An excess of access products: Multiple vendors are developing devices that support DSL services

Facing the continuing challenge of supporting data and voice traffic, carrier networks are clamoring for multiservice access devices and multiplexers that can maximize transmission lines for high-speed throughput at a reasonable price. This demand has caused a flurry of activity among access device vendors, many of which are designing products based on or supporting digital subscriber line technologies.

"We are seeing a tremendous demand from our carriers, particularly from customers in the [competitive local exchange carrier] space who are requesting DSL-types of technologies," said David Weissman, senior marketing manager at Telco Systems. Driving this is the cost-effectiveness of DSL and its ability to maximize bandwidth. Asymmetrical DSL, probably the most common of these technologies, is used primarily in the residential space to support Internet traffic with voice, Weissman said.

But the evolution of data communications products is leading to high bit-rate DSL-based products, which offer repeaterless T-1 type transmission and supports voice and data. The most intriguing new types of access products are those that use HDSL technologies, said Beth Gage, senior broadband analyst at TeleChoice.

"HDSL has been around for a few years...in the telco access infrastructure, but it's starting to be used more to deliver T-1 and fractional T-1 without the customer knowing it," she said. To the customer, it looks like a regular time division multiplexed (TDM) pipe, she said.

The new wave of HDSL-enabled products sits on the customer premises side of the demarcation line, as opposed to devices that sit on the carrier site, Gage explained. This shift is good for certain types of service providers and commercial customers, she added. CLECs can incorporate DSL technologies and get access to unbundled copper loops, as in the case of ADC Telecommunications.

"[Carriers] need to deploy service quickly and cheaply, and HDSL can do that," she said. Repeaters are traditionally required every 6000 feet, but with HDSL, one line can reach 12,000 feet.

The adoption of HDSL plays to the trend of smaller carriers being able to differentiate themselves by offering bundled services and to the maturity of HDSL, Gage said. ADC, Telco Systems and Premisys Communications each recently announced HDSL access products. The scope of these products can vary quite a bit, however. For example, ADC partnered with Carrier Access Corp. todevelop the EZT-1/DI-HDSL voice and data multiplexer. The EZT-1 supports up to 24 voice lines and one HDSL or T-1 network connection and transmits at T-1 speeds.

Telco Systems built a similar product by integrating PairGain Technologies' HDSL offering into its products, the Access45 multiplexer and the Access60 integrated access device. Telco Systems created plug-in HDSL modules called Line Interface Cards, which can provide up to two HDSL interfaces per module or combine T-1 and HDSL on the same module. The Access60 can support as many as 48 voice channels and 10 HDSL lines.

"What is unique about our solution," Weissman said, "is that the HDSL card could be configured as a two-port HDSL [slot] to maximize the slots, or one port could be HDSL and the other a T-1 interface. Traffic coming off a router could be migrated into the HDSL transport from the same line card without having to use up the capacity." Opting for two HDSL ports per slot can double the number of voice channels to 96, he added.

Premisys announced a products suite that can transmit voice and data over an asynchronous transfer mode network at T-1 speeds. The top of the line Q-155 is a broadband access device that integrates HDSL into ATM and supports TDM, frame relay, ATM, Internet protocol, Sonet and synchronous digital hierarchy (see figure on page 70).

This introduces another trend in access devices: creating multiservice switches. Adding interfaces as needed bodes well for carriers, Gage said. "Telco Systems and ADC are adding interfaces so you can multiplex data traffic and voice traffic on the same line," she said. "With this bundled service approach, you don't have to deploy separate lines for the voice and data traffic."

Adtran and Nortel are taking the multiservice approach a step further. These companies have created access products that support numerous interfaces in one box. With its Q-155, Premisys fits this model, too.

One drawback of the HDSL products is that some still use TDM technology, which limits their effectiveness for carriers in the long term. "You still have different channels [for voice and data]," Gage said. "It's fixed [bandwidth]. If the voice channels are unused, the bandwidth is not available for the data traffic. Telco Systems is still using straight TDM and ADC does some stat multiplexing," meaning that the bandwidth is available for whatever purpose needed.

Still, she continued, "ADC and Telco Systems seems to be toward the top of the pack [of vendors that] incorporate DSL technology, and DSL is becoming more accepted in the marketplace."

PLUGGING ATM In a move that could lead to national availability of ATM service, BellSouth has filed an interstate tariff to permit interconnection to its ATM network. Under the Exchange Access ATM service, BellSouth's carrier customers would be able to establish permanent virtual connections based on the quality of service necessary for various traffic types.

SWITCHING FOR VIDEO AG Communication Systems has added switched virtual circuit capability to its family of video products. With this functionality, all of AG's video products, including its scheduling and management software and its video codec, can operate in SVC-based ATM networks.

One size fits all takes on new meaning as companies such as Adtran develop multiservice devices that can support multiple technologies simultaneously in a single box. Carriers can add or swap modules within a shelf, adapting their device depending on their current technology needs. Competitive local exchange carriers, competitive access providers and Internet service providers can build out their networks without having to bank on a single technology.

Adtran's Total Access Optical Multiservice Platform has modules for high bit-rate digital subscriber line, ISDN, T-1, DS-2 and integral DS-3 multiplexing in a single shelf. It sits between the telco transports and the local loop and can support a DS-1 with either a DS-3 or a Sonet network interface.

"It's highly scalable," said Tom Jenkins, broadband analyst with TeleChoice. "It has just about every interface known to man on it."

In today's deregulated environment, a flexible solution provides the telcos with a way to build for the future without betting the farm on one or two technologies, Jenkins noted. Flexible multiservice devices are most attractive to the CLEC, CAP and ISP environments, which are more nimble than incumbent LECs.

"CAPs and CLECs are more aggressive in deploying new technologies," he said. "They are willing to invest because they don't have the infrastructure yet."

"In some cases they'll buy it because they haven't started on anything yet, and in other cases it will be a replacement for something that's outdated," said Tom Stanton, vice president of telco marketing at Adtran.

The multiservice devices take up less rack space in a collocation space, and can support various services in a single box. That makes it a more cost-effective solution for small but growing service providers-and not just in terms of space. A CLEC can buy the multiservice device and train one person to manage it. That means carriers outlay less capital for equipment and reduce the cost system maintenance, monitoring and troubleshooting.

"We've worked hard to make sure it is eminently manageable," said John Bartell, product manager at Adtran.

"A lot of service providers are looking for ways to make the back office more efficient, and a single box will do that," Jenkins said. "It's much easier, but it's high risk."

Before, if the device lost DSL capability, everything else still worked. In a multiservice device, "it better be working flawlessly or they better have great backup plans," he said.

The industry should watch this space because more access products are on their way, Jenkins predicts.

"We'll see many more partnerships. Companies that are historically frame relay will partner with companies in DSL," he said. "And we'll see more functionality in a single box. Instead of having a switch at the edge, or a remote access concentrator, or a modem for dial-in, all that will be internalized."