Siemens A53457 Installation & Maintenance page 33

If a known route to an office device exists for that LLL, the WAG will send the ATCS messages to
that IP address at the "ATCS Server User Datagram Protocol (UDP) Port number" configured into
the WAG. The expiry timer for the "Active route list" entry for that LLL is refreshed.
If there is no known route toward the office for the LLL, the WAG will issue a "route request" out
into the broadcast medium (which should be IP Ethernet) requesting anyone who is interested in
the LLL to report the fact.
The "route request" is transmitted out into the "Routing Region Domain" IP addresses configured
into the WAG. There are two "Routing Region Domains" possible, only one of which is required
for proper OSI operation. If only one is configured with a valid IP address, the "route request" is
sent out that one, otherwise if both are configured, a copy of the "route request" will be sent out
both IP addresses.
The LLL is entered into the "Pending route links" list and a timer is started. The ATCS message is
saved so that if an office device expresses interest in the LLL, the ATCS message can be sent.
If an office device responds with a "route update" for any pending LLLs, the WAG will move the
"pending" entries into the "active" list and any pending ATCS message is sent to the office. At that
time, the timer for the "pending" entry is marked as "Expired" and the timer for the newly created
active entry is started.
If no activity for an LLL in the "Active route links" list is seen before the timer counts down to the
end, the WAG will issue another "route request" for the LLL to determine whether the office
device is still interested in the LLL.
If the office responds, the timer for that LLL entry is refreshed; otherwise as the timer continues
to count down the WAG will issue the "route request" again, doing so three times before the LLL
is moved from the "Active" list to the "Pending" list. Once the entry expires from the "Pending"
list, it is marked as "Expired" until such time as the field device with that LLL attempts to send
another message toward the office.
As this route discovery process takes place, if tracing is enabled for OSI, there will be trace
information offered out the serial and Telnet session.
When a route to the office is known, ATCS messages may flow between the office and the field
device. If tracing for OSI is enabled, every time an ATCS message is passed through WAG, it is
traced out the serial and Telnet session.
The "status" command described later can be used to show the contents of the
"Pending route links" list and the "Active route links" list.
Document No.: COM-00-05-16
Version: C.1
NOTE
1-11
DESCRIPTION
June 2006, Revised June 2014