One of the most exciting communications technologies at the moment is Voice over IP. It provides less expensive calls to any point all over the world but still making owners of IP telephony systems very reach people. So everyone is satisfied when using VoIP solutions. In one of our projects we have developed VoIP software that is completely integrated with Microsoft Live Communications Server and provides IM and VoIP services to consumers.

The consumer can call anywhere and does not care if he or his partner is under firewall or network translator. The solution is completely customizable and can fit any needs of end users. To get the calls controlled and IM messages delivered the system works using SIP (Session Initiation Protocol). It is the most reliable protocol ever used in VoIP. Our VoIP system is optimized to get call accessible for any network architecture.

The methods for sound processing don't touch data compression problems but they are required in phone systems. In our systems we use:
    Sound stream re-sampling and streams mixing
    Applying 3D effects
    Sound buffering for permanent and stable playback
    Sound packet size calculation depending on network speed and load
    General sound stream transformation: channels count changing, transformation between 8, 16, 32 bit per sample streams, u-law and a-law streams transformations

In systems where disparity between the moment of sound generation and the moment of receiving is critical the UDP protocol is used. For example when transmitting the voice information the low-level protocol is UDP and the high-level protocol is RTP/RTCP. During video data transmitting the MPEG codec and TCP protocol are used. This combination guarantees delivery of data.

The tunnel mechanism is used to solve problems connected with address translations and firewalls which “close” the necessary ports. This method is implemented for TCP and UDP protocols and it allows transmitting video-data the same way as standard HTTP/HTTPS browser does.

Tunneling system allows creating bi-directional tunnels for UDP packets transferring through TCP connection. Current system consists of two applications: Tunnel Client and Tunnel Server. Tunnel client application can be launched on any network host (in corporate network which is separated by proxy/firewall) under any Microsoft Windows OS which supports input-output completion ports and Winsocks2 while tunnel server can be launched on some server in the Internet (OS requirements are the same + services support).

Architecture of this system makes it fast, reliable and scalable. It can be used for building high performance client/server systems which allow supporting 1000s connections at a moment for data exchange with minimal delays (up to 50 msec) on transferring of each data packet. A lot of highly-sophisticated applications use input-output completion port (IOCP) for data transmission.