Omni 56K Plus Series User’s Guide

Table 2-4 Physical Layer Capacity

STANDARD

BIT RATE [BPS]

BAUD RATE [BAUD]

MODULATION

CARRIER FREQUENCY [HZ]

 

 

 

 

 

V.32 uncoded

9600

2400

16-QAM

1800

 

 

 

 

 

V.32

4800

2400

4-DPSK

1800

 

 

 

 

 

V.23

1200/75

1200/75

FSK

 

 

 

 

 

 

V.23

600/75

600/75

FSK

 

 

 

 

 

 

V.22bis

2400

600

16-QAM

1200 Call

 

 

 

 

2400 Ans

 

 

 

 

 

V.22

1200

600

4-DPSK

1200 Call

(BELL 212A)

 

 

 

2400 Ans

 

 

 

 

 

V.21

300

300

FSK

 

 

 

 

 

 

BELL 103

300

300

FSK

 

 

 

 

 

 

2.5.2 Flow Control

This feature refers to stopping and restarting the flow of data into and out of the modem’s transmission and receiving data buffers. Flow control is necessary so that a device does not receive more data than it can handle. The Omni 56K Plus provide two kinds of flow control methods.

2.5.3 Hardware CTS/RTS Flow Control

This is a bi-directional flow control where CTS and RTS are RS-232 signals which must be available on your computer. When the modem’s transmission buffer is almost full, the modem will drop CTS to signal the DTE that it cannot accept data any more. Turn on the CTS to notify the DTE that it can keep sending data to the modem. On the computer software side, when the receiving buffer of the software is almost full, it will drop RTS to signal the modem to stop sending data to the DTE. Turn on the RTS and the modem will start sending data again to the DTE.

2.5.4 Software XON/XOFF Flow Control

This is a bi-directional flow control. XON and XOFF character defaults are decimals 17 and 19.These can be changed by modifying the S-Registers S31 and S32.Both the modem and the DTE will treat XOFF as a signal to stop transmitting data and will treat XON as a signal to restart sending data. Modems will not send these characters received from the local DTE to the remote modem.

2.5.5 Error Control

Error control keeps the modem data link error-free by detecting and re-transmitting erroneous data. The Omni 56K Plus modems support both MNP and V.42 error control protocols. The MNP protocol was an industry standard developed and licensed by Microcom, Inc. Omni 56K Plus modems support level 4 and 3 error control protocols, commonly denoted as MNP4 and MNP3.

V42 is a developed standard by CCITT. V.42 supports both LAPM and MNP4. A V.42 handshaking will try an LAPM connection first, and if not successful, it will try MNP4. The maximum data block size used in the Omni 56K Plus modem is 256 bytes.

Specifications and Function Description

2-5