Modbus
Cellular
Gateway
Index
skipping
is
used
to
reserve
slots
for
new
function
insertion,
when
required.
58
transfer
mission
instantly
by
only
changing
routing
path
to
failover
interface.
The
dialing
‐
up
time
of
failover
connection
is
saved
since
it
has
been
connected
beforehand.
For
some
mission
‐
critical
applications,
this
gateway
supports
“Seamless
Failover”
8
to
shorten
switch
time
during
WAN
interface
failover
process.
So,
the
initial
status
of
two
WAN
connections
for
Seamless
Failover
is
shown
in
following
diagram.
Cellular
Network
WAN
‐
1:
ADSL
ISP
DSLAM
Gateway
WAN
‐
2:
3G/4G
Connected and
Data Transferring
Initial Status
Connected but just
Keep Alive
Next,
Failover
and
Failback
processes
are
shown
in
following
diagram.
Their
steps
are:
S
1:
When
system
discovers
the
primary
WAN
connection
is
failed.
S
2:
System
starts
the
failover
process.
S
3:
System
changes
the
data
routing
path
to
the
failover
WAN
interface
for
further
data
transmitting.
It
is
faster
than
the
one
in
the
normal
mode
of
failover
since
routing
change
is
simpler
than
dialing
up
a
new
WAN
connection.
S
4:
System
keeps
trying
to
recover
the
failed
primary
WAN
connection.
Once
it
is
recovered,
system
starts
the
failback
process.
S
5:
When
failback
process
starts,
system
will
leave
alive
the
current
WAN
connection
via
Failover
WAN
interface,
but
no
more
data
transmitting.
S
6:
System
changes
the
data
routing
path
back
to
the
primary
WAN
interface
as
same
state
as
at
the
beginning
of
system
normal
operation.
