Quigley offers ISPs a rough sketch of NBN architecture

NBN Co has developed a rough architecture for the build-out of the National Broadband Network in an attempt to keep ISPs and carriers in the loop as to how their services will intersect with it.

Responding to questions posed by iTnews, NBN Co chief executive Mike Quigley said the company has "put a stake in the ground" as to how and where the NBN and the operations of retail service providers will interconnect.

NBN Co intends to build a GPON (gigabit passive optical network), providing Layer 1 and Layer 2 of the network, leaving layers 3 and above to service providers.

In the OSI network model, Layer 1 refers to the provision of bit stream (in this case, light) across the fibre. Layer 2 refers to the encoding and decoding of this light into bits. The five layers above refer to switching and routing, connections, security, applications and quality of service.

In other words, NBN Co wants to offer very little more than the most basic physical layer - enabling service providers access in such a way that it almost feels like they are using their own network.

"Where we see the network boundary at the moment - we see ourselves as providing a Layer 2 bit stream type service," Quigley said. "The service will have the functionality to cover voice, video and high speed Internet - only with the service provider, rather than NBN Co, providing these services."

Quigley said he would expect the NBN Co's domain to "end at an Optical Network Terminal (ONT)... on the side of the house."

This ONT, a modem built for fibre networks, is likely to feature several Ethernet ports so that it can support multiple service providers if need be, and also incorporate POTS connectivity - such that it can also be used for traditional telephony.

NBN Co intends that this outdoor terminal will connect back into the network via a splitter (which connects an optical fibre distribution frame to multiple premises), which in turn connects into the Ethernet aggregation network.

From here, NBN Co hands off to retail service provider to provide applications and content.

Quigley said that access to the network is likely to be sold to service providers via a combination of fixed cost (per user) and variable costs (connection speed and Quality of Service attributes).

Quigley emphasised that the plans to date are merely "stakes in the ground", and that his final decisions will depend on feedback from service providers.

"It's very important as we design the network that we get their input in," he said. "At the end of the day they are potential customers."

Two equipment vendors

NBN Co also intends to use just two networking equipment vendors to gain a good price on networking kit while reducing supply chain risk. Products will be chosen on the basis that they adhere to global standards - to ensure both good prices and interoperability.

"We will go through a process of expressions of interest and assess the capabilities of the technologies," Quigley said. "We'll aim for a shortlist which will come down to two primary vendors."

The two primary vendors will be asked to "resolve interoperability issue" between their products by building an integration layer, he said.

At the systems layer, Quigley expects a single vendor to be selected, working with partners. But for the build of the physical network, he expects numerous private contractors and sub-contractors to be

Read on for information on roles, prices and timetables...