Given the GPON rates (2.488 Gbps/1.244 Gbps) per 32 subscribers, the aggregate NBN data capacity is immense. However, there are other factors which will limit data rates seen by NBN subscribers.
A given Service Provider connects their backhaul to an NBN “Point of Interconnect” or POI, each POI covers a given “Connectivity Serving Area”. The NBN will eventually comprise 121 POIs. Each Connectivity Serving Area requires backhaul (either 1 Gbps or 10 Gbps) to connect to the wider network. The actual data rates seen by NBN subscribers will be determined by this backhaul capacity, which, due to cost, will be only a small fraction of the total Connectivity Serving Area capacity.
Hence Service Provider backhaul capacity will have a key influence on the average or sustained data rates available to subscribers. Backhaul capacity is likely to be a major NBN bottleneck.
Also, Service Providers purchase capacity within the NBN, via a “Connectivity Virtual Circuit” or CVC, which serves the subscribers connected to a given NBN Point of Interconnect. CVC capacity cost is $20 per Mbps per month. CVC capacity (or lack thereof) will also constrain NBN subscriber data rates.
NBNCo proposes peak rates of up to 1 Gbps. The NBN Fibre to the Premises (FTTP) architecture is based on the GPON standard, which provides 2.488 Gbps shared amongst 32 users. This supports the 1 Gbps NBNCo peak rates (downstream and upstream). XG-PON, the next version of the GPON standard, will provide 10 Gbps downstream, shared among 32 subscribers, allowing multi Gbps subscriber services. However, actual NBN data rates will be constrained by backhaul and Connectivity Virtual Circuit capacity.