Chapter 9. Cable DetailsGauge, D-Shield or T-Screen Type, and Other Factors In most areas, 22 AWG is the preferred cable for most types of T1. In some metropolitan areas, limited 24 AWG and 26 AWG are used. Keep in mind the different attenuation characteristics of each. Larger sizes, such as 19 AWG, were never very popular for T1 because of the economics of buying copper wire versus buying electronic systems. D-shield is a type of cable with one half of the pairs (transmit in one direction) organized into one D-shaped half of the cable, as viewed in cross-section. This shielding effectively makes one-cable operation almost as good as two-cable operation in terms of crosstalk reduction. Consult the cable manufacturers for complete details. Filled cable contains a gel that prevents ground water from easily leaking into the cable. Although this cable has higher initial cost, it tends to produce longer cable life in rainy regions. Note that filled cable has slightly different cable attenuation figure compared to unfilled cable. Selection of Conductors T1-class cables are commonly manufactured with multiples of 25-pair bundles. For single-cable operation, the standard choice is the east-west direction of transmission to be in one bundle and the west-east direction to be in a separate bundle. Furthermore, 104-pair cables are organized with two bundles for each direction and four pairs for the various voice-frequency circuits associated with T1 lines (order wire, fault locate, etc.). If the cable does not have this bundle organization, then it becomes necessary to test for potential crosstalk (distortion factor, or D-factor) from every cable pair to every other cable pair to determine which pairs have the most coupling loss.
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