Hi,
the question will be regarding Lync Siren 7 on 16 kbps RTP payload format, as its size (size of RTP payload) does not fit the calculated frame size for Siren 7 codec on sample rate 16000 / bitrate 16000.
In this case, expected payload size is 40 octets, while the real payload size is different. 
Corresponding RTP packets as sniffed from Lync session via Wireshark show this.

Siren 7 is frame-based codec.

Due to standard,
coded octets should be aligned to RTP payload octets, and RTP payload should contain 1 or more coded frames. Frames cannot be split between RTP packets. So, Lync Siren 7 payload contains some extra information, and so the question is about payload format. 

Your problem is related about the Siren 7 itself, I recommend that you consultant Polycom experts.

Check the following link that may help you:

http://www.polycom.com/company/about-us/technology/siren/siren-faq.html#faq28

Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.

Hi, thank you for your answer.

I will try to describe the issue in more details.
1. Polycom FAQ mentioned in the link http://www.polycom.com/company/about-us/technology/siren/siren-faq.html
- was the start point of our integration on Siren codec.

2. As for RTP payload, Polycom refers to RFC 5577 on its format as stated in the link you mentioned
What is the total data rate when Siren is encapsulated within RTP? 
http://www.polycom.com/company/about-us/technology/siren/siren-faq.html#faq28

and RFC 5577 (RTP Payload Format for ITU-T Recommendation G.722.1) http://tools.ietf.org/html/rfc5577#section-3.2

states following:

"For the purposes of packetizing the bit stream in RTP, it is only necessary to consider the sequence of bits as output by the G.722.1 encoder and to present the same sequence to the decoder.  The payload format  described here maintains this sequence."

3. On 16kbps bitrate, 16000 sample rate (in use in MS Lync conference) - Siren 7 (Polycom) encoder produces frames of size = 40 octets

Heres the formula Polycom G.722.1 / Siren uses to get the Siren coded frame size for current bitrate:

Bytes per frame = bitrate / 50  / 8 = 16000 / 50 / 8 = 40 octets

4. Windows Live Messenger used Siren 7 to code voice also. Its RTP packets contain strictly 40 octets of payload when Siren is in use.

5. MS Lync uses Siren 7 in conference scenarios under several conditions.
And it produces RTP payload of variable size (51 and 57 octets, 51 - in case if were no contributing sources, 57 - is there were 2 contributing sources).

This means that MS Lync as a Polycom codec client, supplies the overhead into the RTP payload basing on some internal algorithms. It's up to client how to present the coded information during the transmission, meant, it can be encrypted, or Forward Error Correction algorithms may be applied on data before to transmit it. But, definitely, Lync changes coded data before to transmit it as it has from 11 to 17 octets overhead.

It's the client's (Lync) changes and they are not related to Polycom codec,

as codec simply produces the output of fixed size and it does not compose either Ethernet / IP / RTP headers and payloads.

Please, help us to resolve this issue with RTP payload format, it's really important for us.

 

Hi,

If you require more in-depth level of support. Please visit the below link to see the various paid support options that are available to better meet your needs.
http://support.microsoft.com/default.aspx?id=fh;en-us;offerprophone

This thread is marked as resolved.
For those who encounter the same issue:
The reason for extra 11 bytes in payload is 11 bytes padded to the payload for encryption:
1 byte    - Master Key Identifier
10 bytes - MHAC authentication tag

SRTP Standard link:
http://tools.ietf.org/html/rfc3711


 

• Marked as answer by Elena Viter 1 hour 17 minutes ago

This thread is marked as resolved.
For those who encounter the same issue:
The reason for extra 11 bytes in payload is 11 bytes padded to the payload for encryption:
1 byte    - Master Key Identifier
10 bytes - HMAC authentication tag

SRTP Standard link:
http://tools.ietf.org/html/rfc3711


 

• Marked as answer by Elena Viter Monday, February 03, 2014 10:31 AM
• Edited by Elena Viter 14 hours 53 minutes ago

This thread is marked as resolved.
For those who encounter the same issue:
The reason for extra 11 bytes in payload is 11 bytes padded to the payload for encryption:
1 byte    - Master Key Identifier
10 bytes - HMAC authentication tag

SRTP Standard link:
http://tools.ietf.org/html/rfc3711


 

• Marked as answer by Elena Viter Monday, February 03, 2014 10:31 AM
• Edited by Elena Viter Monday, February 03, 2014 8:57 PM