sreekanth@rgb.dec.com (Jon Sreekanth) (02/21/90)
In article <4057@accuvax.nwu.edu>, schweige@cs.nps.navy.mil (Jeffrey M. Schweiger) writes... >1. Can someone point me in the right direction for the technical >specifications for the various modem protocols in common use over >phone lines (i.e., Bell 103 for 300bps, Bell 212A for 1200bps, CCITT >V.22 for 1200bps, V.22bis for 2400bps, V.32, V.42, etc). I'm I'm not sure about the Bell Standards. For CCITT, you'll need one of the fascicles of the Blue Book (it's really called that), Fascicle VIII.1, "Data communication over the telephone network, Series V recommendations". The entire set of volumes is expensive, so try the larger university libraries, or order from the United Nations bookstore in NYC, at 212-963-7680. About $50 for each fascicle. >2. I've seen it mentioned that the max data rate over voice grade >line is basically capable of is 2400 baud, but have not found a >reference for how this number is determined. A pointer to an >appropriate reference here would also be appreciated, along with >similar references for what the various grades of telecommunications >lines are (T1, etc.). Just browse through the telecommunication/digital communication sections of any large university library. From my dim recollection, the standard telephone line is guaranteed from 300Hz to 3000Hz, and there is a requirement (deriving from someone's theorem) that the signalling rate should be less than the bandwidth. The important point here is the difference between baud and bits per second. The two terms are often confused, but baud refers to the number of symbols you can send per second, which is limited to about 3000; but each symbol can consist of several bits. For example 4800 bps or 9600 bps modems (incorrectly called 4800 baud or 9600 baud) put 2bits or 4 bits per symbol, encoding each symbol by a different amplitude and phase. The limit, of course, is imposed by the sensitivity of the receiver in distinguishing between the various encodings. Jon Sreekanth