A glimpse at the NBN's service models

NBN Co has started to explain the network's proposed operational models. Richard Chirgwin explains how their plans will work.

At this week’s NBN Industry Connection 4, NBN Co began spelling out some of the operational details of the proposed network. So how do the technical details of the NBN relate to the services it will eventually offer?

One aspect of the NBN that’s widely misunderstood is that it’s intended to be more than just a fast consumer Internet connection. For consumers, this will mean among other things that the initial 100 Mbps may not mean all of the 100 Mbps is for Internet access: it will depend on the mix of services the customer buys.

If someone decides they want the fibre to deliver some kind of broadcast television service as well as their Internet access, then some of the capacity will have to be set aside for that service, leaving less for Internet access. This isn’t the downside it looks like, however, for two reasons. First, more services on the network means more chance to spread the cost of the network itself; second, the network’s quality of service (QoS) support (currently under discussion both within NBN Co and in the NBN working groups of the Communications Alliance) could allow a more dynamic use of capacity than consumers are currently accustomed to. It may be possible for “reserved” capacity to be freed if not in use (for example, if nobody is watching TV, capacity could be made available to services that are in use).

All of this is in the future, since the QoS definitions – and how they might be applied in practice – are still under discussion.

Aspects of Migration

Because the NBN’s designers are acutely aware of the migration challenges ahead of them, they’re also hard at work considering how that migration may be made as smooth as possible. This brings us to discussions of how to migrate today’s most common “legacy” services: voice, DSL, and TV.

All of these depend at least in part on the definition of the devices that will end up being bolted to the side of the home: the ONT, or optical network terminal.

NBN Co has stated that as well as the data interface, at least one legacy interface, emulating analogue TV, will be part of the ONT, so that no consumer suffers a loss of telephone service during the migration.

The others two, DSL and television, are still under discussion.

DSL emulation, if it were provided, would exist to provide a smooth migration for the existing DSL user. Whether or not this is necessary would depend on the relationship between he NBN Co and individual service providers; it’s therefore not certain that a DSL-emulating port will be required on the ONT.

The third legacy interface mooted for the ONT would allow broadcast television to be carried on the network – if it were to be included in the device. There are, however, several policy issues that would have to be solved: an access regime for television to that part of the network, deciding what organisations (and how many) would have access to the “RF space” under what conditions.

And it may not be viewed as strictly necessary: the network is also designed to support multicast, which means an access seeker such as a television network would be able to access customers without needing legacy “RF” support.

QoS on the NBN

Apart from DSL, NBN Co assumes (fairly) the legacy services won’t be of much interest to the business user: QoS on the Ethernet port is more vital.

For the first time, the NBN will give service providers the ability to deploy an end-to-end QoS model. The QoS delivered to the end user will be transparent, even though the service provider doesn’t own the infrastructure through which that QoS is delivered.

And that means even SMEs will be able to buy QoS-enabled services. Instead of having to manage competing traffic types themselves (for example, by running one router for data traffic and another for VoIP, which is more common than you might expect in eve medium-sized offices), the customer will be able to use a single Ethernet port, confident that the VoIP server has access to a higher grade of QoS than the data traffic.

But is it neutral?

It’s quite likely that this aspect of the NBN will spark some level of controversy that NBN Co (and, for that matter, the government, the Communications Alliance, and service providers) will have to manage.

This is at odds with what might be described as the “strong network neutrality” position (here, I am referring to positions taken in America, where the neutrality debate is far more polarised than in Australia), in which at least some authorities consider the application of any QoS protocols over any Internet-connected service by a service provider as a violation of net neutrality. It is, perhaps, fortunate that NBN Co has chosen the Layer 2 Ethernet model rather than building an IP network – in this way, it is clear that the bandwidth devoted to a “best effort” Internet service is subject to the user’s choice rather than NBN Co.

For the business customer, the NBN approach will mean more than just “better VoIP services” (for example) by allowing service providers to buy not just the wholesale service, but by applying QoS to that service. It will, over time, tend to equalise costs between urban and regional locations.

The four QoS models currently under consideration by NBN Co cover best-effort services, “priority” services (for business-grade data), “expedited” services (suitable for video-on-demand), and “critical” services with the lowest levels of latency and jitter. The model is, however, still under development and may change before the wholesale NBN Co products are finalised.

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