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Mux is a Telecom term for the hierarchy between DS0, DS1, and DS3 circuits. Mux (Multiplexing) is a method of combining slower speed circuits (i.e. 24 DS0 circuits) onto the next level of Digital Service. Terminology:
Theory Lesson. In its basic form, any DS-Level circuit can be broken down into multiple "channels" where each represents a time slot. Divide a 1.544 MHz DS1 by 24 (less 8kb for framing and line coding) and the result is 24 x 64 Kb circuits. These DS0s can be voice or data, provided that the service can be combined into a 64 Kb data stream. The concept of multiplexing is combining several slower speed circuits (or services) into a single higher speed circuit. This practice is very commonplace in the Telecommunications infrastructure. DS0s are combined into DS1s and DS1s are combined into DS3s. DSn-level circuits are carried by copper pairs. Once you exceed the 45 Mb speed reached by DS3s, a conversion to optical circuits takes place. (For this discussion, we'll not address OC-level multiplexing) How is Multiplexing performed? Multiplexing is performed by different devices, depending upon what services are being multiplexed, and at what level. DS0s are multiplexed into T1s by typically a Channel Bank, where each time slot is represented by 1 DS0, and each DS0 is terminated by the appropriate card type. Several types of cards exist for DS0 circuits to terminate, depending upon whether they are voice or data circuits, and what type. A fully loaded T1, multiplexed by a Channel Bank will have a combination of 24 channel bank cards. The extra 8kb mentioned earlier refers to the bandwidth required to "clock" or "frame" the DS0 channels, as well as the line coding for the DS1 itself. Carriers have the ability to use this 8kb to perform testing, both in-service (using Extended Super Frame) or out-of-service (using Alternate Mark Inversion) line coding.  DS3s are typically multiplexed by an M13, referring to the device that M uxes DS 1 s to DS 3 s. Just as a channel bank has DS0-level cards for each circuit, an M13 has DS1 cards for each circuit as well. A fully loaded DS3 will contain 28 DS1s, with each DS1 terminating into its own card. Other Options. At the DS1 level, more options exist for multiplexing other than just a channel bank. A D/I Mux (drop and insert mux) will have a DS1 signal as its input, and its output can be DS1-N plus N, where two signals exist, N represents 1 to 4 DS0s dropped off (typically for a few data circuits) and a DS1-N signal (at 1.544 MHz) with the "dropped" channels missing. This application is typical for a business user that needs 20 voice circuits and 4 data circuits (multiplexed on the same DS1). This scenario will typically be far less expensive than leasing 24 DS0 loops from the Telco for the equivalent capacity, as well as the CPE cost (customer premises equipment) for terminating a voice T1 is less expensive (and complicated) than purchasing 20 analog voice cards. Common Names / Muxing Levels:
Typical Applications. T1s are generally used in "Channelized" or "Non-Channelized" applications. Channelized refers to the services carried by the T1 as multiple DS0 circuits multiplexed on to a T1 access line. Non-Channelized service refers to a single service (i.e.: 1.544 MHz service for Internet Access). DS0s are typically used as voice-level or dial-up data channels. DS1s are typically used as either private point-to-point circuits between facilities, or more typically, access from a business to either their local or long distance provider. DS3s are typically used where more than one DS1 is needed for capacity. While a T1 might be deployed for capacity reasons, not all DS0 timing slots must be activated, so if a company needs 256KB of capacity, a typical installation might have a T1 established for "access" and only 4 DS0s "activated" on the T1 facility. |
Mux
