Xref: utcsri comp.dcom.isdn:3503 comp.answers:3246 news.answers:16517 Newsgroups: comp.dcom.isdn,comp.answers,news.answers Path: utcsri!utnut!cs.utexas.edu!uunet!MathWorks.Com!noc.near.net!mv!fastball.unimaster.com!cherkus From: cherkus@UniMaster.COM (Dave Cherkus) Subject: comp.dcom.isdn Frequently Asked Questions Nntp-Posting-Host: fastball.unimaster.com Keywords: ISDN FAQ telecom Followup-To: comp.dcom.isdn Approved: news-answers-request@MIT.Edu Sender: usenet@mv.mv.com (Mark E. Mallett) Organization: UniMaster, Inc. Date: Tue, 4 Jan 1994 08:16:07 GMT Supersedes: Message-ID: Summary: This posting contains a list of Frequently Asked Questions (and their answers) about ISDN. Expires: Tue, 1 Feb 1994 00:00:00 GMT Reply-To: cherkus@UniMaster.COM (Dave Cherkus) Distribution: world Lines: 1341 Archive-name: isdn-faq Last-modified: 1994/01/04 Version: 3.1 [Ed. Note: I'm using 3.x version numbers now because I'm now using RCS for file management. Also, there is new material in this faq vs. version 2.02. New Year's resolution: keep up with the faq!] ----- Frequently Asked Questions and Answers comp.dcom.isdn These questions and answers have (almost entirely) been extracted from comp.dcom.isdn. Please post any comments or new material that you have, or email them to the current FAQ editor, cherkus@unimaster.com. In particular, the vendor equipment chart is incomplete. If you want to share vendor equipment info, just cut and paste the headers from the chart below and create a new entry for the new information, and send or post it. This FAQ consists almost entirely of information posted to this group. There are a fair number of holes and some potentially outdated information in it. There is no claim of completeness or guarantee of accuracy of any kind, and no warranties for merchantability or fitness for a particular purpose. If you have some useful information that you would like to share, email it to me or post it to the group. My goal is to have the FAQ mirror the information provided to the newsgroup itself. The next-to-last section of this FAQ gives references that provide much more information than this FAQ does. I would like to thank Sean Welch for creating the previous edition of the FAQ. His work is still responsible for the majority of the information gathered here. I hope to continue the fine example that Sean has set. Questions with answers: 1) What is ISDN? 2) What does an ISDN network connection look like? 3) What will Basic Rate (2B+D) ISDN look like in my house/office? 4) Can the existing local loop lines be reused for ISDN? 5) How does this compare to regular phone line services? 6) Is caller ID available on ISDN? 7) What do I get above and beyond plain old telephone service? 8) What do ISDN phones cost? 9) Can you use existing telephone equipment with the voice portion? 10) What is National ISDN? 11) What is ATM? 12) What is B-ISDN? 13) What is BONDING? 14) Data Encapsulation for IP over ISDN 15) Full Motion Video over ISDN 16) How do I find out about getting ISDN in my area? 17) Where can I find what all of these acronyms mean? 18) What are the relevant standards? 19) Who is shipping what? 20) How about that SPARCstation 10? 21) Will an ISDN terminal equipment that works in one country work properly when it is installed in another country? 22) Will ISDN terminal equipment that works with one vendor's ISDN switch work properly when it is used with another vendor's switch? 23) Do different manufacturers Terminal Adaptors interoperate when used asynchronously? 24) Why do I get only about 19.2k throughput from my TA? 25) How long should call setup take when using a TA? 26) Where can I read more? 27) Who do I have to thank for this list? Questions for which I have not yet put together an answer, but for which I am accepting suggestions: a) What programming API's are useful for creating ISDN applications? (e.g. Sun, Microsoft, NIUF ASI, ETSI(?), German(?), French(?), more(?)) b) What is a SPID? --- 1) What is ISDN? ISDN stands for "Integrated Services Digital Networks", and it's a 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, France, Japan, and Singapore, with the UK and Germany somewhat behind, and USA availability rather spotty. eleskg@nuscc.nus.sg (Winston Seah) goldstein@carafe.enet.dec.com (Fred R. Goldstein) paul@suite.sw.oz.au (Paul Antoine) --- 2) 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). TA's do not interoperate with the modem; it replaces the modem. Another common type of equipment can be used to implement a bridge between local area networks using the ISDN channel to transport the data. 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. The BRI will require a device to perform the role of Network Termination, or NT. In the case where the TA is attached to a PBX (defined below), the PBX will play the role of the NT. In most residential situations, a seperate standalone device will perform the role of NT, or if there will be only one device attached to the BRI, the one device can logically replace the NT device. 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 ISN 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 NT only implements part of the channel sharing scheme; the other devices participate as well, and the communication protocol used by the NT and the other devices is an integral part of the channel sharing scheme. The NT 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 betyeen 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 provides the U interface instead of the S/T interface; more on this in the next section, and in the references). 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). 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) turtle@newshub.sdsu.edu (Andrew Scherpbier) cherkus@UniMaster.COM (Dave Cherkus) oj@world.std.com (Oliver Jones) KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) ---- 3) What will Basic Rate (2B+D) ISDN look like in my house/office? An ISDN BRA U-Loop is 2 conductors from the CO to the customer premises. At the customer premises the U-loop is terminated by an NT1 (network termination 1). The NT1 drives a T-bus which is 4 wires. You can only have one device on the T-bus. If you run the T-bus into a NT2 which has an S-bus (the passive bus) on the other side, you can connect up to 8 physical devices. Electrically, the S and T reference points are the same (which is why they are almost always referred to as the S/T bus). Some NT1 may include between 24v and 53.5v power on the T-bus (making it 6 wires), however this would be model/vendor dependent. There are also 8 wire T-bus connection (power + 2 extra?). Australia and Europe are similar except the NT1 is owned by the PTT. Either a ECH (Echo Canceling Hybird), like is used in the US, or a form of time division multiplexing using AMI is used to achieve bidirectional transmission an a single pair. +-+ S Bus +-------+ T Bus +-------+ U Loop | |?|=-=-=-=-=-=| NT2 |===========| NT1 |--------------[| wall +-+ 4-8 wires +-------+ 4-8 wires +-------+ 2-4 wires | Some ISDN hardware plugs into the U loop, some with the T Bus, and some with the S-Bus. In the US (at least) there is a power supply between the wall and the NT1. cliff@Berkeley.EDU (Cliff Frost) curt@kcwc.com (Curt Welch) dror@digibd.com (Dror Kessler) glarson@bnr.ca (Greg Larson) paul@suite.sw.oz.au (Paul Antoine) pturner@eng.auburn.edu ( Patton M. Turner) ronnie@cisco.com (Ronnie B. Kon) -- 4) 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. whs70@cc.bellcore.com (sohl,william h) --- 5) 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 DNs / lines. - conferencing features. - forwarding features. - speed call. - call park. - call pickup. - ring again. curt@kcwc.com (Curt Welch) glarson@bnr.ca (Greg Larson) --- 6) 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). curt@kcwc.com (Curt Welch) glarson@bnr.ca (Greg Larson) KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) --- 7) 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, 64kpbs 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 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 it that instead of the CO sending an AC ring signal to activate your bell, it sends a digital package 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). curt@kcwc.com (Curt Welch) etxorst@eos.ericsson.se (Torsten Lif) oj@world.std.com (Oliver Jones) Helge.Oldach@Stollmann.DE (Helge Oldach) --- 8) What do ISDN phones cost? [Ed. note: this is probably out of date. Does anyone have recent info? ] 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. keyman@doorway.Eng.Sun.COM (Dave Evans) huntting@futureworld.advtech.uswest.com (Brad Huntting) spike@coke.std.com (Joe Ilacqua) --- 9) Can you use existing telephone equipment with the voice portion? Terminal Adapters (TA'a) 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. pturner@eng.auburn.edu ( Patton M. Turner) spike@coke.std.com (Joe Ilacqua) --- 10) 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. KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) cherkus@UniMaster.COM (Dave Cherkus) ---- 11) 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 speed 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. art@acc.com (Art Berggreen) cherkus@UniMaster.COM (Dave Cherkus) -------- 12) 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, electronic newspaper, TV distribution With user presentation control -- remote education, teleadvertising, news retrieval More information: ITU TSS Rec. I.211. KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) -------- 13) 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 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 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://www.hep.net:70/11/info_center/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 marc@dumbcat.sf.ca.us (Marco S Hyman) "Bob Larribeau" "David E. Martin" --- 14) 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 checksumed and HDLC bit-stuffed packet. 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. sklower@toe.CS.Berkeley.EDU (Keith Sklower) cherkus@UniMaster.COM (Dave Cherkus) KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) -------- 15) Full Motion Video over ISDN In ISDN, video isn't a "service being offered" - at least not for low/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. The only requirement is that the ISDN provider must offer 64 kbps unrestricted channels - for the time being, some US providers won't give you more than 56 kbps usable capacity. Consider that a temporary limitation (and it often applies to long distance calls only). Video telephony over narrowband ISDN is governed by a suite of TSS (formerly CCITT) interoperability standards. The overall video telephony suite is known informally as p * 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. There is no standard identification format for any other videophone standard. Of course the data stream may be identified as an (arbitrary) V.110 coded 56 kbps, the recipient may accept the call, read the first blocks of data and determine whether it has the capabilities required to handle it. But this remains a non-ISDN videophone, only using ISDN as a carrier for some other videophone standard (or non-standard). An H.320-compatible terminal can support audio+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, under laboratory conditions, achieve 15 frames/second at CIF. In practice, 2B video phones achieve a very usable 7-10 frames per second. 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 impressing (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. ketil@edb.tih.no (Ketil Albertsen,TIH) kevin@newshost.pictel.com (Kevin Davis) oj@world.std.com (Oliver Jones) mikes2@cc.bellcore.com (Mike Souryal) --- 16) How do I find out about getting ISDN in my area? [Ed. Note: I would appreciate anyone adding info for this section. I would hope that the info would be for an ISDN specific operation, not a generic telephone company office] Australia: Telecom: 008 077 222 (voice), (07) 220 0080 (fax) Germany: Deutsche Bundespost Telekom IfN - Ingenierubuero fuer Nachrichtentechnik Haidelmoosweg 52 D - 78467 Konstanz Tel: +49 7531 97000-0 FAX: +49 7531 74998 North America: 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 United Kingdom: British Telecom ISDN Helpdesk 0800 181514 from within the UK, +44 272 217764 from outside. Mercury Data Communication 0500 424194 from within the UK, +44 81 914 2335 from outside. United States: I work in the industry and suggest that you call the local telephone service center office and ask for the name and number of the Marketing Product Manager for ISDN services. If the service rep cannot make heads or tails of your question, ask to speak to the local service center manager for complex business services. This person should be able to direct you to the right place. For the Bell companies, this position is normally part of the telephone company's core marketing staff at their headquarters location. Bellcore national ISDN information clearing house hotline: 800 992-4736 Bellcore's "ISDN Deployment Data", Special Report (SR) 2102. Bellcore document ordering: US: 1-800-521-2673, other: 1-908-699-5800 Bell Atlantic: 800-570-ISDN Ameritech: 800-8326-328 You can call Pacific Bell at [800] 995-0346. This is an extensive menu-driven system (yuck) that allows Pac Bell customers to enter their area code and prefix to find out what services are available. It doesn't tell you which switch, though. GTE has a similar service at [800] 4GTE-SW5. Combinet "BBS": By popular demand, the Combinet "BBS" providing information on ISDN availability in many areas of the US is now available via the Internet. The information is supplied by Bell Communications Research and various Operating Companies and is updated periodically as new information becomes available. To access the service, telnet to bbs.combinet.com and login as isdn (no password is required). After entering an area code and three-digit prefix, the service displays the availability of ISDN. Also displayed is information about carrier installation prices and monthly charges. For those without direct Internet access, the service continues to be available on a dialup basis using a 2400 bit/sec modem at (408) 733-4312. bharrell@garfield.catt.ncsu.edu (Ben Harrell) elitman@wam.umd.edu (Eric A. Litman) marc@Synergytics.COM (Marc Evans) varney@ihlpf.att.com (Al Varney) bernot@inf-wiss.uni-konstanz.de (Gerhard Bernot) jhonan@kralizec.zeta.org.au (Jamie Honan) dav@genisco.gtc.com (David L. Markowitz) Peter Ilieve p00210@psilink.com (Gerald L. Hopkins) KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) fenton@combinet.com (Jim Fenton) --- 17) Where can I find what all of these acronyms mean? An archive of telecommunication related files are maintained on lcs.mit.edu in the telecom-archives sub directory. There is a glossary of general telecom acronyms, as well as an ISDN specific list. jms@romana.Tymnet.COM (Joe Smith) asks: PMW1@psuvm.psu.edu (Peter M. Weiss) ---- 18) What are the relevant standards? There are numerous CCITT standards on ISDN. References in the book bibliography (especially Stallings and appendix B of Kessler) contain more details. Q.921 (aka I.441) "ISDN User-Network Interface Data Link Layer Specifications", 1988 The D channel protocol. Found in Blue book Fascicle VI.10 Q.931 (aka I.451) "ISDN User-Network Interface Layer 3 Specification for Call control" 1988. The messages that are sent over the D channel to set up calls, disconnect calls etc. Found in Blue book Fascicle VI.11 Q.930: General Overview Q.931: Basic ISDN call control Q.932: Frame Relay Call Control Q.93B: B-ISDN extensions to Q.931 G.711: Pulse Code Modulation (PCM) of Voice Frequencies G.722: 7-kHz Audio Coding Within 64 kbit/s G.728: Coding of Speech at 16 kbit/s Using Low-Delay Code Excited Linear Prediction (LD-CELP) H.320: Narrow-band Visual Telephone Systems and Terminal Equipment H.221: Frame Structure for a 64 to 1920 kbit/s Channel in Audiovisual Teleservices H.230: Frame Synchronous Control and Indication Signals for Audiovisual Systems H.242: System for Establishing Communications Between Audiovisual Terminals Using Digital Channels up to 2 Mbit/s H.261: Video Codec for Audiovisual Services at p x 64 kbits/s H.243: Basic MCU Procedures for Establishing Communications Between Three or More Audiovisual Terminals Using Digital Channels Up to 2 Mbit/s I.2xy "ISDN Frame Mode Bearer Services", 1990 I.310 ISDN - Network Functional Principles I.320 ISDN protocol reference model I.324 ISDN Network Architecture I.325 Reference configs for ISDN connection types I.326 I.330 ISDN numbering and addressing principles I.331 Numbering plan for ISDN (and several more in I.33x relating to numbering and addressing and routing) I.340 ISDN connection types I.350/351/352 refer to performance objectives I.410-412 refer to user-network interfaces as do I.420 and 421 I.430/430 Layer 1 specs I.440/441 Layer 2 specs (Q.921) I.450-452 Layer 3 specs (Q.931) I.450: General Overview I.451: Basic ISDN call control I.452: Extensions I.460-465 Multiplexing and rate adaption I.470 Relationship of terminal functions to ISDN V.110 (aka I.463) "Support of DTE's with V Series Type Interfaces by an ISDN" Terminal rate adaption by bit stuffing. C.f. V120. V.120 (aka I465) "Support by an ISDN of Data Terminal Equipment with V series Type Interfaces with Provision for Statistical Multiplexing" 1990 (This has been amended since the blue book). An alternative to V.110 V.25bis calling mechanism under synchronous. dave@philips.oz.au oj@vivo.com KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) --- 19) Who is shipping what? Equipment by Vendor: +------------------+----------------------------------+ | | Equipment Type | | Vendor +----+----+----+----+----+----+----+ | | IF | TA | BR | RO | TE | IC | TS | +------------------+----+----+----+----+----+----+----+ | AMD | | | | | | x | | | AT&T | x | x | | | x | x | x | | Ascend | | | | x | | | | | AT&T Microelect. | | | | | | x | | | Combinet | | | x | | | | | | CPV-Stollmann | x | x | x | x | | | | | diehl isdn | x | | | | | | | | DigiBoard | | | x | | | | | | Digital Eq. | x | | | x | | | | | Gandalf | x | x | | | | | | | Hayes | x | x | | | | | | | IBM | x | | | | | | | | ISDN Systems | x | | | | | | | | Motorola UDS | | x | | | | | | | netCS | x | | | X | | | | | Network Express | | | x | x | | | | | Paxdata | | | x | | | | | | Spider Systems | | | | x | | | | | Sun Microsystems | x | | | | | | | | Telrad Telecomm. | | | | | | | x | +------------------+----+----+----+----+----+----+----+ Key: IF: Interface Card TA: Terminal Adapter (Standalone) BR: Bridge RO: Router TE: Telephones IC: Integrated Circuit TS: Test Equipment Vendor Info: Advanced Micro Devices 901 Thomson place Mailstop 126 Sunnyvale, CA 94086 (408) 732 2400 (voice) American Telephone and Telegraph 1-800-222-PART: Quick access to small quanity orders of ISDN products. Personal Desktop Video or TeleMedia Connection System: Visual Communications Products 8100 East Maplewood Avenue 1st Floor Englewood, CO 80111 (800)843-3646 (800)VIDEO-GO Prompt 3 Ascend Communications, Inc. 1275 Harbor Bay Pkwy Alameda, CA 94501 (510) 769-6001 info@ascend.com AT&T Microelectronics Allentown, PA (800) 372-2447 Distributer: CoSystems at 408.748.2190 mktg: Steve Martinez at 408.748.2194 (steve@cosystems.com) tech: Gary Martin at 408.748.2195 (gary@cosystems.com) Combinet 333 West El Camino Real, Suite 310 Sunnyvale, California 94087 (408) 522 9020 (voice) (408) 732 5497 (fax) CPV-Stollmann Vertriebs GmbH Gasstrasse 18 P.O. Box 50 14 03 D-22761 Hamburg D-22714 Hamburg Germany Germany Phone: +49-40-890 88-0 Fax: +49-40-890 88-444 Electronic Mail: Info@Stollmann.DE (general inquiries) Helge.Oldach@Stollmann.DE (IPX router technical contact) Michael.Gruen@Stollmann.DE (IP router technical contact) diehl isdn GmbH Bahnhofstrasse 63 D-7250 Leonberg Germany Tel. 49/7152/93 29 0 Fax. 49/7152/93 29 99 email: bode@diehl.de DigiBoard 6400 Flying Cloud Drive Eden Prarie, MN 55344 (612) 943 9020 (voice) (612) 643 5398 (fax) Digital Equipment Co REO2 G/H2 DEC Park Worton Grange Reading Berkshire England Gandalf Cherry Hill Industrial Center Building 9 Cherry Hill, NJ 08002 (800) GANDALF (voice) Hayes ISDN Technologies 501 Second St., Suite 300 San Francisco CA 94107 (415) 974-5544 (voice) (415) 543-5810 (fax) ISDN Product Manager: Chris Brock (cbrock@hayes.com) International Business Machines (800) 426-2255 ISDN Systems Corp. Vienna VA USA 703-883-0933 Motorola UDS 5000 Bradford Drive Huntsville, AL 35805 (205) 430 8000 (voice) netCS Informationstechnik GmbH Feuerbachstr. 47-49 12163 Berlin 41 Germany Tele: +49.30/856 999-0 FAX: +49.30/855 52 18 E-Mail: sales@netcs.com / support@netcs.com Network Express Andrew Hasley Jim Hietala Randy Sisto (East Coast) VP, Marketing hietala@netcom.com randys@access.digex.net 2200 Green Road 342 Lester Ct. 11566 Ivy Bush Court Ann Arbor, MI 48105 Santa Clara, CA 95051 Reston, Virginia 22091 (313) 761-5005 (voice) Tel. 408-241-5165 Phone: (703) 264-5095 (313) 995-1114 (fax) Fax. 408-241-6246 Fax: (703) 264-5176 Paxdata Networks Limited Communications House Frogmore Road Hemel Hempstead HERTS HP3 9RW UK 0442 236336 (voice) 0442 236343 (fax) mktg: Jim Fitzpatrick (jim@paxdata.demon.co.uk) tech: Giles Heron (giles@paxdata.demon.co.uk) Spider Systems UK France Germany Spider Systems Limited Spider Systems SA Spider Systems Limited Spider House Les Algorithmes Schadowstrasse 52 Peach Street Saint Aubin 91194 D-4000 Dusseldorf 1 Wokingham Gif-sur-Yvette Germany England Paris Cedex RG11 1XH France 0734 771055 (voice) (1) 69 41 11 36 (voice) (0211) 93 50 120 (voice) 0734 771214 (fax) (1) 69 41 12 27 (voice) (0211) 93 50 150 (fax) Sun Microsystems Computer Company (SMCC) Mountain View, CA (800) USA-4SUN Telrad Telecommunications, Inc. 135 Crossways Park Drive Woodbury, New York 11797 (516) 921-8300 1 800 645-1350 Many of the references, especially Kessler, provide information on ISDN equipment. kenow@stpaul.ncr.com (TONY KENOW) garym@netcom.com (Gary Martin) bob_clemmons@smtp.esl.com (Bob Clemmons) marc@dumbcat.sf.ca.us (Marco S Hyman) dav@genisco.gtc.com (David L. Markowitz) bear@holly.ho.att.com (James J Allen +1 908 834 1713) giles@paxdata.demon.co.uk (Giles Heron) --- 20) How about that SPARCstation 10? The hardware on the SS10 supports 2 B channels (64K+64K) and 1 D channel (16K) for a grand total 144K in marketing speak. Typically you might use both B channels for data, 1 channel for voice and 1 channel for data, or 1 channel for data to 1 point and 1 channel for data to another point. In some parts of the world it's also popular to run X.25 over the D channel. Info from the SPARCstation 10 full announcement e-mail: - What Becomes Available When: o ISDN Chip on the motherboard (done) ISDN Drivers on Solaris 2.1 or greater (done) Teleservices API Q1 CY93 Solaris 2.x Wide Area Networking software Q1 CY93 Solaris 2.x The chip on the motherboard provides a BRI (basic rate interface) ISDN connection that is integrated with workstation audio. The drivers provide a low level interface to the hardware. The Teleservices API enables application development for workstation/telephony integration - providing functions like call setup, transfer, hold, confer, etc. The API is hardware independent so that it will work with third party non-ISDN telephony hardware and software. The WAN software enables data communication - running IP over ISDN (in other words, applications that run over ethernet will run over ISDN). In the first release, Sun will support data communications in the US (for the AT&T 5ESS switch), the UK, France, Germany and Japan. We will support voice services in the US (for the AT&T 5ESS switch) only. This is also now available on the SPARCstation LX, and available as an SBus card for any SBus workstation running Solaris 2.1 or later. The current set of ISDN drivers for Solaris 2.1 or greater support the AT&T 5ESS switch; the next release is expected to support DMS-100 and national standard. Get API_xtel* from sunsite.unc.edu:/pub/sun-info/white-papers for more information on the API itself. The XTel libraries, etc., are not bundled with either Solaris 2.x or SunLink ISDN at this time. SunLink ISDN description (quoted from Fall/Winter '93 SunExpress catalog): The SunLink ISDN software included in both kits is based on the international CCITT standard, and supports the following carrier-dependent implementations: o AT&T 5ESS (U.S.) o France Telecom VN2 (France) o DBT 1TR6 (Germany) o Britsh Telecom ISDN2 (U.K.) o NTT INS-Net 64 (Japan) Sunlink ISDN software provides the following features: o Transparent IP connectivity, to allow you to run most existing IP applications, without modification, over ISDN o Graphics User Interface (GUI)-based configuration tool, for easy installation and administration o Security features, including callback, calling address, and PPP authentication password o Inactivity timer, for transparent open/close connections o Integrated network management with SunNetManager agent dank@blacks.jpl.nasa.gov (Dan Kegel) kessler@Eng.Sun.COM (Tom Kessler) Greg.Onufer@Eng.Sun.COM dav@genisco.gtc.com (David L. Markowitz) --- 21) Will ISDN terminal equipment that works in one country work properly when it is installed in another country? There are three 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 can be switched, 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 because each country can decide whether or not to allow the telephone echange to offer a given service and because 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 equpipment 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. There are attempts to remidy 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. msun@ntmtv.com (Ming Sun) marc@dumbcat.sf.ca.us (Marco S Hyman) jwb@capek.rdt.monash.edu.au (Jim Breen) keyman@Eng.Sun.COM (Dave Evans) oj@world.std.com (Oliver Jones) wmartin@nsa.bt.co.uk (William Martin) -------- 22) Will ISDN terminal equipment that works with one vendor's ISDN switch work properly when it is 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] Before National ISDN-1 is implemented, the ATT 5ESS switches and Northern Telecom DMS100 switches speak different call setup dialogues. That's why you will see ISDN TE listed as 5ESS, DMS100 or both. Jim.Rees@umich.edu (Jim Rees) jerry@watchman.sfc.sony.com (Jerry Scharf) -------- 23) 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. wmartin@nsa.bt.co.uk (William Martin) -------- 24) 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 seems to be easier. Many machines that will happily chuck data at a TA at 38.4, but choke down to around 19.2k or l ower when receiving (with lots of retries on ZMODEM file transfer). wmartin@nsa.bt.co.uk (William Martin) -------- 25) 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. wmartin@nsa.bt.co.uk (William Martin) -------- 26) Where can I read more? "ISDN In Perspective" Fred R. Goldstein Addison-Wesley ISBN 0-201-50016-7 [Ed. Note: the second edition is new...] "ISDN: Concepts, Facilities, and Services, Second Edition" Gary Kessler McGraw-Hill, 1993 (2/e). ISBN 0-07-034247-4 "Sensible ISDN Data Applications" Jeffrey Fritz jfritz@wvnvm.wvnet.edu West Virginia University Press "ISDN and Broadband ISDN" (2nd edition) William Stallings Macmillan ISBN 0-02-415475-X "Networking Standards: A Guide to OSI, ISDN, LAN and MAN Standards" William Stallings Addison-Wesley "A Catalog of National ISDN Solutions for Selected NIUF Applications" North American ISDN User's Forum (use NIUF information above or order via Bellcore, document GP-1, $43) The 1990 ISDN Directory and Sourcebook Phillips Publishing Inc. 7811 Montrose Road Potomac, MD 20854 (301) 340-2100 ISDN Sourcebook Information Gatekeepers Inc. 214 Harvard Ave, Boston, MA 02134 (617) 232-3111 1 800 323-1088 Bellcore National ISDN Specifications SR-NWT-001953 SR-NWT-002361 US: 1-800-521-2673, other: 1-908-699-5800 Bellcore ISDN Availability Report WR-NWT-2102 ($103) US: 1-800-521-2673, other: 1-908-699-5800 AT&T Technical Journal special issue on ISDN (Volume 65, Issue 1) January/February 1986 [If anyone can tell me how to get ahold of the next two documents in terms of either ISBN, a publishing company, or an ftp site, I'd appreciate it.] "A subnetwork control protocol for ISDN circuit switching" Leifer, Gorsline, & Sheldon "Multiprotocol Interconnect on X.25 and ISDN in the Packet Mode" Malis, Robinson, & Ullmann EFFector. Issue 2.01, Issue 2.06, Issue 2.08 ftp.eff.org:pub/EFF AT&T Documents -------------- "5ESS(rg.tm) Switch National ISDN Basic Rate Interface Specification - 5E8 Software Release" AT&T document number 235-900-341 "5ESS(rg.tm) Switch ISDN Basic Rate Interface Specification - 5E7 Software Release" {Custom BRI} AT&T document number 235-900-331 "5ESS(rg.tm) Switch ISDN Primary Rate Interface Specification - 5E7 Software Release" AT&T document number 235-900-332 "5ESS(rg.tm) Switch Interface Specification to a Packet Switched Public Data (X.75) Network - 5E8 Software Release" [as in CCITT X.75] AT&T document number 235-900-317 "5ESS(rg.tm) Switch X.75' Intranetwork Interface Specification - 5E8 Software Release" [as in Bellcore's TR-000310] AT&T document number 235-900-325 "5ESS(rg.tm) Switch Documentation Description and Ordering Guide" [list/description of 5ESS documents] AT&T document number 235-001-001 AT&T documents ordering: 1-800-432-6600 USA 1-800-225-1242 Canada +1 317 352-8557 elsewhere AT&T Customer Information Center Order Entry 2855 N. Franklin road Indianapolis, IN 46219 (317) 352-8484 (fax) Northern Telecom Documents -------------------------- NTP 297-2401-100 ISDN System Description NTP 297-2401-010 ISDN Product Guide --- 27) Who do I have to thank for this list? Lots of people, in one way or another. "Bob Larribeau" Greg.Onufer@Eng.Sun.COM Helge.Oldach@Stollmann.DE (Helge Oldach) Jim.Rees@umich.edu (Jim Rees) KUMQUAT@SMCVAX.SMCVT.EDU (Gary C. Kessler) PMW1@psuvm.psu.edu (Peter M. Weiss) SYSGAERTNER@cygnus.frm.maschinenbau.th-darmstadt.de (Mathias Gaertner) apsteph@cs.utexas.edu (Alan Palmer Stephens) art@acc.com (Art Berggreen) awillis@athena.mit.edu (Albert Willis) bernot@inf-wiss.uni-konstanz.de (Gerhard Bernot) bharrell@garfield.catt.ncsu.edu (Ben Harrell) blsouth!klein@gatech.edu (Michael Klein) bob_clemmons@smtp.esl.com (Bob Clemmons) cherkus@UniMaster.COM (Dave Cherkus) cliff@Berkeley.EDU (Cliff Frost) craig@aland.bbn.com (Craig Partridge) curt@kcwc.com (Curt Welch) dank@blacks.jpl.nasa.gov (Dan Kegel) dav@genisco.gtc.com (David L. Markowitz) dave@philips.oz.au dem@hep.net (David E. Martin) dror@digibd.com (Dror Kessler) dwight@hyphen.com (Dwight Ernest) earle@poseur.JPL.NASA.GOV (Greg Earle - Sun JPL on-site Software Support) eleskg@nuscc.nus.sg (Winston Seah) elitman@wam.umd.edu (Eric A. Litman) etxorst@eos.ericsson.se (Torsten Lif) fenton@combinet.com (Jim Fenton) garym@netcom.com (Gary Martin) giles@paxdata.demon.co.uk (Giles Heron) glarson@bnr.ca (Greg Larson) goldstein@carafe.enet.dec.com (Fred R. Goldstein) huntting@futureworld.advtech.uswest.com (Brad Huntting) jerry@watchman.sfc.sony.com (Jerry Scharf) jfritz@wvnvm.wvnet.edu (Jeffrey Fritz) jhonan@kralizec.zeta.org.au (Jamie Honan) jik@pit-manager.MIT.EDU (Jonathan I. Kamens) jms@romana.Tymnet.COM (Joe Smith) jwb@capek.rdt.monash.edu.au (Jim Breen) kenow@stpaul.ncr.com (TONY KENOW) kessler@Eng.Sun.COM (Tom Kessler) ketil@edb.tih.no (Ketil Albertsen,TIH) kevin@newshost.pictel.com (Kevin Davis) kevinc@aspect.UUCP (Kevin Collins) keyman@Eng.Sun.COM (Dave Evans) keyman@doorway.Eng.Sun.COM (Dave Evans) kph@cisco.com (Kevin Paul Herbert) lmarks@vnet.ibm.com (Laurence V. Marks) marc@dumbcat.sf.ca.us (Marco S Hyman) marc@Synergytics.COM (Marc Evans) mikes2@cc.bellcore.com (Mike Souryal) msun@ntmtv.com (Ming Sun) oj@world.std.com (Oliver Jones) p00210@psilink.com (Gerald L. Hopkins) paul@suite.sw.oz.au (Paul Antoine) peter@memex.co.uk (Peter Ilieve) pturner@eng.auburn.edu ( Patton M. Turner) pturner@eng.auburn.edu (Patton M. Turner) rachelw@spider.co.uk (Rachel Willmer) randys@access.digex.net (Randolph A. Sisto) rdavies@janus.enet.dec.com (Rob Davies) rjl@fawlty1.eng.monash.edu.au (Russell Lang) rogers@eplrx7.es.dupont.com (Wade T. Rogers) ronnie@cisco.com (Ronnie B. Kon) sanjay@media.mit.edu (Sanjay Manandhar) scott@labtam.labtam.oz.au (Scott Colwell) sklower@toe.CS.Berkeley.EDU (Keith Sklower) sorflet@x400gate.bnr.ca (Winston WL Sorfleet) spike@coke.std.com (Joe Ilacqua) tnixon@microsoft.com (Toby Nixon) turtle@newshub.sdsu.edu (Andrew Scherpbier) varney@ihlpf.att.com (Al Varney) wb8foz@scl.cwru.edu (David Lesher) welch@watchtower.Berkeley.EDU (Sean N. Welch) whs70@cc.bellcore.com (sohl,william h) wmartin@nsa.bt.co.uk (William Martin) ---- Dave Cherkus UniMaster, Inc. cherkus@unimaster.com