NXU-2B Operations Manual
8-4
What is NAT?
NAT (Network Address Translation) is a scheme by which many network devices can share one
IP address. The NAT router translates packets passed through it between the single public IP
address it holds and the private IP addresses used by devices on its network. This means that no
computers behind the NAT router are directly accessible from outside the network since none of
them have public (or routable) IP addresses.
How does NAT affect the NXU-2B?
Using NAT does not directly affect the operation of the NXU-2B. Special considerations should
be made only in the event that multiple server units will be located behind a NAT router. In that
case, each unit will need to be assigned a different VoIP port and the NAT router configured to
allow both TCP and UDP traffic for the VoIP ports of all the units behind it. Client units are not
affected by NAT and no special considerations need be made.
Should I use NAT with the NXU-2B?
The only time it is advisable to use NAT with the NXU-2B is when you wish to have multiple
units on a network, but have only one public IP address. An example of this would be a bank of
NXU-2Bs sharing a broadband type connection such as DSL or cable modem where only one IP
address is allocated by your ISP.
After installing a pair of NXU-2B's, the LINK ACTIVE light comes on, stays on for about 20
seconds, and then goes out. This cycle repeats endlessly. What's going on?
The most likely cause is a firewall, which is preventing UDP traffic on port 1221. See the
question above about firewall configuration.
I want to connect my NXU-2B serial port to the ACU-1000 serial port, but the cable you
supplied doesn't work. What kind of cable do I need?
The RS-232 serial cable supplied with the NXU-2B is a straight-through cable used to connect
the NXU-2B to a PC serial port. In order to connect the NXU-2B port to an ACU-1000 you need
a DB-9 male-male null modem cable, also called a crossover cable.
Why do I need a null modem cable to connect the NXU-2B to the ACU-1000? I don't need
one when I connect my PC.
RS-232 serial devices are divided into two types. Devices that provide control information are
called DTE (Data Terminal Equipment) devices. Devices that accept control information are
called DCE (Data Communication Equipment) devices. In the "old days" the DTE devices were
terminals and computers, while the DCE devices were modems. The RS-232 standard specified
that DTE devices would connect to DCE devices using a straight-through cable. If you wanted
to connect two like devices (DTE to DTE or DCE to DCE) then you needed a null modem
(crossover) cable. The PC is a DTE device, and the NXU-2B and ACU-1000 are DCE devices.
That is why you need a crossover cable for connecting an ACU-1000 to an NXU-2B.
Summary of Contents for NXU-2B
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Page 18: ...NXU 2B Operations Manual 1 10 End of Section One...
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