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56 536EX Chipset Developer’s Manual
Intel Confidential
Error Correction and Data Compression
Error Correction and Data
Compression 4
The 536EX 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.42 bis 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 6. V.42 bis data compression requires
V.42 (LAPM only). MNP 5 requires MNP 2-4.
The 536EX chipsets support four operating modes: buffer (normal), MNP reliable, V.42 auto-
reliable, and V.42 reliable. 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). See
Table 1 on page 11 for all DTE-to-DTE data rates. The modem-to-modem data rates are listed in
Table 2 on page 11. See Table 3 on page 11 for the modem-to-ISP data rates. Each operating mode
is explained in more detail in the following tables.
Table 20 lists connection types corresponding to +ES settings.
Table 19. Operating Modes
Mode Features
Buffer (Normal)
+ES=1, 0, 1
No error correction/data compression, but speed buffering is supported.
MNP Reliable
+ES=4, 4, 6
MNP 2–5 connection only. If an MNP connection cannot be established, the modem
hangs up.
V.42 Auto-Reliable
+ES=3, 0, 2
V.42/V.42 bis with fallback to MNP 2–5 or normal mode.
V.42 Reliable
+ES=3, 2, 4
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.