Feb 05

Skype4Business, upcoming voice (OPUS) codec. Will it be in there? No, not in initial release

All Unified Communications vendors talk SIP nowadays, but the SIP standards leaves so much room for vendor additions that different SIP implementations do not automatically talk to each other. That’s why often a Session Border Controller is need for voice or video to make sure things are made compatible. Let’s talk a about codecs currently used in Lync 2013:

Voice Codecs

G.711 (standard) and RTAudio Narrow Band and Wide Band are supported codecs by Lync 2013 and G.729 (comparable to a GSM call) can be used if an SBC transcodes G.711 to G.729 to for example towards a SIP trunking provider. Main reason is to the compression so less MPLS bandwidth is needed. The G.729 codec is not a supported codec in Lync itself. The quality of voice codes can be measured by the MOS values, Mean Opinion Score.  Explanation of MOS can be found here on Wikipedia, together with scoring of a few codecs.  

For conferencing modalities currently Siren (patented by Polycom) and G.722 are used. This gives a much better conferencing experience than the traditional audio conferencing calls where everybody dials into to a bridge from their car. Which forces the bridge to mix G.729 calls and can be a horrible experience with 20+ people in the same call.

On the Skype side the SILK codec has been used and is now also introduced into Microsoft Lync. SILK is a foundation (with CELT) of the hybrid codec Opus (at the time called “Harmony”) that was submitted to the IETF in September 2010,[13] and was chosen as the final candidate for the new standard. Opus was published as an IETF proposed standard in September 2012.  The OPUS codec based partially on SILK, the voice codec that Skype has developed Now OPUS has been ratified as an official standard. But which known vendors already support this standard:

A very brief reference was made to the OPUS codec, by Jeff Schertz, Microsoft Lync MVP working at Polycom. He always makes excellent blogs, this is one of those beauties.

When I have more or someone else have more information on support, please let me know I will update the blog. Advantages of using the OPUS.

Impact on the Microsoft and Unified Communications eco-system when it gets introduced:

  • Most likely the old codecs will still be supported, so no direct impact, just as SILK is now supported
  • Vendors supporting OPUS will have an advantage, better quality, less bandwidth needed

Why are codecs and standardization important. That’s for four reasons:

  1. Interoperability
  2. Bandwidth usage
  3. voice and video quality
  4. Control, a proprietary codec can create a deliberate lock-in into a certain architecture and thus creating more revenue for a vendor.

Lync 2010 and Lync 2013 Bandwidth calculator A good way today to estimate impact of a Lync implementation on you network can be done by using the Lync 2013 Bandwidth calculator. Whatever Microsoft will change on the codec side, they will surely come up with a new version of this tool for Skype4Business.


Note. Update on February 2015. The Skype4Business release is planned somewhere H12015. We just has the Office 365 Summit in Amsterdam with two days of presentations on Skype for Business. The slides can be found here. The OPUS codec will not be in the initial release, a lot of the communications will be based on SILK. Even though OPUS is partially based and has input of SILK the two codecs won’t be able to interoperate with each other.

From a standardization perspective and with the all the trends on WebRTC it would be good if the Microsoft will adopt the Opus codec quickly as with other vendors, so this can be the new G.729 and G.711 and commonly supported throughout different platforms.

1 ping

  1. […] Skype consumer. I found a very good blog around this describing it. In February 2005 I wrote a blog if the new OPUS codec (based on SILK) was to be used in Skype for Business. It wasn’t, but it is […]

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