ISDN Remote Access Servers
The need for remote access servers is increasing as more employees work at home or on the road. In the past most connections to a RAS have been through analog modems. The increase in popularity of faster connection methods like ADSL, cable modems, and ISDN have made the old, slow analog RAS systems seem almost archaic. While many multiport cards will support faster modems there has been a lack of single-board solutions. Digi’s Datafire RAS line and Multitech’s MultimodemISI Hybrid series intends to fill that void.
We asked both vendors for their ISDN RAS products and used them head-to-head in matched pairs of servers for a month. We tested both units in dual PII 266MHz CPU system with 128MB RAM. The Digi Datafire card runs under UnixWare 7 while Multitech’s MultmodemISI runs under OpenServer 5 (although the manual makes passing reference to UnixWare installation; we didn’t have time to try it under this operating system). While the use of two SCO operating systems doesn’t make for identical comparisons of the two cards, it does provide users with a choice of ISDN RAS boards for either operating system. We configured each server with the SCO operating system the card required, optimized for remote access behavior, then installed the RAS card. Individual card details are mentioned in their relevant sections. Each Multitech ISIHP card supports two ISDN lines, so Multitech supplied two cards which we ran side-by-side in the OpenServer 5 server.
To test the Datafire RAS 4 B4U and the Multitech MultimodemISI ISIHP-2S/2U under load we used a DMS 100 switch configured with a dozen ISDN lines, four of which ran to each server through the single Datafire RAS 4 B4U or dual Multitech ISIHP boards. Four other lines were connected to two Windows NT servers running Mercury Interactive’s WinRunner. We used WinRunner scripts to emulate four users dialing into the UnixWare and OpenServer servers and conducting large file transfers, Web server accesses, and routine directory searches. We measured the performance of the UnixWare and OpenServer server using standard utilities before the RAS boards was installed, after installation but with no ISDN load, and with one and four ISDN channels heavily loaded.
Digi’s Datafire series comprises several models, all designed to provide multiple channels on a single PCI card. Cards are available to support all speeds from analog to T1. The Datafire RAS 4 B4U is a new addition to the Datafire line with four ISDN modems built onto the card. The Datafire RAS 4 B4U runs under a number of operating systems including SCO UnixWare 7 (but not OpenServer 5).
The Datafire RAS 4 B4U is a single three-quarter length PCI board with four ISDN jacks on the backplane. Four ISDN cables accompany the card. The Datafire RAS 4 B4U is designed to support 2B+D (Basic Rate Interface or BRI) ISDN, the most widely available type. There is no printed documentation accompanying the Datafire RAS 4 B4U other than a small two-fold installation guide. To read anything more about the card you have to go to the CD-ROM supplied with the system. (We really would prefer printer documents, but Digi appears to be yet another company moving to CD-ROM only.) To make matters worse, the CD-ROM documentation has nothing to say about either the Datafire RAS 4 B4U card (only a generic section that applies to the whole series of cards) and absolutely nothing to say about SCO operating systems. The CD’s contents apply only to Windows NT and Novell NetWare. We had to obtain drivers for UnixWare 7 from the Digi FTP site, but we could find no release notes there to do with UnixWare.
Installation of the Datafire RAS 4 B4U is a snap: install the card in any available PCI slot and boot the system. We installed the downloaded drivers under UnixWare and it found and configured the Datafire card. The character-driven interface is not elegant, but it does allow you to configure the channel information for each ISDN port. The installation and configuration process under SCO UnixWare is weak, though, and desperately could use improvement. The Datafire RAS 4 B4U supports National ISDN 1, AT&T 5ESS and Nortel DMS 100 switches. We tested using the common National ISDN 1 and also using a Nortel DMS 100. Each ISDN channel on the Datafire RAS 4 B4U allows for circuit-switched data and voice over the B channels, allowing for analog devices over the digital circuit. This permits you to use standard telephones, analog modems, and fax machines over the each ISDN line, two per ISDN port.
System requirements for UnixWare systems seem to be relatively benign. It’s difficult to assess them accurately because Digi provides requirements only for Windows NT (64MB RAM plus 2MB for each ISDN channel). Our test system had 128MB RAM which worked perfectly. To try lower RAM complements we yanked a 64MB chip and used the Datafire RAS 4 B4U without problems on a 64MB system. We did try the Datafire RAS 4 B4U on an older Pentium Pro 150MHz system with 32MB RAM, running UnixWare 7.0 and it functioned well there, too, although system performance was slower for X sessions when the Datafire RAS 4 B4U was in use.
The addition of the Datafire RAS 4 B4U with no load to the UnixWare server had no appreciable effect on the server’s performance. As we started to load the ISDN channels, performance started to take a hit. With a single ISDN channels running at full tilt, performance of the server started to slow a little, averaging five percent slower. With all four ISDN channels at full blast we slowed the server by fourteen percent. Considering the CPUs are fairly typical PII 266MHz units, the performance hit of the Datafire RAS 4 B4U under four heavily loaded lines was noticeable to other users. As a comparison test we installed on a dual PIII 450MHz system again running UnixWare 7.1 and measured an eight percent performance hit. Finally, we repeated the full four-channel blast test on the PIII 450MHz system running under Windows NT Server 4.0 and measured an eleven percent performance hit (which bears out previous tests that UnixWare is a more efficient operating system than NT).
As a final test we compared the behavior of the Datafire RAS 4 B4U (four ISDN modems on a single card) to a similar setup with a Digi Acceleport 4r PCI multiport card with four external Motorola ISDN modems attached. With all four ports of the fast Acceleport card configured for ISDN, we repeated the one and four-channel full load tests. With a single ISDN modem in heavy use performance of the system was a hair faster than using the Datafire RAS 4 B4U, but with all four channels loaded, the Datafire RAS 4 B4U was slightly faster than the Acceleport and external ISDN modem setup. The differences were not enough to warrant a preference of either setup.
The Datafire RAS 4 B4U does take its toll on the UnixWare server. While four 128kbps channels might seem like a light load to a server, the same performance hit is measured with 24 38.8kbps channels over a multiport RAS system, so the performance is in line. Bear in mind that we were pushing the ISDN lines to their limit, forcing the CPUs to handle full throughput on all four lines at once, which is unlikely in most server configurations.
One slight problem we did encounter in the test systems was heat. When the Datafire RAS 4 B4U was subjected to continual use on a test circuit (122Mbps on each of the four channels for four hours straight) the board became quite warm to the touch. When the board was not heavily used, the board ran cooler. The heat was easily dissipated by the server’s cooling fans, but if the Datafire RAS 4 B4U is positioned next to other heat-generating boards like a high-end video card, multiport serial card, or any board with a high-speed dedicated processor (our test unit had a satellite interface board next to the Datafire RAS 4 B4U), heat may become a problem. Mounting an addition cooling fan over the PCI boards is easy thanks to quiet forced-air miniature fans available for only a few dollars. They can straddle the PCI boards with clips and are powered off the internal transformer. The heat is unlikely to be a problem in most systems unless your system is heavily loaded (as servers tend to be).
The Datafire RAS 4 B4U supports Microsoft’s TAPI (Telephony Application Program Interface) and CAPI (Common ISDN Application Interface version 2.0). Both TAPI and CAPI are used for Windows 95 applications, not UnixWare, but the future porting of compliant applications is likely. The Datafire RAS 4 B4U should work under practically any operating system that supports a PCI bus: a Linux driver is under development according to one of the Linux Web sites.
UnixWare certification tests for the Datafire RAS 4 B4U have been completed by Digi and submitted to SCO for verification. By the time you read this, the Datafire RAS 4 B4U should be completely certified for SCO. Unfortunately, Digi has no plans to continue its certification efforts to support OpenServer 5.
Multitech MultimodemISI Hybrid ISIHP-2S/2U
The Multitech MultimodemISI Hybrid ISIHP-2S/2U (hereafter just MultimodemISI to save space!) arrived a couple of weeks after the Digi Datafire so we couldn’t provide the same variety of alternate operating system platforms for it. However, we did test the MultimodemISI for a month under SCO OpenServer 5 and under Windows NT. As mentioned earlier, each MultimodemISI board supports two ISDN lines, so to make a fair comparison with the Digi Datafire Multitech supplied two boards.
Physically, the MultimodemISI is a full-length card with card guides at the end. The MultimodemISI is a PCI card with a third-size daughterboard attached at one end. The backplane of the card has two ISDN jacks and two status LEDs for each port. The MultimodemISI’s two ISDN BRI lines appear as eight ports to the server, allowing any combination of ISDN digital and analog calls into the board. Each MultimodemISI board has four V.90 56kflex modems to handle the incoming analog calls (both data and fax). In addition, the board has two terminal adapters, which appear as two ports to the server, designed for routing the modems. The combination of V.90 and ISDN modems on a single board provides for some excellent flexibility from the MultimodemISI. The only limitation is that only four analog connections are supported per board, although any combination of ISDN and analog is possible. With our dual boards, we had eight V.90 modems, two BRI ISDN lines, and sixteen ports. The design of the board and the ability to mix analog and digital lines in this manner is a very strong point for the MultimodemISI. We configured a couple of the lines for faxes and then bombarded the boards with ISDN traffic, all successfully.
The MultimodemISI is shipped with a User’s Guide which includes simple installation instructions for SCO OpenServer 5, Windows NT and 95/98. NetWare, and Linux. The shipping container also includes two ISDN cords and a driver disk with ISDN Wizard (for Windows only). On an OpenServer 5 platform 800kb of disk space is required for the drivers. There is no minimum RAM recommendation in the User’s Guide, but we would expect a 32MB effective minimum. Of course, the more RAM the better. Our test server’s 128MB RAM handled the MultimodemISI under full load with no swapping.
The MultimodemISI plugs into any 66MHz PCI bus. The board will apparently not work with the newer 100MHz PCI buses at the faster speed although we didn’t try this due to lack of time. The driver software is installed using custom and reads from the diskette. The installation process asks for the number of MultimodemISI cards being installed, making our setup of dual cards simple. After setting an I/O base address and IRQ for each card, the system rebuilds the kernel and after a reboot the cards are operational. The ports used by each MultimodemISI card are numbered using standard notation: the lower four ports of each card are assigned to terminal adapters, which the upper four are for the analog modems. The entire installation process took about forty-five minutes, including setting up the ports.
Server load on the OpenServer 5 system was minimal under light to moderate loads, as our before and after load tests showed. The MultimodemISI’s onboard processing works effectively to offload the server CPU. However, as the traffic on the sixteen ports starts to build up, inevitably some effect is noticed. We tested primarily using ISDN access so we would have comparable numbers to the Digi Datafire RAS B4U board. With a single ISDN channel running at maximum capacity, a four percent performance effect was recorded on the dual-CPU system. However, as we loaded a second and then all four ISDN channels to full blast, the CPUs assumed more of the load. With all four ISDN lines at full tilt, we measured a seventeen percent drop in performance. This is more than with the Datafire board, but part of the difference is attributable to the operating system efficiency. Even with a seventeen percent hit, unless the servers are heavily loaded with users few would notice the performance difference. Since we were artificially loading the system with X applications, we did see a slowdown but this is not indicative of normal server usage.
As we did with the Datafire RAS 4 B4U we installed the MultimodemISI boards briefly into a dual PIII 450MHz system running OpenServer 5 and remeasured the four-line performance drop. In this case we recorded a ten percent performance hit. When we reloaded that system with Windows NT and did a four-channel blast test on the system we measured a fifteen percent performance hit. Again this bears out tests that show OpenServer 5 is a more efficient operating system than Windows NT. The MultimodemISI GUI interface under Windows NT is more attractive than the SCO version, but that’s to be expected.
Since we had compared the Digi Datafire boards to standard multiport cards with external modems, we tried the same test with the MultimodemISI. We reused the Digi Acceleport 4r PCI multiport card with four external Motorola ISDN modems attached. With all four ports of the fast Acceleport card configured for ISDN, we ran one and four-channel full load tests. With a single ISDN modem in heavy use performance of the system was a faster than the MultimodemISI by about four percent, but with all four channels loaded, the MultimodemISI outperformed the Digi multiport card by eight percent.
As we noted with the Digi Datafire board, heat is a problem with the MultimodemISI. We configured our two boards in adjacent PCI slots because of a lack of full-length slots on most motherboards. Ideally, the two cards would be separated by shorter PCI cards to aid air circulation. As our server was set up, both MultimodemISI cards heated up noticeably when under full-load tests, especially since the daughterboards with four V.90 modems on them allow only a little room for air movement. After extended testing of sixteen hours with all four ports at full throughput the cards became too warm to comfortably touch. Mounting a small exhaust fan on the front of the case to pull air over the cards solved the problem quickly. If you have a server with little room inside for air circulation you really need to consider enhancing air movement with additional fans. (We’ve started configuring all our servers with three fans, two pushing and one pulling, just to help keep the system and cards cool.)
The performance results were mentioned in each board’s description above, and are summarized in the table. As you can see there is little real difference in performance between the two boards. You might expect a dual-board solution to have better performance than a single board (because of duplicate CPUs and caches) but that doesn’t seem to be a factor here. If anything, the difference in performance between the Datafire and MultimodemISI boards is more attributable to the operating systems than anything else. Unfortunately we simply couldn’t test the MultimodemISI under UnixWare (and the Datafire won’t run under OpenServer 5).
The Datafire RAS 4 B4U card performed well throughout the tests, although the installation and configuration routines were much easier under Windows NT than UnixWare. Hopefully Digi will have updated the CD-ROMs to include SCO support in the latest shipping versions of the Datafire RAS 4 B4U. As it is, forcing users to download drivers and instructions from the Digi Web site is annoying. The Datafire RAS 4 B4U is a fine card and the ability to house four ISDN modems in the server chassis instead of involving external modems and the cable hassles this involves makes the card a valuable asset. The Datafire RAS 4 B4U is expensive compared to a traditional four or eight port serial card plus four ISDN modems, but the all-in-one aspect may make this worthwhile for administrators.
The Multitech MultimodemISI has a couple of interesting benefits. First, if you only want two ISDN ports, you can start with one card and add a second (or more) later. Second, the configurability of the card between analog and digital (ISDN) ports is very nice, especially since it lets you hang voice and fax lines off the same set of ports users may use to access remotely. The documentation included with the MultimodemISI is typical Multitech fare: good and succinct, and certainly beats on-line documentation in our opinion.
Although the choice of a RAS solution may be made simply on the basis of which SCO operating system you choose, you won’t go wrong with either of these cards. Both are impressive in their performance, capabilities, and the ability to provide ISDN access to remote users. Neither setup is inexpensive but they do their jobs superbly. Our Top of the World award goes, by a hair, to the Multitech MultimodemISI. Why? First, SCO operating system support is better with the MultimodemISI . Also, the extra flexibility the card provides, as well as slightly better driver support across multiple operating systems all helped. However, the margin between the two cards is extremely thin, but the nod goes to the MultimodemISI.
Datafire RAS 4 B4U $2995
10000 West 76th Street
Summary: The Datafire RAS 4 B4U offers four internal ISDN modems on a single PCI card. SCO support was minimal, but the Datafire RAS 4 B4U works well once properly configured.
2205 Woodale Drive
Summary: Although it takes two MultimodemISI boards to match the four lines in the Datafire, the MultimodemISI provides a little more flexibility with no sacrifices. It gets our Top of the World for that reason.
Performance: these numbers show the affect on server CPU performance under varying ISDN loads. The lower the number the better. Test systems were dual PII-266 CPUs with 128MB RAM. Light loads were average throughputs on each channel of less than 20kbps. Heavy loads were averages in excess of 95kbps.