 traffic. For example, DS3 channel runs at a nominal rate of 44,736,000 bits per second. To keep the channel unique and separate from peer channels, framing bits, also called overhead, are required. What is left is called payload. In the case of a DS3, the framing overhead amounts to 526,306 bits per second, which leaves the remainder of 44,209,694 available for payload. (See Table 4-1 for other PDH and Table 4-3 for SONET/SDH channel and payload rates.) However, 672 DSO (voice channels) running at 64Kbs amounts to only 43,008,000. What about the other 1,201,694 bits? This is where the technique of bit stuffing comes in. These "left-over bits" can be divided up amongst lower order streams to make them fit within a time window compatible with the higher order multiplexed stream. This allows them to wander around, within certain well-defined tolerances, and enables the network accommodate them. APPENDIX At the other end of the path, the stuffed bits are dropped, and what remains is payload. Bit stuffing and reversal may occur in premises equipment, inside the network, or both. Bit stuffing inside the net- work is used to cope with signals from different multiplexers or sources that are synchronous within a specific range or tolerated amount of difference between their clock and the network clock. Transmission channel interfaces enable the network to carry aggre- gated traffic by configuring contiguous DSO or higher rate digital signals from multiple DSO into DS1 (T1/J1), E1, E3, and DS3 (T3/J3) interfaces. When network transmission channels are configured with these interfaces, the resulting channel is unchannelized or clear channel. Bit stuffing outside the network is usually very application specific, such as in a data or video application that may require the equivalent of several DSOs, less than a DS1, DS2, or DS3, as a stand-alone requirement. Bit stuffing might be used to make up any difference between the application's requirement and the fixed, standard net- work channel is configured to provide. The concep