfer. ISDN works in concert with ITU-T (International Telecommunications Union-Telecommunications Standards Sector) Group 4-compliant facsimile (fax) implementations to facilitate dependable transmission of high-resolution images such as blueprints and medical scans. In addition, ISDN provisions non-switched service for information transport via dedicated leased lines.

ISDN is designed as a global public telecommunications network service. However, in reality, multiple ISDN networks are implemented for achieving interconnectivity within and across local, metropolitan, regional, national, and international boundaries. Interoperable links to out-of-state locations not served by ISDN technology are established with the use of Switched 56 services. Switched 56 solutions support data-only connections at speeds up to 56 Kbps (Kilobits per second). However, Switched 56 solutions are not capable of supporting out-of-band D (Delta) Channel signaling provisioned by ISDN configurations. In contrast to ISDN, Switched 56 services also cannot provision concurrent voice, video, and data transmissions. In comparison to the always-on and always-available capabilities of competitor technologies such as DSL (Digital Subscriber Line) and cable networks, ISDN readily enables connections to be established and discontinued. In an ISDN implementation, after the transmission ends and the communications link is idle, the ISDN connection is automatically terminated.

ISDN supports development of an end-to-end digital network by converting every standard analog POTS (Plain Old Telephone Service) line into a high-speed digital connection for enabling information transport. With ISDN, multiple channels support diverse applications simultaneously on the same twisted pair circuit enabling POTS delivery. Prior to ISDN implementation, separate phone lines were required for accessing telephone calls, fax transmissions, and computing services.

[mindreader]

ISDN TECHNICAL FUNDAMENTALS

BASIC ISDN INSTALLATION REQUIREMENTS

ISDN implementation involves determining the number of locations and types of devices that will be attached to the configuration and bandwidth or transmission rate requirements. In addition, ISDN deployment requires reconfiguration of PC (Personal Computer) software to support ISDN links and rewiring or replacing a single phone jack with a dual port to enable ISDN connections. The installation of additional PSTN wiring at the subscriber premise may also be required. In addition, ISDN implementations also involve utilization of ISDN Terminal Equipment (TE), ISDN Network Termination (NT) devices, and ISDN Terminal Adapters (TAs).


ISDN TERMINAL ADAPTERS (TAS)

ISDN supports cost-effective digital information transport at considerably faster rates than conventional analog telephony service. As part of the ISDN implementation process, subscribers purchase ISDN-compatible equipment such as ISDN Terminal Adapters (TAs) instead of modems to facilitate conversion of analog voice signals into digital signal formats that are fully compatible with ISDN telephony service and ISDN TAs at the local telephone exchange. The local telephone exchange is also known as the telephone company central office (CO). Available as stand-alone units or PC (Personal Computer) cards, Terminal Adapters (TAs) allow non-ISDN equipment to support operations via the in-place ISDN configuration. In addition to enabling digital data and analog voice devices to interwork via ISDN connections, TAs also distinguish between voice and non-voice signals so that voice calls and data frames can be directly routed to designated destination addresses.


ISDN TERMINAL EQUIPMENT (TE)

ISDN works in tandem with two types of terminal equipment (TE). Devices that employ ISDN directly and foster ISDN services are called Terminal Equipment Type 1 (TE1). By contrast, non-ISDN devices are called Terminal Equipment Type 2 (TE2). TE2 devices are not compatible with the ISDN specification. As a consequence, these devices require the use of Terminal Adapters (TAs).


ISDN NETWORK TERMINATION (NT) DEVICES

ISDN employs two types of network termination devices. Network Termination Type 1 (NT1) refers to a network terminal device situated at the customer premise for handling Physical Layer or Layer 1 and Data-Link Layer or Layer 2 connections. NT1 devices enable B (Bearer) Channel and D (Delta) Channel multiplexing activities. Moreover, NT1 devices also handle the physical link over the local loop extending from the subscriber site to the local telephone exchange and support network monitoring and performance assessment. As with NT1 devices, Network Termination Type 2 (NT2) devices perform Physical Layer and Data-Link Layer functions. In addition, NT2 equipment enables voice and data switching and seamless aggregation or BONDING (Bandwidth On- Demand Interoperability Group) of multiple ISDN channels.


ISDN CODECS (CODERS AND DECODERS)

In ISDN implementations, a codec or chip performs digital-to-analog and analogto- digital conversions. In addition, a codec supports compression to minimize redundancies in voice, data, and video transmissions for facilitating high-quality videoconferences. To enable clear and robust ISDN telephony services, a codec converts analog signals into digital formats at call setup for network transmission and then reconstructs the digital signals into analog formats at call reception.


ISDN DIGITAL PIPE

The access path from the local telephone exchange to the customer premise over the last mile or the local loop in an ISDN network is commonly called a digital pipe. The size of the digital pipe for ISDN transmission depends on variables such as customer application requirements and fees established by the communications carrier.


ISDN REFERENCE POINTS

For transparent transmission, ISDN defines reference points indicating protocols employed between different functional devices. R, S, T, and U are the commonly defined reference points for an ISDN configuration. The R reference point refers to communications between TE2 and TA devices. The S reference point refers to communications between TE1 or TA devices and Network Termination (NT) equipment or NT1 and NT2. The T reference point indicates links between customer premise switching equipment (NT2) and local loop termination (NTI) devices. Defined by the ISDN communications carrier, the U reference point refers to the link between the local telephone exchange and NT1 equipment. Every U interface frame consists of 240 bytes.

[mindreader]

B (BEARER), D (DELTA), AND HYPER (H) CHANNELS

B (BEARER) CHANNEL

The B (Bearer) Channel is the basic building block in an ISDN configuration. Capable of supporting circuit-switched and packet-switched connections, the B Channel carries digitized voice, video, and data at rates up to 64 Kbps and provisions asynchronous, synchronous, and isochronous services for dependable and reliable information transport. B Channel protocols include the Point-to-Point Protocol (PPP) for transporting diverse LAN traffic over telecommunications links and the multipoint PPP (ML-PPP) for extending PPP services.
BONDING (Bandwidth On-Demand Interoperability Group) enables the aggregation of six B channels into one H Channel or HyperChannel for achieving high throughput via the PSTN and provisioning bandwidth required by advanced ISDN voice, video, and data applications. Typically, ISDN employs BONDING (Bandwidth On-Demand Interoperability Group) or inverse multiplexing to combine separate B (Bearer) Channels into a single virtual wideband digital channel or digital pipe for supporting interactive videoconferences over the PSTN.


D (DELTA) CHANNEL

The D (Delta) Channel enables signaling and control capabilities such as call acknowledgment, call setup, and automatic number identification for each ISDN line installed. In terms of operations, the D Channel is a 16 Kbps or 64 Kbps circuit, depending on the specified network interface that supports communications between the ISDN device and the switch at the local telephone exchange. The D Channel also fosters asynchronous packet data transport at 9.6 Kbps (Kilobits per second) and works in concert with the X.25 protocol for facilitating access to PSTN services. The D Channel rarely employs all of its available bandwidth. As a consequence, the excess capacity typically supports data transport. Defined by National ISDN-1 (NIPhase 1), ISDN switch protocols control the initiation and termination of telephone calls over D Channels.


H (HYPER) CHANNEL

In an ISDN configuration, B Channels can be combined into H Channels or Hyper- Channels through BONDING or inverse multiplexing. H Channels typically enable high-performance applications such as Group 4 fax (facsimile) transmission, highspeed file transfer, and videoconferencing. As noted, six B Channels form a single H Channel or HyperChannel. A HyperChannel supports full-duplex rates to enable transmissions at H0 or 384 Kbps. By BONDING two B Channels and one D Channel, the H11 Channel supports transmissions at 1.544 Mbps (Megabits per second). This rate is equivalent to ANSI (American National Standards Institute) T-1 carrier line speed.

[mindreader]

BASIC RATE ISDN (BRI) AND PRIMARY RATE ISDN (PRI) SERVICES

ISDN service levels are called BRI (Basic Rate ISDN) and PRI (Primary Rate ISDN). B, D, and H Channels serve as the framework for establishing BRI and PRI solutions.


BASIC RATE ISDN (BRI) SERVICES

BRI (Basic Rate Interface Service) transforms a single twisted pair telephone line into the equivalent of two conventional telephone lines consisting of two independent 64 Kbps B Channels for user information and one 16 Kbps D (Delta) Channel for call signaling, call control, and slow data transfer. As a consequence, BRI service is also known as 2B+D. BRI employs echo cancellation to eliminate noise and 2B1Q (2 Binary 1 Quaternary) data encoding methods for enabling relatively high-speed transmission rates over the local loop via a single copper pair telephone line. The local loop refers to the distance between the customer premise and the local telephone exchange. The BRI Physical Layer specification is defined by the ITU-T I.430 Recommendation. For BRI service, the U interface or reference point supports two-wire and four-wire links.

With BRI service, the two B Channels and one D Channel can be consolidated for remote LAN connectivity and Web exploration at a rate of 144 Kbps. A single BRI connection supports as many as eight devices and 64 separate phone numbers. Equipment typically employed for BRI service depends on application requirements. For example, an inverse multiplexer is required for BRI videoconferencing sessions. Initially designed for telephone operations, BRI service is also a popular solution for enabling fast Internet connectivity and desktop videoconferencing in SOHO (Small Office/Home Office) venues, small-sized enterprises, public and private K–12 schools, and post-secondary institutions. As with ADSL (Asynchronous Digital Subscriber Line) implementations, ISDN subscribers must be within 18,000 feet of the local telephone exchange in order to utilize BRI services effectively. Coverage beyond this distance requires installation of ISDN signal repeaters.


PRIMARY RATE INTERFACE (PRI) SERVICES

A sophisticated solution for bandwidth-intensive applications, Primary Rate ISDN (PRI) service is popularly known as 23B+D in North America and Japan. PRI service supports utilization of 23 independent B Channels that are capable of supporting 23 simultaneous digital telephone calls and one D (Delta) Channel. Each channel supports data transmission at 64 Kbps. PRI service in North America and Japan supports bi-directional transmission rates at 1.544 Mbps or T-1 speeds.

T-1 Fundamentals

Established by ANSI, the North American T-1 digital hierarchy serves as the basis for defining ISDN PRI rates and services. The basic building block for T-1 transmission is a single 64 Kbps DS (Digital Signal) Channel or digital voice circuit. In terms of operations, the letter “T” refers to hardware that generates signals for transmission and the letters “DS” refer to transmission rate and signal structure. The terms “DS-1” and “T-1” are used interchangeably.

A T-1 transmission line consists of 24 DS Channels, with each channel operating at DS0 or 64 Kbps. T-1 and E-1 private carrier lines require modification of the inplace infrastructure including the installation of repeaters to regenerate signals every 3,000 to 5,000 feet. Two sets of twisted copper pair wires for transmission are required as well.

[mindreader]

ISDN FRAMES

ISDN frame formats differ, depending on whether the frame is inbound from the network to the ISDN terminal at the subscriber premise in the downstream direction or outbound from the ISDN terminal at the subscriber premise to the network in the upstream direction. An ISDN frame typically consists of 48 bytes, with 36 bytes allocated for data and 12 bytes designated for overhead functions such as synchronization, device activation, adjustment of byte value, and contention resolution in the event that several nodes contend for channel access simultaneously. ISDN employs specially designed equipment for transmission of ISDN formatted frames. ISDN frames conform to V.120 encapsulation specifications and carry payloads and sequencing information for ensuring error-free delivery. ISDN signaling specifications determine frame setup and the pathway for frames to move through the network.

Because certain ISDN devices function with only one particular switch, ISDN subscribers must identify the vendor and type of switch supporting their own ISDN service in order to ensure ISDN equipment interoperability with devices used by other ISDN subscribers. Equipment in use for ISDN service from one communications carrier does not necessarily interwork with ISDN devices in use by a competitive communications carrier.

[mindreader]

ISDN PROTOCOLS

STATISTICAL TIME-DIVISION MULTIPLEXING (STDM)

ISDN provides a digital framework for voice, text, video, and still-image transmission by utilizing Statistical Time-Division Multiplexing (STDM). Also called intelligent TDM, STDM is a sophisticated form of TDM (Time-Division Multiplexing).
Conventional TDM divides bandwidth into fixed timeslots so that information from each channel is transported in a predetermined rotation. Multiplexing refers to the process of combining multiple information channels that consist of numerous analog or digital signals into a single, high-capacity transmission link.

In an ISDN configuration, STDM divides available bandwidth on a single ISDN line into B (Bearer), D (Delta), and H (Hyper) Channels. These channels or circuits function as timeslots for transmission of data, video, and audio signals generated by devices linked to the ISDN configuration. STDM enables multiple ISDN devices to receive or transmit video, voice, and data concurrently by assigning a fixed amount of time for transmission to each ISDN node.
With STDM, numerous ISDN signals are combined into composite signals that transit the communications channel via fixed timeslots at specified intervals. Individual signals are subsequently separated from composite signals and routed to designated termination points. In comparison to TDM, STDM facilitates more effective utilization of available bandwidth capacity.


LAP-D (LINK ACCESS PROTOCOL-D CHANNEL)

Operating above the Physical Layer or Layer 1 of the OSI Reference Model, the D Channel employs the Link Access Protocol-D Channel (LAP-D) to enable acknowledged and unacknowledged information transfer services that support Layer 2 or Data-Link Layer operations. The LAP-D frame format features a 2-octet address field, a 2-octet CRC (Cyclic Redundancy Check) field for determining data errors, a 7-byte terminal endpoint identifier field, and a 6-byte SAPI (Service Access Point Identifier) field. ISDN Data-Link Layer capabilities are defined by the ITU-T QSeries of Recommendations.


ISDN USER-TO-NETWORK SIGNALING PROTOCOL

The ISDN User-to-Network Interface (UNI) signaling protocol defines Layer 3 or Network Layer operations. This protocol enables the establishment, maintenance, and termination of network connections via circuit-switched or packet-switched BChannel connections. ISDN Layer 3 signaling specifications are defined in the ITUT I.43 and the ITU-T I.431 Recommendations.


Open Systems Interconnection (OSI) Reference Model

ISDN features a layered protocol stack that conforms to the format developed by the Open Systems Interconnection (OSI) Reference Model established by the ISO (International Standards Organization). (See Figure 1.4.) ISDN operations take place at the Network Layer or Layer 3, the Data-Link Layer or Layer 2, and the Physical Layer or Layer 1 of the seven-layer OSI Reference Model. At the Physical Layer or Layer 1, ISDN supports Basic Rate Interface (BRI) and Primary Rate Interface (PRI) service levels.

Developed by the International Standards Organization in the 1980s, the OSI Reference Model describes the way in which voice, video, and data are transmitted between any two points in a telecommunications network. Communications technologies such as ISDN describe functions in terms of their relationship to the seven layer OSI Reference Model. The Application Layer or Layer 7, the Presentation Layer or Layer 6, the Session Layer or Layer 5, and the Transport Layer or Layer 4 delineate the process of transmitting a message to or from a network user. The Network Layer or Layer 3, the Data-Link Layer or Layer 2, and the Physical Layer or Layer 1 establish the process for enabling message transmission across a physical medium such as coaxial cable, optical fiber, hybrid optical fiber and coaxial cable (HFC), and twisted copper pair. Messages can be directly forwarded to another network or passed via the upper OSI Layers to the designated recipient.

OSI Reference Model and TCP/IP Protocol Suite

Developed by DARPA (United States Department of Defense Advanced Research Agency) in the 1960s, the TCP/IP Protocol Suite is an open system that serves as the framework for the present-day Internet. An affordable, flexible, and dependable interconnect solution, TCP/IP describes standardized protocols for enabling internetworking services between computers that vary in size, feature diverse operating systems, and enable functions in all types of government, research, educational, and corporate networks worldwide.

Like the OSI Reference Model, the TCP/IP Protocol Suite consists of a layered communications architecture with each layer responsible for a particular facet of the communications process. In contrast to the seven layers defined by the OSI Reference Model, the TCP/IP Protocol Suite describes four layers, specifically the Application Layer or Layer 4, the Transport Layer or Layer 3, the Network Layer or Layer 2, and the Physical or Media-Access Layer or Layer 1. The Application Layer defines services performed by protocols such as HTTP (HyperText Transfer Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and SNMP (Simple Network Management Protocol). Two of the most widely used TCP/IP protocols, TCP provides Transport Layer services and IP enables Network Layer operations and functions as a network overlay in conjunction with technologies such as ISDN and ATM.

TCP/IP is a streamlined architectural model that supports layers that are functionally equivalent to the Application, Transport, Network, and Physical Layers of the OSI Reference Suite. As with OSI, upper TCP/IP Layers employ the functions provisioned by the lower layers for enabling reliable telecommunications applications and services.

[mindreader]

ISDN SERVICE ENHANCEMENTS

ISDN is no longer regarded as a universal network solution. However, ISDN technology continues to overcome physical and electrical local loop impairments, thereby enabling additional bandwidth capacity for accessing multimedia services at the customer premise. To encourage widespread ISDN utilization, vendors, standards organizations, and user groups promote routine deployment of AO/DI (Always On/Dynamic ISDN), CPE (Customer Premise Equipment) Diagnostics, and ISI (Initialization Simplification Initiative) service enhancements.


ALWAYS ON/DYNAMIC ISDN (AO/DI)

Always On/Dynamic ISDN (AO/DI) refers to network applications that utilize the ISDN D (Delta) Channel for X.25 packet data service and maintain always-on connectivity between the communications carrier and the ISDN subscriber. With an AO/DI constant virtual connection, ISDN enables low-bandwidth transmissions at speeds up to 9.6 Kbps.
When additional bandwidth is required to support information access and delivery, AO/DI automatically provisions use of the B (Bearer) Channel to support network operations at 64 Kbps. With two B Channels, ISDN enables rates reaching 128 Kbps without compression and rates up to 512 Kbps with compression. When extra bandwidth is no longer required, one or both of the B Channels are dropped from the connection. The D Channel remains in place for packet-switched services.


AO/DI Supporters

In the United States, AO/DI implementations are supported by ATF (Access Technologies Forum) members that include Ascend, Cisco Systems, 3Com, and Microsoft. National ISDN Council participants such as Ameritech, Verizon, BellSouth, and SBC (Southwestern Bell and Pacific Bell) endorse AO/DI functions as well. Participants in the European AO/DI Interest Group include Deutsche Telekom, France Telecom, Swiss Telecom, TeleDanmark, BT (British Telecom), Telia, and Telenor. Organized in 1999, the European AO/DI Interest Group participates in the Global ISDN Industry Forum (GIIF). The GIIF promotes EuroISDN implementation by each member state in the European Union.


CUSTOMER PREMISE EQUIPMENT (CPE) DIAGNOSTICS

CPE (Customer Premise Equipment) Diagnostics is a program for monitoring ISDN operations in subscriber equipment. CPE loopback, fault management, and state management tests aid in the identification and correction of equipment problems at the subscriber premise that adversely impact ISDN performance.


INITIALIZATION SIMPLIFICATION INITIATIVE (ISI)

To facilitate ISDN implementation, the Initialization Simplification Initiative (ISI) provides mechanisms for automating ISDN installation procedures. A component of the ISI, autoSPID (Automatic Service Profile Identifier) enables automatic SPID detection by the communications carrier. AutoSPID eliminates the tedious and timeconsuming process of providing detailed ISDN information by the subscriber to the communications carrier. Generic SPIDs are also in development to further streamline the initialization process.

[mindreader]

ISDN MARKETPLACE

Regional ISDN communications providers and interexchange carriers in the United States include AT&T, Ameritech, Verizon, BellSouth, GTE, SBC, Sprint, Southwestern Bell, and U.S. West. ISDN is available worldwide in countries that include the United Kingdom, Germany, Italy, Canada, France, Switzerland, the Netherlands, Israel, New Zealand, Australia, Indonesia, and Japan.


SIEMENS

Available from Siemens, the Optiset series of ISDN desktop terminals is equipped with snap-in Terminal Adapter (TA) modules for interlinking multiple analog devices. Optiset ISDN desktop terminals also support a TA for MPD (Multi-Purpose Data) to facilitate access to Web resources at rates up to 115.2 Kbps. In addition to provisioning cost-effective ISDN services, the Optiset series of desktop terminals streamlines the ISDN implementation process at the customer premise by eliminating the need for every ISDN device to be equipped with an interface and an applicationspecific TA.


TELCORDIA TECHNOLOGIES

As a service to ISDN equipment manufacturers, Telcordia conducts a series of tests to verify the capabilities of standards-compliant ISDN customer premise devices such as modems, phones, multiport LAN bridges or routers, and TAs and software products.

[mindreader]

ISDN COMPETITOR TECHNOLOGIES

BROADBAND RESIDENTIAL ACCESS SOLUTIONS

Demand for fast access to the Web contributes to the popularity of wireline and wireless broadband residential access solutions based on cable modem, LMDS (Local Multipoint Distribution System), MMDS (Multichannel Multipoint Distribution System), and DSL technologies. As with ISDN implementations, these competitor solutions provide dependable connections to voice, video, and data services via the local loop or the first mile between the subscriber premise and the local telephone exchange.


N-ISDN (NARROWBAND-ISDN) AND B-ISDN (BROADBAND-ISDN) INSTALLATIONS

ISDN is the core N-ISDN (Narrowband-ISDN) technology. ATM is the core B-ISDN technology. In comparison to ATM implementations, ISDN deployments are limited in enabling access to high-performance Web-based multimedia applications. Moreover, ISDN is viewed as an interim step in the evolution to multi-service, high-speed, and high-capacity boradband networks. ISDN is also regarded as an outmoded network technology without much promise for the future.

Nonetheless, as demonstrated by the initiatives that follow, ISDN solutions continue to support current and emergent applications in sectors that include education, medicine, and business. ISDN videoconferences interlink geographically dispersed individuals in virtual classes for enabling interactive tele-instruction, teletraining sessions, and telecollaborative workgroup activities in public and private K–12 (Kindergarten through Grade 12) schools and post-secondary institutions. Moreover, ISDN technology also supports teleconsultations, telesurgery, and virtual grand rounds in the field of telemedicine.

[shankariarvind]

hi thanks buddy,
I came across tech-arena while browsing for my presentation...and your threads..really helping me out....i am still trying to get the hold of this community...

[Mwambula Mayaka]

Excellent material