From: ken@cs.cornell.edu (Ken Birman)
Subject: Re: Groups in a mixed media setting
Organization: Cornell Univ. CS Dept, Ithaca NY 14853
Date: Tue, 26 Jan 1993 21:43:28 GMT

In article <1993Jan26.165131.28041@comp.lancs.ac.uk> nigel@comp.lancs.ac.uk (Nigel Davies) writes:
>...
>1) I seem to remember that there was some talk of collaboration between APM
>   (the developers of ANSAware) and Cornell a year or so ago. Did this ever
>   come to anything ? (The most recent version of ANSAware still does not
>   provide support for groups so I am guessing not ...)

When ISIS and APM became commercial, they sort of went different directions.
We are now working on extending ISIS into a Corba-complient environment,
which we call RDOM, but have not been working directly with ANSA/APM, although
the ASNA ideas certainly have had a huge impact on our thinking.

>2) It is some time since I have seen any ISIS documentation. Does ISIS support
>   hierarchies of groups, and if so what sort of event ordering guarantees
>   does it provide ?

Yes; I'll ask Robert or Brad to answer on this because they did the work.

>3) One of the reasons for using the group abstraction for describing multicast
>   /multidrop continuous media configurations was to provide the programmer
>   with similar tools for carrying out both invocation and continuous media
>   transmission. However, judging by the recent postings there may not be a 
>   requirement for multidrop invocation groups.

We are more and more interested in this.  Right now, you do this (you can do
this) by binding each of a set of groups to different transport protocols.
For example, the ipmcast code I just added to Isis is a "transport" for
multicast messages.  One could bind some groups to video transport, some to
audio, some to packets.  Isis then would synchronize between the groups,
so that you see what you would expect in terms of ordering properties.
In Horus we are carrying this even further -- but starting with ISIS V3.0.8
where the isis_transport stuff is really solid and used, you could get the
same effect.  

The other side of the coin, though, is that this raises a huge number of
hard technical questions and much research is needed.  The whole issue of
mixing real-time and non-real-time software (as one would be doing here)
is in need of much study and thought.  So, we may have more of a framework
for solving such problems then a solution, at first.

One hope is that we may be able to draw on technology from INESC, which
has more background in such mixed mode systems, and we are trying to
standardize interfaces now so that INESC software and ISIS software can
inter-operate.  INESC has done a lot in these sorts of multimedia and
real-time communication problems, and we would like a way to benefit without
redoing the same work.  The hope is that in our new system, Horus, we
will be able to do so.
>
>4) We are now considering an implementation of the platform using mobile
>   radio as the communications medium (supporting a _very_ limited range of
>   media types). Does anyone have any experiences in implementing group 
>   protocols over a radio link ?  More generally, does anyone know of any 
>   distributed systems work aimed at such an environment ?

Xerox Parc is doing work on this.  The company that sells Isis plans to
explore this area too, and also ATM communications.  I am especially
interested in hand-held devices and how they might be connected to "news".
But, we don't have anything concrete here yet.  In fact, I think the
devices out there right now are still just a little too weak to use for
something really fancy.  But, they are close...
-- 
Kenneth P. Birman                              E-mail:  ken@cs.cornell.edu
4105 Upson Hall, Dept. of Computer Science     TEL:     607 255-9199 (office)
Cornell University Ithaca, NY 14853 (USA)      FAX:     607 255-4428
Newsgroups: comp.sys.isis