o evolve into circuit switched 64 Kbs channels. These channels are multiplexed into higher order bit streams. An OC192 transmission facility configured to handle only voice traffic contains 192-DS3 equivalents, each capable of 672 64 Kbs channels for a total of 129,024 unique, independent segments of bandwidth. An STM64 configured to handle only voice traffic contains 122,880 band- width segments. What about using some of this bandwidth to carry something of a different nature than a 64 Kbs voice? It is entirely pos- sible, and that's where network channel interface comes into play. From a network transmission facility perspective, a bit is a bit. The transmis- sion network doesn't know or care if the bit carries voice, data, or any- thing else, including errors, as long as it meets network clocking and time duration parameters. What this means is that the transmission network will accept access and egress or drop and insert segments of bandwidth that just happen to be sized and structured to fit in place of 24 (T1), 32 (E1), 480 (E3), 672 (T3) voice grade equivalent, or 64 Kbs channels. Another point of confusion is unchannelized or clear channel rates. This type facility is used for non-voice channel applications such as 4 NETWORK TECHNOLOGY AND METHODOLOGY Internet access, wholesale encrypted traffic (encryption applied to a T1 or group of individual channels rather than individually encrypt- ing each channel), asynchronous transfer mode (ATM) network, physical convergence layer protocol (PLCP) access, compressed pro- gram content over E3 or DS3, and other applications that require contiguous bandwidth that cannot operate over 64 Kbs channelized facilities. IP routers are likely to have a PDH wide access network interface at T1/E1/J1 or E3/J3/DS3. SYNCHRONOUS OPTICAL NETWORK/SYNCHRONOUS DIGITAL HIERARCHY MULTIPLEXING SONET/SDH multiplexing techniques are built around a fixed size row and column structure that contains overhead (OH) and a syn- chronous payload envelope (SPE). The SPE is designed to carry synchr