4. How many T1 facilities the company needs between its office and the PSTN if it has 47 digital telephones, each operating at 64kbps
3 low-speed video machines, each operating at 384kbps
1 interactive video system, requiring 1.536 mbps.

Need 4 T1's.

Each T1 can accomodate 28 channels.
► 47 digital channels

► 3 low speed V.machines at 384 kbps.
=384/64=6channels

► 1 interactive video systemat 1.536mbps.
=153664=24 channels.

So total=47+6+24=89 channels
each T1 requires 1 synchronizing channel & 1 signalling channel.
So 4 T1 requires 8 channels.
Total=89+8=97 channels.

4T1's =112 channels-96 channels=15 channels(remains free)

7. Frequency at which VOICE is sampled is?
a) 4 KHz
b) 8 KHz
c) 16 KHz
d) 64 KHz

The voice signals have a bandwidth of 4Khz (300hz-3400hz signal bandwidth + 450*2hz guard bands= 4000hz) according to Nyquist criteria, the sampling rate must be at least double of this total bandwidth. thus sampling rate= 2*4Khz = 8Khz. this is the required sampling rate to avoid loss of voice signals in transmission.

8. What is the maximal decimal number that can be accommodated in a byte?
a) 128
b) 256
c) 255
d) 512

ITS 256.

SINCE, 1 BYTE=8 BITS

THE LOGIC IS 2^8=256(2 TO THE POWER OF 8)