Subject: [AVT] RFC2833 (and draft) question regarding packet format

From: "Wong, David" <[email-masked]>
Date: Fri, 30 Aug 2002 14:19:42 -0400

I wanted to make sure that my understanding of the packet formats for named
events is correct.
 
In section 3.6 of RFC2833 (and the draft), there is the statement "If there
has been no new event in the last interval, the event SHOULD be
retransmitted three times or until the next event is recognized." Say an
event for the digit "9" is detected and is to be transmitted. Does this mean
that the packet containing the event for digit 9 should be sent out 3 times,
without incrementing the RTP timestamp or changing the RTP header, but
perhaps only changing the identifier in the IP header? How strictly should
this be interpreted (ie. would this be interpreted as a "must" in this
case).
 
In section 3.7, there is the statement "During an event, the RTP event
payload format provides incremental updates on the event." Sections 3.8 and
3.9 contain an example of the digits "911" being dialed. Should the format
of the packet described in Figure 2 be taken as a "must" for the format? Ie.
as long as the time offset can fit into 14 bits, that information should be
included in the packet?
 
I also have a question for transmitting both in-band and out-of-band
information. Take the example of "911" in the RFC/draft with the pauses in
between the digits. If audio clips for the digits are to be transmitted in
addition to named events, then the audio clips would be the primary encoding
and the named events the redundant info? Would it be correct to send out a
silence audio clip between the digit audio clips?

David Wong
Software Engineer
Communications Infrastructure Test Group

p| 978.661.1241 f| 978.988.0148
email | [email-masked]
205 Lowell Street | Wilmington, MA | 01887

E M P I R I X
http://www.empirix.com <http://www.empirix.com/>