In T1 CAS, where are the signaling states and control features carried for Super Frame robbed-bit signaling?
A.
6th and 12th frame
B.
6th, 12th, 18th, and 24th frame
C.
the first and seventeenth time slot
D.
the first and sixteenth time slot
Explanation:
Each T1 has 24 channels ( or 24 DS0 digital signal level 0) that can transmit 8 bits per channel each. This give us a total of 192 bits. One more bit is used for framing, bringing the total to 193 bits. Super Frame bundles 12 of these 193-bit frames for transport. The picture below shows the structure of a T1 Super Frame
The T1 CAS signaling looks at every 6th & 12th frames for signaling information, these bits are referred to as the A and B bits. The A and B bits can represent different signaling states or control features (on hook or off hook, idle, busy, ringing, and addressing)
According to Nyquist theory, we sample voice 8000 times per second, that means we need to send 8000 of these 193-bit frames every second. So 8000 x 193 = 1,544 Mbps.
Extended super frame (ESF), due to grouping the frames in sets of twenty-four, has four signaling bits per channel or timeslot. These occur in frames 6, 12, 18, and 24 and are called the A-, B-, C-, and D-bits respectively. So if the question asks about ESF, the answer should be B.
