an MSN compared with having separate networks for voice and data. Appendix 4: Dimensioning Media Gateways and Associated Telephony Servers Capacity with separate networks Capacity with MSN Required capacity Saved capacity Required capacity Voice Time of day Time of day Morning Afternoon Evening Morning Afternoon Evening Figure A4.4 Reducing required capacity with a multi-service network MSG Dimensioning Let us now start looking at the dimensioning of the MSGs. This means to dimension the TDM/circuit emulation interfaces (voice traffic) on the access side, and the ATM interfaces on both the access side (data traffic) and the backbone side (voice and data). An MSG is typically built in a modular way, where each module (or sub-rack) has switching capacity of e.g. 10 Gigabits per second. One sub-rack is, for example, configured with 16 interface boards plus two processor boards (for reliability) and two switch boards (for reliability). See Figure A4.5. The assumed basic configuration for an MSG sub-rack is defined as: two central pro- cessor boards, two switch core boards and two ATM boards (on the backbone network side). This leaves 14 slots for optional line interface boards, such as E1 CE, STM-1 CE or ATM boards. Figure A4.6 shows some possible interface boards that can be used in an MSG. The MSG will be equipped with a number of circuit emulation boards (E1 and/or STM-1), which are used as interfaces towards the TDM-based network. The ATM part of the MSG should support the standardized ATM UNI 3.1 or 4.0 signalling. Also PNNI and AINI signalling should be supported, implying that an MSG can either be connected to the ATM backbone network or can be a part of it. The ATM Configuration for MSG (10 Gbit/S) Control processor Switch core 1 STM-4 1 STM-1 (data) 1 STM-1 16 slots for interface cards Figure A4.5 Typical configuration of a multi-service gateway Understanding Changing Telecommunications - Building a Successful Telecom Business Each 10 Gb/s module has 16 slots available, which can be configured with a mixture