al signalling traffic should be calculated using busy hour traffic, mobile-originated calls/ sub- scriber, mobile-terminated calls/subscriber, SMS traffic and number of signalling messages per call. The total signalling traffic can be divided into three categories: - SIGTRAN based traffic, which constitutes traffic generated by SCCP applications; - SIP based traffic, which is inter-MSC traffic and has to flow over the IP; TDM traffic, which is the traffic generated due to emergency calls, data/fax and handovers and has to be routed, normally using CCS7/TDM. Mobile Packet Core Architecture Planning 4.12.3 Bandwidth Calculations The bandwidth is required for transfer of one voice call. It is known that 13 kbps is required per full rate timeslot. It is assumed that the Ethernet overhead is 38 bytes, the IP header is 20 bytes and the UDP header is 8 bytes. Assuming no voice activity detection and no header compression, the total of these comes to 13 kbps + (66 bytes X 8 bits X 50 samples/5)/1000 = 39.4 kbps. Hence it can be stated that the bit rate requirement from the IP backbone is 39.4 kbps per call in the one-way direction: Total bit rate voice = number of voice channels X 39.4 kbps The bandwidth required on the IP backbone for SIP messages (ISUP signalling between MSCs) can be calculated as follows: Average size of each SIP message = 600 bytes Number of SIP messages flowing per call = 8 Calls per second = Erlangs/mean holding time Bit rate required = calls per second X 8(messages) X 600(bytes) X 8(bits/byte) The bandwidth required for SIGTRAN (SCCP based) messages can be calculated in the same way as for the voice call. The following overheads are added for each signalling message: - M3UA: 24 bytes - SCTP: 28 bytes - IPv4: 20 bytes - Ethernet: 38 bytes Note that for each of above three categories, a calculation should be made of how much traffic would flow over the LAN (between network elements in the same site) and how much over the IP backbone (between network elements in different sites). The next step in ban