 jitter Voice 64kb/s CS- time slots Voice 64kb/s AAL1 Voice compressed AAL2 Data AAL5 Data IP Voice over IP Data FR Voice over FR Figure 8.30 Examples of transfer mode models Understanding Changing Telecommunications - Building a Successful Telecom Business Terminal Client Management Gateway server IP network Gateway Gatekeeper telephone Conference IP phone server Figure 8.31 An example of a set of VoIP components The opposite is to use IP in the central network part, taking advantage of the non-distant depending charging in IP networks. This is the voice trunking VoIP solution mentioned earlier in this chapter and represented by Figure 8.31. The IP network serves here as carrier network for packets containing signalling and traffic data. Dedicated IP phones or IP software clients can be attached directly to the IP network. Originally, the gateway hosted all the functions required to set up and execute the IP telephony call. However, later a clear division between media translation (coding/decoding) and all the signalling and 'administrative' functions, was seen as beneficial and thus the original VoIP gateways began to be divided into different system components. The gatekeeper was created to be the host for all the 'administrative' tasks, thus allowing the gateway to concentrate on its main task, coding and decoding between different types of networks. The gatekeeper also offers user authentication and collection of call detail records that are used for billing. Connected clients communicate with their corresponding gatekeeper, register to it as users and make all address requests to the gatekeeper. Users are also compelled to authen- ticate to be able to use certain services at the gatekeeper. Users must follow the gatekeeper directions on routing since the gatekeeper controls the available resources (bandwidth and connections). The gatekeeper is a signalling component only - no traffic streams pass through the gatekeeper. The gatekeeper is thus a control layer server in the H.323 standard. The gatekeeper has 