ginating site, with its embedded clock intact, into the communi- cations network, and then moving it from there to one or more sites, extracting it from the telecom clock time base and transferring it to the time base of the receiving site. One last tip is the fact that a communications network referenced to a global positioning source (GPS) or other source of universal time becomes attractive if the content being transported is also GPS refer- enced. A good middle of the road, practical design trade off is to reference the MPEG codec-to-station sync and reference the network interface equipment to the service provider facility. If the network bit-error rate is of sufficient level, then the network will be stable and always timed to the same source as the station is. If clock reference is lost, then the network becomes subject to the internal references of the interface equipment, and clock slips become more of a problem because they cause disturbances in picture and sound quality and 5 NETWORK ARCHITECTURE, FACILITIES, AND SERVICES may cause loss or corruption of closed caption or other similar content. COMMUNICATIONS NETWORK SWITCHING AND TRANSMISSION ARCHITECTURE Telecom network architecture in 2004 is very much a child of many years of growth and technical evolution driven by telephone calls. Telephone calls require 64 Kbs and are point-to-point connections used for short periods. Telephone service economics where the longer the distance between two points of a call costs more money influenced most of the traffic into local and regional calling patterns. These regional calling patterns led to hierarchical network architecture with high capacity switch sites in fewer numbers piecing together circuits to enable regional and national telephone calls. Figure 5-8 is an illustration of the hierarchical nature of the telephone network. The access tandems and certain designated transmission facilities are generally referred to as the access network. These switches formed the technical and economic basis for a philoso