Strict parameters imposed on traffic flow in the Layer 2 UFB contract between Crown Fibre and local fibre companies will create problems, particularly for domestic users with older equipment, says a Chorus technical expert involved in the rollout.
What’s more, it’s not clear to him how a standard of less than one millisecond in frame-delay variation (jitter) found its way into the Crown Fibre-Chorus contract, says Chorus principal solutions architect Curtis Owings, who attended the NZ Computer Society’s Wellington meeting on “making the most of Ultra-Fast Broadband.”
In conversation after the formal part of the event, he described the frame-delay-variation condition as “draconian”. “It means you have to be very rigid about what frames you allow,” he said.
“So if your equipment in your home is putting things on the wire with more than 1 millisecond frame-delay variation [the link to the fibre] will start throwing frames away because you’re out-of-spec.” This in turn will slow down throughput.
The onus will not be on the local fibre company but on the retail service provider to meet a specification which is unnecessarily rigid for normal domestic use, by adding expensive customer premises equipment, Owings said.
The same condition is included in Crown Fibre’s service-level agreement with Enable Networks, which is building the UFB network in Christchurch, Rangiora and surrounding areas.
Enable CEO Steve Fuller agrees that the 1 millisecond standard is probably “unnecessarily low” for the needs of the typical UFB user. “No doubt about it, it’s a tough challenge,” he says; “but we’ve designed for it, selected our equipment and tested it.”
Unlike Owings, he sees no downstream problem for the retail service providers or users; “these are our SLAs on our network and they’re our responsibility,” he says; “we won’t drop packets.”
There are conflicting reports of how the 1 millisecond limit found its way into the contract, Owings says. One version of the story says Chorus objected to it and it was taken out of the agreement, but somehow reappeared.
“But that’s only anecdotal,” he says
Computerworld sought clarification from Crown Fibre strategy director, Rohan MacMahon. “The standards were developed by a TCF [Telecommunications Carriers Forum] working group and approved back in March 2011,” MacMahon replied in an email. However, the document he refers to contains no specified limit for frame-delay variation.
“A lot was discussed in the TCF meetings,” Owings says, “but no-one ever put those numbers on a whiteboard.”
It’s only when the development process “hits the labs” that the full practical effect of such strictures becomes evident, he says.
As Computerworld’s print edition went to press, MacMahon was in the process of “clarifying the issue” with Crown Fibre and Chorus.