Motorola V186 - Cell Phone - GSM System Planner Manual page 108

Communications
Configuring NTP Servers
An Ethernet or RS232 PPP port can be configured for NTP protocol (NTP is UDP port
number 123.) In this case, the RTU will retrieve its time from a set of NTP servers
specified by the user. The clock offset between the RTU and these servers depends on
network delays, and may be up to 100 milliseconds in some wireless media. The clock
offset on LAN in the same Ethernet network is approximately 1 millisecond.
Note: It is possible to define an NTP server with a full host name (e.g. www.mysite.com).
To do so, the user must set DNS servers for this port, either statically, or from a DHCP
server or PPP modem.
User Protocol over IP
Both Ethernet and PPP ports provide an interface for a user application written in the 'C'
Toolkit using MOSCAD_socket() functions, also known as "User protocol over IP". An
MDLC over IP port can serve a user application at the same time as it serves MDLC
which is built in the socket API. MDLC takes one logical UDP port number (2002 by
default); other applications can use other TCP or UDP port numbers. For more
information on the 'C' Toolkit socket functions, see the ACE3600 RTU 'C' Toolkit User
Guide.
Dynamic IP Address
Many wireless networks do not allocate a fixed IP address to a PPP modem (such as the
GPRS network). For the FEP to communicate with the RTU it must know its address or
host name. Since these networks do not provide a name for each modem, there is no
option of setting them in the FEP beforehand. In this case, the FEP should not be
assigned an IP conversion table with that link ID (port). The RTUs should be associated
with a table which has the FEP's IP address. If the network operator assigns a host name
to the FEP instead of a numeric address, this can be set in the IP conversion table. When
the RTU detects that its modem is connected, it will notify this address, the FEP, of its
new IP address, thus updating its table in runtime.
Since this process does not guarantee that the FEP will be updated, it is highly
recommended that user application periodically send a message to the FEP. For example,
if the user application expects an interrogation every two minutes from the FEP, and it
has not received that, it will send a message to the FEP. This will update the RTU address
in the FEP.
MDLC over IP Port Routing
In the example mentioned in Dynamic IP Address above, for RTU-to-RTU (modem to
modem) communication, set 'Enable routing of MDLC over IP port' parameter in the
FEP. Then assign to the RTUs an IP conversion table which list the RTUs' site IDs as
having the FEP IP address.
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