How much network bandwidth does the NXU-2 consume?

The NXU-2 bandwidth usage varies depending on the application. When COR is inactive and no audio is being transmitted across the link the bandwidth usage is essentially zero, since a small “keep-alive” packet is only sent every 4 seconds. When COR is activated audio will be sent across the link at approximately 15Kbps. If a full-duplex connection is active (COR is active on each end) then the total bandwidth usage for audio will be approximately 30Kbps. If RS-232 data is being sent simultaneously then the bandwidth will be increased by the RS-232 data rate plus the TCP overhead.

Can I use the NXU-2 on a dialup connection?

No. The NXU-2’s network connection is via Ethernet. Most dialup (telephone line) modems only provide RS-232 connections, but even if an Ethernet connection to a dialup is available, the NXU-2 may not operate properly since the connection speed is not guaranteed on a dialup connection. Poor telephone lines or varying line conditions may cause a dialup modem to reduce its connection speed without the user being aware of this condition. For this and other reasons, dialup connections are not supported by the NXU-2.

My network is behind a firewall. How can I make the NXU-2 work?

Firewalls provide network security by limiting access into the network from the outside. Sometimes this causes difficulty when installing network equipment such as the NXU-2. There are two solutions to this problem. You can install the NXU-2 on the outside of the firewall, or you can open a hole in the firewall so that the port specifically used by the NXU-2 is accessible. The NXU-2 does not pose a security risk to other computers or devices on the network, since it cannot be made to access files or forward information to other systems. If you choose to open a hole in your firewall, you will need to allow access to port 1221 (or to the port you have selected if you have used the PORT command) for TCP and UDP services. Contact your network administrator for approval and assistance with firewall settings.

My application does not provide a COR line. What should I do?

COR is usually obtained from a radio and indicates that a signal is being received. If you do not have a COR line, or a line that performs this function then you will have to tie the NXU-2 COR line to its active state. The only disadvantage to doing this is that data will flow continuously across the link, even if no audio is present.

I want to use a number of NXU-2’s but I only have one (or a few) IP addresses from my Internet Provider. What can I do?

One solution is to use a Network Address Translating (NAT) Router to connect the NXU-2 units to your network. A NAT router allows a number of devices to share a single IP address. If you decide to use a NAT router you’ll have to change the default port number from 1221 to a unique port number for each NXU-2 Client/Server pair.

I want to connect several NXU-2 Clients to a single NXU-2 Server simultaneously. How can I do that?

NXU-2s provide a point-to-point connection over a network between a single client/server pair. Only one Client can be connected to a Server at any given time.

I have a 100 Mbps Ethernet. Can I connect the 10 Mbps port on the NXU-2 to my network?

Most 100Mbps equipment (hubs, switches, routers) will work with either 10Mbps or 100Mbps connection, so it should work without any problems. Check with your network administrator if you’re unsure about your network equipment capabilities.

Where can I find a description of the VoIP protocol used by the NXU-2?

The NXU-2 protocol is proprietary and not available to end-users.

My system uses pilot tones and/or tone keying. Does the NXU-2 support this?

Yes. Pilot tones and keying tones are not normally needed on the NXU-2, (due to its support for hardware COR and PTT lines) but are supported and will work.

Can I hook one NXU-2 directly to another one via their Ethernet ports?

Yes, if you use a crossover Ethernet patch cable. A straight-through patch cable (such as the one supplied with the unit) can only be used to attach the NXU-2 to network interface equipment such as hubs, switches, or routers. You can directly connect a pair of NXU-2 units up to 100 meters apart using a CAT5 crossover cable. When directly connecting NXU-2 units in this fashion you should set the subnet mask to 255.255.255.0 and the gateway IP address to 0.0.0.0.

After losing power on one end of an NXU-2 link, it takes a while for the units to re-establish communications. Why is this?

The NXU-2 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 with a dynamic IP address, it 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?

The problem with IP addresses is there are not enough to go around. There are "only" about 4 billion IP addresses available. You would think that would 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, there is no point in using up an IP address if you don't need it. By the way, there are plans for an upgraded IP addressing system that will fix the problem of not having enough IP addresses, but for now it is with us.

What kind of IP address does the NXU-2 need?

NXU-2's 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 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-2 without checking with the network administrator first.

What happens if two NXU-2's have the same IP address?

Bad things. Well, not bad things, but obviously it will not work properly. Both units will respond at the same time, causing network errors. The extreme case would be if an NXU-2 is programmed to have the same IP address as an existing computer on the same network. This would likely render that computer unusable for network functions, and could cause other users to have problems as well. The bottom line is that two devices cannot share the same IP address, period.

What is a firewall and how does it affect NXU-2 operation?

A firewall is a device, which prevents people outside a network from accessing computers, or devices inside the network. It's a security device. Here at JPS our firewall prevents incoming network connections, so no one outside JPS can access our computers via the Internet. This is a Good Thing, but can cause problems with devices like the NXU-2 since it requires both incoming and outgoing connections. Fortunately, it is possible to program the firewall to allow selected incoming connections so that things like the NXU-2 can work but computers are still protected from outside attacks.

How can I program my firewall to allow the NXU-2 to work?

The NXU-2 uses two methods of communicating over IP (Internet Protocol.) These two methods are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol.) With both methods the NXU-2 uses IP port 1221 to communicate. If a firewall is preventing the NXU-2 connection then the network administrator must program the firewall to allow TCP and UDP traffic on port 1221. This is often referred to as "opening a hole in the firewall" and should only be done with the cooperation of the network administrator.

After installing a pair of NXU-2'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-2 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-2 is a straight-through cable used to connect the NXU-2 to a PC serial port. In order to connect the NXU-2 port to an ACU-1000 you need a DB-9 male-male null modem cable, also called a cross-over cable.

Why do I need a null modem cable to connect the NXU-2 to the ACU-1000? I don't need one when I connect my PC.

RS-232 serial devices are divided into two types. Devices, which provide control information, are called DTE (Data Terminal Equipment) devices. Devices, which 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 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-2 and ACU-1000 are DCE devices. That is why you need a crossover cable for connecting an ACU-1000 to an NXU-2.

Can I change the vocoder on the NXU-2?

Yes. This is the voice compression method used to convert the audio signal into a digital format. There are times when the user may want or need higher voice quality or transparency to certain kinds of signaling tones. The VOCODER command allows the selection of different vocoders, albeit at the expense of network bandwidth.

Can I pass modem tones over the voice port of the NXU-2?

Some types of modem tones (such as FSK) will work if you select one of the higher bit rate vocoders, such as VOCODER 4 or VOCODER 5. Complex modem waveforms (such as 56K modem data) will not pass. Pilot tone, keying tones, and other similar signaling tones will work properly. In general the RS-232 port should be used to send data, however.

I've connected my radio to the NXU-2, I have the levels turned all the way up and can still barely hear the audio. What's wrong?

The NXU-2 uses balanced audio on the input. If, instead of connecting to both balanced input lines, you connect your audio to one audio input and ground, you'll get the effect described above. There is enough leakage in the transformer to get some audio through, but it won't work properly.

I've connected my radio to the NXU-2 and it works, but the audio sounds very "tinny" and doesn't have much bass.

Make sure you haven't used the discriminator output, which is sometimes available on FM receivers and transceivers. Discriminator audio is pre-emphasized, and there is no de-emphasis circuitry in the NXU-2. You'll need to use your regular audio output instead.

I've connected the NXU-2 to my computer serial port as described in section 3.3 of the NXU-2 manual, but I can't put the NXU-2 into Command Mode as described in 3.3.1. What do I do now?

First, if you're using HyperTerminal (the serial terminal program included with Windows) you need to make sure that you have the flow control set to 'None' in the serial port configuration menu. Also, you may have to exit HyperTerminal and start the program again in order for program configuration changes to take effect. Second, you must follow the instructions in 3.3.1 exactly. Wait 10 seconds and then type three plus signs +++ and nothing else. If you type more than three plus signs the procedure won't work. Wait a few seconds and try again. Also, the three plus signs must be typed within a 1 second period in order to be recognized.

I've configured HyperTerminal and followed the procedure exactly, and I still can't get the 'OK' prompt telling me that the NXU-2 is in Command Mode. Now what?

If the NXU-2 has been configured previously and the baud rate was changed to something other than the factory default of 9600 then you'll need to set your terminal program to use the new baud rate in order to enter the Command Mode.