The service is aimed to connected institutions as the whole. CESNET SIP server also maintains some of the SIP domains of institutions, so it allows registration of end devices but only in demonstration mode without tighter integration with institution infrastructure.

Basic driving element of the implementation of SIP protocol in CESNET2 network is a SIP proxy server running on Linux platform and SIP Express Router (SER). The server acts as registration and proxy server. SIP clients can register in form of software clients or hardware telephones and can communicate with surrounding world through this server. SIP proxy maintains calls routing on gateways of connected institutions according to telephone prefixes.
Most of the gateways are connected directly by SIP protocol. If the hardware does not allow it, calls are routed through SIP/H.323 gateway. Proxy server also maintains calls which are received and headed to other SIP domains, for example, iptel.org or bts.sk.

SIP proxy operates in multidomain mode. That means, that except its mother domain cesnet.cz, it is also able to operate with domains of other institutions. Our goal is to let institutions try SIP system and after that used it and integrated it into their systems which will be for example multidomain proxy in Cesnet. Telephone numbers with 95007 prefix are only valid on the multidomain proxy in Cesnet (they will not be assigned directly to institutions for server maintaining) and so they are assigned as aliases.