User's Guide

The Operational View SB300 Series
Page 58 Proprietary and Confidential 2110059 Rev 1.0
Based on field experience using the &F5 settings, the following limits are recommended:
• V.32bis talking to cellularly aware landline modem – 9600 bps (S37=9)
• V.32bis talking to standard wireline modem – 4800 bps (S37=7)
• V.34 talking to cellularly aware modem – 12000 bps (S37=10)
• V.34 talking to standard wireline modem – 9600 bps. (S37=9)
If only a small amount of data is being transferred, it is recommended that a data rate of 4800 bps
(S37=7) is used. This will give optimal performance and coverage area. Error Correction should
always be enabled. Flow control should be used (hardware recommended).
For situations where even 4800 bps does not hold a connection, the last suggestion is to try a data
link at 1200 bps (s37=5).
6.5.2. Connections to ETC Enabled Modems
Enhanced Throughput Cellular (ETC) is a protocol enhancement designed to optimize cellular
data communications. It is described in Section 4.5.2.1.
This is the best case scenario and it should be possible to achieve speeds of 9600 – 19200 bps if
the host supports V.34 and ETC. The table below lists some of the steps for troubleshooting bad
connections at both the SB320 end and the Host modem end. As a rule, when starting the
troubleshooting procedure, both modems should be reset to their respective factory defaults
settings. If problems still persist, then a more thorough analysis of each modem’s settings needs
to be done as outlined below.
6.5.3. Connections to Non-ETC Compatible Modems
If the remote modem does not support LAPM and V.22bis then you will have to allow the SB320
to use alternative protocols. The &F0 command is used. This AT command configures the
modem in CSC data mode but without ETC enabled.
An additional series of AT commands and S-Register settings should also be set to optimize the
modem to operate in a cellular environment without the benefits of the ETC protocol. This non-
ETC configuration will then allow the modems to negotiate other protocols such as MNP, etc.
The following additional commands should be sent to configure the modem for CSC mode use
with non-ETC compatible modems:
\N3 Enables V.42 LAPM error control but also allows MNP and will even tolerate a
non-error controlled link. A setting of 2 is also possible if you want to
disconnect if neither LAPM nor MNP error control can be negotiated.
-K0 This is a companion to the above command indicating a preference for LAPM
when using V.42.
*H2 This sets the Link Negotiation Speed for the initial connection to 4800 bps. The
policy of “start slow and train up” guarantees that the initial negotiation phase
has more chance of success. Start-up speeds of 4800 bps and 9600 bps (*H3)
may be used. In addition if a connection has not been established after 60
seconds, the modems will fall back to 1200 bps.
S7=120 The Wait for Carrier should be set higher than the default 50 seconds to allow for
the added time of cellular (and possibly modem pool) connections. This sets the
wait to 120 seconds.
S10=100 Lost Carrier Hang-up Delay is set to 10 seconds. The default is 0.6 seconds but
cellular links can be interrupted during cell changes and due to other “noise” so
the modem will wait longer to determine if the connection is truly lost.
S51=15 This sets the V.34 symbol rate to 2800 symbols per second and the carrier
frequency control to automatic for transmissions. The default would allow 3429
symbols per second, which is likely to lead to more failures and retransmissions.