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From: [e-mail] (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
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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 [e-mail];
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
[e-mail]


-----------------------------------------------------------------------------
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:

    [e-mail]

To un/subscribe, or send other notes to the list management, please use:

        [e-mail]
        [e-mail]


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:

    [e-mail]

To un/subscribe, or send other notes to the list management, use the address:

    [e-mail]

    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:

    [e-mail]

To un/subscribe, or send other notes to the list management, use the address:

    [e-mail]

    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:

    [e-mail]

To un/subscribe, or send other notes to the list management, use the address:

    [e-mail]


-----------------------------------------------------------------------------
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 [phone].  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 [e-mail] and her phone
number is [phone].



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.: [phone]
    Fax.: [phone]

2. ATM Test Tool, Siemens AG
    Tel.: [phone]
                     7077
    Fax.: [phone]
    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.: [phone]
          [phone]
    Fax.: [phone]

5. Alcatel 8643 ATM Traffic Generator Analyzer, and Alcatel 8640, Alcatel STR,
    Tel.: [phone]
    Fax.: [phone]
    or Alcatel Network Systems Inc., Richardson, TX
    Tel.: [phone]
    Fax.: [phone]

This list is provided for information purposes only.  There is no implied
claim that this list is correct or complete.

(Source: A. Gavras, [e-mail])


-----------------------------------------------------------------------------
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, [e-mail])!!!!!

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 [phone].  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:
[e-mail].  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: [phone]  Fax: [phone]  (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: [phone]


-----------------------------------------------------------------------------
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, [e-mail])

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: [e-mail] (Carl Symborski)
Followup-To: [e-mail]
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
[e-mail]
Newsgroups: comp.dcom.cell-relay
Subject: revised FAQ
Summary: comming soon
From: [e-mail] (Carl Symborski)
Followup-To: [e-mail]
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
[e-mail]
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: [e-mail] (Carl Symborski)
Organization: University of Maryland, College Park
Keywords: cell-relay, ATM, SMDS, communications
Approved: [e-mail]
cc: [e-mail]

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 [e-mail];
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
[e-mail]


-----------------------------------------------------------------------------
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:

    [e-mail]

To un/subscribe, or send other notes to the list management, please use the
address:

    [e-mail]


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:

    [e-mail]

To un/subscribe, or send other notes to the list management, use the address:

    [e-mail]

    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:

    [e-mail]

To un/subscribe, or send other notes to the list management, use the address:

    [e-mail]

    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:

    [e-mail]

To un/subscribe, or send other notes to the list management, use the address:

    [e-mail]


-----------------------------------------------------------------------------
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 [phone].  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 [e-mail] and her phone
number is [phone].



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.: [phone]
    Fax.: [phone]

2. ATM Test Tool, Siemens AG
    Tel.: [phone]
                     7077
    Fax.: [phone]
    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.: [phone]
          [phone]
    Fax.: [phone]

5. Alcatel 8643 ATM Traffic Generator Analyzer, and Alcatel 8640, Alcatel STR,
    Tel.: [phone]
    Fax.: [phone]
    or Alcatel Network Systems Inc., Richardson, TX
    Tel.: [phone]
    Fax.: [phone]

This list is provided for information purposes only.  There is no implied
claim that this list is correct or complete.

(Source: A. Gavras, [e-mail])


-----------------------------------------------------------------------------
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, [e-mail])!!!!!

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 [phone].  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:
[e-mail].  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: [phone]  Fax: [phone]  (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: [phone]


-----------------------------------------------------------------------------
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, [e-mail])

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.


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TOPIC:     E)   TOPIC: ATM VS. XYZ TECHNOLOGY
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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.