d. With all possibilities and layers, facilities management becomes somewhat cumbersome. An overall approach for multi-layer traffic engineering is called GMPLS, generalized MPLS, from IETF. GMPLS is briefly described in section 12.11. A combination of stack reduction and a more general approach to resource handling, like GMPLS, would have impact on CAPEX and OPEX. This will be covered below. 12.5 THE DISTRIBUTED DIMENSION Most of the figures show a limited backbone network. In reality it is global. A single operator can operate networks with hierarchical switches/routers. The similarities with the large circuit-switched telephone networks are clear. See for example the router hierarchy in Figures 12.15 and 15.4. 12.6 TRAFFIC Of the total inter-node traffic the largest volume is originated by fixed residential and SOHO broadband xDSL and cable modem accesses, and corporate accesses over Understanding Changing Telecommunications - Building a Successful Telecom Business (S)HDSL, Ethernet over fibre, frame relay, ATM also over fibre, or possibly radio, such as LMDS. See Chapter 13. Fixed voice traffic decreases its share in comparison with fixed broadband. Traffic from mobile networks constitutes a lower share than one would expect, since the data traffic is still very low and therefore not very bandwidth consuming. Provided it is designed for that, the (mobile or multi-service) backbone transports mobile voice traffic as ATM AAL2 cells or IP packets with compressed headers. 12.7 ATM SOLUTIONS 12.7.1 ATM AND IP OVER ATM ATM is a VC (virtual circuit) switching technology that was standardized starting in the late 1980s. ATM uses fixed-length payloads with a length of 48 bytes and a 5-byte header, yielding 53-byte long ATM cells. Among the 40 header bits of a cell, 28 are reserved to identify the virtual circuit to which the cell belongs. The corresponding fields are called VCI/VPI (virtual circuit identifier/virtual path identifier). The VCI/VPI fields are updated at each switch. The prime network niche for ATM is in