T1 Line Speed

A T1 represents a circuit running at a line speed of 1.544Mhz. Within this 1.544Mhz range, a minimum of 8khz is required (using ESF/B8ZS line coding and framing) for proper operation. Consider the 8khz the "minimum overhead" required for a T1 to operate in a non-channelized, contiguous bandwidth application. Non-Channelized refers to the T1 not being multiplexed into the typical 24 channels for voice and/or data. Contiguous bandwidth refers to "continuous" or un-interrupted (opposite of channelized). The strength of a basic T1 is that the T1 line speed should not significantly vary - it should be quite consistent.

Also referred to as 1.5Mb, a T1 represents the line speed capacity of 1.5Mb either upstream or downstream, or a simple combination of up and down rates that cannot exceed 1.5Mb. T1s are capable of symmetrical line speeds, meaning that depending upon the need, it can be used as 1.5Mb up or down. DSL and Cable-based services are not symmetrical, since they have (by design) different upload and download capabilities.

Other Measures (low end) . T1 Speed can also refer to lines carried on the T1 itself. If it is a channelized T1, the T1's speed can refer to the individual line speeds of all services that may be multiplexed on the T1 for "T1 access" transport. For instance, if a T1 access line carries three 512kb circuits, one might refer to the T1's speed as 3x512k, since the T1 facility is used to carry all three circuits, and since access loops are available in DS0, DS1 (T1), and DS3, a T1 would be required for transporting any circuit speeds greater than 64kb, but no greater than 1.5Mhz.

Other Measures (high end). T 1 speeds can also refer to applications that require greater than 1.5Mb. In the case of high-resolution imaging applications, or near-broadcast quality video, individual T1s can be multiplexed together to combine greater aggregate line speeds. For example, 4 T1s can be combined by inverse multiplexers on both ends to create a single 6Mb circuit. Some may refer to this arrangement as a 6Mb T1, although it is actually the combination of 4 T1s using inverse multiplexers to create a contiguous 6Mb of bandwidth.

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