Protocols; Mnp/Reliable Mode; Auto-Reliable; Constant-Speed Interface - Black Box 325 User Manual

Table of Contents

CHAPTER 9: Protocols

9. Protocols

9.1 MNP Reliable Mode

MNP (Microcom Networking Protocol) provides error detection and automatic retransmission of data

upon detection of an error. The modem supports MNP levels 2, 3, 4 and 5. Level 2 is the asynchronous

version. Level 3 is the synchronous version and level 4 is synchronous with optimized headers for

increased efficiency. Level 5 compresses the data for increased effective throughput.

Allows the modem to operate in a non-reliable mode if a reliable connection cannot be established.

The modem serial port adapts to the data rate of the DTE and does not change speed if the (modem)

data link connects at another speed. Therefore the DTE-to-DCE interface speed is constant.

A technique of replacing repeated characters in a file being transmitted by a shorter symbol allowing a

higher effective data rate.

No error control with or without constant-speed DTE interface. Data is buffered.

The DTE speed and DCE speed are forced to be the same. No error correction or buffering.

If the serial-port speed exceeds that of the modem connection, characters may be sent by the DTE to the

modem faster than it can send them to the remote modem. The modem holds characters in an internal

buffer until they can be transmitted. When this buffer is full, the modem uses flow control to cause the

DTE to stop sending characters. As the modem continues to transmit data and the buffer empties, flow

control is again used to cause the DTE to resume sending data.

135

Table of Contents

325 card