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Re: [Ccrtp-devel] Payload padding
From: |
Federico Montesino Pouzols |
Subject: |
Re: [Ccrtp-devel] Payload padding |
Date: |
Mon, 10 Jan 2005 17:33:21 +0100 |
User-agent: |
Mutt/1.5.6+20040907i |
Hi,
you are right, padding is not mandatory for data packets. It is a bug
in ccrtp. I would propose a new method, say setPadding, with an
integer parameter 'p' to set padding to a multiple of 'p'. 0 (no
padding) would be a good default value.
Thanks for spotting this.
On Sat, Jan 08, 2005 at 04:50:46PM +0100, Michel de Boer wrote:
> 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
>
>
>
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