Data Communication and Host Modes
Rev 3.0B Feb.08
55
•
TCP
auto
answer
is
enabled
(
S1
),
a
TCP
connection
request
is
received,
and
the
modem
is
not
in
a
data
session.
•
Data
is
received
on
the
serial
port
and
·
The
Startup
Mode
Default
(
MD
)
is
4
(auto
TCP)
·
The
remote
TCP
destination,
as
defined
in
S53,
success
‐
fully
responds
to
the
TCP
connection
request.
The
value
of
S7
(TCP
Connection
Time
‐
out)
specifies
the
number
of
seconds
to
wait,
after
initiating
a
TCP
connection
attempt,
for
a
successful
connection
to
be
established.
If
the
connection
has
not
been
successfully
established
before
the
time
‐
out
occurs,
ERROR/BUSY
is
returned.
TCP
packet
assembly
is
affected
by
the
values
of
S50
(PAD
Forwarding
Time
‐
out)
and
S51
(PAD
Forwarding
Character).
Data
received
in
the
serial
buffer
will
be
transmitted
when
the
idle
inter
‐
character
time
‐
out
specified
in
S50
(in
tenths
of
seconds)
occurs
or
when
a
character
is
received
that
matches
S51
(if
non
‐
zero).
The
TCP
session
will
be
terminated
if
no
data
is
transmitted
or
received
for
the
time
interval
specified
in
TCPT
and
TCPS
.
TCPT
is
the
number
of
minutes
(TCPS=0)
or
seconds
(TCPS=1)
used
for
this
idle
time
‐
out.
Caution: TCPT should never be 0 when using the TCP mode. A
broken TCP session can result in the modem being left with a TCP
half-open connection that can only be terminated with a reset.
TCP Auto Answer
TCP
auto
answer
(S0=1|2)
also
allows
a
TCP
connection
request
to
be
“answered”
when
the
modem
is
idle,
not
in
a
data
session.
The
TCP
connection
request
ʹ
s
destination
port
has
to
match
the
modem
ʹ
s
device
port.
Note: UDP auto answer may also be set simultaneously with TCP
auto answer. Then, when in the idle state, the modem will accept
either a TCP connection request or UDP incoming packet, and enter a
TCP or UDP session as appropriate.
Hybrid Modes
Hybrid
modes
are
supported
mainly
for
legacy
implementa
‐
tions.
Some
previous
hybrid
modes
(MD=5,
6)
are
no
longer
implemented
as
special,
unique
modes.
Now
that
UDP
auto
answer
(UDP
Half
‐
open,
S82=2)
can
be
enabled
in
conjunction
