ss facility. There are two types of facilities: switched and private lines (Table 4-7). Switched access is limited to low-bandwidth telephone service and Internet access provided by ILEC, CLEC, and cable operators. Classical voice grade dial service using dual-tone multifrequency (DTMF) sig- naling supports connections that enable voice conversations and Inter- net ccess-"computer-to-computer" communications up to 56 Kbs. Higher speed services are available from local exchange carriers and cable operators using DSL and cable modem technology, respectively. DSL is capable of a few hundred kilobits per second, while cable modems achieve speeds well over a megabit per second. Private line access is required to use any form of higher speed switched services from all service providers. All the service providers use equipment from one or more manufacturers that make TABLE 4-7 Facility or Frame Packet technology Facility type duration Frame type Bandwidth PDH/SONET/SDH Transmission 125usec Fixed Timeslot fixed 64Kbs-10Gbs fixed Cross Connect Circuit Switch 125usec Fixed Timeslot 64Kbs-10Gbs Circuit Switch 125usec Fixed Timeslot fixed Kbs-1.5 Mbs fixed Circuit Switch 125usec Frame Relay Packet Switch frame variable variable ATM CBR Cell Switch 125usec fixed fixed ATM VBRrt Cell Switch 125usec fixed variable ATM VBRnrt Cell Switch 125usec cell or PDU variable variable ATM ABR Cell Switch 125usec ATM UBR Cell Switch 125usec Ethernet Packet Switch frame variable variable IP Routing Packet Switch Packet PRACTICAL IP AND TELECOM FOR BROADCAST ENGINEERING AND OPERATIONS standardized subscriber interface at layer 1 and 2. Layer 1 will be T1/ E1, T3/E3, or at the lower SONET/SDH OC3/STM1. Layer 2 will depend on the capabilities of the subscriber and the service pro- vider's equipment at each end of the access facility. A variety of technology is employed in access and transport facilities that enables all the various services available in any given service provider's network. The service set offered depends on the configur- atio