Although most of us manage servers using remote protocols such as Windows Terminal Services or VNC, this approach doesn't allow us to perform some actions, notably anything that requires an OS to be up and running on the server. So you can't, for example, hit F2 to enter the BIOS setup of a remotely managed PC.
The AdderLink IP fills this gap. It connects into the keyboard, mouse and monitor ports on the server you want to manage, and communicates with remote clients via the VNC protocols. Because the VNC host service is on the AdderLink, not the controlled machine, it doesn't matter what state the controlled machine is in - commands are sent to the controlled machine via the keyboard and mouse, and anything on the monitor is replicated in your VNC session.
It can connect either directly into a computer or into the front of a traditional KVM switch, which means you can control as many systems from the AdderLink as your KVM switch supports. The only caveat is that you must be able to switch the KVM box between computers via some kind of key sequence - it's not very helpful if the only way to select a host machine is to press a button on the front panel of the KVM unit!
Setup is pretty straightforward. You connect everything up and turn on, and you are asked to configure the network settings. You can use DHCP if you wish, but you probably want a static IP address. Once the device knows its address, it sits and listens for VNC connections - simple as that. You don't need a password to connect to the box as standard, but most of us would want the added security, and it's a quick job to set one up.
We connected the unit up to our lab network, and linked it into a Belkin four-port KVM switch. This has a button on the front panel to switch between computers, but you can also send it the key sequence ScrollLock-ScrollLock-n, where n is the system number, between 1 and 4. Although the VNC client (this is supplied on CD, or there's a Java version that you can download straight from the AdderLink instead) doesn't natively pass these sequences, it includes a facility for defining special key sequences, so all we had to do was plonk the appropriate entries in the 'special' table and we could toggle happily between the four machines hooked onto our KVM unit.
The video image sent by the unit is an encoding of exactly what appears on the remote screen. This can be a bit weird, for example if the screen image is a bit fuzzy (one of our lab machines has a very long, badly shielded video cable) then it will be equally fuzzy in the VNC client window. However, because there is a disconnect between the viewed image and what's actually happening at the remote end, you may need to calibrate the AdderLink so that the VNC mouse pointer and the real cursor on the screen marry up. This is an automatic process, fortunately - you just tell it to calibrate itself and wait a few seconds while it lines everything up.
As well as linking the KVM world to the VNC world, the AdderLink can also interface to external devices via a serial port. So if you have a power control unit that can talk RS-232, you can control that via VNC too. Alongside this 'power control port' is a traditional modem port that you can use to connect to the device over a phone line, which is useful as a backup.
The AdderLink IP is an interesting and useful box, whose key feature is the ability to extend KVM functionality over the WAN, and to allow access from anywhere to anyone with a VNC client and the right passwords. It's a neat idea, cleverly implemented.
If you're planning to use it with a traditional KVM switch, make sure that you'll be able to toggle between systems correctly.