Final answer:
c. 30. An E1 circuit has 32 channels, but only 30 are available for voice, video, or data as two are used for framing and signaling. The correct answer is 30 available channels.
Step-by-step explanation:
An E1 circuit is a digital telecommunication carrier format widely used worldwide, excluding North America and Japan where T1 circuits are common. An E1 link provides a total bandwidth of 2.048 Mbps, which is partitioned into 32 channels, each having a bandwidth of 64 Kbps. However, not all these channels are available for voice, video, or data transmission.
Out of the 32 total channels, one channel (channel 0) is reserved for framing and synchronization purposes, and another channel (channel 16) is typically used for signaling and control information. This leaves us with 30 channels that are available for user data, which includes voice, video, or data communication. Therefore, when considering how many channels on an E1 circuit are available for these purposes, the correct answer is c. 30.