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A T1 channel bank is a Telecom term for a device that is used to de-multiplex a 1.544Mhz T1 (DS1) facility into up to 24 DS0 channels. Each channel could be carrying either a voice or data circuit of varying types. The T1 channelbank serves as the de-multiplexer, re-establishing each circuit to its original speed and interface. De-multiplexing the 1.544Mhz circuit requires the channel bank to act as a "timing manager" where the T1 data stream is made up of a cyclical series of samples of each of the 24 timeslots. For example, a simplistic view of a T1 data stream would look like frames from Ch1, Ch2, Ch3. Ch24, Ch1, Ch2. and so on, with a consistently repeating pattern. This "timing" is critical to maintain, and is done so that the channelization will remain synchronized throughout the telecommunications link. Timing is maintained throughout the network by referencing a Stratum timing clock (in-depth explanation of T1 operation). Channel Cards. In order for a channel bank to provide the interface required for each circuit, a channel bank card is placed into each timeslot which is manufactured specifically for the appropriate the of circuit. For instance, Nortel manufactures 22 different channel cards for a wide range of voice and data circuits. The most common channel bank manufacturers include Nortel, Siemens, Newbridge, Rockwell, and Telco Systems. Standards. Different manufacturers make channel banks and brands can be mixed in any typical installation. However, channel cards are manufacturer-specific, so for instance, only a Newbridge card will work in a Newbridge channel bank. Standards also affect channel banks in the areas of timing and framing and line coding. If network timing is intermittent, the T1 facility will start to "slip", causing a T1 alarm and the services carried by the T1 to fail or severely degrade. If timing is lost, the T1 will alarm and all services carried will be lost. The alarm, in its most basic form, is generally a lamp indication on a CSU (Channel Service Unit). The CSU is sometimes combined with the channel bank that reduces equipment placements and additional wiring. Whether the CSU is a separate unit, or is combined into the channel bank, it performs line equalization and remote testing functions. Line equalization allows the channel bank to be either zero (cable) feet away, or up to a hundred (cable) feet away. This is a setting that is established at the time of the original installation and is seldom ever changed.
ESF/B8ZS T1s also have the benefit of ESF monitoring, which allows the carrier to setup ESFMUs (monitoring units) to watch the performance of the T1 itself without disrupting the services carried by the T1. ESFMUs track performance using the 8kb ESF channel for statistics. ESF/B8ZS is required for Fractional T1s since the access T1 is not channelized, and contiguous bandwidth is required to allow a single circuit greater than DS0 speed. 
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T1 Channel Bank
