How many timeslots are available for calls in PRA signaling?

The correct answer is C. 30. In PRA (Primary Rate Access) signaling, based on the E1 frame structure, there are 32 total timeslots - but two are reserved for overhead: timeslot 0 (used for frame synchronization) and timeslot 16 (used as the D-channel for signaling). That leaves exactly 30 B-channels…

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How the community answered

(21 responses)

A
5% (1)
C
86% (18)
D
10% (2)

Explanation

In PRA (Primary Rate Access) signaling, based on the E1 frame structure, there are 32 total timeslots - but two are reserved for overhead: timeslot 0 (used for frame synchronization) and timeslot 16 (used as the D-channel for signaling). That leaves exactly 30 B-channels available for actual calls, making C correct.

Why the distractors are wrong:

A (32): This is the total number of timeslots in an E1 frame - it ignores the two that are reserved for non-call purposes.
B (31): This would only account for subtracting one overhead slot, not both.
D (29): There is no valid reason to remove a third timeslot; only two are consumed by framing and signaling.

Memory tip: Think "32 minus 2 = 30" - start with 32 E1 slots, subtract 1 for sync and 1 for signaling, and you're left with 30 slots ready to carry calls.

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