Verilink Productivity 500 (34-00236) Product Manual - Manual (Page 58)

Page 58 500 TA Call Placement
Escape Sequence (Async Data Mode Only)
If the 500 TA is in the asynchronous data mode, the escape sequence can be
sent to return the 500 TA to the command mode and remain online. The escape
sequence consists of a pause (normally 1 second), three escape characters, and
then another pause. The default escape sequence characters are ‘+ + +’.
The escape sequence character is stored in S-register two (S2) and can be
changed if necessary. The escape sequence can also be disabled to prevent any
possibility of false escapes into the command mode.
After entering the escape sequence, the 500 TA will return to the AT command
mode, but will not hang up or break the connection with the remote unit. AT
commands can now be entered to the 500 TA. The ATO command returns the
500 TA to the data mode. The ATH command hangs up the call.
CALL PLACEMENT STRATEGIES
Before a data call is placed, the 500 TA should be configured correctly. Correct
configuration depends on the type of data to be sent, PC speed, and ISDN
speed. For more information on how to configure the 500 TA, refer to Applica-
tion Examples on
page 23 , and Option Configuration on page 37 .
Rate Adaption
When a data call is placed, the 500 TA will try to establish a physical data con-
nection on the ISDN B-channel. The B-channel is a digital channel that can
transfer data at either 56 kbps or 64 kbps, depending on the path the network
chooses when routing the call.
A rate adaption protocol will be needed if the user's PC is asynchronous or PC
rate is at any rate other than 56kbps or 64kbps. A rate adaption protocol adapts
the lower speed of the PC to the higher speed of the ISDN B-channel. The
AT%A2= command can be used to select a rate adaption protocol.
The 500 TA supports the V.120 rate adaption protocol. V.120 rate adaption pro-
tocol is an error-correcting protocol ensuring error free data transfer at speeds
up to 115.2 kbps. Note, however, that throughput is limited by the channel
speed to about 75 kbps. When using a rate adaption protocol, both the calling
and called units must use the same protocol. Also, unless they are using V.120
in asynchronous mode, the PCs on both ends must be set to the same PC speed
before data can be transferred.