Configure Protocol Switch software
Digi TransPort User Guide
569
• The router first looks up the Called NUA/NUI in the
Configuration > Network > Protocol
Switch > NUA to Interface Mappings
mapping table to determine the IP address to use in
the event that the call ends up being switched to a TCP or XOT interface. If a match is found on
the Called NUA/NUI the router assigns the matching IP address from the table to the call. If IP
address mapping table does not contain an entry for the Called NUA/NUI and the call is
eventually switched to a TCP or XOT channel then the default IP address (
IP Stream
or
XOT
Remote IP Address
) is used.
• The router then determines from the source interface of the incoming call which interface
type it should be switched to, from the
Switch from
parameters on the
Protocol Switch
page.
• For example, if the call arrived via a LAPB 0 interface and the Switch from LAPB 0 to
parameter was set to LAPD, then the outgoing interface would LAPD.
• If the outgoing interface is LAPD the router changes the Calling NUA field of the incoming
call to the D-Channel NUA value (as defined on the
Protocol Switch
page). If the outgoing
interface is NOT LAPD processing proceeds as at step 6.
• The router then searches the
Configuration > Network > Protocol Switch > NUA Mappings
table to see if there are any matches for the
Called
or
Calling NUA
values on the specified
interface. When the
Interface Description
is
Off
/
None
data is not switched from or backed-
up from this protocol is a match, the
NUA In
value is substituted by the
NUA Out
value, as the
mapping is applied individually to both the
Calling NUA
and
Called NUA
for the packet.
• The router checks the leading characters of the
Calling NUA
to see if there is a match with the
Call Prefix
parameter. If there is a match, the prefix digits are removed before the outgoing
X.25 call is made. Otherwise, the call is made anyway, and the switching process is complete
for this call.
• If after step 3, the router has determined that the outgoing interface is not LAPD, it checks if
the outgoing interface is LAPB. If it is, it checks to see if the
Called NUA
field in the call packet
matches the
LAPB 0
NUA parameter. If it does, it selects
LAPB 0
as the outgoing interface. If
the
Called NUA
field does not match
LAPB 0
NUA, it checks for a match with
LAPB 1
NUA. If
there is a match, it sets the outgoing interface to
LAPB 1
.
• If the
Called NUA
field in the calling packet matches neither the
LAPB 0
NUA or
LAPB 1
NUA
parameters, the outgoing interface is set to the interface specified by the relevant
Switch from
parameter.
• If the call is being switched over
LAPB 0
. the router sets the
Called NUA
to the
TE NUA
(
LAPB 0
) value. If the call is being switched over
LAPB 1
, the router sets the
Called NUA
to the
TE NUA
(
LAPB 1
) value.
