SBC allows relay support for MS Lync/Skype for business Desktop sharing application media streams. The application sharing media streams are relayed transparently through the SBC over TCP connections. Interactive Connectivity Establishment (ICE) is completed over this TCP connection by the peer endpoint.
When SBC communicates with an MS Lync/Skype for business client, SBC expects the TCP connection to be established by the peer endpoint. Hence, SBC does not initiate the TCP connection on its own. This is an acceptable behavior as the SBC is not situated behind a Network Address Translator (NAT).
SBC can also be configured to initiate and establish the TCP connection towards the third-party device to support interoperability when SBC relays an application sharing media stream. This functionality is supported only when the Lync compatible peer endpoint and SBC are not situated behind a NAT.
The following functionalities are included to enhance MS Lync/Skype behavior:
- SBC supports application sharing media streams in Session Description Protocol (SDP).
- SBC accepts and establishes TCP connection with media IP/port of the peer application stream.
- SBC exchanges STUN messages over the TCP connection to negotiate ICE.
- Once ICE is completed, SBC relays desktop share data transparently end-to-end.
If the parameter sourceAddressFiltering is enabled, SBC filters incoming media packets, which do not match the expected source IP address and UDP port. In the Lync desktop sharing, the SBC accepts incoming TCP connection that matches any of the source addresses in the candidate lines of the ICE SDP received from the peer. When the SBC has not received an SDP from the peer, before the peer attempts to establish the TCP connection, SBC ignores source address filtering and allows the TCP connection to be established on the application sharing stream.
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