GE MDS iNET 900, Reference Manual

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62 iNET Series Reference Manual 05-2806A01, Rev. J
Serial Encapsulation
Transparent encapsulation, or IP tunneling, provides a mechanism to
encapsulate serial data into an IP envelope. Basically, all the bytes
received through the serial port are put into the data portion of a TCP or
UDP packet (TCP or UDP are user configurable options). In the same
manner, all data bytes received in a TCP or UDP packet are output
through the serial port.
When data is received by the radio through the serial port it is buffered
until the packet is received completely. There are two events that signal
an end-of-packet to the radio: a period of time since the last byte was
received, or a number of bytes that exceed the buffer size. Both of these
triggers are user configurable.
One radio can perform serial data encapsulation (IP-to-Serial) and talk
to a PC. Two radios (or one radio and a terminal server) can be used
together to provide a serial-to-serial channel.
TCP Client vs. TCP Server
A TCP session has a server side and a client side. You can configure the
transceiver to act as a server, a client, or both.
TCP servers listen and wait for requests from remote TCP clients to
establish a session. A TCP client is a program running on a device other
than the TCP server. Alternately, TCP clients actively attempt to estab-
lish a connection with a TCP server. In the case of the transceiver, this
happens whenever data is received on the serial port.
The transceiver operates in either client or server mode, depending on
which event occurs first, either receiving data on the serial port, or
receiving a request to open a TCP connection from a remote client.
The transceiver keeps a TCP session open until internal timers that mon-
itor traffic expire. Once a TCP session is closed, it must be opened again
before traffic can flow.
UDP Multicast
IP provides a mechanism to do a limited broadcast to a specific group of
devices. This is known as “multicast addressing.” Many IP routers, hubs
and switches support this functionality.
Multicast addressing requires the use of a specific branch of IP
addresses set apart by the Internet Assigned Numbers Authority (IANA)
for this purpose.
UDP multicast is generally used to transport polling protocols typically
used in SCADA applications where multiple remote devices will
receive and process the same poll message.