Xref: helios.physics.utoronto.ca comp.dcom.cell-relay:1690 comp.answers:1322 news.answers:10483 Path: helios.physics.utoronto.ca!skule.ecf!utnut!cs.utexas.edu!math.ohio-state.edu!darwin.sura.net!haven.umd.edu!umd5.umd.edu!not-for-mail From: carl@umd5.umd.edu (Carl Symborski) Newsgroups: comp.dcom.cell-relay,comp.answers,news.answers Subject: comp.dcom.cell-relay FAQ: ATM, SMDS, and related technologies Followup-To: comp.dcom.cell-relay Date: 16 Jul 1993 16:39:31 -0400 Organization: University of Maryland, College Park Lines: 1442 Sender: carl@macbeth.umd.edu Approved: news-answers-request@MIT.Edu Message-ID: <2273m3$h5n@macbeth.umd.edu> NNTP-Posting-Host: macbeth.umd.edu Summary: General information and answers to questions related to or seen in the comp.dcom.cell-relay group. Keywords: cell-relay, ATM, SMDS, communications Archive-name: cell-relay-faq Last-modified: 1993/07/16 This article mostly contains general information but also answers to some Frequently Asked Questions (FAQ) which are related to or have been seen in comp.dcom.cell-relay. It is posted to provide information of general interest to both new and experienced readers. This list includes answers to questions, which are loosely grouped into categories. Questions marked with a "+" are new in this issue; those with significant changes of content since the last issue are marked by "*": A) TOPIC: COMP.DCOM.CELL-RELAY BASIC INFORMATION A1) What is the CELL-RELAY group? A2)* What is the archive site for this group? A3)* Is there a parallel mailing list for this group? A4) What other mailing lists are related to ATM? B) TOPIC: INDUSTRY FORUMS AND VENDOR INFORMATION B1)* How can I contact the ATM Forum? B2) What vendors are working on ATM technology? B3) What vendors are working on ATM hardware/chips? B4)+ What vendors are selling ATM test equipment? C) TOPIC: ATM REFERENCES C1) What are some good getting started ATM references? C2) Where/What is the "Network Compatible ATM for LANs" document? C3)* Where are hosts with ATM related information? C4) How can I get the ATM Forum's Interface Specification? C5) List of CCITT Recommendations concerning ATM. C6) Internet drafts from IETF working groups. C7) ATM Tutorials. C8) Contact information for ANSI T1S1 specifications. D) TOPIC: ATM TECHNOLOGY QUESTIONS D1) What are the various ATM Access layers? D2) Are ATM cells delivered in order? D3) What do people mean by the term "traffic shaping"? D4)* What is happening with signalling standards for ATM? D5) What is VPI and VCI? D6) Why both VPI *and* VCI? D7)* How come an ATM cell is 53 bytes anyway? E) TOPIC: ATM VS. XYZ TECHNOLOGY E1) How does ATM differ from SMDS? If you have suggestions or corrections for any of these answers or any additional information, please send them directly to carl@umd5.umd.edu; the information will be included in the next revision (or possibly the one after that). This posting is intended to be distributed every few months. New versions are archived along with other comp.dcom.cell-relay traffic on ftp.nwnet.net. See subject A2 for instructions to access the archive. The information contained herein has been gathered from a variety of sources. Most derived from a consensus of postings on the group. If you would like to claim responsibility for a particular item, please let me know. Enjoy! Carl Symborski carl@umd5.umd.edu ----------------------------------------------------------------------------- TOPIC: A) TOPIC: COMP.DCOM.CELL-RELAY BASIC INFORMATION ----------------------------------------------------------------------------- SUBJECT: A1) What is the CELL-RELAY group? The purpose of this group is to provide a forum for the submission of articles and inquiries dealing with networks using Cell Relay as a transport; including local, metropolitan, and wide area networks. The name cell-relay was chosen as a compromise over objections to the name "ATM" during the creation of this group. The acronym ATM in the context of this group stands for Asynchronous Transfer Mode, not Automatic Teller Machines or Adobe Type Manager. The term "cell" in cell-relay is taken to mean a small, fixed sized, information bearing unit that provides the foundation for transport and multiplexing of user traffic. This topic area is not related to cellular phones or intra-cellular organisms. SUBJECT: A2) * What is the archive site for this group? The archives for comp.dcom.cell-relay are available via anonymous ftp to ftp.nwnet.net as: user-docs/cell-relay/archive/YY-MM.mbox where YY=year and MM=month. There are available in both compressed and normal formats. SUBJECT: A3) * Is there a parallel mailing list for this group? A direct mailing list has been setup which is a mirror of the USEnet newsgroup comp.dcom.cell-relay. To send mail TO the list, send it to: cell-relay-newsgroup@netnews.nwnet.net To un/subscribe, or send other notes to the list management, please use: cell-relay-request@cascade.nwnet.net cell-relay-newsgroup-request@cascade.nwnet.net SUBJECT: A4) What other mailing lists are related to ATM? There are three lists described below. One is for an IETF group working on the issue of IP over ATM. This work is on going and primarily focused on that task. General ATM questions and blue-skying are inappropriate and discouraged by the members on the list. To send mail TO the list, send it to: atm@sun.com To un/subscribe, or send other notes to the list management, use the address: atm-request@sun.com Another list is associated with the general problem of IP over large public networks. As with the ATM list above, its purpose is for an IETF working group. The same restrictions apply. To send mail TO the list, send it to: iplpdn@NRI.Reston.VA.US To un/subscribe, or send other notes to the list management, use the address: iplpdn-request@nri.reston.va.us Related to cell-relay technology is the Distributed Queueing mailing list. The distributed queueing list is intended for discussion about protocol design, variants, extensions, associated with the use of DQ for arbitrating access to cells in shared-medium cell-relay networks. To send mail TO the list, sent it to: dqlist@atri.curtin.edu.au To un/subscribe, or send other notes to the list management, use the address: dqlist-request@atri.curtin.edu.au ----------------------------------------------------------------------------- TOPIC: B) INDUSTRY FORUMS AND VENDOR INFORMATION ----------------------------------------------------------------------------- SUBJECT: B1) * How can I contact the ATM Forum? Similar to the Frame Relay Forum, the ATM Forum is an open public forum with over 300 contributing and auditing companies. Membership includes many international companies. Some companies also participate in ANSI T1S1 and other standards bodies. Those interested in joining the forum or needing additional information should contact the ATM Forum's secretariat, Interop Inc. The ATM Forum Information Line number is (415) 962-2585. Audit membership of the Forum is $1500/year. The fastest way is to send mail to Anne Ferris (Executive Director, ATM Forum) at Interop. Her e-mail is aferris@interop.com and her phone number is +1 415-962-2570. SUBJECT: B2) What vendors are working on ATM technology? It is tough to get a number on this. Increasingly there are companies with hardware they can demonstrate. More who have made product announcements. Many more who have stated product intentions. Some are building big central office switches, others smaller ones for the LAN market. Workstation vendors are working on ATM interface boards. Chip companies are working on ATM chip sets, etc. Previously (in 1992) there was an attempt here to list most of the major players in the ATM arena. This was possible in 1992. At this time *everyone* is doing something or paying lip service to ATM. It is simply not practical to keep a fair and accurate list here in this FAQ. SUBJECT: B3) What vendors are working on ATM hardware/chips? As with ATM technology vendors, the number of companies developing board level components is growing and soon will be hard to track. For starters, there is a group in North America working on low-cost SONET-based ATM physical layer chips for local nets using optics and twisted pair interfaces. This group is called the Saturn Development Group, and consists of PMC-Sierra, Sun Microsystems, Ungermann-Bass, Bell-Northern Research, Interphase, Optical Data Systems, SynOptics Communications, Newbridge, Themis Computer, BBN, MPR Tetltech, and the University of British Columbia. Contact PMC-Sierra for information: PMC-Sierra, Inc. 8999 Nelson Way Burnaby, BC Canada V5A 4B5 604-293-5755 Adaptive has designed an ATM/AAL chipset for use in equipment (computer, workstation, router, etc.) which connects to an ATM network. That chipset is now licenced to two chip manufacturers, TransSwitch and National Semiconductor. The TransSwitch product is called SARA and consists of a segmentation chip and reassembly chip. Together they can form the basis of an ATM/AAL controller which can process up to 8000 packets simultaneously at speeds of up to 155.52 Mbit/s. The chip set implements BISDN adaptation layers AAL3/4 and AAL5 in addition to supporting constant bit rate (CBR) traffic. Presumably the National Semiconductor product is similar. SUBJECT: B4) + What vendors are selling ATM test equipment? There exist already a number of vendors that hava ATM test equipment available. To name a few: 1. ATM-100, Wandel & Goltermann Tel.: +49 7121-862143 Fax.: +49 7121-862054 2. ATM Test Tool, Siemens AG Tel.: +49 30-386-4173 7077 Fax.: +49 30-386-7934 The Siemens tool is the same as the Wandel & Goltermann tool 3. HP 75000 Series 90 ATM Analyzer, contact your local Hewlett Packard sales office 4. HP Broadband Series protocol test system, IDACOM Telecom Division, Hewlett Packard (Canada) Ltd. Edmonton, Alberta Canada T6E 5R6 Tel.: +1-800-661-3868 +1-403-462-4545 Fax.: +1-403-462-4869 5. Alcatel 8643 ATM Traffic Generator Analyzer, and Alcatel 8640, Alcatel STR, Tel.: +41 1 4652860 Fax.: +41 1 4652319 or Alcatel Network Systems Inc., Richardson, TX Tel.: +1 214-996-5000 Fax.: +1 214-996-5409 This list is provided for information purposes only. There is no implied claim that this list is correct or complete. (Source: A. Gavras, ag@fokus.gmd.de) ----------------------------------------------------------------------------- TOPIC: C) ATM REFERENCES ----------------------------------------------------------------------------- SUBJECT: C1) What are some good getting started ATM references? Generally it is hard to pick up any communications related technical journal, conference, or trade publications and not find something about ATM. Most of what has been written in the 1985 through 1990 time frame primarily deals with the application of ATM to Broadband ISDN. These provide the foundation on which other applications of ATM have been based and therefore should not be over looked. Note that because of the pace of ATM standardization, reference books rapidly become out-of-date. Specifically, there have been major changes to the specification of the AALs subsequent to the publication of these books and articles. However, the following references do offer a good base of background information. --General: "Data Communications Special Guide", IEEE Spectrum, 8/91, p.22. o Hi-level overview of high-speed lans, wans, bisdn, atm, with glossary and bibliography. IEEE Communications Magazine, April 1992, VOL. 30, NO. 4 o This is a special issue with six articles on gigabit networks technology. "Cell Relay Switching", Data Communications, 9/91, p.58. o Looks at cell relay and switching in general, not just ATM. Rainer Handel and Manfred Huber. "Integrated Broadband Networks: An Introduction to ATM-Based Networks". Addison-Wesley, 1991. ISBN 0-201-54444-X. 230 pp. --ATM: "Overview of ATM Networks: functions and procedures", Computer Communications, 12/91, p.615. o Cell headers, bit definitions and the like. 33 References, including good list of CCITT recommendations. "Broadband ISDN and Asynchronous Transfer Mode (ATM)", IEEE Communications, 9/89. o Describes most of the jargon as well as the paradigm and unresolved issues. One point to note is that the article is fairly old (1989) and some things have changed. For example, the ATM cell headers described are no longer valid. "Asynchronous Transfer Mode: Solution for Broadband ISDN", Martin de Prycker, Ellis Horwood, New York, 1991. ISBN 0-13-053513-3 --SWITCH FABRICS: These papers offer a fast jump start on ATM switch architectures, design issues and tradeoffs. H. Ahmadi and W. Denzel, "A Survey of Modern High-Performance Switching Techniques", IEEE J on Selected Areas in Comm, Vol. 7, No. 7, Sept 1989, p. 1091-1103 F. Tobagi, "Fast Packet Switch Architectures for Broad-band Integrated Services Digital Networks", Proceedings of IEEE, Vol. 78, No. 1, Jan. 1990, p. 133-167 Joseph Y. Hui, "Switching and Traffic Theory for Integrated Broadband Networks", Kluwer Academic Publishers, 1991, ISBN 0-7923-9061-X o A back to basics text book explaining core switching concepts like batcher/banyon, clos, min, buffering, etc. SUBJECT: C2) Where/What is the "Network Compatible ATM for Local Network Applications" document? "Network Compatible ATM for Local Network Applications", V1.01, October 19, 1992. A proposal for a 150 Mb ATM LAN from Apple, Bellcore, Sun and Xerox. Available in standard postscript and compressed standard postscript from: thumper.bellcore.com: /pub/nclatm/nclatm.ps /pub/nclatm/nclatm.ps.Z ftp.apple.com: /pub/latm/nclatm.ps /pub/latm/nclatm.ps.Z parcftp.xerox.com: /pub/latm/nclatm.ps /pub/latm/nclatm.ps.Z SUBJECT: C3) Where are hosts with ATM related information? Here's a list of sites that that seem to cater to the ATM/broadband/real-time continuous-media crowd: cc-hw.bbn.com Rec_I_cls.ps, Rec_I_cls.hqx icsi-ftp.Berkeley.EDU Research, Continuous media wuarchive.wustl.edu Research, ATM Hardware datanet.tele.fi Standards drafts (see below) nsco.network.com HIPPI gregorio.stanford.edu IP Multicast ftp.nwnet.net cell-relay archives, etc. (see below) If you have ftp access, ftp to ftp.nwnet.net as user anonymous and look in /user-docs/cell-relay for: 1) In /user-docs/cell-relay/bib A bibliography of ATM research. This includes several to reference books and LOTS of citations. 2) In /user-docs/cell-relay/docs Some papers on ATM-related topics, standards, etc. 3) In /user-docs/cell-relay This FAQ list! 4) In /user-docs/cell-relay/conferences A bunch of files describing upcoming conferences !!!!!(Special thanks to Allen Robel, allen@nwnet.net)!!!!! Additionally, there are some draft standards, RFCs, technical papers, etc. on ATM available at datanet.tele.fi in the directory called /atm The collection includes draft AAL5 CCITT standards. SUBJECT: C4) How can I get the ATM Forum's Interface Specification? The ATM Forum has produced a document called the User-Network Interface specification. For those which are not ATM Forum members, hard copies are available (for use within the purchasing organization) for $25 from The ATM Forum Secretariat. The Secretariat can be reached at 01-214-963-2585, or The ATM Forum 480 San Antonio Rd, Ste. 100 Mountain View, CA 94040 Note, a revised UNI spec (Version 3.0) is being finalized, and will be published and available in early 3Q93. SUBJECT: C5) List of CCITT recommendations concerning ATM This list is provided for informational purposes only. No guarantee as to its completeness or correctness. Also, although they are not formally published, many of the following recommendations have been substantially updated since first published. If you can find a CCITT participant you should try to get the later versions, which are very close to frozen. The translated versions will be tabled at the Plenary Assembly in June 1993 for approval to publish. You can buy these on paper from the ITU: ITU Place des Nations CH-1211 Geneva 20 Switzerland. The fax number of the sales office is +41 22 730 5194. They are also available commercially from at least 2 sources in the U.S.: Information Gatekeepers in Boston, MA (1-800-323-1088) Phillipps Publishing (1-800-OMNICOM) Phillips usually has documents in stock & has fast delivery. =CCITT Recommendations Concerning ATM = E.164 Numbering plan for the ISDN era 08/91 G.707 Synchronous digital hierarchy bit rates 04/91 G.708 Network node interface for the synchronous 04/91 digital hierarchy G.709 Synchronous multiplexing structure 04/91 I.150 !! B-ISDN asynchronous transfer mode functional 04/91 characteristics I.211 !! B-ISDN service aspects 04/91 I.311 !! B-ISDN General Network aspects 04/91 I.321 B-ISDN protocol reference model and its 04/91 application I.327 B-ISDN functional architecture 04/91 I.330 ISDN numbering and addressing principles 1988 I.332 Numbering principles for interworking between 1988 ISDNs and dedicated networks with different numbering plans I.361 !! B-ISDN ATM layer specification 04/91 I.362 !! B-ISDN ATM adaptation layer (AAL) functional 04/91 description I.363 !! B-ISDN ATM adaptation layer (AAL) specification 04/91 I.413 B-ISDN user-network interface 04/91 I.432 B-ISDN user-network interface - Physical layer 04/91 specification I.610 !! OAM principles of the B-ISDN access 04/91 Q.11 bis Numbering plan for the ISDN era 1988 Q.11 ter Timetable for coordinated implementation of the 1988 full capability of the numbering plan for the ISDN era (Recommendation E.164) Q.931 ISDN user-network interface layer 3 1988 specification for basic call control Those marked with !! are being revised through the efforts of Study Group XVIII, Questions 2, and 13. Certainly the others are being updated as well. Also, there are two new Recommendations yet to be published: I.364 Temp Doc 58 (XVIII) 'Support of Broadband Connectionless Data Service on B-ISDN' I.371 Temp Doc 64 (XVIII) 'Traffic Control and Congestion Control in B-ISDN' SUBJECT: C6) Internet drafts from IETF working groups. Various work items of the IP over Asynchronous Transfer Mode Working group and other working groups of the IETF currently available include: draft-ietf-atm-address-resolve-00.txt draft-ietf-atm-address-translation-00.txt draft-ietf-atm-multipro-05.txt draft-ietf-atm-nbma-00.txt draft-ietf-iplpdn-directed_arp-01.txt Internet-Drafts are available by anonymous FTP. Internet-Drafts directories are located at: o East Coast (US) nnsc.nsf.net (128.89.1.178) o West Coast (US) ftp.nisc.sri.com (192.33.33.22) o Pacific Rim munnari.oz.au (128.250.1.21) o Europe nic.nordu.net (192.36.148.17) Internet-Drafts are also available by mail. Send a message to: mail-server@nisc.sri.com. In the body specify the filename requested. For example type: "SEND draft-ietf-atm-multipro-05.txt". SUBJECT: C7) ATM Tutorials. The following ATM tutorials are available via anonymous FTP. The focus of this paper is running IP over ATM, but there is an extensive tutorial on ATM, followed by discussion IP over ATM networks. Machine: ftp.magic.net Path: pub/magic File: ip-atm.ps (PostScript) ip-atm.ps.Z (Compressed PostScript) This paper is also a good starting point: Machine: datanet.tele.fi Path: atm File: atm-intro.txt Additionally there are reasonable tutorials available from two commercial communications companies. Specifically: "ATM In Private Networking", Anthony Alles, Hughes LAN Systems, Spring 1993. This was handed out at the Spring Interop for free. Contact information is Hughes LAN Systems, Inc., 1225 Charleston Road, Mountain View, CA 94043. Phone: (415) 966-7330 Fax: (415) 960-3738 (Note no guarentee that they will send out a copy.) "Asynchronous Transfer Mode: Bandwidth for the Future", Jim Lane, Telco Systems, 1992. To order a free copy simply call 1-800-447-2537 SUBJECT: C8) Contact information for ANSI T1S1 specifications. These documents can be obtained directly from the Secretariat for the ANSI T1 Telecommunications committee. Exchange Carriers Standard Association 1200 G. Street N.W. Suite 500 Washington, D.C. 20005 All orders and requests for quotations on prices must be in writing. Their FAS number is: (202) 393-5453 ----------------------------------------------------------------------------- TOPIC: D) ATM TECHNOLOGY QUESTIONS ----------------------------------------------------------------------------- SUBJECT: D1) What are the various ATM Adaptation layers? In order for ATM to support many kinds of services with different traffic characteristics and system requirements, it is necessary to adapt the different classes of applications to the ATM layer. This function is performed by the AAL, which is service-dependent. Four types of AAL were originally recommended by CCITT. Two of these have now been merged into one. Also, within the past year a fifth type of AAL has been proposed. Briefly the four ATM adaptation layers (AAL) have/are being defined: AAL1 - Supports connection-oriented services that require constant bit rates and have specific timing and delay requirements. Example are constant bit rate services like DS1 or DS3 transport. AAL2 - Supports connection-oriented services that do not require constant bit rates. In other words, variable bit rate applications like some video schemes. AAL3/4 - This AAL is intended for both connectionless and connection oriented variable bit rate services. Originally two distinct adaptation layers AAL3 and 4, they have been merged into a single AAL which name is AAL3/4 for historical reasons. AAL5 - Supports connection-oriented variable bit rate data services. It is a substantially lean AAL compaired with AAL3/4 at the expense of error recovery and built in retransmission. This tradeoff provides a smaller bandwidth overhead, simpler processing requirements, and reduced implementation complexity. Some organizations have proposed AAL5 for use with both connection-oriented and connectionless services. A recent document which describes these (except AAL2) with frame formats is: "Asynchronous Transfer Mode (ATM) and ATM Adaptation Layer (AAL) Protocols Generic Requirements", Bellcore Technical Advisory, TA-NWT-001113, Issue 1, August 1992. This can be obtained by writing to: Bellcore Document Registrar 445 South Street - Rm. 2J125 P.O. Box 1910 Morristown, NJ 07962-1910 SUBJECT: D2) Are ATM cells delivered in order? Yes. The ATM standards specify that all ATM cells will be delivered in order. Any switch and adaptation equipment design must take this into consideration. SUBJECT: D3) What do people mean by the term "traffic shaping"? Traffic shaping is forcing your traffic to conform to a certain specified behavior. Usually the specified behavior is a worst case or a worst case plus average case (i.e., at worst, this application will generate 100 Mbits/s of data for a maximum burst of 2 seconds and its average over any 10 second interval will be no more than 50 Mbit/s). Of course, understand that the specified behavior may closely match the way the traffic was going to behave anyway. But by knowing precisely how the traffic is going to behave, it is possible to allocate resources inside the network such that guarantees about availability of bandwidth and maximum delays can be given. (Source: Craig Partridge, craig@bbn.com) A variety of techniques have been investigated to implement traffic shaping. Reference the literature for keywords such as "leaky bucket", "congestion", "rate control", "policing". SUBJECT: D4) * What is happening with signalling standards for ATM? The Signaling Sub-Working Group of the ATM Forum's Technical Committee is nearing completion of its implementation agreement on signaling at the ATM UNI. The protocol is based on Q93B with extensions to support point-to-multipoint connections. Agreements on addressing specify the use of GOSIP-style NSAPs for the (SNPA) address of an ATM end-point at the Private UNI, and the use of either or both GOSIP-style NSAPs and/or E.164 addresses at the Public UNI. The agreements are being documented as part of an updated UNI specification. Many of the changes to the spec are now frozen however some sections are still open for comment. It is hoped that closure on the revised specification will take place at the next Forum meeting at the end of July. Additionally, the ANSI T1S1 as well as the CCITT sudygroup XI are concerned with ATM signalling. SUBJECT: D5) What is VPI and VCI? ATM is a connection orientated protocol and as such there is a connection identifier in every cell header which explicitly associates a cell with a given virtual channel on a physical link. The connection identifier consists of two sub-fields, the Virtual Channel Identifier (VCI) and the Virtual Path Identifier (VPI). Together they are used in multiplexing, demultiplexing and switching a cell through the network. VCIs and VPIs are not addresses. They are explicitly assigned at each segment (link between ATM nodes) of a connection when a connection is established, and remain for the duration of the connection. Using the VCI/VPI the ATM layer can asynchronously interleave (multiplex) cells from multiple connections. SUBJECT: D6) Why both VPI *and* VCI? The Virtual Path concept originated with concerns over the cost of controlling BISDN networks. The idea was to group connections sharing common paths through the network into identifiable units (the Paths). Network management actions would then be applied to the smaller number of groups of connections (paths) instead of a larger number of individual connections (VCI). Management here including call setup, routing, failure management, bandwidth allocation etc. For example, use of Virtual Paths in an ATM network reduces the load on the control mechanisms because the functions needed to set up a path through the network are performed only once for all subsequent Virtual Channels using that path. Changing the trunk mapping of a single Virtual Path can effect a route change for every Virtual Channel using that path. Now the basic operation of an ATM switch will be the same, no matter if it is handling a virtual path or virtual circuit. The switch must identify on the basis of the incomming cell's VPI, VCI, or both, which output port to forward a cell received on a given input port. It must also determine what the new values the VPI/VCI are on this output link, substituting these new values in the cell. SUBJECT: D7) * How come an ATM cell is 53 bytes anyway? ATM cells are standardized at 53 bytes because it seemed like a good idea at the time! As it turns out, during the standardization process a conflict arose within the CCITT as to the payload size within an ATM cell. The US wanted 64 byte payloads because it was felt optimal for US networks. The Europeans and Japanese wanted 32 payloads because it was optimal for them. In the end 48 bytes was chosen as a compromise. So 48 bytes payload plus 5 bytes header is 53 bytes total. The two positions were not chosen for similar applications however. US proposed 64 bytes taking into consideration bandwidth utilization for data networks and efficient memory transfer (length of payload should be a power of 2 or at least a multiple of 4). 64 bytes fit both requirements. Europe proposed 32 bytes taking voice applications into consideration. At cell sizes >= 152, there is a talker echo problem. Cell sizes between 32-152 result in listener echo. Cell sizes <= 32 overcome both problems, under ideal conditions. CCITT chose 48 bytes as a compromise. As far as the header goes, 10% of payload was perceived as an upper bound on the acceptable overhead, so 5 bytes was chosen. ----------------------------------------------------------------------------- TOPIC: E) TOPIC: ATM VS. XYZ TECHNOLOGY ----------------------------------------------------------------------------- SUBJECT: E1) How does ATM differ from SMDS? SMDS is a service offering interface from Bellcore. SMDS provides a datagram service, where a packet has about a 40-octet header plus up to 9188 octets of data. The packets themselves may or may not be transported within the network on top of a connection-oriented ATM service. SMDS uses E.164 (ISDN) addresses. Therefore SMDS is a connectionless packet switched *service*, not a cell-relay service. HOWEVER, the SMDS Subscriber Network Interface is currently defined to use IEEE 802.6 Distributed Queue Dual Bus (DQDB) access across the SMDS user-network interface. DQDB itself *is* a form of cell relay. The lower layers of SMDS fragment the packets into cells with a 5-octet header and 48-octet payload. The payload itself has a 2-octet header, 44-octets of data, plus a 2-octet trailer. An SMDS cell therefore is nearly identical in form to an AAL3/4 cell. Newsgroups: comp.dcom.cell-relay Subject: asd Summary: Followup-To: Distribution: Organization: University of Maryland, College Park Keywords: Cc: Newsgroups: comp.dcom.cell-relay Subject: revised FAQ Summary: comming soon From: carl@umd5.umd.edu (Carl Symborski) Followup-To: carl@umd5.umd.edu Distribution: Organization: University of Maryland, College Park Dosn't seem that much time has past already but I will be re-posting the FAQ list for this group shortly. There has been a lot of requests for the FAQ list lately. So I have made the subtile changes needed to comply with the posting rules for news.answers and related lists. This time the FAQ will be cross posted to these standard FAQ distribution lists. So we should have a wider distribution. Amazing as it seems, someone recently told me that she had downloaded the FAQ, read it, downloaded and/or obtained all the references, read them, and then got herself a job developing ATM products at a vendor. Not a bad testimony for a News "chat group"! :-) Cheers, Carl Symborski carl@umd5.umd.edu Newsgroups: comp.dcom.cell-relay Subject: revised FAQ Summary: comming soon From: carl@umd5.umd.edu (Carl Symborski) Followup-To: carl@umd5.umd.edu Distribution: Organization: University of Maryland, College Park Dosn't seem that much time has past already but I will be re-posting the FAQ list for this group shortly. There have been a lot of requests for the FAQ list lately. So I made the subtile changes needed to comply with the posting rules for news.answers and related lists. This time the FAQ will be cross posted to these standard FAQ distribution lists. So we should have a wider distribution. Amazing as it seems, someone recently told me that she had downloaded the FAQ, read it, downloaded and/or obtained all the references, read them, and then got herself a job developing ATM products at a vendor. Not a bad testimony for a News "chat group"! :-) Cheers, Carl Symborski carl@umd5.umd.edu Newsgroups: comp.dcom.cell-relay,comp.answers,news.answers Subject: comp.dcom.cell-relay FAQ: ATM, SMDS, and related technologies Summary: General information and answers to questions related to or seen in the comp.dcom.cell-relay group. Followup-To: comp.dcom.cell-relay Distribution: From: carl@umd5.umd.edu (Carl Symborski) Organization: University of Maryland, College Park Keywords: cell-relay, ATM, SMDS, communications Approved: news-answers-request@MIT.Edu cc: carl@umd5.umd.edu Archive-name: cell-relay-faq Last-modified: 1993/07/16 This article mostly contains general information but also answers to some Frequently Asked Questions (FAQ) which are related to or have been seen in comp.dcom.cell-relay. It is posted to provide information of general interest to both new and experienced readers. This list includes answers to questions, which are loosely grouped into categories. Questions marked with a "+" are new in this issue; those with significant changes of content since the last issue are marked by "*": A) TOPIC: COMP.DCOM.CELL-RELAY BASIC INFORMATION A1) What is the CELL-RELAY group? A2) What is the archive site for this group? A3) Is there a parallel mailing list for this group? A4) What other mailing lists are related to ATM? B) TOPIC: INDUSTRY FORUMS AND VENDOR INFORMATION B1)* How can I contact the ATM Forum? B2) What vendors are working on ATM technology? B3) What vendors are working on ATM hardware/chips? B4)+ What vendors are selling ATM test equipment? C) TOPIC: ATM REFERENCES C1) What are some good getting started ATM references? C2) Where/What is the "Network Compatible ATM for LANs" document? C3)* Where are hosts with ATM related information? C4) How can I get the ATM Forum's Interface Specification? C5) List of CCITT Recommendations concerning ATM. C6) Internet drafts from IETF working groups. C7) ATM Tutorials. C8) Contact information for ANSI T1S1 specifications. D) TOPIC: ATM TECHNOLOGY QUESTIONS D1) What are the various ATM Access layers? D2) Are ATM cells delivered in order? D3) What do people mean by the term "traffic shaping"? D4)* What is happening with signalling standards for ATM? D5) What is VPI and VCI? D6) Why both VPI *and* VCI? D7)* How come an ATM cell is 53 bytes anyway? E) TOPIC: ATM VS. XYZ TECHNOLOGY E1) How does ATM differ from SMDS? If you have suggestions or corrections for any of these answers or any additional information, please send them directly to carl@umd5.umd.edu; the information will be included in the next revision (or possibly the one after that). This posting is intended to be distributed every few months. New versions are archived along with other comp.dcom.cell-relay traffic on mythos.ucs.indiana.edu. See subject A2 for instructions to access the archive. The information contained herein has been gathered from a variety of sources. Most derived from a consensus of postings on the group. If you would like to claim responsibility for a particular item, please let me know. Enjoy! Carl Symborski carl@umd5.umd.edu ----------------------------------------------------------------------------- TOPIC: A) TOPIC: COMP.DCOM.CELL-RELAY BASIC INFORMATION ----------------------------------------------------------------------------- SUBJECT: A1) What is the CELL-RELAY group? The purpose of this group is to provide a forum for the submission of articles and inquiries dealing with networks using Cell Relay as a transport; including local, metropolitan, and wide area networks. The name cell-relay was chosen as a compromise over objections to the name "ATM" during the creation of this group. The acronym ATM in the context of this group stands for Asynchronous Transfer Mode, not Automatic Teller Machines or Adobe Type Manager. The term "cell" in cell-relay is taken to mean a small, fixed sized, information bearing unit that provides the foundation for transport and multiplexing of user traffic. This topic area is not related to cellular phones or intra-cellular organisms. SUBJECT: A2) What is the archive site for this group? The archives for comp.dcom.cell-relay are available via anonymous ftp to mythos.ucs.indiana.edu (129.79.17.52) as: pub/cell-relay/archive/YY-MM.mbox where YY=year and MM=month. There are available in both compressed and normal formats. SUBJECT: A3) Is there a parallel mailing list for this group? A direct mailing list has been setup which is a mirror of the USEnet newsgroup comp.dcom.cell-relay. To send mail TO the list, send it to: comp.dcom.cell-relay@news-relay.indiana.edu To un/subscribe, or send other notes to the list management, please use the address: cell-relay-request@mail-relay.indiana.edu SUBJECT: A4) What other mailing lists are related to ATM? There are three lists described below. One is for an IETF group working on the issue of IP over ATM. This work is on going and primarily focused on that task. General ATM questions and blue-skying are inappropriate and discouraged by the members on the list. To send mail TO the list, send it to: atm@sun.com To un/subscribe, or send other notes to the list management, use the address: atm-request@sun.com Another list is associated with the general problem of IP over large public networks. As with the ATM list above, its purpose is for an IETF working group. The same restrictions apply. To send mail TO the list, send it to: iplpdn@NRI.Reston.VA.US To un/subscribe, or send other notes to the list management, use the address: iplpdn-request@nri.reston.va.us Related to cell-relay technology is the Distributed Queueing mailing list. The distributed queueing list is intended for discussion about protocol design, variants, extensions, associated with the use of DQ for arbitrating access to cells in shared-medium cell-relay networks. To send mail TO the list, sent it to: dqlist@atri.curtin.edu.au To un/subscribe, or send other notes to the list management, use the address: dqlist-request@atri.curtin.edu.au ----------------------------------------------------------------------------- TOPIC: B) INDUSTRY FORUMS AND VENDOR INFORMATION ----------------------------------------------------------------------------- SUBJECT: B1) * How can I contact the ATM Forum? Similar to the Frame Relay Forum, the ATM Forum is an open public forum with over 300 contributing and auditing companies. Membership includes many international companies. Some companies also participate in ANSI T1S1 and other standards bodies. Those interested in joining the forum or needing additional information should contact the ATM Forum's secretariat, Interop Inc. The ATM Forum Information Line number is (415) 962-2585. Audit membership of the Forum is $1500/year. The fastest way is to send mail to Anne Ferris (Executive Director, ATM Forum) at Interop. Her e-mail is aferris@interop.com and her phone number is +1 415-962-2570. SUBJECT: B2) What vendors are working on ATM technology? It is tough to get a number on this. Increasingly there are companies with hardware they can demonstrate. More who have made product announcements. Many more who have stated product intentions. Some are building big central office switches, others smaller ones for the LAN market. Workstation vendors are working on ATM interface boards. Chip companies are working on ATM chip sets, etc. Previously (in 1992) there was an attempt here to list most of the major players in the ATM arena. This was possible in 1992. At this time *everyone* is doing something or paying lip service to ATM. It is simply not practical to keep a fair and accurate list here in this FAQ. SUBJECT: B3) What vendors are working on ATM hardware/chips? As with ATM technology vendors, the number of companies developing board level components is growing and soon will be hard to track. For starters, there is a group in North America working on low-cost SONET-based ATM physical layer chips for local nets using optics and twisted pair interfaces. This group is called the Saturn Development Group, and consists of PMC-Sierra, Sun Microsystems, Ungermann-Bass, Bell-Northern Research, Interphase, Optical Data Systems, SynOptics Communications, Newbridge, Themis Computer, BBN, MPR Tetltech, and the University of British Columbia. Contact PMC-Sierra for information: PMC-Sierra, Inc. 8999 Nelson Way Burnaby, BC Canada V5A 4B5 604-293-5755 Adaptive has designed an ATM/AAL chipset for use in equipment (computer, workstation, router, etc.) which connects to an ATM network. That chipset is now licenced to two chip manufacturers, TransSwitch and National Semiconductor. The TransSwitch product is called SARA and consists of a segmentation chip and reassembly chip. Together they can form the basis of an ATM/AAL controller which can process up to 8000 packets simultaneously at speeds of up to 155.52 Mbit/s. The chip set implements BISDN adaptation layers AAL3/4 and AAL5 in addition to supporting constant bit rate (CBR) traffic. Presumably the National Semiconductor product is similar. SUBJECT: B4) + What vendors are selling ATM test equipment? There exist already a number of vendors that hava ATM test equipment available. To name a few: 1. ATM-100, Wandel & Goltermann Tel.: +49 7121-862143 Fax.: +49 7121-862054 2. ATM Test Tool, Siemens AG Tel.: +49 30-386-4173 7077 Fax.: +49 30-386-7934 The Siemens tool is the same as the Wandel & Goltermann tool 3. HP 75000 Series 90 ATM Analyzer, contact your local Hewlett Packard sales office 4. HP Broadband Series protocol test system, IDACOM Telecom Division, Hewlett Packard (Canada) Ltd. Edmonton, Alberta Canada T6E 5R6 Tel.: +1-800-661-3868 +1-403-462-4545 Fax.: +1-403-462-4869 5. Alcatel 8643 ATM Traffic Generator Analyzer, and Alcatel 8640, Alcatel STR, Tel.: +41 1 4652860 Fax.: +41 1 4652319 or Alcatel Network Systems Inc., Richardson, TX Tel.: +1 214-996-5000 Fax.: +1 214-996-5409 This list is provided for information purposes only. There is no implied claim that this list is correct or complete. (Source: A. Gavras, ag@fokus.gmd.de) ----------------------------------------------------------------------------- TOPIC: C) ATM REFERENCES ----------------------------------------------------------------------------- SUBJECT: C1) What are some good getting started ATM references? Generally it is hard to pick up any communications related technical journal, conference, or trade publications and not find something about ATM. Most of what has been written in the 1985 through 1990 time frame primarily deals with the application of ATM to Broadband ISDN. These provide the foundation on which other applications of ATM have been based and therefore should not be over looked. Note that because of the pace of ATM standardization, reference books rapidly become out-of-date. Specifically, there have been major changes to the specification of the AALs subsequent to the publication of these books and articles. However, the following references do offer a good base of background information. --General: "Data Communications Special Guide", IEEE Spectrum, 8/91, p.22. o Hi-level overview of high-speed lans, wans, bisdn, atm, with glossary and bibliography. IEEE Communications Magazine, April 1992, VOL. 30, NO. 4 o This is a special issue with six articles on gigabit networks technology. "Cell Relay Switching", Data Communications, 9/91, p.58. o Looks at cell relay and switching in general, not just ATM. Rainer Handel and Manfred Huber. "Integrated Broadband Networks: An Introduction to ATM-Based Networks". Addison-Wesley, 1991. ISBN 0-201-54444-X. 230 pp. --ATM: "Overview of ATM Networks: functions and procedures", Computer Communications, 12/91, p.615. o Cell headers, bit definitions and the like. 33 References, including good list of CCITT recommendations. "Broadband ISDN and Asynchronous Transfer Mode (ATM)", IEEE Communications, 9/89. o Describes most of the jargon as well as the paradigm and unresolved issues. One point to note is that the article is fairly old (1989) and some things have changed. For example, the ATM cell headers described are no longer valid. "Asynchronous Transfer Mode: Solution for Broadband ISDN", Martin de Prycker, Ellis Horwood, New York, 1991. ISBN 0-13-053513-3 --SWITCH FABRICS: These papers offer a fast jump start on ATM switch architectures, design issues and tradeoffs. H. Ahmadi and W. Denzel, "A Survey of Modern High-Performance Switching Techniques", IEEE J on Selected Areas in Comm, Vol. 7, No. 7, Sept 1989, p. 1091-1103 F. Tobagi, "Fast Packet Switch Architectures for Broad-band Integrated Services Digital Networks", Proceedings of IEEE, Vol. 78, No. 1, Jan. 1990, p. 133-167 Joseph Y. Hui, "Switching and Traffic Theory for Integrated Broadband Networks", Kluwer Academic Publishers, 1991, ISBN 0-7923-9061-X o A back to basics text book explaining core switching concepts like batcher/banyon, clos, min, buffering, etc. SUBJECT: C2) Where/What is the "Network Compatible ATM for Local Network Applications" document? "Network Compatible ATM for Local Network Applications", V1.01, October 19, 1992. A proposal for a 150 Mb ATM LAN from Apple, Bellcore, Sun and Xerox. Available in standard postscript and compressed standard postscript from: thumper.bellcore.com: /pub/nclatm/nclatm.ps /pub/nclatm/nclatm.ps.Z ftp.apple.com: /pub/latm/nclatm.ps /pub/latm/nclatm.ps.Z parcftp.xerox.com: /pub/latm/nclatm.ps /pub/latm/nclatm.ps.Z SUBJECT: C3) Where are hosts with ATM related information? Here's a list of sites that that seem to cater to the ATM/broadband/real-time continuous-media crowd: cc-hw.bbn.com Rec_I_cls.ps, Rec_I_cls.hqx icsi-ftp.Berkeley.EDU Research, Continuous media wuarchive.wustl.edu Research, ATM Hardware datanet.tele.fi Standards drafts (see below) nsco.network.com HIPPI gregorio.stanford.edu IP Multicast ftp.nwnet.net cell-relay archives, etc. (see below) If you have ftp access, ftp to ftp.nwnet.net as user anonymous and look in /user-docs/cell-relay for: 1) In /user-docs/cell-relay/bib A bibliography of ATM research. This includes several to reference books and LOTS of citations. 2) In /user-docs/cell-relay/docs Some papers on ATM-related topics, standards, etc. 3) In /user-docs/cell-relay This FAQ list! 4) In /user-docs/cell-relay/conferences A bunch of files describing upcoming conferences !!!!!(Special thanks to Allen Robel, allen@nwnet.net)!!!!! Additionally, there are some draft standards, RFCs, technical papers, etc. on ATM available at datanet.tele.fi in the directory called /atm The collection includes draft AAL5 CCITT standards. SUBJECT: C4) How can I get the ATM Forum's Interface Specification? The ATM Forum has produced a document called the User-Network Interface specification. For those which are not ATM Forum members, hard copies are available (for use within the purchasing organization) for $25 from The ATM Forum Secretariat. The Secretariat can be reached at 01-214-963-2585, or The ATM Forum 480 San Antonio Rd, Ste. 100 Mountain View, CA 94040 Note, a revised UNI spec (Version 3.0) is being finalized, and will be published and available in early 3Q93. SUBJECT: C5) List of CCITT recommendations concerning ATM This list is provided for informational purposes only. No guarantee as to its completeness or correctness. Also, although they are not formally published, many of the following recommendations have been substantially updated since first published. If you can find a CCITT participant you should try to get the later versions, which are very close to frozen. The translated versions will be tabled at the Plenary Assembly in June 1993 for approval to publish. You can buy these on paper from the ITU: ITU Place des Nations CH-1211 Geneva 20 Switzerland. The fax number of the sales office is +41 22 730 5194. They are also available commercially from at least 2 sources in the U.S.: Information Gatekeepers in Boston, MA (1-800-323-1088) Phillipps Publishing (1-800-OMNICOM) Phillips usually has documents in stock & has fast delivery. =CCITT Recommendations Concerning ATM = E.164 Numbering plan for the ISDN era 08/91 G.707 Synchronous digital hierarchy bit rates 04/91 G.708 Network node interface for the synchronous 04/91 digital hierarchy G.709 Synchronous multiplexing structure 04/91 I.150 !! B-ISDN asynchronous transfer mode functional 04/91 characteristics I.211 !! B-ISDN service aspects 04/91 I.311 !! B-ISDN General Network aspects 04/91 I.321 B-ISDN protocol reference model and its 04/91 application I.327 B-ISDN functional architecture 04/91 I.330 ISDN numbering and addressing principles 1988 I.332 Numbering principles for interworking between 1988 ISDNs and dedicated networks with different numbering plans I.361 !! B-ISDN ATM layer specification 04/91 I.362 !! B-ISDN ATM adaptation layer (AAL) functional 04/91 description I.363 !! B-ISDN ATM adaptation layer (AAL) specification 04/91 I.413 B-ISDN user-network interface 04/91 I.432 B-ISDN user-network interface - Physical layer 04/91 specification I.610 !! OAM principles of the B-ISDN access 04/91 Q.11 bis Numbering plan for the ISDN era 1988 Q.11 ter Timetable for coordinated implementation of the 1988 full capability of the numbering plan for the ISDN era (Recommendation E.164) Q.931 ISDN user-network interface layer 3 1988 specification for basic call control Those marked with !! are being revised through the efforts of Study Group XVIII, Questions 2, and 13. Certainly the others are being updated as well. Also, there are two new Recommendations yet to be published: I.364 Temp Doc 58 (XVIII) 'Support of Broadband Connectionless Data Service on B-ISDN' I.371 Temp Doc 64 (XVIII) 'Traffic Control and Congestion Control in B-ISDN' SUBJECT: C6) Internet drafts from IETF working groups. Various work items of the IP over Asynchronous Transfer Mode Working group and other working groups of the IETF currently available include: draft-ietf-atm-address-resolve-00.txt draft-ietf-atm-address-translation-00.txt draft-ietf-atm-multipro-05.txt draft-ietf-atm-nbma-00.txt draft-ietf-iplpdn-directed_arp-01.txt Internet-Drafts are available by anonymous FTP. Internet-Drafts directories are located at: o East Coast (US) nnsc.nsf.net (128.89.1.178) o West Coast (US) ftp.nisc.sri.com (192.33.33.22) o Pacific Rim munnari.oz.au (128.250.1.21) o Europe nic.nordu.net (192.36.148.17) Internet-Drafts are also available by mail. Send a message to: mail-server@nisc.sri.com. In the body specify the filename requested. For example type: "SEND draft-ietf-atm-multipro-05.txt". SUBJECT: C7) ATM Tutorials. The following ATM tutorials are available via anonymous FTP. The focus of this paper is running IP over ATM, but there is an extensive tutorial on ATM, followed by discussion IP over ATM networks. Machine: ftp.magic.net Path: pub/magic File: ip-atm.ps (PostScript) ip-atm.ps.Z (Compressed PostScript) This paper is also a good starting point: Machine: datanet.tele.fi Path: atm File: atm-intro.txt Additionally there are reasonable tutorials available from two commercial communications companies. Specifically: "ATM In Private Networking", Anthony Alles, Hughes LAN Systems, Spring 1993. This was handed out at the Spring Interop for free. Contact information is Hughes LAN Systems, Inc., 1225 Charleston Road, Mountain View, CA 94043. Phone: (415) 966-7330 Fax: (415) 960-3738 (Note no guarentee that they will send out a copy.) "Asynchronous Transfer Mode: Bandwidth for the Future", Jim Lane, Telco Systems, 1992. To order a free copy simply call 1-800-447-2537 SUBJECT: C8) Contact information for ANSI T1S1 specifications. These documents can be obtained directly from the Secretariat for the ANSI T1 Telecommunications committee. Exchange Carriers Standard Association 1200 G. Street N.W. Suite 500 Washington, D.C. 20005 All orders and requests for quotations on prices must be in writing. Their FAS number is: (202) 393-5453 ----------------------------------------------------------------------------- TOPIC: D) ATM TECHNOLOGY QUESTIONS ----------------------------------------------------------------------------- SUBJECT: D1) What are the various ATM Adaptation layers? In order for ATM to support many kinds of services with different traffic characteristics and system requirements, it is necessary to adapt the different classes of applications to the ATM layer. This function is performed by the AAL, which is service-dependent. Four types of AAL were originally recommended by CCITT. Two of these have now been merged into one. Also, within the past year a fifth type of AAL has been proposed. Briefly the four ATM adaptation layers (AAL) have/are being defined: AAL1 - Supports connection-oriented services that require constant bit rates and have specific timing and delay requirements. Example are constant bit rate services like DS1 or DS3 transport. AAL2 - Supports connection-oriented services that do not require constant bit rates. In other words, variable bit rate applications like some video schemes. AAL3/4 - This AAL is intended for both connectionless and connection oriented variable bit rate services. Originally two distinct adaptation layers AAL3 and 4, they have been merged into a single AAL which name is AAL3/4 for historical reasons. AAL5 - Supports connection-oriented variable bit rate data services. It is a substantially lean AAL compaired with AAL3/4 at the expense of error recovery and built in retransmission. This tradeoff provides a smaller bandwidth overhead, simpler processing requirements, and reduced implementation complexity. Some organizations have proposed AAL5 for use with both connection-oriented and connectionless services. A recent document which describes these (except AAL2) with frame formats is: "Asynchronous Transfer Mode (ATM) and ATM Adaptation Layer (AAL) Protocols Generic Requirements", Bellcore Technical Advisory, TA-NWT-001113, Issue 1, August 1992. This can be obtained by writing to: Bellcore Document Registrar 445 South Street - Rm. 2J125 P.O. Box 1910 Morristown, NJ 07962-1910 SUBJECT: D2) Are ATM cells delivered in order? Yes. The ATM standards specify that all ATM cells will be delivered in order. Any switch and adaptation equipment design must take this into consideration. SUBJECT: D3) What do people mean by the term "traffic shaping"? Traffic shaping is forcing your traffic to conform to a certain specified behavior. Usually the specified behavior is a worst case or a worst case plus average case (i.e., at worst, this application will generate 100 Mbits/s of data for a maximum burst of 2 seconds and its average over any 10 second interval will be no more than 50 Mbit/s). Of course, understand that the specified behavior may closely match the way the traffic was going to behave anyway. But by knowing precisely how the traffic is going to behave, it is possible to allocate resources inside the network such that guarantees about availability of bandwidth and maximum delays can be given. (Source: Craig Partridge, craig@bbn.com) A variety of techniques have been investigated to implement traffic shaping. Reference the literature for keywords such as "leaky bucket", "congestion", "rate control", "policing". SUBJECT: D4) * What is happening with signalling standards for ATM? The Signaling Sub-Working Group of the ATM Forum's Technical Committee is nearing completion of its implementation agreement on signaling at the ATM UNI. The protocol is based on Q93B with extensions to support point-to-multipoint connections. Agreements on addressing specify the use of GOSIP-style NSAPs for the (SNPA) address of an ATM end-point at the Private UNI, and the use of either or both GOSIP-style NSAPs and/or E.164 addresses at the Public UNI. The agreements are being documented as part of an updated UNI specification. Many of the changes to the spec are now frozen however some sections are still open for comment. It is hoped that closure on the revised specification will take place at the next Forum meeting at the end of July. Additionally, the ANSI T1S1 as well as the CCITT sudygroup XI are concerned with ATM signalling. SUBJECT: D5) What is VPI and VCI? ATM is a connection orientated protocol and as such there is a connection identifier in every cell header which explicitly associates a cell with a given virtual channel on a physical link. The connection identifier consists of two sub-fields, the Virtual Channel Identifier (VCI) and the Virtual Path Identifier (VPI). Together they are used in multiplexing, demultiplexing and switching a cell through the network. VCIs and VPIs are not addresses. They are explicitly assigned at each segment (link between ATM nodes) of a connection when a connection is established, and remain for the duration of the connection. Using the VCI/VPI the ATM layer can asynchronously interleave (multiplex) cells from multiple connections. SUBJECT: D6) Why both VPI *and* VCI? The Virtual Path concept originated with concerns over the cost of controlling BISDN networks. The idea was to group connections sharing common paths through the network into identifiable units (the Paths). Network management actions would then be applied to the smaller number of groups of connections (paths) instead of a larger number of individual connections (VCI). Management here including call setup, routing, failure management, bandwidth allocation etc. For example, use of Virtual Paths in an ATM network reduces the load on the control mechanisms because the functions needed to set up a path through the network are performed only once for all subsequent Virtual Channels using that path. Changing the trunk mapping of a single Virtual Path can effect a route change for every Virtual Channel using that path. Now the basic operation of an ATM switch will be the same, no matter if it is handling a virtual path or virtual circuit. The switch must identify on the basis of the incomming cell's VPI, VCI, or both, which output port to forward a cell received on a given input port. It must also determine what the new values the VPI/VCI are on this output link, substituting these new values in the cell. SUBJECT: D7) * How come an ATM cell is 53 bytes anyway? ATM cells are standardized at 53 bytes because it seemed like a good idea at the time! As it turns out, during the standardization process a conflict arose within the CCITT as to the payload size within an ATM cell. The US wanted 64 byte payloads because it was felt optimal for US networks. The Europeans and Japanese wanted 32 payloads because it was optimal for them. In the end 48 bytes was chosen as a compromise. So 48 bytes payload plus 5 bytes header is 53 bytes total. The two positions were not chosen for similar applications however. US proposed 64 bytes taking into consideration bandwidth utilization for data networks and efficient memory transfer (length of payload should be a power of 2 or at least a multiple of 4). 64 bytes fit both requirements. Europe proposed 32 bytes taking voice applications into consideration. At cell sizes >= 152, there is a talker echo problem. Cell sizes between 32-152 result in listener echo. Cell sizes <= 32 overcome both problems, under ideal conditions. CCITT chose 48 bytes as a compromise. As far as the header goes, 10% of payload was perceived as an upper bound on the acceptable overhead, so 5 bytes was chosen. ----------------------------------------------------------------------------- TOPIC: E) TOPIC: ATM VS. XYZ TECHNOLOGY ----------------------------------------------------------------------------- SUBJECT: E1) How does ATM differ from SMDS? SMDS is a service offering interface from Bellcore. SMDS provides a datagram service, where a packet has about a 40-octet header plus up to 9188 octets of data. The packets themselves may or may not be transported within the network on top of a connection-oriented ATM service. SMDS uses E.164 (ISDN) addresses. Therefore SMDS is a connectionless packet switched *service*, not a cell-relay service. HOWEVER, the SMDS Subscriber Network Interface is currently defined to use IEEE 802.6 Distributed Queue Dual Bus (DQDB) access across the SMDS user-network interface. DQDB itself *is* a form of cell relay. The lower layers of SMDS fragment the packets into cells with a 5-octet header and 48-octet payload. The payload itself has a 2-octet header, 44-octets of data, plus a 2-octet trailer. An SMDS cell therefore is nearly identical in form to an AAL3/4 cell. ÿ