User's Guide

The Operational View SB300 Series
Page 48 Proprietary and Confidential 2110059 Rev 1.0
PAD ERROR An internal modem error has occurred in the TCP stack. The modem
will have to be reset.
Unlike UDP, a CONNECT message in TCP service does mean that you have established a
communication link with the destination.
Transmitting
Once in data state, the modem uses its PAD management services to assemble the data coming
from the host into packets. See Section 5.8 for a discussion of these services.
Receiving
Incoming packets are accepted from the destination address specified in the Dial command
regardless of whether or not it is contained in the Friends list.
Any packets arriving from an IP other than that in the Dial command are ignored.
If the modem has been placed in command state but is still in on-line condition, incoming data
will be buffered. There is an automatic remote flow control between the modem and the network
to prevent overflow.
5.7.3.2. Escaping Data State
There are two methods to escape data state in TCP packet service. The host can issue the PAD
Time Independent Escape Sequence (TIES) if it is enabled, or the DTR Option can be used if it is
enabled.
TIES
This method is enabled with register +WS60=1 (the default). It is disabled with a setting of 0
(zero).
When enabled, the host can send AT+++ as a packet. The “AT” portion must be in uppercase.
See Section 5.8 for details on packet management and notes regarding the PAD Inter-Character
Timer.
When the TIES is received by the modem, it will enter command state but remain registered and in
on-line condition (the session is kept open). If data arrives at the modem while the session is open
and the modem is in command state, the data is buffered as described above. See below for
instructions on closing the session.
If the session has been kept open, the host can re-enter data state by issuing the On-line command
(O). The modem will respond with CONNECT and data state is restored.
DTR Option
An alternative to TIES is to pre-set the DTR Options (&D) to either 1 or 2 and then switch DTR
off to escape data state. If the option is set to 1 (&D1), the modem will enter command state and
remain registered with the current session still open. If the DTR Option is 2 (&D2) then the
modem will close the session, de-register, and return to command state. Note that if auto-
registration is enabled, the modem will switch off DCD (closing the current session) but will
remain registered.
If the session has been kept open, the host can re-enter data state by issuing the On-line command
(O). The modem will respond with CONNECT and data state is restored.
5.7.3.3. Closing a TCP Session
To end a TCP session, escape data state as described above. If the &D2 DTR option is used then
the session is closed.
If TIES or the &D1 DTR option is used then you must hang-up with either ATH0 or ATH1 to
close the session. Both of these command options will close the current session. If the modem is
set to manual registration, it will also be de-registered by both of these options.