Comrex Access NX, Руководство по эксплуатации продукта

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XXIII.
opErAtINg NX IN A 24/7 ENVIroNMENt
In BRIC Normal mode, the default mode of operation, NX transfers all its audio data via the UDP protocol. This is in
contrast to most web-based connections, such as web browsing and e-mail. These use TCP protocol. UDP, unlike TCP, is
not “connection oriented”; that is, no virtual connection actually exists in this protocol layer between the devices.
In UDP, the transmitter simply launches packets into the network with the correct address, hoping the network will
deliver the packets in a timely fashion. Since there is no intelligent connection built between the codecs, there isn’t
actually any connection to break in the event of network failure.
If a packet is delayed or lost, no error message is sent and no packets are retransmitted. It is up to the receiver to cover
up any lost data, if it can. This allows delivery of the packets with the smallest amount of overhead and delay.
Therefore, the usability of the network is the important factor, not the existence of a physical connection. Loss of the
remote will usually be due to a network failure. (If the network fails and is later restored, the packets stream will be
restored to the decoder.)
For most applications, such as remote broadcasting, it’s useful to simulate a connection-oriented stream, so NX uses a
low-bandwidth sub channel to deliver information back to the encoder about overall connection status. It does this in its
“application layer”, rather than the “transport layer”, which is where UDP exists.
By default, it monitors the health of a connection. If no data is detected as received by the decoder during the preset
user adjustable timeout, it “tears down” this connection and goes back to idle state. This can give an indication to the
user that the network has failed and it’s time to look at the problem.
The good thing about having the connection protocol in the application layer is that its use is optional. For 24/7
operation, there’s no advantage to having the connection end if no data is received for a timeout interval.
To set NX for 24/7 operation, several parameters are changed:
1 The timeout value is set to infinity - the connection will never be torn down regardless of data.
2 NX is configured to re-establish the connection in the event of a power re-cycling.
3 The local Disconnect control is disabled. The Disconnect function on the receiving side is still en-
abled, but will result in an immediate reconnection by the initiating side.