Subject: G.723.1

From: Tzvi Kasten <[email-masked]>
Date: Sun, 25 Jun 2000 09:27:00 +0200

All,

In H.225.0 Annex F ( audio packetization) it is written in the text: 

"The first packet of a talkspurt (first packet after a silence period) is
distinguished by setting the marker bit in the RTP data header"

Would this indicate that the packet needs to start with the talkspurt frame
or could it there be several silence frames in the packet and then the first
not silence frame and that the marker bit does not necessarily refer to the
first frame in the packet?

How has this generally been interpreted?

Thanks

Tzvi Kasten
Networking Infrastructures Group Manager
Research & Development
VCON Ltd.
Tel: 09-9590020 ( 972-9-959-0020)
Email: [email-masked]
http://www.vcon.com

---

From: Mark Handley <[email-masked]>
Date: Sun, 25 Jun 2000 11:04:22 -0700

>first frame in the packet?

The general idea behind the marker bit with audio is as a hint to the
receiver that this is a good time to adjust the adaptive playout
buffer.

RFC 1890 says:
   For applications which send no packets during silence, the first
   packet of a talkspurt (first packet after a silence period) is
   distinguished by setting the marker bit in the RTP  data header.
   Applications without silence suppression set the bit to zero.

If you have a codec that inserts explicit silence frames so that
there's a continuous packet stream even when the sender is not
talking, then I don't think it makes sense to ever set the marker bit.

Cheers,
	Mark