Zhone unveils path to terabit access

Zhone Technologies (NASDAQ: ZHNE) introduced a new access platform today designed to open up bandwidth bottlenecks in the backplane to make way for a rising tide of unicast traffic. Though it’s called the MXK Intelligent Terabit Access Concentrator, it’s not capable of terabit-per-second speeds just yet.

The initial release of the central-office-based 8-rack-unit MXK will be capable of delivering 20 gigabits per second downstream through each of its 4- or 8-port GPON cards or 20-port active-Ethernet cards. And each of its two uplink slots contains two 10-Gb/s ports and eight 1-Gb/s ports, for a total of 28 Gb/s upstream.

But more important than the cards is the newly designed backplane that connects them, Zhone said. While the vendor’s previous access platforms used a bus architecture (with a simple, shared infrastructure) to interconnect uplinks with line cards, the new platform was based on a “dual-star” architecture in which each line card is connected to each of two uplinks through two separate 10-Gb/s paths through the backplane.

Carriers can use this architecture in the traditional way, saving half the paths as standbys in case of failure. Or they can use link aggregation to keep both paths in use at all times, in effect doubling the capacity of the traditional method and getting all 20 Gb/s per card out of those two 10-Gb/s backplane paths.

Because the device does routing and multicast replication, its total capacity is best is expressed not by adding ingoing and outgoing speeds, Zhone said, but by adding the total amount of traffic the 8-rack-unit chassis can contain. Measured that way, said Steven Glapa, Zhone’s vice president of marketing and product management, “It nets out to something north of 400 Gb/s.”

Next year, Zhone hopes to add new line cards containing two 40-Gb/s ports. But if carriers in general end up opting to skip 40-Gb/s interfaces for 100 Gb/s, the vendor may instead introduce cards with four 10-Gb/s ports. And when carriers want it, Glapa said, Zhone can scale the box’s “something north of 400 Gb/s” to well north of 1 terabit per second, hence the product’s name.

Using link aggregation to boost bandwidth instead of reserving redundant paths means that, in case of failure, service will degrade for all users on the affected lines. But Glapa said a link-aggregated dual-star architecture is likely to become increasingly important as the amount of unicast traffic in the network increases.

Of the bus architectures upon which Zhone’s MALC platform, and many of its peers, are based, Glapa said, “That’s okay in an environment where there’s lots of oversubscription, but in the non-blocking, streaming world we’re entering, it doesn’t work.”

Glapa acknowledged that most major equipment vendors have already introduced new backplanes, as Zhone is doing now. “We just happened to have picked fatter switches for ours,” he said.

In addition to the 8-rack-unit chassis, the MXK comes in a 3-rack-unit version. In another month or two, Zhone expects to add ADSL2+ support, using the 3-rack-unit version (or existing outside plant gear) in remote terminals. And in the fourth quarter, the company expects to announce VDSL2 support for the new platform, which has been generally available for more than a month, Zhone said.