Although DSL modems are unlike their V.x cousins, the overall operating principle is the same: A modem within a branch or small office connects via a telephone line to a compatible device owned by the service provider. Once upon a time, anyone with a little IT savvy could go down to his or her local computer store, pick up a new analog modem and get it to work right out of the box. You didn't need to know what equipment your service provider had on the other end. Thanks to standards, it just worked.
DSL has changed all that. While general standards exist on how a DSL modem connects to a device, subtle variations in the way different models work make interoperability with any service provider less than a sure bet. Service providers decide what equipment goes into their networks, and that equipment determines what can be deployed at the customer premises.
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For example, service providers choose and install the DSLAMs (DSL access multiplexers) that will be used in their networks. The DSLAMs then dictate the type of CPE (customer premises equipment) sold. Not every DSL modem is 100 percent compatible with every DSLAM, so the choices can sometimes be very limited, possibly to a single vendor solution at both ends. This means that customers are not always given a choice on what CPE they can use. Vendors are working to make interoperability a reality, so this will eventually change. However, only time will tell if you will ever find DSL modems on store shelves.
Freedom of Choice
Because the choice of CPE is restricted by service providers, enterprise customers don't always get all the functions and features they might like; in fact, they may not even know what's available.
We decided to turn this paradigm around. Knowing what equipment is available gives enterprise customers an extra check box on their service provider wish lists. Armed with knowledge of CPE options, you can demand support for desired gear or features before contracts are signed. Most small or branch offices are looking for features beyond just data delivery, so we narrowed our list to include only those products that support multiple voice lines on top of data connections.
Sometimes vendors are less than eager to submit their wares for our scrutiny. This time, however, a large turnout of companies agreed to talk to us about their products and the state of DSL technologies. The selection criteria for products were simple: Only those devices that offer either voice-over capabilities or other technologies beyond those of simple data modems were considered. Most vendors now offer some sort of voice-over-technology modems, but theses devices are far from having cookie-cutter uniformity.
For example, residential DSL customers generally have an extra POTS connection. In reality, however, there is only one physical line, with the DSL data using a different frequency spectrum than does the analog voice transmission. Multiple calls are placed on the DSL line either by AAL2 (ATM adaptation layer 2) encapsulation of ATM cells or by using VoIP (voice over IP), which is common in LANs, MANs and frame-relay networks.
We talked to Celsian Technologies, Cisco Systems, Copper Mountain Networks, Efficient Networks, Net to Net Technologies, Paradyne Corp., ShareGate, TollBridge Technologies and Vpacket Communications. We didn't do head-to-head testing, so we didn't grade the products. Because there are still too many differences between modem/DSLAM combinations, creating a common DSLAM and test network that would give everyone a fair shake would be virtually impossible. In addition, the product you end up with has a lot to do with the provider you choose, so we decided to evaluate the products on their own merits.
So which DSL IAD (integrated access device) is right for you? That's a hard question to answer, but here are some guidelines.
Because most of these devices are DSL modems with voice and VPN (virtual private network) service added, you can apply the same criteria that you would use when choosing more traditional routers. When determining the number of voice ports needed, you must strike a balance not only among the number of people in the office, but also against the bandwidth available and the quality desired. When it comes to voice lines, we found that customers overwhelmingly prefer quality over quantity (see pie chart).
IADs' use of softswitch technology can be a boon to small businesses or home offices that want the functionality, but not the cost, of a large corporate PBX. In this case, the service provider effectively becomes the PBX, and the small or home office need only have the IAD within its premises.
Home offices can also take advantage of units, such as ShareGate's DSL2000, that let voice and data connections be located at any phone jack within the home without additional wiring. For branch or remote offices, traditional routing and QoS (Quality of Service) features are important concerns. In addition, large offices will find an extra advantage in features like DSL bonding to increase bandwidth. While not offering any voice capabilities, the FrameSaver DSL from Paradyne, in connection with its OpenLane software, is a great way to monitor traffic flow and congestion that may occur at your remote or branch offices.
Six of the companies we spoke with -- Celsian, Cisco, Copper Mountain, Efficient Networks, Net to Net and TollBridge -- offer straightforward IADs with DSL connections on the network side instead of ATM or frame relay hookups. For example, Cisco's 2600- and 3600-series routers have been on the market for two years and require only that a DSL interface be installed.
We did, however, find some exceptions to this rule: Paradyne offers in its FrameSaver DSL line the same management capabilities you'll find in its frame relay products. In addition, ShareGate has taken DSL and allowed voice and data traffic to be deployed easily to anywhere in a home or small office, and Vpacket caught our eye because of the company's attention to voice quality. Enterprise customers with voice-over systems usually don't have the ability to monitor each call's quality, but having that ability on a DSL IAD helps administrators avoid network variations that may degrade quality.
After you read the following evaluations, you will have the knowledge to intelligently assess different CPE offerings. When selecting a service provider, you'll not only consider service guarantees and price points but also DSL CPE choices. The pictures shown are representative of the companies' products; we do not discuss the prices of these products because they will vary widely depending on the plan you purchase from your service provider.
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