Which of the following statements are CORRECT about the PRA protocol? (Multiple Choice)

Question

Options

• AThe protocol consists of the physical layer, data link layer, and network layer.
• BThe protocol is used for link multiplexing and error detection at the physical layer.
• CThe standard protocol used at the data link layer is Q.921.
• DThe standard protocol used at the network layer is Q.931.

• A
  76% (26)
• B
  24% (8)

Explanation

PRA Protocol Explained

PRA (Primary Rate Access) is an ISDN protocol stack that maps directly onto three OSI layers - physical, data link, and network - making A correct. At the data link layer, Q.921 (LAPD - Link Access Procedure for the D-channel) handles framing, error detection, and flow control, confirming C. At the network layer, Q.931 manages call setup, maintenance, and teardown, confirming D.

Option B is wrong because it misplaces functions: link multiplexing and error detection are data link layer responsibilities (handled by Q.921), not physical layer ones. The physical layer (governed by I.431 in PRA) concerns itself with electrical signaling and bit transmission, not multiplexing logic.

Memory tip: The two Q-standards climb with the layers - Q.921 for layer 2, Q.931 for layer 3 (9-2-1 → 9-3-1, counting up). If a choice moves a data-link function down to the physical layer, it's a trap.

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