NBN Co gets survivability right

Labor’s ambitious national broadband network (NBN) is living on borrowed time and will almost certainly be binned after the September election. The NBN may have had its fair share of problems – some legitimate and some self-inflicted – but it has a lot of redeeming features as well, especially when it comes to the network’s architecture. The Coalition’s NBN alternative may seem pragmatic but can it afford to undo the good work done so far?

The NBN design is based upon forward thinking architecture that promotes resiliency and survivability – vital attributes at a time when Australia appears to be facing an increase in natural disasters.

When the decision was made to build a 21st century national wholesale network utilising new transmission infrastructure NBN Co network architects were presented with a rare opportunity to design a network from scratch. Resiliency and survivability were high on the NBN Co key network design criteria list – a list that also included simplicity, efficiency, reliability, upgradability and universal access for customers and retail service providers.

There is a cost versus performance trade-off with all technology systems so how do we know that NBN Co has achieved the right balance?

Technology selection

NBN Co selected  three transmission technologies for the NBN with a vast majority of Australians to be connected to the network through an optical fibre connection (93 per cent) and a mix of fixed wireless and satellite for those who live outside the optical network footprint. There are myriad technologies that might have been selected by NBN Co and some of the technologies overlooked include HFC, FTTN, VDSL, ADSL, Active Ethernet, FD-LTE, and WiMAX.

The technology selection reduces network complexity and this means reduced design costs (for example build scenariosnetwork design rules and specifications), reduced build costs (for example the plant, equipment and infrastructure needed), and the opportunity to increase reliability, resiliency and survivability.

NBN Co chief technology officer Gary McLaren told Business Spectator that “the network was designed to meet the benchmark availability requirement, to improve resiliency and survivability without gold plating the network and achieving a balance between cost and reliability targets.”

Satellite

The NBN satellite services will provide customer connections at 25 Mbps / 5 Mbps, cover the continent and Christmas, Cocos, Norfolk and Lord Howe islands.

NBN Co has commissioned Space Systems/Loral to build two high capacity Ka-band geostationary satellites that are due to be launched in 2015 by Arianespace. 

A total of 10 satellite ground stations will be built to connect the network to customers through the two satellites. The 10 satellite ground stations will be positioned around Australia to permit uplink and downlink frequency re-use which increases the overall capacity of the network to satellite connections.

By launching satellites, NBN Co has improved the resiliency and survivability of the NBN satellite service by reducing the need for interconnections with third party satellite providers. The current design reduces management, control structures and the need to deal with variable service levels and variable disaster recovery scenarios.

A key feature of the satellite network design that improves resiliency is the designation of one of the satellite ground stations as a stand-by that would become operational if another ground station goes offline. Each ground station has two diverse fibre paths coming from separate fibre access nodes (FAN) which is where the fixed wireless network joins the transit network. The diverse fibre paths provide resiliency in the event of FAN or path failure without having to switch to the backup site.

Fixed wireless

The NBN fixed wireless services will provide customer connections at 25 Mbps / 5 Mbps. NBN Co commissioned Ericsson to provide the fixed wireless network utilising TD-LTE (time division) which is a high data capacity variant of the LTE wireless communications system currently offered as “4G”.

TD-LTE is a more flexible implementation that utilises one large spectrum block rather than the two separate and equal sized spectrum blocks used by the alternative FD-LTE (frequency division).

By selecting TD-LTE NBN Co has selected a technology that provides a 10 year upgrade path to IMT-Advanced (true 4G) which will provide customer connections at about 100 Mbps / 10 Mbps.

The fixed wireless service resiliency and survivability will be enhanced by the capability to utilise fibre, microwave or satellite connections between base stations and the network. NBN Co will also have mobile base stations (and be able to access additional mobile base stations from the Australian mobile providers) that can be deployed in case of base station failure.

At the fibre access node aggregation switches may be deployed either individually or in pairs for resiliency. What this means is that NBN Co will consider factors that might delay FAN repair in case of failure and introduce redundancy of key items at the FAN, where necessary.

Transit and aggregation networks

The NBN transit network connects the initial 155 FANs to the Points of Interconnect (POI) which is where retail service providers (RSP) connect to the NBN. The NBN transit network will initially incorporate 23 transmission rings and provide increased resilience by ensuring that if a single link in a loop is cut then customer services will remain in operation.

All networks have key points that are single points of failure and the 2012 Warrnambool exchange fire highlighted the devastating effect that a network key point failure has on a community.

In an instance where an individual POI was to fail, McLaren indicates that some RSPs may need to “re-route traffic between their network and another POI and this would be affected by the number of links that needed to be re-routed. Identifying alternate paths would be a joint activity between NBN Co and RSPs.”

The NBN provides multiple paths between FANs and POIs so traffic on these links will be automatically re-routed with minimal impact on end users and service providers. In the highly unlikely event of a total failure of a facility housing the point of interconnect, service providers and NBN Co will need to work closely together to restore services through another POI. This will cause problems for RSPs that only have services connected to a single POI and may occur if the provider is small or regionally focused or providing special services to customers in one area.

Point of interconnect failure is a major event and NBN Co knows this is one area where there is no room for complacency. As McLaren points out, NBN Co understands the gravity of this situation and understands “what it can do and what might need to be done” to mitigate the effect of a key point failure.

Fibre optical access network

The NBN fibre optic access network will connect customers initially at 100 Mbps / 40 Mbps and increase in 2014 to 1 Gbps / 400 Mbps. Alcatel-Lucent is providing NBN Co with the Gigabit Passive Optical Network (GPON) shared access system , which means that up to 32 customer connections are joined to one fibre that runs to the fibre access node. NBN Co selected GPON to provide fibre access network connections for the majority of customers and also intends to provide point to point fibre connections by including additional fibres in the fibre cables that run past customer premise.

Not only does this provide extra capacity options for the customer but the addition of extra fibres within the cable provides resiliency. GPON is more resilient than active optical fibre networks like active Ethernet or Hybrid Fibre Coax (HFC) because there is a reduced reliance on active components, which require electricity, between the FAN and customer’s premise.

In areas that are flood prone – and this includes many major regional towns built along life sustaining rivers – a reduction in active components increases survivability.

A key feature of the NBN Co fibre access network design is the addition of a ‘cold standby’ distribution fibre diversity path between the FAN and Fibre Distribution Hub (FDH) (fibre spitters contained in a small cabinet located in the street). What this means is that in the event of a fibre failure between the FAN and FDH, a technician will be able to patch and activate an alternate fibre connection.

This is a significant change compared to the copper network, which has not typically included diversity between the exchange and end users. McLaren highlights this point and is confident that “adding extra diversity in the access network brings a big advantage.”

A fresh start

NBN Co’s network design provides balance between cost, performance and the need for resilience and survivability. The digital economy is vital for Australia’s future and every Australian business, from the smallest and most remote to the largest urban based company, must be provided with network connections that provide the greatest possible opportunity to succeed.

The NBN will provide residential customers with an upgrade path that will ensure everyone can access the new and exciting digital services that will become available in time.

The network’s resilience and survivability have benefited from the decision to make a fresh start. It would be a shame to see this work cast aside in a rush to provide a cut price NBN. 

Mark Gregory is a Senior Lecturer in Electrical and Computer Engineering at RMIT University.

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