Modbus
Cellular
Gateway
Index
skipping
is
used
to
reserve
slots
for
new
function
insertion,
when
required.
115
Scenario
Application
Timing
When
a
SIP
phone
is
behind
a
NAT
gateway,
and
it
is
expected
to
make
a
call
to
or
receive
a
call
from
the
Internet.
The
"SIP
ALG"
feature
must
be
activated
in
the
NAT
gateway.
Scenario
Description
The
"SIP
ALG"
feature
in
the
NAT
Gateway
is
enabled
to
monitor,
open
up
ports
and
make
the
address
and
port
translation
for
the
voice
communication
of
the
SIP
phone
behind
the
gateway.
A
SIP
phone
behind
a
NAT
gateway
can
call
another
SIP
phone
with
the
help
of
the
SIP
server
in
the
Internet.
Parameter
Setup
Example
Following
table
lists
the
parameter
configuration
for
the
NAT
gateway
in
above
diagram.
Configuration Path
[Special AP & ALG]-[Configuration]
ALG
SIP ALG
■
Enable
Scenario
Operation
Procedure
In
above
diagram,
the
NAT
Gateway
is
the
gateway
of
Network
‐
A
and
the
subnet
of
its
Intranet
is
10.0.75.0/24.
The
gateway
has
the
IP
address
of
10.0.75.2
for
LAN
interface
and
118.18.81.33
for
WAN
interface.
It
serves
as
a
NAT
router.
Configure
the
NAT
gateway
with
SIP
ALG
being
enabled.
When
the
SIP
Phone
#1
behind
the
NAT
gateway
has
booted
up,
it
will
register
to
the
SIP
server
in
the
Internet.
So,
the
SIP
server
knows
where
the
SIP
Phone
#1
is.
In
the
same
way,
the
SIP
Phone
#2
also
registers
to
the
SIP
server.
A
local
user
wants
to
make
one
call
to
the
SIP
Phone
#2
by
using
the
SIP
Phone
#1,
the
NAT
Gateway
will
monitor
the
calling
process,
open
up
required
service
ports
for
incoming
packets
and
