US Robotics COURIER Manual de usuario descargar pdf (Pagina 121)

U.S. Robotics I-modem Command Reference

Handshaking, Error Control, Data Compression, and Throughput • Page 11-12

¥ A Link Access Procedures for Modems (LAPM) nego-ti-ation phase, during which the

devices identify their capabilities concerning maximum data block size and the number

of outstanding data blocks allowed before an acknowledgment is required.

MNP Error Control

The Microcom Networking Protocol (MNP) is supported by the ITU-T V.42 Recom-

menda-tion. It was originally developed by Microcom, Inc. and is now in the public

domain.

MNP is based on special protocol

frames. If the remote device doesn't recognize an MNP

Link Request, error control isn't possible. (In HST asymmetrical mode, U.S. Robotics

devices use a proprietary scheme similar to MNP.)

Error Control and Flow Control

Flow control of data from the computer is required under error control for two reasons:

¥ The transmitting device buffers a copy of each frame it transmits to the remote end until

it is acknowledged by the receiving device.

¥ If errors are encountered, retransmis-sion activity can cause a steady stream of data from

the computer to overßow the buffer.

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US Robotics COURIER Manual de usuario Pagina 121