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TMC Labs
July 2000


Digital Central Office Switch Simulator 4.0

GL Communications
841F Quince Orchard Blvd.
Gaithersburg, MD 20878
P: 301-670-4784
F: 301-926-8234

Price: Software starts at $18,000; Full 8-span system starts at $70,000
GL Communication's Digital Central Office Switch Simulator -- or DCOSS, for short -- is a Windows-based telephony protocol simulator and bulk call generator.

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Installation: 5
Documentation: 4
Features: 4.5
GUI: 4.5
Operational Testing: 4.75
Overall: A-

We've seen many products over the years that do many of the same tasks, but none seem to equal the DCOSS in usability or comprehensiveness. An engineer from GL Communications visited us, and by the time he left we were smiling from ear to ear, while the gears in our heads were churning, thinking of the creative ways we could use their product. The product can simulate T1, E1, SS7, and ISDN-PRI/BRI. It can test for fax signaling, DTMF tones, line noise/energy, and voice quality. It can also handle multiple trunks and protocols; for example, CAS and robbed bit.

The system we tested came on a portable all-in-one computer running Windows NT Workstation 4.0 with service pack 6. Most systems come turnkey from the vendor, as did ours, but end-users can install the Natural MicroSystems boards and software on their own equipment if they desire. (Although the GL systems are assembled by a third party, we really like the shell design of the portable "lunchbox" PC they sent us. It has a built-in LCD display that tilts out for easy viewing, an integrated removable laptop-style keyboard with touchpad, and front-mounted mouse and keyboard ports. All of the board slots are placed facing one side of the box, right above the CD-ROM and floppy drives, with a cover that keeps them safe. Check out the supplier's Web site at

Configuring the DCOSS system in our laboratory was surprisingly easy. We didn't have a T1-based product handy, which is unusual for us, but we were able to conduct loopback tests across two spans. Our particular system came with two T1/E1 boards, a T1/E1 analyzer board, and an ISDN-PRI board. Running the DCOSS software for the first time requires selecting various setup options for the boards and for the default system settings.

Included is an option to recall the factory recommended settings at any time, which can be handy if too many custom options ever leave you wanting to start from scratch. Starting the system for normal use requires that you first start NMS's board initialization utility and that you open your trunk lines. Of course, you can also load saved configurations. Overall, we were very impressed with how fast the system went from sitting in its shipping crate to successfully simulating T1/E1 trunks on our workbench.

The DCOSS system we received was a beta version, and the documentation was not ready yet. We received the user's manual from the previous version, plus release notes for the new version. The manual was good, with sufficient screen captures, but it's clearly written for a knowledgeable user.

For the online help, all that existed was "About" information. This option actually contains useful details about the product, system files, settings, etc., rather than just the typical copyright information. We feel this is a nice touch and indicates that GL Communications' technical writers are thoughtful in their work.

Sometimes writing about a product's features is the most difficult part of a review, simply because there are so many of them and because they are equally important. This is the case with the DCOSS product. There is the excellent GUI and the moderate learning curve. There is the manual call generator, the bulk call generator and scheduler, and the test/script writing feature. There are the fax tone/DTMF/energy testers, the multistage logging and import/export options. There is T1, E1, BRI/PRI, SS7, CAS, R1, and T1/E1 analysis. And as of this fall, there will also be VoIP testing software.

The Interface
Once the boards are cabled into your test product and the DCOSS software is loaded, and once the board drivers are initialized, the next question is, "What to do?." On top there are four pull-down menus -- File, View, Functions, and Help. Beneath that, there is a toolbar. The meat of the interface has three sections: a call status window on the top left, divided by timeslots of the current trunk; a phone handset status indicator on the bottom left, divided by open channels; and a call records window on the right, which shows real-time data on every call. The windows and their contents change dynamically as you conduct various software operations, but the basic layout stays the same.

Bulk call generation and scheduling are the most important product features, accessed through the Function menu. This option is very complex, much more so than it appears from an initial glance at the control window.

Time Savers
Bulk calling can be accomplished with any combination of timeslots, or with any train of incremental timeslots. To do this, there are options for calls to jump to the next available timeslot, the selected timeslot, or to synchronize all calling to happen simultaneously. You can also configure incremental calling for every Xth timeslot, and you can copy and paste configurations across trunks, which is a great time-saver.

Another time-saver is the ability to release DTMF digits at various points in the calling pattern, using the dial offset and dial duration options. The features are nearly identical for the twin bulk call reception menu, which serves to test your product's inbound calling features. The scripting feature is the most powerful option, whereby you can manually enter each precise call option and action, and you can create templates/library actions for future use. You can even create infinite levels of subscripts, so the bulk call generation is limited mainly by your creativity.

More features are accessed through the pull-down menus. From File, there are setup options for the system, protocols, and system status. This is also where you can configure ANI reception, DID routing, and import/export options. The View menu is equally powerful and has many choices. There are views for call records/detail, call records/all, and call records/incomplete calls. There are two views for call status, plus views for real-time status, phone handset status, and call statistics. Other views include various captured events, energy detection (for testing features like taking action on a long pause in a user's reaction to an IVR), call records queries, and digital trunk alarm status.

Call Generators
From Functions, you can start DCOSS's dual manual call generators. Each call generator lets you control all of the trunk's time slots individually. Within these windows, you also have access to the system phonebook, and to a "release all calls" toggle. For basic testing, the manual call generators are very useful just to see how well your product's intraextension dialing works.

Other Options
The remaining Function menu items, excluding the script configuration utility and a database reset option, have to do with what happens while your test calls are being generated or received. These options are all customizable, and they include voice files, faxes, DTMF/MF tones, frequency tones, and a call quality criteria setting. All of these choices are usable and were clearly designed by people who have legitimate CTI testing experience.

Since we've used the simulators and call generators of several other companies, we had some idea of what to expect from the DCOSS. Unfortunately, those expectations were relatively low; our experience with other T1 simulators dictates that they are very difficult to program. Therefore, you can imagine the joy we experienced when we had multiple T1 spans successfully communicating in (literally) just a few minutes, after one day of training.

At first, we thought that maybe we were actually getting smarter. We soon realized, however, that DCOSS's usability is a result of the Windows interface and intentional simplification of many telephony settings. This concerns us, however, because there is a dilemma when you may actually want to access some of those settings. After a few weeks of using the product, we are convinced that enough of the settings are available for 90 percent of everything you'll need to do.

After placing and receiving hundred of generated calls over both T1 and E1, we began to ponder new ways to test this product. We generated voice prompts, faxes, and DTMF tones, all using the call acceptance criteria tests. The criteria testing made us yearn for a full VoIP tester with PSQM, MOS, etc., all of which we're told is coming in a new version toward the end of this year.

Next, we tested the scripting. One scripting feature left us quite impressed. When developing a bulk call script, the program makes it nearly impossible to go wrong, because only allowable commands can be typed at given points. So, if you try to make a call before selecting a timeslot, or if you try to measure fax quality without first sending or receiving a fax, the system won't let you script it. This makes scriptwriting much easier for beginners, because they don't need to be expert programmers, and the debugging is dynamic.

We also spent many hours testing trunk configurations, scheduling properties, and most of the other miscellaneous features. We like how administrators can interrupt and edit a script in progress, in many cases without having to stop the script. We like the advanced levels of call logging, which also can be frozen, examined, and restarted while the logging continues behind the scenes. Also, we liked the ability to place extension-to-extension calls, and we liked the ease with which we could generate system templates for future testing.

As the GL engineer demonstrated the DCOSS for us, two concerns soon arose. The first is that the system does not ship with a network card installed. We're told that this is to save space for the numerous full-length telephony boards, and that many customers install a network card on their own. In our opinion, this should be a standard feature. Apparently, some people at GL agree, because the second criticism we have -- that there should be a client-server version -- is already a planned feature for the next release, along with the VoIP components mentioned above. Lastly, we'd like to see the bulk call generator and the scheduler integrated into a common GUI.

Whether your interest is the laboratory, the sales call, or the tradeshow floor, the DCOSS system is a great solution, especially because of the minimal training required to use it. It is easier to learn and use than most of its competition, it is fairly priced, and it flaws are all easily fixed or improvements are planned for upcoming versions. We highly recommend this product.

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