Cabletron Systems CSMIM-T1 manual Error Correction

Error Correction

Other Classes of MNP

MNP Class 2 uses standard asynchronous framing techniques for data transmission and error correction. Because of this protocol overhead, the actual throughput is less than the bps rate of the modem.

MNP Class 3 uses synchronous framing techniques. Removing start and stop bits associated with each character prior to transmitting results in a 20% performance increase over Class 2. Thus, actual throughput is greater than the modem’s bps rate.

MNP Class 4 uses synchronous framing techniques plus improvements developed by Microcom Adaptive Packet Assembly and Optimized Data Phase. These enhancements result in better performance for all types of connections.

Adaptive Packet Assembly automatically adjusts the size of the data packets based on the quality of the telephone line. When the line quality is good and there are few retransmissions, the modem increases the packet size. When the line quality is poor and retransmissions are frequent, the size of the packet decreases in order to maintain high throughput during error correction under poor conditions.

Optimized Data Phase is the redesign of the MNP protocol header that reduces the number of overhead bytes per data packet. For example, modems operating at Class 4 service transmit data at 2,900 bps.

MNP Class 6 allows half-duplex, fast-train, high-speed reliable connections with other MNP Class 6 modems at speeds of 4,800 to 9,600 bps.

Universal Link Negotiation allows the modem to automatically connect with other MNP modems at the highest common speed and protocol.

Statistical Duplexing adjusts the line bandwidth and data traffic flow during reliable connections to achieve maximum throughput.

MNP Class 7 provides Enhanced Data Compression, which combined with Class 4 allows throughput of more than twice the connection speed. MNP Class 7 Enhanced Data Compression not only dynamically adjusts to the type of data being transmitted, but allows for the probability of character frequency, for superior compression efficiency.

MNP Class 9 includes enhanced Universal Link Negotiation.

CSMIM-T1 Hardware Installation Guide 6-15