We looked at an earlier version of Comtrol’s RocketPort serial port system a couple of years ago, but the Serialhub Si release from Comtrol makes the system worth examining again. The RocketPort is a network-attached breakout box RS232, RS422 and RS485 system which provides an extra four or eight serial ports, all fully addressable, without tying up an existing serial port. The previous version of the RocketPort we looked at used an internal expansion card and was thus tied through an umbilical to the host computer; the ability to network-connect this Serialhub Si version allows you to place serial ports anywhere there is a network drop. This is a much more convenient and handy approach, obviously. Even further, any number of RocketPorts can be used on a network, allowing virtually unlimited serial port expansion.

The eight-port RocketPort box is a black plastic case about nine inches wide, six inches deep and two inches high. It weighs two pounds. The front of the box has a power LED and eight labeled LEDs for each serial port. The back of the box has a power port for the brick-type transformer (with a normal power lead, hence not typing up more than one socket on a power bar), eight DB-9 serial port connectors, and a 10BaseT RJ45 connector. A rocker power switch completes the back panel. Access to the ports on the RocketPort is through software that resides on Windows 95, 98, 2000 or NT machine, or on a Linux system. (The Windows 95, 98 and 2000 drivers were in testing when we reviewed the RocketPort so we tested under both Linux and Windows NT 4.0 Server.)

To install the RocketPort, you simply connect the power and Ethernet cables on the back of the box and then install the RocketPort drivers on the host computers. Each port is the assigned to the computer for control, and is treated like a numerical COM port (you can assign the COM port numbers). Our only wish was that the RocketPort allowed 100BaseT connections, as we had to use a step-down hub to connect to our high-speed 100Mbps Ethernet backbone. Still, this is nitpicky. One other slightly negative comment (again nitpicky) is that the plastic case feels, well, cheap. A steel case would give more heft but also cost more, so we’ll accept the plastic. Multiple RocketPorts can be stacked one on top of the other, although they make a slightly wobbly tower.

The RocketPort interface on the host computer uses a simple dialog with two page tabs for each port. You can select between RS232, RS422 and RS485 modes with a drop-down dialog. The ability to mix the port types in a single box will appeal especially to industrial applications where RS422 and RS485 are much more common than office environments. Each COM port on the RocketPort can be driven up to 230kbps. The neat part of the RocketPort is that each of the ports in the RocketPort behaves as though it was directly attached to the server, despite the fact the RocketPort box itself may be physically a long way away. Even better, you can allocate different ports in a single RocketPort to be controlled by different host computers, assigning the ports to applications on different machines. You could, for example, have four ports working with a bank of modems driven by a Linux machine for remote access use, another two ports used for serial printers on a Windows NT machine, and the last two ports controlled by yet another Linux machine somewhere else on the network. This kind of flexibility makes the RocketPort unique as far as we know. To the host computers, the RocketPort driver makes the COM ports in the RocketPort look like they are directly attached. Although there is sometimes a short timelag while the RocketPort responds to queries to find the port, it always worked for us on our test setup.

We tested the RocketPort for a week on our test network, driving a range of serial devices from both Linux and Windows NT 4 Server hosts. Serial printers, modems, bar code scanners, X terminals, and a spectrophotometer were all handled easily over the network. We measured effective throughputs just over 200kbps on the spectrophotometer, although we didn’t push the printers and modems over 56kbps. At no point did either the Linux or Windows NT hosts lose the serial ports, even after accidental disconnection of the network drop followed by reconnection. We can see the RocketPort Serialhub Si being a very valuable expansion product for any network, especially those that want to position serial ports away from the host computers. This is an impressive product and highly recommended.

Comtrol
RocketPort Serialhub Si
$995 8-port hub
6655 Wedgewood Rd
Minneapolis
MN 55311
800-926-6876
763-494-4100
612-494-4199 fax
http://www.comtrol.com

Summary: A neat way to position serial ports anywhere on a network, behaving as though they are directly connected to one or more host PCs.