a customer is asking about the amount of concurrent calls it can achieve using a Expressway as Lync GW with MS Interop Option and 10 RMS.
I found this info on documentations... Is a Lync client capable to establish an audio-only call and consume 0,5 RMS?
Interoperability gateway calls (including Microsoft Lync / Skype for Business and third-party call control servers where interworking is required): require one RMS license on the Expressway-C.
■Expressway defines an "audio-only" SIP call as one that was negotiated with a single “m=” line in the SDP. Thus, for example, if a person makes a “telephone” call but the SIP UA includes an additional m= line in the SDP, the call will consume a video call license.
■While an "audio-only" SIP call is being established, it is treated (licensed) as a video call. It only becomes licensed as "audio-only" when the call setup has completed. This means that if your system approaches its maximum licensed limit, you may be unable to connect some "audio-only" calls if they are made simultaneously.
Each rich media session license allows either 1 video call or 2 audio-only SIP traversal calls.
Hence, a 100 rich media session license would allow, for example, 90 video and 20 SIP audio-only simultaneous calls.
Any other audio-only call (non-traversal, H.323 or interworked) will consume a rich media session license.