We are primarily using telephone numbers and as a backup option Ip addresses of units (end devices, video conferencing clients, core units for multi-point conferencing MCU, recording devices and so on.) for calling in H.323 environment.
If you are registered in our infrastructure, you can use the number in the national format for the internal sources (other registered end devices, conference rooms on MCU). If you use the infrastructure of other NREN (free gatekeepers) or need to connect to foreign end devices you can use the number in GDS format (00 prefix). If you are inviting single or multi-point foreign partners you should share the number in GDS format (for example, GDS number: 00420950088888).
GDS is the hierarchy of institutional, national and international routing units for H.323 which main purpose is to connect video conferencing sources of the scientific community of the whole world.
Shared resources of video conferencing infrastructure (MCU) are also available through SIP protocol. Instruction manuals are available on the separate page. The number in national format is sufficient if you are registered on CESNET SIP server. Use URI sip:email@example.com (or sip:firstname.lastname@example.org) from other domains.
The easiest way is by connecting to test room. See the here.