re network SS7 will often appear as an access technology until the MGW has 'conquered' the present local nodes. Q.931 is the ISDN network layer signalling protocol. The V5 interface is used between an access node and the local exchange. V5.1 interface is based on a static multiplexer type principle in which a single E1 link is used to carry the bearer channels and the signalling channels. The bearer channel allocation to the V5.1 subscriber is fixed. The V5.2 interface is based on a dynamic concentrator type principle, typically consisting of 1 to 16 E1 links carrying bearer and signalling channels. The bearer channel allocation to the subscriber is dynamic on a per call basis. 14.5.5 BICC AND BICC IP BEARER CONTROL PROTOCOL IPBCP BICC is a signalling protocol based on ISUP. The basic issue leading to the develop- ment of BICC was that network operators had experienced heavy growth of their voice traffic mainly due to the Internet. PSTN/ISDN networks required major investments to accommodate the growth, while network operators did not want to invest too much in 'old telephony' networks. BICC can support PSTN/ISDN/PLMN services over a broadband connectivity network. It is specified by ITU-T in recommendation 0.1901 and allows any bearer to be used, such as IP, ATM and TDM. The BICC protocol allows operators to offer the complete set of PSTN/ISDN services with operator-grade quality, including all supplementary services, over a variety of packet networks. The BICC network is scalable. BICC supports all currently deployed services on circuit mode, ATM and IP networks, including third-generation wireless, yet does not limit the future introduction of new multimedia, multi-mode services and applications. Figure 12.9 shows the basic BICC network architecture. The general idea of a BICC network is the separation of call signalling on the one hand, and bearer signalling and user traffic on the other hand. The BICC protocol is used for call signalling functions, such as indicating the requested type of ISDN service and ca