nd 24 individual 64 Kbs voice channels or DSO signals. This makes the multiplexing bit oriented. That is, each stream is multiplexed into a specific pattern based on individual bits where each bit in each frame has a specific (theoretical) timing relationship to the same timeslot in peer bit streams. Because of the fact that each of the original 1.544 Mbs bit streams is generated from a clock that runs in the real world, and may not be precisely on the same fre- quency as any of the others generating the T1 signals being multi- plexed, and because the timing of the signals being multiplexed may change due to propagation delay variation in the transmission media, 4 NETWORK TECHNOLOGY AND METHODOLOGY the resulting aggregate signal multiplexing is said to be plesiochro- nous, meaning almost or nearly synchronous, but not asynchronous or non-synchronous. Multiplexing of signals from disparate clocks that are almost or nearly synchronous requires another technique called bit stuffing. Bit stuffing3 is exactly what it's name implies, adding or "stuffing" bits into a multiplexed stream to raise the speed, or number of bits per unit of time, SO there are enough bits to fill the timeslots in the higher order channel. For example, when 4 DSI signals are multi- plexed to make up a DS2 signal, one of the signals is sent at exactly, 1,544,000Bps, one has 364Bps, the third gets 314Bps, while the fourth gets 414Bps, making an aggregate for the DS2 of 6,306,272Bps. When 7 DS2 signals are used to build up a DS3, still more bits are added to each DS2 to enable the network to accommodate the disparate nature of the various DSI clocks and multiplexing oper- ation. The T-carrier concept originated in the United States, but was followed in due course in other countries. Initially designed for four-wire media, it found its way to coaxial cable, wireless, and optical fiber media. An international version of the DS1 is called an E1. It uses the same 8 Kbs sampling and 64 Kbs DS-0 channel rates, and 125-microsecond framing. However, 30 ti