ISDN Jargon Buster
2B+D: A BRI ISDN service providing two B channels and one D channel. NTT's INS64 is a 2B+D BRI.
23B+D: A PRI ISDN service providing 23 B channels and one D channel. NTT's INS1500 is a 23B+D PRI.
30B+D: The PRI ISDN service available in Europe, providing 30 B channels and one D channel.
ADSL (Asymmetric Digital Subscriber Line): A high-speed data network and possible alternative to ISDN. ADSL works over existing twisted-pair copper wiring, and provides an upload transfer rate of 640 kbps, and a download transfer rate of 6.14 Mbps. ADSL is not tried and tested and won't be here for a few more years. In the united States, Bell Atlantic is running trials to test the feasibility of Internet access with ADSL.
Asynchronous mode: The serial transmission mode where individual data bits are enclosed by start and stop bits and transferred at varying intervals. Used in time-insensitive applications. Computer serial ports work in asynchronous mode. ISDN 38.4 kbps and 57.6 kbps services are asynchronous. Contrast with Synchronous mode.
AT Command Set: The command set developed by Hayes Microcomputer to control and configure modems. All commands begin with "AT", which is often explained as "get the modem's ATtention". You may have entered a modem initialization string something like "AT&F1" when you configured your PPP software. You'll need to enter a different initialization string for use with your TA (see your TA's owner's manual).
B channel: The 64 kbps ISDN Bearer channel used to transmit digital information. See also D Channel.
BAP/BACP (Bandwidth Allocation Protocol/Bandwidth Allocation Control Protocol): The protocol for managing dynamic bandwidth allocation with multilink PPP connections, and its control protocol.
Baud: See bps.
BOD (Bandwidth On Demand): The feature that allows a TA to dynamically allocate B channels as and when needed. For example, when downloading a file off the Internet at 64 kbps (i.e., one B channel), the TA will activate the second B channel if throughput is, say, higher than 70% for more than 30 seconds, providing a combined bandwidth of 128 kbps. When the download is complete, or throughput drops under 20% for more than 20 seconds, the second B channel is deactivated and the connection reverts to 64 kbps. Note that bandwidth is not the same as speed, so although the connection jumps from 64 kbps to 128 kbps, Net performance won't necessarily be any quicker. It will, however, mean that you can use more Net services simultaneously, for example, run several FTP downloads while streaming audio and video.
Bonding: A technique used to combine B channels for higher transfer rates. Unlike PPP/MP, bonding is controlled in hardware, and bandwidth cannot not be allocated dynamically once a connection has been established. See also Inverse Multiplexing.
bps (bits per second): The bits-per-second measurement unit for data transmission. Bit rate (bps) is often confused with baud. Baud, however, refers to the rate at which a signal between two devices--two modems, or two ISDN devices--changes per second, and several bits can be conveyed per signal change. So, for example, a 9,600 bps modem that conveys two bits per signal change requires a baud rate of 4,800. With the bit rate being the true measure of data speed, the baud rate is of little interest to us.
BRI (Basic Rate Interface): The basic ISDN interface consisting of two B channels and one D channel. NTT's INS64 is a BRI interface.
B-ISDN (Broadband Integrated Services Digital Network): The second generation of ISDN services with bandwidths of between 150 Mbps and 600 Mbps. With high transfer rates, B-ISDN will make the information superhighway a reality. A single fiber optic feed into the home will provide real-time video, audio, telephone, fax, Internet, and a whole host of other high-bandwidth services simultaneously. See also N-ISDN and FTTH.
CCITT (International Telegraph and Telephone Consultative Committee): The CCITT began making recommendations for international telephone and telegraph networks in 1865. The CCITT is one of several committees operating under the auspices of the ITU (International Telecommunication Union), which has been associated with the U.N. (United Nations) since 1948. CCITT discussions of an integrated services network first took place in 1968. As the driving force behind ISDN, the international ISDN standard in use today is the result of CCITT recommendations. In March 1993, the CCITT was reorganized into the ITU-T (ITU Telecommunication Standardization Sector).
D channel: The Data (or Delta) channel that carries administrative and signaling messages for the two B channels. The D channel for BRI has a transfer rate of 16 kbps (64 kbps for PRI). D channel signals describe the type of service requested for a B channel. The Caller ID system uses the D channel to transmit the calling party's telephone number so that it can be seen by the recipient before voice communication is established via a B channel. See also B Channel.
Dial-In: NTT's optional ISDN service providing additional telephone numbers. With an additional telephone number, fax and telephone can be used independently. ISDN equipment and analog phones and G3 fax machines connected to the analog ports on a TA can be assigned individual telephone numbers. Up to 100 telephone numbers can be used with a single INS64 line. See Dial-In charges.
DP (Dial Pulse): The original telephone dialing system, which has since been replaced by touch-tone dialing. Many DP-type telephone lines are, however, still in use. See also PB.
DSU (Digital Service Unit): The DSU terminates the ISDN line at the customer site, and converts the U-Interface to an S/T-Interface. U-Interface connections use RJ-45 connectors, but only two of the eight available pins are used. The S/T output of a DSU also uses RJ-45 connectors, but this time, four of the pins are used. In the United States, DSUs are commonly referred to as Network Termination devices (NT1).
DTE (Data Terminal Equipment): The TA port that connects to your computer's serial port.
F-Net: NTT's fax network providing high-speed fax transmission between G4 and G3 fax machines. When a G4 fax machine connects to a G3 fax machine, transmission speed is restricted by the G3 machine. By dialing 161 at the beginning of the number, the G4 machine can transmit the fax at high speed to an F-Net buffer. While F-Net spools the fax to the G3 fax machine at the slower speed, the G4 fax machine disconnects. F-Net is an optional service with additional usage charges.
Flash ROM: A type of read-only memory that can be reprogrammed by loading new software. Some TAs feature a flash ROM for future updates.
Flexphone: NTT's Flexphone option consists of four additional services: Call Waiting, Call Transfer, Three-party Service, and Call Deflection.
FTTH (Fiber To The Home): Also, FTTC (Fiber To The Curb). The scheme to provide broadband ISDN services to homes using fiber connections. NTT plan to have the whole of Japan wired for broadband ISDN by the year 2015.
Global: Global is an optional service for use with Dial-In telephone numbers. When a caller dials the subscription right telephone number, all devices configured for use with Global ring.
G1 fax: The CCITT issued the Group 1 fax standard in 1968. Group 1 is an obsolete analog system, which took about six minutes to send an A4 page. Most G1 equipment has been replaced by G3 equipment.
G2 fax: The CCITT issued the Group 2 fax standard in 1976. G2 fax machines were all analog, and took about four minutes to send an A4 page. Most G2 equipment has been replaced by G3 equipment, making G2 obsolete. G2 equipment hasn't been sold for many years.
G3 fax: The CCITT issued the Group 3 fax standard in 1980. Most fax machines in use today are of the G3 type, and transmit data at speeds of up to 9,600 kbps. Although scanning, encoding, and compression techniques are performed digitally, the actual transmission is still performed by what is essentially a built-in analog modem. In 1991, error correction, improved data compression, and the higher speed of 14.4 kbps were added to G3. Fax modems for use with personal computers often feature the higher speed of 14.4 kbps, but the speed automatically falls back to 9,600 kbps when the receiving device does not support the higher speed. Two fax resolutions are usually provided, the standard 200 x 100 dpi mode, and a 200 x 200 fine mode.
G4 fax: Group 4 fax machines are all digital and can interface directly with an ISDN line. It takes about six seconds to transmit an A4 page between G4 fax machines, compared to 37 seconds for a basic G3 machine, or 25 seconds for a 14.4 kbps machine. If the receiving fax is a G3, transmission speed is restricted. Fax resolutions up to 400 x 400 dpi are possible with G4 fax machines, which is as good as many laser printers in use today.
INS (Information Network Service): NTT uses the name INS for its ISDN BRI and PRI services: INS64 and INS1500.
INS64: NTT's INS64 is an ISDN Basic Rate Interface (BRI). It consists of two B channels (Bearer channels) for voice, data, and fax transmission and one D channel (Delta or Data channel), which is used to control the B channels. The D channel can also be used to transfer packet data. Each B channel can transfer data at up to 64 kbps. INS64 can be used with existing copper telephone cables, making conversion both simple and cheap. The two B channels can be multiplexed for a combined data rate of 128 kbps.
INS64 Lite: With INS64 Lite, you don't have to pay the hefty ¥72,000 subscription right fee to have a new ISDN line installed. Instead you pay an extra ¥640/month.
INS1500: NTT's INS1500 is an ISDN Primary Rate Interface (PRI). It consists of 23 B channels (Bearer channels) for data transmission and one D channel (Delta or Data channel). Unlike INS64, INS1500 requires a fiber optic connection between the customer and NTT. INS1500 can be boosted up to 24 B channels by using a separate INS64 line for the D channel. The 23 B channels can be multiplexed together for a maximum data rate of 1.5 Mbps.
INS line connector: NTT's name for internal ISDN connections, and the jack on an ISDN device or TA that can be connected to the output of a DSU. See also S/T (Subscriber/Terminator).
Inverse multiplexing: The technique used to combine B channels for higher transfer rates. See also Bonding and PPP/MP.
ISDN (Integrated Services Digital Network): In simple terms, an ISDN is a completely digital telecommunications network that can carry voice, fax, computer data, video, and the like. In technical terms, an ISDN is a digital network that can be used to integrate several disparate systems, such as public telephone networks, packet switching networks, and cable television, into one standard set of user interfaces. See also B-ISDN and N-ISDN.
ISDN-bus: Once an ISDN line has been terminated by a DSU, it can be distributed to up to eight ISDN devices using a simple bus connection. With the two B channels, any two devices, including analog devices connected to a TA, can be used simultaneously. With NTT's Dial-In option, each device can be allocated its own telephone number.
ISDN modem: "ISDN modem" is an oxymoron. Modems modulate and demodulate digital computer signals so they can be transmitted over analog telephone lines. Since ISDN is all digital, there is no need to modulate and demodulate. When people refer to an ISDN modem what they really mean is a TA. To your computer, TAs and modems look alike because communications are performed using similar AT commands.
ITU-T (International Telecommunication Union, Telecommunication Standardization Sector): See CCITT.
JATE (Japan Approval Institute for Telecommunications Equipment): The institute that approves telecommunications equipment for use with Japan's public telephone network. Approved equipment bears a JATE approval mark or number.
kbps (kilobits per second): The thousand-bits-per-second measurement unit for data transmission. This abbreviation is often confused with kilobytes per second. Since a binary kilo (kilobyte) equals 1,024 bits, a 64 kilobyte transfer rate would be 512 kilobits per second. A nice thought, but not yet available.
Logical channels: ISDN B and D channels are described as logical because they share the same physical cable. INS64, for example, provides two B channels and one D channel through a single twisted-pair connection.
Mbps (Megabits per second): The million bits per second measurement unit for data transmission.This abbreviation is often confused with megabytes per second. As a binary mega (megabyte) equals 1,048,576 bits, a 1.5 megabyte transfer rate would be 12 megabits per second, which is obviously incorrect.
Multiplexing: See Inverse multiplexing.
N-ISDN (Narrowband Integrated Services Digital Network): The first generation of ISDN services with bandwidths of between 64 kbps and 1.5 Mbps. INS64 and INS1500 are N-ISDN services. See also B-ISDN.
NT1: Network Termination device. This term is often used in the United States to describe what NTT call a DSU.
NT1 Plus: Network Termination Plus device. This term is commonly used in the United States to describe a TA/DSU combination unit. In Japan this type of device is usually called a TA with built-in DSU, or TA/DSU.
NTT (Nippon Telegraph & Telephone): The organization responsible for the public telephone system in Japan. The Japanese counterpart of AT&T Bell in the United States, or British Telecom (BT) in the UK.
OCN (Open Computer Network): NTT's Internet access network, providing dial-up Internet access for only ¥2,300/month for up to 15 hours (¥1/minute thereafter), or a dedicated 128 kbps ISDN connection for only ¥38,000/month, including all usage charges. The latter service, called OCN Economy, is ideal for those looking to setup their own e-mail and Web servers, and is the cheapest dedicated Internet connection service in Japan, which is somewhat surprising for NTT.
PB (Push Button): The touch-tone dialing system. Most telephone lines in use today use the PB dialing system. See also DP.
PBX (Private Branch Exchange): A private telephone switch system used by large organizations to handle multiple telephone lines.
PCMCIA (Personal Computer Memory Card International Association): The association that developed the PCMCIA standard for plug-in cards for laptop and portable computers. Often referred to as simply "PC Cards". Some PCMCIA cards can be used with either Windows PCs or Apple PowerBooks.
POS (Point of Sale): POS equipment is used for retail outlet transactions, cash registers, card readers, bar-code scanners, and the like.
POTS (Plain Ordinary Telephone Service): An acronym for the original analog telephone network. See also PSTN.
PPP (Point-to-Point Protocol): The protocol used to connect computers to networks using TCP/IP, such as the Internet.
PPP/MP (Point-to-Point Protocol/Multilink Protocol): An extension to the PPP protocol that supports inverse multiplexing of two B channels for 128 kbps operation. TAs that support 128 kbps usually come with a PPP/MP version of the PPP software. See also Bonding.
PRI (Primary Rate Interface): In Japan, the United States, and Canada the primary ISDN interface consists of 23 B channels and one D channel (23B+D). NTT's INS1500 is a 23B+D PRI interface. In Europe PRI consists of 30 B channels and one D channel (30B+D).
PSN (Packet Switched Network): A computer network where data is broken up and transmitted as individually addressed packets. As each packet contains the destination address, packets may travel via different routes. The receiving device assembles the packets to recreate the original data. The TCP/IP protocol transfers data in packets.
PSTN (Public Switched Telephone Network): When a caller dials a telephone number, the telephone network uses a system of switches to create a direct circuit to the other party. Once the circuit has been established, nobody else can use the same parts of the circuit until the call is completed. POTS and ISDN are switched networks.
RJ-11: The six-way modular plugs and jacks used with analog telephone equipment in Japan, the United States, and many other countries. The analog ports of a TA use RJ-11 jacks. A similar but wider connector is used in the UK.
RJ-45: The eight-way modular plugs and jacks used to connect ISDN equipment via the S/T interface. ISO8877 is the international standard for RJ-45 connectors. ISDN devices and TAs are connected to the DSU using RJ-45 connectors. RJ-45 connectors are also used with 10Base-T networks, and some 10Base-T cables can also be used with ISDN.
S/T-Interface (Subscriber/Termination): The six wire interface used to connect ISDN equipment. Two wires are for incoming data and two for outgoing data. The S/T connection between the DSU and TA uses two additional lines as a power feed to the DSU. TAs with a built-in DSU connect directly to the U-Interface. S/T connections use RJ-45 connectors.
SPID (Service Profile Identifier): The number assigned to each device on an ISDN line, and what seems to be the most bothersome aspect of ISDN in the United States and Canada. Fortunately, NTT's simplified ISDN services do not require customers to deal with SPIDs.
Sub-address: By entering a specified sub-address number after the telephone number a caller can direct a call to a specific device on an ISDN line. Up to 19 sub-addresses can be used per line. However, the caller must be using an ISDN telephone to use sub-addressing.
Subscription right: To install a telephone line in Japan you have to buy a subscription right from NTT, which costs ¥72,000 and is not returnable.
Synchronous mode: The serial transmission mode where data bits are transmitted at fixed intervals. Used in time-sensitive applications. ISDN 64 kbps and 128 kbps services are synchronous.Contrast with Asynchronous mode.
TA (Terminal Adaptor): A TA interfaces the ISDN line with your communications equipment, typically performing digital-to-analog and analog-to-digital conversions for analog telephone, fax, or modem equipment, and digital data rate adaptation for computers.
TCP/IP (Transmission Control Protocol/Internet Protocol): The communication protocol used on the Internet.
TE (Terminal Equipment): The term used in the United States for any device connected to an ISDN line. NTT refers to TE devices simply by device type. For example, ISDN telephone, G4 fax, or TA.
TE1 (Terminal Equipment 1): The term used in the United States for ISDN equipment that can be connected directly to an ISDN line, such as a ISDN telephone, G4 fax machine, or TA.
TE2 (Terminal Equipment 2): The term used in the United States for non-ISDN devices, analog phones and G3 faxes. TE2 equipment connect to the ISDN line via a TA.
Twisted-pair: A typical telephone line consists of a pair of insulated copper wires twisted together. POTS and ISDN BRI services use the twisted-pair wiring.
U-Interface: The two wire ISDN connection coming into the customer site from NTT. The U-Interface uses existing twisted-pair copper wiring, and is terminated by a DSU.
USB (Universal Serial Bus): A high-speed (12 Mbps) serial bus for connecting up to 63 peripherals, including, modems, TAs, CD-ROMs, printers, and keyboards.
V.110: The rate adaption protocol for transmitting 9.6, 19.2, or 38.4 kbps asynchronous data over a 64 kbps synchronous ISDN B channel. Widely used in Japan.
V.120: The newer rate adaption protocol and successor to V.110. In addition, V.120 supports the transmission of data compressed using the V.42bis protocol, which can compress data by more than 4:1. With V.120, data travels at 64 kbps to the TA but at a much higher speed between TA and computer. V.120 is widely used in the United States.
V.34: The communication protocol for 28.8 kbps modems. Also known as V.Fast.
V.34 Plus: The communication protocol for 33.6 kbps modems.
<--Previous TOC Home Next--> Created: 16 May 1997. Modified: 4 October 1998.
Copyright (c) 1998 Paul Findon. All rights reserved.