X.21 is —
2018
X.21 is —
- A.
a method of determining which device has access to the transmission medium at any time
- B.
a method access control technique for multiple access transmission media
- C.
very common but oriented at linked protocol issued to ISO
- D.
a network access standard for connecting stations to a circuit switch network
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Correct answer: D
X.21 is an ITU‑T standard used for connecting data terminal equipment (DTE) to a circuit‑switched network. Key points: It is an ITU‑T recommendation that defines the physical, electrical and procedural characteristics of the interface between terminal equipment and a circuit‑switched network.
Primarily describes the DTE–DCE interface used for synchronous digital connections to circuit‑switched telecommunication networks.
Specifies connector pinouts and signaling conventions used to interconnect equipment and the network.