Forum Defines IP-Based Architecture For DSL Services


The DSL Forum has released two technical reports Tuesday, dubbed TR-058 and TR-059, that define quality of service (QoS) and equipment requirements for setting up an Internet protocol-based architecture for DSL networks.

Traditionally, DSL services have been deployed using ATM permanent virtual circuits (Paces). With DSL subscriber totals approaching 50 million worldwide, this approach has been a success, said Tom Starr, president and chair of the DSL Forum.

With the release of TR-059 and TR-058, the DSL Forum is looking to push the architecture forward in order to introduce new services and revenue opportunities while easing the setup and management of DSL connections. "We're now going to take this to another level," Starr added.

Current ATM PVC-based deployments are based on the rollout of statically provisioned pipes that offer a set at a rate and only provide best-effort connectivity. Through the release of TR-058 and TR-059, the DSL Forum is adding a QoS capability that allows carriers to identify several levels of priority flows, Starr said.

Then, using a newly defined bandwidth management scheme, carriers can change the bit rate of the link to address the data requirements of services holding different priorities, he added.

In a traditional DSL network, users pay for a certain bandwidth, typically in the few hundred-kilobit range. However, to support the transfer of video streams or to support voice services, customers must buy a higher data-rate package from carriers.

TR-058 and TR-059 change this model significantly. By providing priority levels and adapting bit rates, carriers can provide end users the ability to access and a video service "on demand" without having to purchase an entirely new service. Once the video transfer is complete, carriers can send bandwidth down to its normal rates. "The customer pays by the drink," Starr said.

To make this flexibility possible, the TR-058 document defines the IP-based QoS capabilities. TR-059, on the other hand, describes the requirements for developing a broadband remote access server (B-RAS) and a routing gateway architecture for customer premise equipment designs.

The B-RAS connects multiple digital subscriber loop access multiplexes (DSLAM) to the transport network. This gateway device handles downstream traffic management in the network while also policing upstream flows created by the CPE device. To handle policing, the TR-059 defines a policy server that tells the B-RAS what bandwidths to provision to a customer while also billing the customer, said Bob Escalle, DSL marketing manager at Texas Instruments.

B-RAS systems are not a new element in current DSL networks. According to Starr, the new spec provides mechanisms for carriers to tap into the existing B-RAS elements in the field while offering the QoS and bandwidth adjustment features. "The migration requires only a small capital outlay," Starr said.

Escalle said that in older networks there is a potential for the need for a new B-RAS. However, in many networks, especially newer deployments, he agreed with Starr that the cost could be relatively low.

The cost of upgrading the CPE equipment will also probably be minimal. "Most CPE chip sets already support a routing function," Escalle said. "Now chip set vendors just have to make sure their protocol stacks support the new functionality."

The "small capital outlay" that Starr and Escalle hinted at is just one benefit for carriers. By allowing users to dynamically select and receive services, carriers are opening the door to new revenue streams over their existing DSL networks, a theme that will play well with today's cash-strapped telcos.

The new architecture also brings some efficiencies on the backhaul front. According the Starr, the new B-RAS architecture lets carriers better aggregate traffic and more easily link up with IP or Ethernet transport networks, thus cutting backhaul costs.

Carriers don't appear to be wasting any time in making the technology come to life. Starr said he expects carriers to begin rolling the technology out in 2004.

For the services to roll, carriers will now need upgrades to their network management systems to support the dynamic bandwidth capabilities laid out in TR-058 and TR-059. Realizing this concern, Starr said the DSL Forum will begin working to define changes in the operational system at its next meeting.

This story courtesy of TechWeb.