[codec] it MUST NOT exceed 1275 bytes?

["Christian Hoene" <[e-mail]>]

Hi,

I am reading "draft-ietf-codec-opus-07", chapter 3 page 11:

   No length is transmitted for the last frame in a VBR packet, or any
   of the frames in a CBR packet, as it can be inferred from the total
   size of the packet and the size of all other data in the packet.
   However, it MUST NOT exceed 1275 bytes, to allow for repacketization
   by gateways, conference bridges, or other software.

I do not understand:

1) What must not exceed 1275 bytes, the total length of the payload or the
length of the last VBR frame?

2) What are the calculations behind 1275?

3) The requirement "Repacketization by gateways, conference bridges, or
other software." is not listed in the requirements draft. As I still believe
in the end-to-end principle, I also do not see the need for this
requirement. Why do you need an Opus-to-Opus gateway if have can have
end-to-end or if you can use a TURN server? 
BTW conference bridges mix audio streams.

Thanks for explaining me.

 Christian

----------------------------------------------------------------------------
-----
Dr.-Ing. Christian Hoene, University of Tübingen, Computer Science, Chair of
Communication Networks, Research Group Interactive Communication Systems
(ICS)
Sand 13, 72076 Tübingen, Germany, Tel [phone],
www.net.uni-tuebingen.de