[Ccrtp-devel] Payload padding

[Michel de Boer]

Hi,

I am using ccrtp 1.1.2 to send and receive a GSM encoded voice stream.
The size
of a single GSM encoded payload is 33 bytes. I noticed that ccrtp adds 3
bytes padding
to make the payload a multiple of 4 and sets the P-bit in the RTP headers.

I have seen this topic before in this mailing list and then it was said
that the RFC requires
the padding. That is not true.

RFC 3550 only requires padding to a multiple of 4 for header
information. Payloads do not
have to be padded. The padding of a payload may only be needed for
certain encryption
schemes. Here is what RFC 3550 says:

  padding (P): 1 bit
     If the padding bit is set, the packet contains one or more
     additional padding octets at the end which are not part of the
     payload.  The last octet of the padding contains a count of how
     many padding octets should be ignored, including itself.  Padding
     may be needed by some encryption algorithms with fixed block sizes
     or for carrying several RTP packets in a lower-layer protocol data
     unit.

For my own purpose I have disabled padding in my own copy of ccrtp in
the RTPPacket
constructor.

I think it would be good if payload padding would be optional in a next
version. By
default I would prefer the padding to be disabled.

Regards,
Michel