On 1/6/14 8:36 PM, Magnus Danielson wrote:
Bob,
It works the other way around. The standard Bell handset (103A I believe
the designation was) has the 300-3400 Hz response, and with not so fancy
analogue filtering, you can handle 4 kHz and thus 8 kHz sampling rate.
The ITU-T G.711 A-law (where naturally the americans wanted their own,
so u-law appeared) does non-linear pseudo-dynamic compression into 8
bits. T1s cram 24 channels into one frame, and adding 1 bit for framing,
giving 24*8+1=193 bits per frame, giving the 1544 kb/s rate. 193 being a
prime have caused a bit of headache over the years. In Europe, cramming
30 channels into a bundle was preferred, and allowing 2 bytes for
framing and signalling. In T1, you do signalling by bit-stealing every
6th LSB on a channel. Caused some grey hairs for modem designers back in
the day, and followed along over into the ISDN, as the primary rates was
over E1 and T1. T1 also had three different line-encodings, of which
only one was really transparent to all binary combinations.
Oh the joy of early digital telephony. Many lessons where hard to learn.
Synchronization was only one of them.
Don't forget the length of ATM cells.. 53 bytes.. because of how big
France is.
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