Which standard is designed for interoperability via Plain Old Telephone Service (POTS)?

• A. H.261
• B. H.320
• C. H.263
• D. H.324

Answer: (D)

Interoperability over traditional telephone lines requires a standard built for the narrow bandwidth of Plain Old Telephone Service. H.324 was created to operate over PSTN/POTS networks, handling both audio and video in a way that different vendors’ equipment can work together on those low-bandwidth connections. It specifies how multimedia data is carried and how control signaling negotiates sessions over those circuits, typically using a simple signaling/control framework suited for 64 kbps-class channels.

In contrast, H.320 targets ISDN networks rather than POTS, and the other options are codecs or standards focused on video compression rather than the network access layer for plain telephone lines. So, the standard designed for interoperability via POTS is H.324.