Term of the Day: G.SHDSL

[Keefe]

Also known as G.991.2, G.SHDSL is an international standard for symmetric DSL developed by the ITU. G.SHDSL provides for sending and receiving high-speed symmetrical data streams over a single pair of copper wires at rates between 192 kbps and 2.31 Mbps. G.SHDSL was developed to incorporate the features of other DSL technologies, such as ADSL and SDSL and will transport T1,E1, ISDN, ATM and IP signals. This is the first DSL technology to be developed from the ground up as an international standard.

[Keefe]

Here is a follow-up article from Broadband Week

Distance limitations and provisioning nightmares might one day become ghost stories for the digital subscriber line sector, reduced from reality to no more than scary tales from the technology's developmental days.

At least, that's the hope now that the International Telecommunication Union (ITU) formally has reached agreement on its G.991.2 global standards, intended to help erase such problems from the symmetric DSL market.

After weeks of anticipation leading up to the formal announcement, the ITU finally has agreed on the official recommendation for Single pair High bit-rate DSL (SHDSL). With the standard in effect immediately, rapid deployments and rollouts could begin in the second half of 2001.

G.SHDSL long has captured the attention of the DSL provider community because it's a symmetric DSL flavor that will allow service providers to cater to valuable business customers. Benefits include easier installation due to smoother interoperability with other flavors of DSL, and an ability to carry out service to distances as far away as 20,000 feet and beyond from the central office.

"As a company, we believe strongly that this standard will propagate quickly, especially in the business sector," says Dano Ybarra, vice president of commercial access for DSL equipment maker Efficient Networks. "We believe it will eventually replace the other standards for symmetric DSL service."

SHDSL will provide high-speed symmetric data transmission over existing copper wires, without requiring the installation of additional cable. The technology will operate at speeds from 192 kilobits per second to 2.3 megabits per second and will transport T1, E1, ISDN, ATM and IP signals. As the acronym indicates, SHDSL combines elements from both SDSL and HDSL.

Peter Wery, chairman of the ITU Study Group 15 that passed the standard, says the G.SHDSL project first appeared on the ITU's agenda in late 1998. The work was essentially done last year, before it was ratified in February.

"Essentially, the standard was developed inside of 18 months," Wery says. "For a complex device, that's not a bad time."

The new standards complement the numerous existing ITU standards for ADSL network architecture and system management, which to date has been the DSL flavor of choice for residential service.

The broadband network equipment vendors weren't waiting around for the ITU to act. Anticipating that the standard was on its way, many of the vendors took their solutions into full testing at the University of New Hampshire InterOperability Lab's G.SHDSL testing workshop in late January. Efficient was one of 18 member companies that took part in the tests of the ITU standard, making sure its SHDSL CPE products were interoperable with the DSLAMs and chipsets of other vendors. The next testing session at the university's lab will take place next month.

"We usually spend months and months getting into all the vendor's labs to test for interoperability," says Ybarra. "When we pull everyone together in the same forum at the same time, everyone can get immediate feedback on how they interpreted the standard and we can make adjustments."

All the effective work that takes place in the consortium labs goes a long way in speeding up the deployment of high-speed services, which in the current market has become the crucial bottom line. Ybarra says trials and initial rollouts of SHDSL already have begun in Europe, where the older SDSL technology never was widely accepted. Adoption in the United States has been on a slightly slower curve, because many data CLECs invested so richly in deploying current SDSL technology. That should change in the second half of 2001.

"The standard that was approved by the ITU has been mostly meant for replacement of T1 and E1 in the local loop," Wery says. "Obviously, there's been wide interest."