NXU-2B Operations Manual
8-2
After losing power on one end of an NXU-2B link, it takes a while for the units to re-
establish communications. Why is this?
The NXU-2B will wait up to 20 seconds before determining that the link has been disconnected.
After that, it will attempt to close the IP connection, which may take several seconds. Then it
has to open a new connection. This process may take 30 to 45 seconds, depending on your
network.
What is the difference between a static IP address and a dynamic IP address?
On an IP network such as the Internet, the IP address is like a phone number. It is a unique
number that identifies the network device, and it allows connections to be made between network
devices. There are two kinds of IP addresses, those that are permanently assigned and those that
are assigned temporarily. Permanently assigned IP addresses are called static IP addresses, while
temporary IP addresses are called dynamic IP addresses. Static and dynamic IP addresses work
the same way, but a dynamic IP address is like having a telephone number that nobody else
knows; it effectively limits you to making outgoing calls only.
Why do we need static and dynamic IP addresses? Why not just assign addresses
permanently like phone numbers?
One problem with IP addresses is there are not enough to go around. There are "only" about 4
billion IPv4 addresses available. On the surface that would appear to be enough, but some
companies use a lot of them, the military uses a lot of them, and all the millions and millions of
people using the Internet use a lot of them. To ease this problem, many Internet providers only
assign an IP address to a computer when someone actually dials in to connect to the Internet.
When they disconnect, the IP address goes back into the pool of addresses so someone else can
use it. This makes sense in cases where computers might sit for a long time without needing to
access the Internet, as there is no point in tying up an IP address when it’s not being used. There
are plans for an upgraded IP addressing system (IPv6) that will fix the problem of too few IP
addresses, but for now it is a limitation we must live with.
What kind of IP address does the NXU-2B need?
NXU-2Bs are configured to be either a client (the one that establishes the connection) or a server
(the one that accepts the connection.) The client can have either a static or a dynamic IP address,
but the server MUST have a static IP address. However, it is best if both units have static IP
addresses.
Who assigns IP addresses?
For Internet access, your Internet Service Provider (ISP) will assign IP addresses to you. If you
are on a private network, (like a WAN or LAN) then your network administrator will assign IP
addresses. You should never program an IP address into an NXU-2B without checking with the
ISP or network administrator first.
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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