Comtrol RocketPort and RocketModem

Running out of serial ports is a common problems for Windows NT users. The standard two serial ports are usually used up quickly by a mouse and a modem, so anything else that comes along that requires a serial interface forces you to use a switching box or add new serial ports. For a while, the only way to add serial ports was with an add-in serial card that gave one or two new ports as COM3 and COM4. If you didn’t have the room for one or two expansion cards, or needed even more than four ports, well, tough luck.

To help alleviate the serial port crunch, a lot of vendors who specialized in multiport cards for Unix systems started to offer Windows NT drivers. These cards allowed many serial devices to be driven off a single interrupt. One of the better performing serial port systems we’ve tested is from Comtrol Corporation. Their RocketPort product is available in several versions, some with backplane-mounted connectors and some with breakout boxes attached by a thick umbilical cord. If you need to drive a stack of modems, Comtrol has a specialized serial card called the RocketModem, which offers up to eight internal modems on a single card. We tested a RocketPort and RocketModem setup in a dual-processor ALR Revolution 2XL system running Windows NT Server 4.0. Up to four different Comtrol cards can reside in a system at a time, allowing for combinations of modem and serial cards.

Both the RocketPort and RocketModem cards we received were ISA bus, with the RocketModem a full length card. The RocketPort is a little shorter, and can fit in most ISA motherboard slots. PCI versions of the RocketPorts are available, too. Installing either of the cards is a simple matter. Onboard jumpers can be used to alter their default settings, but unless you have a system with more than two serial ports already used, the defaults will probably work fine. After installing the cards, a utility loads the drivers into Windows NT. After a reboot, the cards are recognized right away, and can be configured through a supplied application.

The RocketPort we tested had eight DB9 connectors at the end of the umbilical configured by default as COM3 through COM10. The ports don’t need much configuration except for setting baud rates for some peripherals. Different baud rates can be mapped to each port, allowing the slower baud rates that are standard with serial devices to be remapped to higher speeds for fast peripherals (such as remapping 300 baud to faster speeds for ISDN or 56kbps modems). A nice touch is the ability to configure several of the ports as RS-485 ports with 5V supplied. To do this, you need to plug in a power-edge connector on the RocketPort board. Since few common serial devices need this source of power, most users won’t bother.

We configured our eight-port RocketPort with four modems, two serial printers, a recording whiteboard, and an interface slot for Pilot handhelds. With all four modems running at full blast transferring files and both printers churning away there was no delay on any of the ports. The affect on the host processors was not noticeable. Applications that were driving the serial devices didn’t complain, although a few did have configuration problems when told to talk to COM10! Finding the right balance between standard serial ports and expansion ports (COM5 through COM10) will require a check of the applications that must address the ports, as some will not handle anything above COM2 or COM4.

The RocketModem is a heavily-loaded board with eight modems attached (a four modem version is available). Each modem is fully compliant with all the speeds for asynchronous modems and fax devices, although 56kbps technology is not supported. A set of eight RJ11 connectors on the backplane allow telephone cables to be snaked in neatly. The RocketModem on our test system replaced a stack of six external modems, a bunch of serial cables, and a mess of telephone cords. When using the RocketModem with the six telephone cables neatly bundled together, the difference behind the server was amazing!

We configured the RocketModem to use two ports for faxes and the rest for dial in and dial out use. As a remote access server, the RocketModem worked perfectly. An onboard 36MHz processor and a chunk of RAM helps minimize the RocketModem’s impact on the host processor. We loaded the RocketModem up by having three lines out calling another three in, and the two fax lines sending pages to each other. With all data modems going at V.34 and the fax lines at 14.4kbps, the RocketModem kept up without strain.

We’ve tried several other multiport cards in our Windows NT servers over the last two years, and none have installed and configured as easily as Comtrol’s two cards. The ease with which they can be managed makes a system administrator’s load minimal. With host CPU offloading, and enough ports to keep any system happy, the Comtrol RocketPort and RocketModem are definite necessities for Windows NT systems.

Comtrol
RocketPort 485 $679
RocketModem 8-port $2895
RocketModem 4-port $1595
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MN 55112
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