From: rasp@xlnt.com (Ron Perloff)
Newsgroups: comp.dcom.lans.fddi
Subject: Re: FDDI vs. ATM
Date: 21 Aug 92 01:58:22 GMT
Organization: xdi

In article <1992Aug19.172633.26728@cbfsb.cb.att.com> 1841hss@cbnewsb.cb.att.com
(anil.verma) writes:
>I want to know about the pros/cons of FDDI vs. ATM.  In my opinion, ATM 
>can provide more bandwidth that makes it suitable for Wide Area Links
>but this is not an advantage in the LAN environment because computers 
>today can't even exceed FDDI throughput limits.  Also, are there any
>ATM cards available for computers like the prolifiration of FDDI cards?
>Actually, the prices for FDDI cards are getting lower all the time -
>something that was always one of my big complaints about FDDI.
>
>Please post your views on FDDI vs. ATM or Email me directly.
>
>TIA
>
>Anil Verma
>Email: attmail!averma
>
In my view, the choice is between a mature FDDI and a newer,
potentially more capable ATM.

FDDI is a fast LAN technology with interoperable adaptor cards
and hub products available from a wide variety of sources. Of the
standards which define the protocol, the PMD, PHY and MAC documents
are accepted standards and the latest draft of (7.2) SMT is very close
to that which will ultimately be adopted. Interoperability has been
demonstrated time and time again.

FDDI offers synchronous service which is not to be confused with
isochronous service. Synchronous service guarantees bandwidth to
individual stations, but the delivery can be jittery. Isochronous
service which is available in the not-yet-standardized FDDI-II
and ATM guarantees bandwidth and low-jitter delivery. That feature
is helpful for transmitting real-time voice and video.

Please note that you do not need isochronous delivery for all voice
and video applications. Take a look at any macintosh to see that you
can send voice and video across any network quite nicely as long
as you do not need to access it directly from the network. Applications
such as video conferencing, however, work much better with the low jitter
isochronous service.

FDDI signalling is not directly compatible with public networks. To leave
a facility, you must bridge, route or gateway onto the public network
or you must own the fiber which connects you to another facility.

If you are developing you own adaptor or hub product you have AMD, Motorola
and National chip sets from which to select plus a PHY chip from AT&T.
Sumitomo also has a chip set that may not be universally available.

ATM is a relatively new protocol which employs signalling directly
compatible with the public networks. Some chip sets are becoming available
as are a few switch products. Still, however, there are a number of services
one expects to find in LANs that ATM does not yet implement. Broadcast
and multicast service, and address discovery protocols which rely on them,
have not yet been worked out. Further, the participants in the ATM Forum
have not yet agreed on a common, interoperable signalling mechanism.

ATM is potentially an excellent protocol, but will require some time to
reach the same level of completion that FDDI has currently achieved.
If you must have the features it offers, you must either go with one of
the existing proprietary solutions or wait for the protocol to mature.
If FDDI meets your needs, then buy it. You have no reason to wait.

Ronald S. Perloff     rasp@xlnt.com
XLNT Designs, Inc.  (XDI)
15050 Avenue of Science
Suite 106
San Diego, CA  92128
619 487 9320   -   FAX: 619 487 9768