DCT Antares SB, User Manual

Page: 54 / 238

3.8. OVER THE AIR
1. First, the unit tries to match the remote peer address with
the UDP Network set with the
XAUN
command. If the remote
peer address does not match the UDP network, or if the UDP
network is not defined (default state), the second validation
mechanism is performed.
2. The second validation is done according to the Destination
Points list. If the server address is found on the list the server
is validated an the TAIP command is accepted (as long as the
corresponding Destination Point has the TAIP console access
enabled (default state)).
The Destination Points list can be set and consulted with the
XADP
command.
There are some considerations to be taken when the unit is working
behind a NAT (very common when the unit has Internet access):
If the Destination defined for TAIP console access is also the AVL
server which listens for the unit’s periodic and exceptional reports
there has to be some reporting criteria that guarantees that the unit
will not be silent for a period of time longer than the NAT’s port
expiration time. If the unit is silent for a longer period, the NAT
server on the cellular carrier’s side will silently close an active TCP
connection or eliminate any UDP port translation making it impos-
sible for the AVL server to send queries to the unit until the unit
reports again. In a similar situation when the TAIP-console access
is granted to an IP host other than the AVL server which recollects
the unit’s reports, a periodic time-only criteria has to be defined to
generate a report to the IP host so it can consult the unit at any time.
For TCP this time is around 1 hour and for UDP is around 5 minutes
but this is dependent on the cellular operator and may be different
in your case.
This situation has two possible workarounds:
1. From a SMS Destination (mobile number) that has TAIP con-
sole access, send a SMS with a command that instructs the unit
to send a “hello-type” report to the IP host which is going to
interact with the unit. Thus this SMS will have to be sent only
when the communication via IP is lost due to a NAT expiration
time. This eliminates the need of a keep-alive for TCP or UDP
report and depending on the SMS’ charging value it may lead
to a cost effective solution for having the unit’s TAIP console
remotely available all the time. For a ”‘hello-type”’ report see
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