Audio/video chat between ProCall Desktop for Windows and ProCall Mobile

Szenario

• In ProCall Mobile sessions, an audio or video chat is initiated; the other party is a ProCall Enterprise user using ProCall Desktop for Windows or
• In this ProCall Desktop for Windows , an audio or video chat is initiated; the other party is a ProCall Enterprise user with ProCall Mobile for iOS or Android.
• Both participants in the audio or video chat communicate via this connection.
• The estos ProCall Mobile app is connected to the mobile data network.
• External estos ProCall Enterprise users are connected via estos UCConnect.

Notes

With regard to the media flow paths between two instances of ProCall Desktop for Windows or ProCall Mobile , audio and video chats differ significantly from SIP softphone calls.

In an audio/video chat, the exchange of SRTP packets (Secure Real-time Transport Protocol) takes place directly between the clients.
The media streams are therefore not routed via the estos UC Media Server, as is the case with a SIP softphone call.

Diagram/Topology: UCServer Service – ProCall Desktop for Windows – UCConnect Services – ProCall Mobile – SRTP Audio/Video via TURN:

The estos UC Media Server does not handle any relay or transcoding tasks for audio and video chats. Furthermore, the telephone system connected to the estos ProCall Enterprise Server is not involved in these scenarios and therefore has no information about active chats. The UCServer SIP Gateway is not active during SIP signalling and media stream negotiation. This lack of communication with the telephone system may be relevant for the control of call protection or the Busy on Busy status. 

The topology shows a typical ProCall Enterprise installation, including an estos UCConnect connection, assuming unrestricted communication between the estos ProCall Mobile app and estos UCConnect.

It is also assumed that standard operating procedures apply with regard to Google’s and Apple’s push notification services; the actual signalling path for push notifications between estos UCConnect and an Android or Apple smartphone is shown here in the diagrams only in a highly simplified form.

ProCall Desktop for Windows establishes a connection to ProCall Enterprise Server on port 7222 (the default setting) via a dynamically assigned TCP port. The client uses this connection to exchange requests and events with the server.

Both the ProCall Mobile App and the estos UCServer establish a connection to estos UCConnect port 443 via a dynamically assigned TCP port and set up WebSocket communication over this connection. Via this connection, the Mobile App and the UCServer exchange requests and events via UCConnect in order to process telephony events or carry out telephony activities.

To exchange RTP media packets during an audio or video chat, the clients use the ICE handshake to establish a direct connection via UDP with one another (WebRTC standard). Ports in the range 1024 to 65535 are used for this (all ports with the exception of well-known ports). Where necessary, the clients also take available STUN and TURN servers into account to optimise the media path.

The ICE protocol (Interactive Connectivity Establishment, as defined in RFC 8445), which is integrated into WebRTC, attempts to determine the optimal path between the ProCall Desktop for Windows and ProCall Mobile clients when establishing a connection. Even during an existing connection, ICE verifies the best route in the background. If, due to a change in the situation on the internet or mobile data network, a route proves to be better than the one currently in use, this may result in one or more route changes between these two endpoints during the course of an audio/video chat.

If the ICE protocol determines that a direct exchange of audio packets between the LAN and the internet is not possible via the firewall or NAT router, this may – as in the scenario illustrated in the topology/diagram above – also result in a media connection between the clients via a TURN server. The specific nature of the connection – whether it is a relay-srflx/prflx connection or a relay-relay connection (as shown here) – is not considered further here.

Firewall rules

The firewall rules listed here represent the minimum requirements that can be assumed without specific knowledge of the relevant environment.

Further information

• Release ports for estos products – which network interfaces are used?
• Push Notification Service
• estos ICE test tool