COMP.DCOM.ISDN FAQ PART 2 OF 5: GENERAL TOPICS Archive-name: isdn-faq/part2 Last-modified: $Date: 1995/07/01 18:41:07 $ Version: $Revision: 4.3 $ ------------------------------ 2.01) What is ISDN? ISDN stands for "Integrated Services Digital Networks", and it's a ITU-T (formerly CCITT) term for a relatively new telecommunications service package. ISDN is basically the telephone network turned all-digital end to end, using existing switches and wiring (for the most part) upgraded so that the basic "call" is a 64 kbps end-to-end channel, with bit-diddling as needed (but not when not needed!). Packet and maybe frame modes are thrown in for good measure, too, in some places. It's offered by local telephone companies, but most readily in Australia, Western Europe, Japan, Singapore, and portions of the USA, and with other portions of USA asomewhat more behind. In France, ISDN is known as "RNIS". firstname.lastname@example.org (Winston Seah) email@example.com (Fred R. Goldstein) firstname.lastname@example.org (Paul Antoine) email@example.com (Tilman Schmidt) ------------------------------ 2.02) What does an ISDN network connection look like? A Basic Rate Interface (BRI) is two 64K bearer ("B") channels and a single delta ("D") channel. The B channels are used for voice or data, and the D channel is used for signaling and/or X.25 packet networking. This is the variety most likely to be found in residential service. Equipment known as a Terminal Adapter (TA) can be used to adapt these channels to existing terminal equipment standards such as RS-232 and V.35. This equipment is typically packaged in a similar fashion to modems, either as standalone units or as interface cards that plug into a computer or various kinds of commmunications equipment (such as routers or PBXs). TAs do not interoperate with the modem; they replace the modem. There may be cases where there is no need to interface to existing terminal equipment or to emulate exisiting terminal equipment, or there may equipment with synchronous interfaces present. In these cases, standalone units or computer interfaces can provide high speed synchronous connections to the B channels without converting to an asynchronous standard. Another common type of equipment can be used to implement a bridge between local area networks using the ISDN channel to transport the data. These devices typically provide features such as demand dialing and/or data compression. Of course, more traditional devices such as telephones and fax machines can be attached to the BRI, assuming they have the proper interface hardware and software. Another flavor of ISDN is Primary Rate Interface (PRI). Inside North America and Japan, this consists of 24 channels, usually divided into 23 B channels and 1 D channel, and runs over the same physical interface as T1. Outside of these areas the PRI has 31 user channels, usually divided into 30 B channels and 1 D channel and is based on the E1 interface. It is typically used for connections such as one between a PBX (private branch exchange, a telephone echange operated by the customer of a telephone company) and a CO (central office, of the telephone company) or IXC (inter exchange carrier, a long distance telephone company). kevinc@aspect.UUCP (Kevin Collins) keyman@doorway.Eng.Sun.COM (Dave Evans) firstname.lastname@example.org (Andrew Scherpbier) cherkus@UniMaster.COM (Dave Cherkus) email@example.com (Oliver Jones) firstname.lastname@example.org (Gary C. Kessler) ------------------------------ 2.03) What will Basic Rate (2B+D) ISDN look like in my house/office? An ISDN BRI U-Loop is 2 conductors from the CO (telephone company central office) to the customer premises. Its maximum length may be 5.5 km (18000 ft). The equipment on both sides of the U loop has to be carefully designed to deal with the long length of the U loop and the noisy environment it operates in. At the customer premises the U-loop is terminated by an NT1 (network termination 1) device. The NT1 drives an S/T-bus which is usually 4 wires, but in some cases it may be 6 or 8 wires. In these optional cases, the extra wires are used provide power to operate telephones when normal power fails. Alternately, 'phantom' power may be derived from the standard four wires. Outside of North America emergency mode operation provides power for basic voice service only in the case of loss of local power. In emergency mode operation the NT1 receives up to 1.2W from the central office. In North America there is no provision for emergency mode operation. The name of the S/T bus comes from the letters used in the ISDN specifications used to refer to two reference points, S and T. Point T refers to the connection between the NT1 device and customer supplied equipment. Terminals can connect directly to NT1 at point T, or there may be a PBX (private branch exchange, i.e. a customer-owned telephone exchange). When a PBX is present, point S refers to the connection between the PBX and the terminal. Note that in ISDN terminology, "terminal" can mean any sort of end-user ISDN device, such as data terminals, telephones, FAX machines, etc. This picture shows what a residential ISDN connection looks like. Point T Point U | +--------+ 4-8 wires +-------+ 2-4 wires | |Terminal|-----+-----| NT1 |-------------[| wall (to telco CO) +--------+ | +-------+ | +--------+ | | |Terminal|-----+ +--------+ | : +--------+ | |Terminal|-----+ +--------+ The T bus is a multipoint bus in this configuration. It is sometimes called the passive bus because there are no repeaters on the line between the NT1 and the devices. It can be implemented using the same cable and connectors as is 10 base T Ethernet. There may be up to 8 devices on the S/T bus. The bus may be formed with splitters and T connectors - it is a bus, not a star. The D channel is used to control the attachment of the one to eight devices to the two B channels. No two devices attach to the same B channel at the same time. In this configuration, the major function of the NT is to allow more than one device to have access to the 2 B channels provided by the ISDN BRI. For instance, you may have an ISDN telephone, an ISDN fax and an ISDN computer interface attached to the BRI. Each device can listen for calls and only connect to a B channel when it identifies a message requesting a service it can provide. The NT1 only implements part of the channel sharing scheme; the other devices participate as well, and the communication protocol used by the NT1 and the other devices is an integral part of the scheme. The NT1 also performs other functions; it translates the bit encoding scheme used on the lines between it and the telephone company (the U loop) to the encoding used between it and the devices. These schemes are different because the device to NT encoding was designed to enable channel sharing whereas the NT to telco encoding was designed to allow transmission across long distances. In the United States, the customer pays for the NT device, so don't forget to include the cost of this unit in your cost estimates, or if you don't need the multiple device attachment feature, try to find a device that does not require the NT device (i.e. it attaches directly to the U loop). If you are not in the United States the telephone company provides the NT device, but remember there is no such thing as a free lunch - you are probably paying for it through increased rates, or increased taxes, etc. (flames to sci.economics or alt.talk.politics). Unfortunately, the NT1 is not an inexpensive device. It has to convert between the signalling used on the U loop (which is operates over long distances (5.5 km, 18000 ft) in a noisy environment and does not have to deal with contention between devices) and the signalling of the S/T bus (which operates over shorter distances in a quieter environment but it does have to deal with contention between devices and other protocol functions). It also provides diagnostic functions such as loopback mode, and it may have to provide power, as descibed above. This picture shows what an ISDN connection looks like when a PBX is present. Point S Point T Point U | +--------+ 4-8 wires +-------+ 4-8 wires +-------+ 2-4 wires | |Terminal|-----------| NT2 |-----------| NT1 |-----------[| wall +--------+ | (PBX) | +-------+ | Point S +---+---+ | +--------+ _________/ | |Terminal|/ | Point S +--------+ | +---+----+ |Terminal| +--------+ In this configuration, the wires at points S and T are point-to-point links. Electrically, the S and T points are the same, which is why the name S/T bus is almost always used. This makes sense; the terminal should see the same physical interface whether it is hooked up with or without a PBX. But, logically they are different. The telephone company needs to know that there is a PBX between itself and the user so that it can coordinate its efforts with the PBX. So, in cases where the difference is important, the specifications use the S and T terminology. When there is no PBX in the configuration, the NT1 device is usually a standalone device that is packaged a lot like a modem: in a small box when there are only a few, and in a rackmount when you need a lot of them. In the United States, the customer buys the NT1 but in most of the rest of the world the telephone company provides the NT1. When there is a PBX the rackmounted NT1s are quite common. Also, when there is a PBX the use of PRI lines instead of BRI lines is common. email@example.com (Dave Cherkus) cliff@Berkeley.EDU (Cliff Frost) firstname.lastname@example.org (Curt Welch) email@example.com (Dror Kessler) Eric_Boll-RXNN70Q@email.sps.mot.com (Eric Boll) firstname.lastname@example.org (Greg Larson) email@example.com (Kevin J. Rowett) firstname.lastname@example.org (Mark Anderson) email@example.com (Paul Antoine) firstname.lastname@example.org ( Patton M. Turner) email@example.com (Ronnie B. Kon) ------------------------------ 2.04) What is a NT1? Who sells them? [ Ed Note: Some may feel that there's a bit of overlap between the preceding sections and this one, but the preceding sections are hard to write without integrating NT1 information and this one is so informative and well-written that it can stand on its own so I think I should leave it as is. Comments? ] Reply: What's an NT1, why do I need one, and where do I get one? An NT1 (network terminator 1) is a device which provides an interface between the two-wire twisted pairs used by telephone companies in their ISDN Basic Rate (BRI) network and an end-user's four-wire terminal equipment. The NT1 also provides power for the terminal equipment if necessary (most ISDN phones need power from the NT1, but most data terminal adapters--TAs--don't). Most ISDN central office equipment (including AT&T 5ESS and Northern Telecom DMS-100 switches) sends data to your home or office via what's known in ITU-T lingo as a U interface on a single twisted pair. The NT1 hooks up to this twisted pair, and converts the signals from the U interface to the four-wire S/T interface. Most terminal equipment (for example, the IBM Wave Runner add-in-card TA and most telephones) offers the S/T interface. In North America, you have to buy and maintain your own NT1 device. The telephone company offers end-users a U interface. In Europe and Japan, the telephone company provides the NT1, owns it, and offers end-users a S/T interface directly. In North America, some ISDN equipment vendors offer devices which connect directly to the U interface (for example, the Combinet CB160). If you have one of these devices, you don't need to buy a separate NT1. The U interface can't be built in to the device when it's offered for sale in Europe or Japan. (This is unfortunate for vendors, who must build and test separate products for the relatively small North American market if they want to offer the convenience of a U-interface.) Many types of NT1s require an external power supply, although some include a built-in supply. There are typically two classes of external power supplies. One class provides ten to twelve watts--enough power for both the NT1 and for the terminal equipment. The other class provides about two watts--enough power for the NT1 alone. Many good power supplies offer at least a few seconds of battery backup, to cover for glitches in line power. Physically, the NT1 is a little plastic box with LEDs on it which can be screwed to a wall. The external power supply (if one is included) is a typical plug-wart. If you're using a lot of BRI lines, you can buy a rack holding a dozen or so NT1s with a built in power supply. It's a good idea to install your NT1 in a permanent fashion. If you unplug the ISDN line (the U interface twisted pair) from the NT1, it shows up as a sign of line trouble in the central office. Some telephone companies respond to this so-called "trouble" by disabling your ISDN line at the central office, and require you to place a service call on your analog telephone to get your ISDN service restored. All the vendors shown here accept credit card orders and ship promptly. All the vendors have well-organized telesales operations with friendly and reasonably knowledgeable sales people. Prices are in US dollars, as of 10/26/94, for single-unit purchases. Pricing is becoming volatile; competition seems to be heating up. AT&T, Northern Telecom, and Tone Commander NT1s can be ordered from: Bell Atlantic Teleproducts West Building, Suite 150 50 E. Swedesford Rd Frazer Pa, 19355 tel +1-215-695-2300 or 800-221-0845 Maker Description Part No. Price ----- ----------- -------- ------ Northern Telecom NT1 standalone IN51000 108.00 Northern Telecom 10w power supply IN61000 72.00 Northern Telecom 2w power supply IN61005 36.00 AT&T NT1U-220 IA51007 276.00 AT&T NT1U-230 IA51009 165.00 AT&T 10w power supply IA61000 105.00 Tone Commander manufactures a variety of standalone and rack-mount NT1s and racks. The NT1U-100 series is intended for locally powered terminal adapters - no power is provided through the NT1. The NT1U-200 series provides PS1 and PS2 power for voice terminals and also has additional status indicators. Specific features, pictures, and more detailed information is available at the Tone Commander home page: http://www.halcyon.com/tcs/ Tone Commander Systems 11609 49th Place West Mukilteo, WA 98275 voice: (800)524-0024 or (206)349-1000 fax: (206)349-1010 Prices listed below are Dealer List Prices. Additional 5% discounts are provided for VISA/MC sales; 8% discounts for COD sales. Tone Commander products are also available through various distributors. Maker Description Part No. Price -------------- -------------------------------- ------------- ------ Tone Commander Standalone NT1 with power supply NT1U-100TC 169.00 Tone Commander Rack-mount NT1 circuit card NT1U-110TC 159.00 Tone Commander 16 card rack for NT1U-110TCs NT1U-100 Rack 399.00 Tone Commander Standalone or rack-mount NT1 NT1U-220TC 195.00 Tone Commander Power supply for NT1U-220TC 901034 30.00 Tone Commander 12 unit rack for NT1U-220TCs NT1-220 Rack 595.00 Tone Commander UPS for NT1-220 Rack NT1-200 Backup 450.00 Tone Commander Add-on battery for NT1-200 Backup NT1-200 Add-on 385.00 Adtran offers their own NT1 products for sale. Adtran, Inc. 901 Explorer Blvd Huntsville, AL 35806-2807 USA +1 205 971 8000 fax +1 205 971 8030 Maker Description Part No. Price ----- ----------- -------- ------ Adtran NT1 NT1 ACE 395.00 Adtran Power Supply PS2 150.00 Adtran Power Kit 74.00 Adtran Standalone NT1 NT1/T400 575.00 (incl 7W supply) Adtran Rackmount NT1 NT1/T400 395.00 IBM sells the RoadRunner, an NT1 device with added value: it can operate either as a standard NT1 or in extended mode. In extended mode it provides an intergrated voice terminal adapter and a connection to which POTS telephone devices (including modems, FAXs, and answering machines) can be attached. This allow a home POTS line to be replaced with an ISDN line. When operating with a DMS-100 switch, one B channel is devoted to the analog phones and one B channel is devoted to the data terminal adapter. When attached to a 5ESS switch, the B channels may be allocated dynamically. The analog phones may use either B channel that is available, and the data terminal device may use either or both B channels. The device includes a built in power supply and a back up battery, providing up to 18 hours of on-hook, or 6 hours of off-hook operation during a local power failure. IBM 800-426-2255 +1-404-238-2157 Maker Description Part No. Price ----- ----------- -------- ------ IBM 7845 Network 82G6060 350.00 Terminator Extended Motorola UDS offers the NT100 Network Termination Unit. This is an NT1 with added value: a series of diagnostic tests can be chosen via a front-panel rotary switch. Motorola UDS 5000 Bradford Drive Huntsville AL 35805-1993 +1 205 430 8000 800 451 2369 fax +1 205 830 5657 Maker Description Part No. Price ----- ----------- -------- ------ Motorola UDS Net. Term. Unit NT100 Thanks to the following people who helped uncover this information. firstname.lastname@example.org (Ed Tynan) email@example.com (Russell Pierce) "H.A. Kippenhan Jr."
csederholm@VNET.IBM.COM The people who compiled the NIUF solutions catalog Steve Hill (firstname.lastname@example.org) Special thanks to email@example.com (Oliver Jones) for editing this section. ------------------------------ 2.05) Can the existing local loop lines be reused for ISDN? The ISDN pairs are the same wires as used for regular telephone service. If you became an ISDN user at home, the same wire pair that now provides your telephone service would be used to provide ISDN (assuming you no longer have the regular line). Most of the lines do not require any special conditioning. Yes, if a line has load coils on it they must be removed, BUT load coils are usually only found on existing lines that are 15,000 feet or longer. As to lines with bridge taps, the 2B1Q line transmission scheme (not to be confused with 2B + D channelization) is tolerant of a certain amount of bridge taps and, therefore it is only a minimal subset of existing lines (lines with bridge taps whose total length is greater than 3000 feet for the bridge taps) that would require special "de-conditioning." With those things as the criteria, (in North America) we find than generally around 90% or so of existing telephone lines need no "de-conditioning" in order to be used for ISDN BRI service. firstname.lastname@example.org (sohl, william h) ------------------------------ 2.06) How does this compare to regular phone lines? The ISDN line may act like two independent phone lines with two numbers. Depending on the CO equipment, conferencing features etc. may be available (conferencing in the telephone switch). BRI ISDN phones can support key-set features such as you would expect to get on an office PBX like: - multiple directory numbers per line. - multiple lines per directory number. - conferencing features. - forwarding features. - voice mail features. - speed call. - call park. - call pickup. - ring again. - textual status displays. email@example.com (Curt Welch) firstname.lastname@example.org (Greg Larson) ------------------------------ 2.07) Is caller ID available on ISDN? Caller ID (name or number display) may be supported (depending on the CO setup). The availability of caller ID for residential phones would depend on the capabilities of the local phone network and legislation allowing or disallowing caller ID. The availability of Caller ID relies on the underlying switching protocol used by the switches that make up the telephone system (e.g. SS7). email@example.com (Curt Welch) firstname.lastname@example.org (Greg Larson) email@example.com (Gary C. Kessler) ------------------------------ 2.08) What do I get above and beyond plain old telephone service? Plain old telephone service is transmitted between the central office to your home or office telephone set (or modem, or fax) in analog form. At the central office, the analog signal is converted to a series of digital samples at a rate of 8000 samples per second. Each sample is seven or eight bits in length. As the signals for a telephone call move around the central office, or between central offices, they are transmitted in digital form. Thus, a telephone call consumes a transmission bandwidth of either 56 or 64 kilobits per second. The theoretical (Nyquist) limit for the frequency response of a signal sampled 8000 times per second is 4kHz. However, due to various losses in the telephone system, the frequency response of an ordinary telephone call is usually quoted as 3.1kHz. Ordinary modem-based data transmission uses schemes for encoding data in an analog signal so it fits in this 3.1kHz bandwidth. 14.4kbps is a commonly available transmission rate at the high end of the scale. With this transmission rate, over three-quarters of the bitrate handled by the central office is wasted. Notice that in telephony, 64 kbps means 64000 bits per second, whereas in computer engineering 64k bytes typically means 65536 bytes. ISDN brings the digital signal all the way to your home or desktop. With ISDN, you can place a data call which uses all 56kbps or 64kbps, because there is no need to convert the signal to analog in your modem and back to digital at the central office. The availability of the full bandwidth presents some interesting technological opportunities: -- transmission of high-fidelity compressed audio -- transmission of encrypted audio -- transmission of lots of data -- transmission of other compressed signals, such as video Basic-rate ISDN (BRI) offers two channels of this service. In BRI, the connection between your site and the central office offers 64kbps bidirectionally on each channel. Each of these channels may be used for a voice call, for circuit-switched data, or for X.25 packet switched data. Thus, the existing POTS circuit [POTS: Plain Old Telephone Service, i.e. traditional analog telephony] can be conditioned to carry two calls at the same time. (Your mileage may vary; you have to specifically order and pay for the various services from your telephone company, just as you have to order and pay for Call Waiting for an ordinary phone line. Also, not all services are available everywhere; X.25 connectivity between COs is a notable problem in the Greater Boston area as of 9/93, for example.) Incidentally, ISDN brings another interesting service to your home or desktop: a highly reliable 8000Hz clock signal. In most cases, the central office switches, long-distance carriers, and ISDN terminal equipment all operate with exactly the same clock frequency. In a real-time communications environment (like a voice phone call) this means that there's no need to compensate for differences between the sampling rates at each end of the call. One of the other features is that instead of the CO sending an AC ring signal to activate your bell, it sends a digital packet that tells WHO is calling (if available), WHAT TYPE of call (speech, datacomm?), the NUMBER DIALED (maybe one of your aliases) and some other stuff. Your equipment can then analyze this stuff and make an "intelligent" decision what to do with it. For example, a phone (with speech-only capacity) would completely ignore a datacomm call while a Terminal Adapter (ISDN "modem") or a phone with built-in datacom functions would respond to it. If you have several "aliases" tied to your line, you can program certain phones to answer calls for certain numbers only. Datacomm calls contain baud rate and protocol information within the setup signal so that the connection is virtually instantaneous (no messing around with trying different carriers until both ends match). firstname.lastname@example.org (Curt Welch) email@example.com (Torsten Lif) firstname.lastname@example.org (Oliver Jones) Helge.Oldach@Stollmann.DE (Helge Oldach) ------------------------------ 2.09) What do ISDN phones cost? The ISDN sets can cost between $180 for an AT&T 8503T ISDN phone from Pacific Bell up to $1900 depending on what/how many features are needed. A recent report states that the price is $536.90 for an AT&T 7506 with the RS-232 port on the back and $102.70 to get the 507A adaptor to hook analog devices to my 7506. Recent quotes were "$200" for a Coretelco 1800 and "$600" for a Fujitsu SRS 1050. keyman@doorway.Eng.Sun.COM (Dave Evans) email@example.com (Brad Huntting) firstname.lastname@example.org (Joe Ilacqua) email@example.com (Scott Turner) ------------------------------ 2.10) Can you use existing telephone equipment with the voice portion? Terminal Adapters (TA's) are available that will interface non ISDN terminal equipment (TE), called TE2, to the S/T interface. At least one RBOC provides a modem pool to allow for interchange of data with POTS subscribers. Bellcore may approve a standard to allow a analog pair to interface to POTS sets from a NT1. Also w/o a NT2 only one set can be connected to a B channel at a time. This prevents 2 sets from participating in the same voice call. firstname.lastname@example.org ( Patton M. Turner) email@example.com (Joe Ilacqua) ------------------------------ 2.11) What is National ISDN? Because of the breadth of the international ISDN standards, there are a number of implementation choices that vendors of ISDN equipment can make. Given the number of choices vendors can make, different vendors equipment may not interoperate. In the United States, Bellcore has released a series of specifications to try to avoid these interoperability problems. These are the National ISDN specifications. Contact the Bellcore ISDN hot line listed below for more information. firstname.lastname@example.org (Gary C. Kessler) cherkus@UniMaster.COM (Dave Cherkus) ------------------------------ 2.12) What is the NIUF? North American ISDN Users Forum (NIUF) is an org. of ISDN-interested parties, coordinated by NIST (National Institute of Stds. and Tech.) Contact: NIUF Secretariat National Institute of Standards and Technology Building 223, Room B364 Gaithersberg, MD 20899 (301) 975-2937 voice (301) 926-9675 fax (301) 869-7281 BBS 8N1 2400 bps Bellcore has made the PostScript files for "A Catalog of National ISDN Solutions for Selected NIUF Applications, Second Edition" accessable via anonymous ftp from the machine info.bellcore.com. This document has a tremendous amount of information about ISDN products and vendors, among many other things. See the item below for details. The currently approved documents for the Application Software Interface (ASI) from the North American ISDN User's Forum (NIUF) are available via anonymous FTP from dsys.ncsl.nist.gov. The documents are in Postscript and found in uncompressed ASCII (foo.ps), compressed (foo.Z) and zipped (foo.zip) files. These documents describe the Implementation Agreements made by the NIUF for an API to ISDN services. The file sizes are approximate and intended to help determine space requirements for transfer. Part 1: Overview and Protocols - Approved: 10/4/91, Updated: 10/30/92 ~ftp/asi/docs/part1.ps - 347853 bytes ~ftp/asi/docs/part1.Z - 119655 bytes ~ftp/asi/docs/part1.zip - 89545 bytes Part 2: MS-DOS Access Method - Approved: 6/5/92 ~ftp/asi/docs/part2.ps - 146474 bytes ~ftp/asi/docs/part2.Z - 44450 bytes ~ftp/asi/docs/part2.zip - 31599 bytes Part 3: Enhanced DOS/Protected Mode Shell Access Method - Approved: June 5, 1992, Updated: 10/30/92 ~ftp/asi/docs/part3.ps - 285344 bytes ~ftp/asi/docs/part3.Z - 91273 bytes ~ftp/asi/docs/part3.zip - 68331 bytes Part 4: UNIX Access Method - Approved: 10/30/92 ~ftp/asi/docs/part4.ps - 151809 bytes ~ftp/asi/docs/part4.Z - 47765 bytes ~ftp/asi/docs/part4.zip - 33465 bytes For further information regarding these documents please contact Robert Toense (email@example.com) (phone: +1 301 975 2930). cherkus@UniMaster.COM (Dave Cherkus) firstname.lastname@example.org (Vance Shipley) ------------------------------ 2.13) What is ATM? ATM (Asynchronous Transfer Mode) is a switching/transmission technique where data is transmitted in small, fixed sized cells (5 byte header, 48 byte payload). The cells lend themselves both to the time-division- multiplexing characteristics of the transmission media, and the packet switching characteristics desired of data networks. At each switching node, the ATM header identifies a "virtual path" or "virtual circuit" that the cell contains data for, enabling the switch to forward the cell to the correct next-hop trunk. The "virtual path" is set up through the involved switches when two endpoints wish to communicate. This type of switching can be implemented in hardware, almost essential when trunk speeds range from 45Mb/s to 1Gb/s. One use of ATM is to serve as the core technology for a new set of ISDN offerings known as Broadband ISDN (B-ISDN). For more information, read comp.dcom.cell-relay. This group has a Frequently Asked Questions list; it is posted to news.answers and is in various archives as cell-relay-faq. email@example.com (Art Berggreen) cherkus@UniMaster.COM (Dave Cherkus) ------------------------------ 2.14) What is B-ISDN? Broadband ISDN refers to services that require channel rates greater than a single primary rate channel. While this does not specificially imply any particular technology, ATM will be used as the switching infrastructure for B-ISDN services. B-ISDN services are categorized as: INTERACTIVE Conversational -- such as videotelephony, videoconferencing, ... Messaging -- such as electronic mail for images, video, graphics,... Retrieval -- such as teleshopping, news retrieval, remote education,... DISTRIBUTION Without user presentation control -- electronic newspaper, TV distribution With user presentation control -- remote education, teleadvertising, news retrieval More information: ITU ITU-T Rec. I.211. firstname.lastname@example.org (Gary C. Kessler) ------------------------------ 2.15) What is BONDING? An inverse multiplexing method of the Bandwidth ON Demand INteroperability Group, implemented by most (all?) inverse multiplexor vendors to interoperate with inverse multiplexors of other vendors. BONDING is a set of protocols developed by U.S. inverse multiplexor vendors that supports communication over a set of separate channels as if their bandwidth were combined into a single coherent channel. For example it supports a single 384 kb/s data stream over 6 64 kb/s channels. The specification defines a way of calculating relative delay between multiple network channels and ordering data such that what goes in one end comes out the other. Most (all?) vendors also have their own proprietary methods that usually add features and functions not present in BONDING mode 1. Mode 1 is the mode used for recent interoperability testing between vendors. Chip Sharp at Teleos has made available electronic copies of the BONDING (Bandwidth on Demand Interoperability Group) 1.0 and 1.1 specifications. The specs are available via WWW, gopher, anonymous FTP, DECnet COPY, and AFS (see instructions below). The following files are available: - aaareadme-networks help file (in ascii text) - bdmain.doc main body of BONDING 1.0 specification (Word for Windows 2.0 format) - bdmain.ps main body of BONDING 1.0 specification (Postscript) - bdannex.doc annex of BONDING 1.0 specification (Word for Windows 2.0 format) - bdannex.ps annex of BONDING 1.0 specification (Postscript) - bd_v1_1.doc changes for BONDING 1.1 specification (Word for Windows 2.0 format) - bd_v1_1.ps changes for BONDING 1.1 specification (Postscript) Transfer Instructions: WWW: server: www.hep.net URL: gopher://hepnrc.hep.net:70/11/networks/bonding Gopher: server: gopher.hep.net Bookmark: Name=Bandwidth on Demand Interoperability Group (BONDING) Documents Type=1 Port=70 Path=1/info_center/networks/bonding Host=gopher.hep.net Anonymous FTP: server: ftp.hep.net directory: networks/bonding DECnet COPY (only for those on HEP-NSI DECnet): HEPNET::[ANON_FTP.NETWORKS.BONDING] AFS: /afs/hepafs1.hep.net/public/anon_ftp/networks/bonding email@example.com (Marco S Hyman) "Bob Larribeau" "David E. Martin" firstname.lastname@example.org (Brad Carlson) ------------------------------ 2.16) Data Encapsulation for IP over ISDN A decision was made at the Amsterdam IETF to state that all systems wishing to guarantee IP interoperability should implement PPP. Such systems may also implement the Frame Relay or X.25 encapsulations, and an RFC will be published delineating how, when it is known that the encapsulations are limited to that set of three, they may be distinguished by examination of the first correctly checksummed and HDLC bit-stuffed packet. Many implementations are using PPP so that they can negotiate compression and/or multilink operation. There is an Internet Draft from the Point-to-Point Protocol Working Group of the Internet Engineering Task Force that describes the use of PPP over ISDN. This draft is named draft-ietf-pppext-isdn-NN.txt in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, munnari.oz.au, Germany.EU.net and on many, many other mirror archives. This is also discussed in RFC 1356 by Malis, et. al. A common practice in most European countries is raw IP packets delimited by HDLC flags. Another common practice is an encapsulation using simple HDLC in layer 1, X.75 (LAPB, usually I-frames) in layer 2 and, sometimes, T.70 in layer 3. PPP is used instead of HDLC/X.75/T.70 when the network doesn't provide the callers telephone number eg. when emulating a modem or the callers number is lost on telephone company borders. In this case, caller authentication is done via PAP/CHAP instead. sklower@toe.CS.Berkeley.EDU (Keith Sklower) cherkus@UniMaster.COM (Dave Cherkus) email@example.com (Gary C. Kessler) firstname.lastname@example.org (Juergen Ernst Guenther) cabo@Informatik.Uni-Bremen.DE (Carsten) ------------------------------ 2.17) Full Motion Video over ISDN In ISDN, video isn't a "service being offered" - at least nolow/midrange quality. You buy the proper equipment for both subscribers, plug it in, and place the call. Just like speaking French on ISDN isn't something being offered - it is something you just do, yourself. Video telephony over narrowband ISDN is governed by a suite of ITU-T (formerly CCITT) interoperability standards. The overall video telephony suite is known informally as p * 64 (and pronounced 'p star 64'), and formally as standard H.320. H.320 is an "umbrella" standard; it specifies H.261 for video compression, H.221, H.230, and H.242 for communications, control, and indication, G.711, G.722, and G.728 for audio signals, and several others for specialized purposes. A common misconception, exploited by some equipment manufacturers, is that compliance with H.261 (the video compression standard) is enough to guarantee interoperability. Bandwidth can be divided up among video, voice, and data in a bewildering variety of ways. Typically, 56kbps might be allocated to voice, with 1.6kbps to signalling (control and indication signals) and the balance allocated to video. An H.320-compatible terminal can support audio and video in one B channel using G.728 audio at 16 kb/s. For a 64 kb/s channel, this leaves 46.4 kb/s for video (after subtracting 1.6 kb/s for H.221 framing). The resolution of a H.261 video image is either 352x288 (known as CIF) or 176x144 (known as quarter-CIF or QCIF). The frame rate can be anything from 30 frames/second and down. Configurations typically use a 2B (BRI) or a 6B (switched-384 or 3xBRI with an inverse multiplexer) service, depending on the desired cost and video quality. In a 384kbps call, a video conferencing system can achieve 30 frames/second at CIF, and looks comparable to a VHS videotape picture. In a 2B BRI call, a standard video phone can achieve 15 frames/second at CIF. Those who have seen the 1B video call in operation generally agree that the quality is not sufficient for anything useful like computer based training - only for the social aspect of being able to *see* Grandma as well as hear her (sort of like the snapshot pictures you make with that $5 camera with no controls). A 2B picture, on the other hand, is for all practical purposes sufficient for remote education, presentations etc. Rapidly changing scenes are still not very well handled, but as soon as the picture calms down, the sharpness and color quality are impressive (considering that only two plain phone channels are being used). With 2B+D being the standard BRI, this kind of picturephone will be usable "everywhere" (including private homes). However, it should still be noted that 6xB or H0 does allow for dramatic improvement in picture quality compared to 2xB. In particular, H.320 video/audio applications will often allocate 56kbps for audio, leaving only 68.8kbps for video when using 2xB. On the other hand, using H0 would get you 326.4kbps for video with 56kbps for audio. Alternative audio algorithms can improve picture quality over 2xB by not stealing as many bits. Note that 6B is not identical to H0; the latter is a single channel which will give you 80kbps above that of six separate B channels. Inverse multiplexors can be used to combine B channels. There is now a videoconferencing FAQ available at http://www.bitscout.com/faqtoc.htm jsteer@BitScout.com (Jon Steer) email@example.com (Ketil Albertsen,TIH) firstname.lastname@example.org (Kevin Davis) email@example.com (Oliver Jones) firstname.lastname@example.org (Mike Souryal) ------------------------------ 2.18) What is a SPID? How come my ISDN device won't work without one? SPIDs are Service Profiles IDs. SPIDs are used to identify what sort of services and features the switch provides to the ISDN device. Currently they are used only for circuit-switched service (as opposed to packet-switched). Annex A to ITU recommendation Q.932 specifies the (optional) procedures for SPIDs. They are most commonly implemented by ISDN equipment used in North America. When a new subscriber is added, the telco personnel allocate a SPID just as they allocate a directory number. In many cases, the SPID number is identical to the (full ten digit) directory number. In other cases it may be the directory number concatinated with various other strings of digits, such as digits 0100 or 0010, 1 or 2 (indicating the first or second B channel on a non-centrex line), or 100 or 200 (same idea but on a centrex line) or some other, seemingly arbitrary string. Some people report SPIDs of the form 01nnnnnnn0 for AT&T custom and 01nnnnnnn011 for NI-1, where n is the seven digit directory number. It is all quite implementation dependent. The subscriber needs to configure the SPID into their terminal (i.e. computer or telephone, etc., not their NT-1 or NT-2) before they will be able to connect to the central office switch. When the subscriber plugs in a properly configured device to the line, Layer 2 initialization takes place, establishing the basic transport mechanism. However if the subscriber has not configured the given SPID into their ISDN device, the device will not perform layer 3 initialization and the subscriber will not be able to make calls. This is, unfortunately, how many subscribers discover they need a SPID. Once the SPID is configured, the terminals go through an initialization/identification state which has the terminal send the SPID to the network in a Layer 3 INFOrmation message whereby the network responds with an INFO message with the EID information element (ie). Thereafter the SPID is not sent again to the switch. The switch may send the EID or the Called Party Number (CdPN) in the SETUP message to the terminal for the purpose of terminal selection. SPIDs should not be confused with TEIs (terminal endpoint identifiers). TEIs identify the terminal at Layer 2 for a particular interface (line). TEIs will be unique on an interface, whereas SPIDs will be unique on the whole switch and tend to be derived from the primary directory number of the subscriber. Although they are used at different layers, they have a 1-to-1 correspondence so mixing them up isn't too dangerous. TEIs are dynamic (different each time the terminal is plugged into the switch) but SPIDS are not. Following the initialization sequence mentioned above the 1-to-1 correspondence is established. TEIs are usually not visible to the ISDN user so they are not as well known as SPIDs. The "address" of the layer 3 message is usually considered to be the Call Reference Value (also dynamic but this time on a per call basis) as opposed to the SPID, so the management entity in the ISDN device's software must associate EID/CdPN on a particular TEI and Call Reference Number to a SPID. There are some standards that call for a default Service Profile, where a terminal doesn't need to provide a SPID to become active. Without the SPID however, the switch has no way of knowing which terminal is which on the interface so for multiple terminals an incoming call would be offered to the first terminal that responded, rather than to a specific terminal. email@example.com (winston (w.l.) sorfleet) firstname.lastname@example.org (Chuck Storry) ------------------------------ 2.19) Will ISDN terminal equipment that works in one country work properly when it is installed in another country? There are four major problem areas. The first has to do with voice encoding, and is only a problem if the equipment is a telephone. Equipment designed for use in North America and Japan uses mu-law encoding when converting from analog to digital, whereas the rest of the world uses A-law. If the equipment has a switch for selecting one or the other of these encoding types, then there will not be a problem with the voice encoding. The second has to do with the way the equipment communicates with the telephone exchange. There are interoperability problems because * there are so many different services (and related parameters) that the user can request and * each country can decide whether or not to allow the telephone exchange to offer a given service and * the specifications that describe the services are open to interpretation in many different ways. So, as with other interoperability problems, you must work with the vendors to determine if the equipment will interoperate. This is a basic problem; it impacts all ISDN equipment, not just voice equipment. The third has to do with homologation, or regulatory approval. In most countries in the world the manufacturer of telephone equipment must obtain approvals before the equipment may be connected to the network. So, even if the equipment works with the network in a particular country, it isn't OK to hook it up until the manufacturer has jumped through the various hoops to demonstrate safety and compliance. It is typically more expensive to obtain world-wide homologation approvals for a newly-developed piece of ISDN equipment than it is to develop it and tool up to manufacture it. A fourth issue is in the US the TA and NT1 are both provided by the customer, while in Europe the NT1 is provided by telephone company. Stated differently, if you walk into a store in the US and buy something to plug into an ISDN line it may be designed as a one-piece unit that connects to point U. In Europe you would get something that plugs into point T. Thus you might take a piece of US-originated equipment to Europe and find that it won't work because the jack in Europe is a T interface and the plug on your US equipment is a U interface. There are attempts to remedy this situation, particularly for BRI ISDN. In North America, the National ISDN User's Forum is coming up with standards that increase the uniformity of ISDN services. In Europe, a new standard called NET3 is being developed. email@example.com (Ming Sun) firstname.lastname@example.org (Marco S Hyman) email@example.com (Jim Breen) keyman@Eng.Sun.COM (Dave Evans) firstname.lastname@example.org (Oliver Jones) email@example.com (William Martin) firstname.lastname@example.org (Carl Oppedahl) ------------------------------ 2.20) Will ISDN terminal equipment that works with one vendor's ISDN switch work properly when used with another vendor's switch? [Ed. Note: The title is edited from the previous faq to try to fit in with the preceding question] [Also, this seems to imply that there are only two implementations to worry about and it is very US-centric. This section needs to be reworked] When the National ISDN-1 standard is implemented, there will be a single standard for how TE communicates with the CO (the call setup dialogue). Until that time, you may encounter two different varieties of CO equipment, each with its own call setup dialogue: * ATT 5ESS * Northern Telecom DMS100 Some ISDN TE equipment can be configured to communicate with either; some works with only one variety. Jim.Rees@umich.edu (Jim Rees) email@example.com (Jerry Scharf) ------------------------------ 2.21) Do different manufacturers' Terminal Adaptors interoperate when used asynchronously? There is a standard up to 19.2k (V.110) but above that there is no real standard implemented. However, in practice there is a fair degree of interoperability (even when the TA's manual tells you otherwise) because many TAs use the same chip set (supplied by Siemens) which happily goes up to 38.4. TAs from different suppliers that are using the Siemens chips have a fair chance of interoperating at up to 38.4k. firstname.lastname@example.org (William Martin) ------------------------------ 2.22) Why do I get only about 19.2k throughput from my TA? The problems in using TA's are the same as those in using fast modems. You only get the throughput that your serial port can handle. The serial ports of many machines struggle to receive at 19.2k. Sending is easier to implement efficiently. Many machines will happily send data to a TA at 38.4, but choke down to around 19.2k or lower when receiving (with lots of retries on ZMODEM file transfer). email@example.com (William Martin) ------------------------------ 2.23) How long should call setup take when using a TA? The "less than a second" call setup sometimes claimed seems to be rare. TAs have a negotiation phase and it typically takes around 4 seconds to get through to the remote site. firstname.lastname@example.org (William Martin) -- Dave Cherkus ----- UniMaster, Inc. ----- Contract Software Development Specialties: UNIX TCP/IP X OSF/1 AlphaAXP AIX RS/6000 Performance ISDN Email: cherkus@UniMaster.COM Tel: (603) 888-8308 Fax: (603) 888-4598 The Internet runs on its programmers, and programmers run on coffee!!!