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56K V.92 Data, Fax, and Voice Chipset
Programmer’s Guide Intel Confidential 63
4. ERROR CORRECTION AND DATA
COMPRESSION
The MD566X chipsets support two types of data mode error correction (MNP
2–4 and V.42) and
data compression (V.44, MNP 5 and V.42 bis). V.42 error correction uses LAPM as the primary
error-control protocol and uses MNP 2-4 as an alternative.V.44 provides enhanced data
compression over the existing V.42bis standard. Data compression is up to on average 40% faster
than previous methods. This provides for faster web browsing and data downloading. The +DS44
command configures the operation of V.44. There are nine parameters associated with the +DS44
command. For a detailed description of this command, refer to Table 4-2 V.42 bis data compression
requires V.42 (LAPM only). MNP 5 requires MNP 2-4.
The MD566X chipsets support four operating modes: buffer (normal), MNP reliable, V.42 auto-
reliable, and V.42 reliable. These four modes are selected by the \Nn command. They allow the
DCE to communicate with remote modems that may or may not support error correction and data
compression. Speed buffering, which is used for all operating modes, allows the DTE-to-modem
data rate to be different from the modem-to-modem data rate. This is accomplished by using
transmitter and receiver buffers in the modem. Thus, the DTE-to-modem data rate can be set for
2400 bps when the modem-to-modem data rate is 300 bps without causing any data errors. In all
data modes, the DTE-to-modem data rate can be set for any valid speed between 300 bps to
115,200 bps (that is, the modem autobauds up to 115,200 bps). The modem-to-modem data rates
can be set to 300, 1200, 2400, 4800, 7200, 9600, 12,000, 14,400, 16,800, 19,200, 21,600, 24,000,
26,400, 28,800, 31,200, and 33,600 bps. Each operating mode is explained in more detail in the
following tables.
When V.80 mode (synchronous access mode) for videoconferencing becomes available in the
future, the +ES=m commands for data correction/compression will supersede the \Nn commands.
Control reverts to the \Nn command upon exiting V.80 mode.
Operating Modes
Mode Features
Buffer (Normal)
\N0 or \N1
No error correction/data compression, but speed buffering is sup-
ported.
MNP Reliable
\N2
MNP 2–5 connection only. If an MNP connection cannot be estab-
lished, the modem hangs up.
V.42 Auto-Reliable
\N3
V.42/V.42 bis with fallback to MNP 2–5 or normal mode.
V.42 Reliable
\N4
V.42, V.42 bis or MNP 2–5 only connection. If a V.42/V.42 bis/MNP 2–
5 connection cannot be established, the modem hangs up.