Advantech PCM-3601 user manual Communications Protocol, Speeds of the Modem

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2.3Communications Protocol

Two popular groups of communications protocol are currently used in data communications throughout the world, the Bell standard and the CCITT recommendation. For 1200bps protocols, the Bell standard is used mainly in the United States and Canada, while the CCITT standard is used in most other countries. For 2400bps and faster protocols, the CCITT standards are used internationally. The following table shows common communications protocols listed from the highest to the lowest DCE speed.

DCE Speed	Bell	CCITT		Synchronous
56000bps	N/A	V.90		async
33600bps	N/A	V.34+		async
28800bps	N/A	V.34		async
14400bps	N/A	V.32bis (TCM)		async
9600bps	N/A	V.32	(QAM & TCM)	async
2400bps	N/A	V.22bis		async
1200/75bps	N/A	V.23	Main (host)	async
75/1200bps	N/A	V.23	Back (user)	async
1200bps	212A	V.22		async
0-300bps	103	V.21		async

Data communications requires that both modems on a link use the same protocol. The protocol determines the communications speed and transmission standard (Bell or CCITT). To change protocols, you can issue a B command and the modem automa- tically goes to the highest speed of that protocol. If you want to specify a particular protocol speed, issue a %B command.

2.4Speeds of the Modem

During an on-line communications path, your modem is located between the local computer and remote modem. It has to

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