 4 Circuit Core Network Ethernet Ethernet Figure 4.21 Call Control Protocol stacks for the Nc interface Dimensioning BICC and SIP interfaces follows a general procedure as outlined below. When BICC signalling is used, it is assumed that one signalling message size is 40 bytes (also used for ISUP). A total of six BICC messages are required per call. Two of the messages (IAM (initial address message) and APM (application transport mechanism)) contain the SDP (session description protocol) payload of approximately 150 bytes. This results in 4 X (40 + 12 + 28 + 20) + 2 X (40 + 150 + 12 + 28 + 20) = 900 bytes/call or 450 bytes/call/direction. As an example, assuming 50k users, each initiating 1 BHCA, then 450 bytes/call/direction X 8 bits <50 000 calls/h/3600 = 50 kbps are made including the M3UA (12 bytes), SCTP (28 bytes) and IPv4 (20 bytes) overheads. When SIP is used, the calculation of number of messages and size is more complex as it depends on the call case, the lists of codecs supported and even the length of domain names selected by the operator for signalling addresses of network elements. When no better estimation from measurements is available, then it is assumed that one signalling message is 500 bytes. A total of 14 messages are required per call in both directions. This results in 14 X (500 + 8 + 20) = 7392 bytes/call or 3696 bytes/call/direction. Assuming 50k users, with 1 BHCA per subscriber then 3696 bytes/call/direction X 8 bits X 50 000 calls/h/3600 = 410 kbps are made including the UDP (8 bytes) and IPv4 (20 bytes) overheads. MAP Interfaces C, D, E, F and G The MAP-C interface connects the MSS/GCS to the HLR. The MSC server fetches the subscriber location information from the HLR via the MAP-C interface. The 3GPP release 4 circuit core standards recommend the use of BICC-CS2 as the signalling protocol in the Nc interface. The BICC-CS2 is able to establish bearer channels for user plane connections both with the ATM and IP based backbone. Moreover, the BICC-CS2 is independent from the signalling me