Subject: Announcement Times

From: [email-masked] (Kevin C. Almeroth)
Date: Tue, 25 Apr 1995 12:37:13 -0400

Mark,

   One of the issues that came up at the IETF was that of background
bandwidth caused by sd advertisements being broadcast.  My opinion is
that the group essentially said these advertisements don't require that
much bandwidth.  For these reasons, we decided to leave in the field
identifiers, and to keep the fields as text.

   However, an issue that I haven't seen anything about is that of 
time-between-advertisements.  Should anything be specified in the standard 
about the frequency of announcements, limits on advertisement lengths, etc?
There are several policies which could be adopted to minimize bandwidth
and still maintain an effective announcement frequency.

Kevin Almeroth ([email-masked])
Networking and Telecommunications Research Group
College of Computing, Georgia Institute of Technology
http://www.cc.gatech.edu/computing/Telecomm/people/Phd/kevin/kevin.html

---

From: Mark Handley <[email-masked]>
Date: Tue, 25 Apr 95 17:59:35 +0100

>identifiers, and to keep the fields as text.

Correct.  Sending them in a binary format would save ~50% of the
bandwidth.  However, that's not really important compared to the other
scaling issues involved.

>and still maintain an effective announcement frequency.

Actually, there is a section in the current draft on announcement
frequencies.  The current section describes what my version of sd is
designed to do, but is not what sd does right now.  However, the
general principle is the same.

There are a number of optimisations on this that we could consider.
For instance, the announcement rate could depend on whether the
session is active or not, and if its not active, it could depend on
the time since until the session.  It could also start by being more
frequently advertised when the session is created, and then backoff
down to a lower rate until the session starts.

However, a lot of this depends on the characteristics of the
distribution architecture, which is not really discussed properly in
the current draft.  This is one reason why I'd like to split the draft
into an SDP draft and an SDP distribution draft.  

Mark