T1/PRI For T1 or PRI applications (only PRI on the ESI-50; it doesn’t support T1), an ESI Communications Server can use a compatible digital line card (DLC)1: • ESI-1000, ESI-600, ESI-200, ESI-100 — DLC and DLC12, each for either T1 or PRI. • ESI-50 — DLC82 for only PRI. Depending on how you configure it, each supports either (a.) a single T1 circuit at 24 DS0 channels or (b.) a PRI circuit supporting 23 “B” (bearer) channels and one “D” (data link) channel. The DLC12 and DLC82 each also support 12 digital stations. The T1 or PRI line is connected via the last two pairs of the industry-standard 50-pin amphenol cable connector on the front of the DLC. Each ESI Communications Server has a different maximum number of system-wide DLCs (see “Port card options,” page A.4). Partial T1 or PRI applications are supported through line programming. Each DLC has built-in CSU functionality. The integrated CSU can be enabled or disabled via system programming2. The following functionality is provided: line, payload, DTE and none (normal operation) loopback modes with the ability to respond back controlled via system programming; alarm conditions, and both ANSI T1.403 and TR 54016 performance messages for ESF only.