rts required and the type of switch will vary from case to case during actual implementation. A more in-depth dimensioning and planning exercise should be done during the project planning phases, immediately after the successful conduct of the tendering activity. For the core switch, there are two redundancy options: duplication on the module level or duplication on the network element level. The required redundancy option would greatly depend on the operator's policy. A minimum card requirement (in terms of 48 ports per card) is calculated. Two ports will be required per equipment connected to the switch per VLAN if LAN interface redundancy is required. Each packet processing unit, charging units and operations and Maintenance Units in the SGSN are connected separately to ports under separate VLANs created in the core switch. 4.12 IP backbone Planning and Dimensioning In traditional 2G GSM networks, CCS7 (common channel signalling 7) traffic is carried over PCM links. SIGTRAN and SIP make it possible to carry this over the IP backbone. SIGTRAN is a set of protocols that defines a framework to transmit signalling like the SCCP over the IP. It can be applied to all mobile applications like MAP, RANAP, INAP and CAP, which use the SCCP. When SIGTRAN is implemented in a network, in the beginning there is no need to make any changes in the applications. Later on, however, applications can be optimised to take full advantage of higher efficiencies provided by SIGTRAN. SIGTRAN provides a much wider bandwidth as compared to 64 kbps per link in CCS7. Messages with a length longer than 272 octets are supported. Hence there is no need for segmentation. Load sharing and automatic re-routing of traffic is also supported. The IP and SCTP add overhead to the messages. The SIP is used to transfer ISUP signalling between mobile switching centres (MSCs). SS7 links are not as efficient as the IP backbone in terms of capacity. The IP provides a much higher capacity and bandwidth than PCM links. Recently telecom operators worldwide h