2002 - cesnet

VoGWs of members involved in the project are usually connected via ISDN,which allows for the storage of detailed records concerning the calls in the SQLdatabase on the RADIUS server. The IP telephony network has been orientedon the H.323 protocol (min. version 2). The internal elements of the VoGW andGK (Gatekeeper) network are based on the Cisco platform, which proved to bebeneficial with respect to the extension and management of the network.CESNET2GKOstravaGKPrahaCERN412276xxxxxGKAliatelSLAC1650926xxxxCesnet-extLinux GKAARNET61xxxxFigure 8.2: Scheme of interconnection among control elementsFor purposes of foreign H.323 connectivity of other entities, there is the externalLinux GK located in Prague. As regards the hierarchy, this GK is linked over theinternal GKs in Ostrava and Prague. Each internal GK is provided with a backupand all GWs in the network log in to both elements with a priority according totheir geographic location. In the usual operation mode, logging with a higherpriority is active. The requirements for calls outside VoIP network of CESNET2are rerouted by the Internet (NIX.CZ) to the Aliatel GK.Figure 8.3 shows a scheme of the IP telephony network. Many thousands of usersconnected to private exchange branches have access to the services afterdialling the required prefix. Dialing in CESNET2 is carried out according to thepublic numbering plan, in accordance with the valid telephone directory (without420). For international calls, 00 is dialled before the code of the country, e.g.,0043 for Austria.High-speed National Research Network and its New Applications 2002111