User guide

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Chapter 5 - AT Commands
TA determines the type of call by checking for protocol information in the SETUP message or
by matching protocol information received on the B-channel once connected if no protocol
information is available in the SETUP message. Once the protocol is determined, the TA will
switch its data protocol to match. Upon disconnect the TA will revert its data protocol
selection back to the protocol that was selected before the call was received when S52=1
“Detect”. If S52=2 “Detect and Select”, then the TA will not revert the protocol selection,
rather it will keep the detected data protocol as the new protocol selection. “Detect and
Select” is useful for applications where the TA receives a call and then the software performs
callback. Callback calls should be made with the same protocol that was used by the client so
“Detect and Select” enables this possibility. However, if an initialization string or &Fn
command is given to the TA that changes the protocol after the disconnection, then “Detect
and Select” will not be effective. Make sure no commands are given to the TA that will
change the data protocol when using “Detect and Select” if callback is involved to ensure that
the callback call uses the correct data protocol.
S53 Maximum X.75 Buffer Size
Usage: S53=n; S53?
Unit: 1 bytes
Range: n=64-2048 (64-2048 bytes)
Default: 2048 (2048 bytes)
S53 allows the maximum buffer size of an X.75 frame to be customized. Typically a smaller
frame size is more compatible with software packages on a PC (such as HyperTerminal).
Larger frame sizes introduce larger delay which some software cannot deal with appropriately.
S54: B-Channel Origination Rate
Usage: S54=n; S54?
Unit: Decimal ASCII code
Range: n= 0 (64Kbps, but use Progress Indicator IE),
n=56 (54Kbps),
n=64 (64Kbps)
Default: 0 (64Kbps, but use Progress Indicator IE)
S54 allows you to force the TA to originate digital calls with a 56Kbps or 64Kbps B-channel
rate. In some situations it is necessary to force a 56Kbps connection. Such a situation may
occur when an originated call fails to connect because the end-to-end connection is not
64Kbps and the originating TA or the answering TA is not informed of this situation by the
network. In some situations it is necessary to force a 64Kbps connection when the originating
TA is first informed that the call changed to 56Kbps but then later returned to the ISDN and
switched back to 64Kbps. By default the TA will check for Progress Indicator Information
Elements indicating changes in the routing of digital calls to determine whether the call needs
to switch to 56Kbps or remain at 64Kbps.
S55 POTS Port Call Control
Unit: Decimal ASCII code
Range: 1, 2, 17, 18
Default: 1
Allows you to set the type of information transfer capability for calls placed from the POTS
port either by a telephone, modem, or fax. Some Central Office (CO) switches keep track of