Australia's National Broadband Network uses several different physical technologies to deliver internet to homes. Which one you have significantly affects the speeds you can actually achieve.
FTTP — Fibre to the Premises
The best option: fibre optic cable runs all the way from the exchange directly into your home. Supports speeds up to 1Gbps and beyond. Very reliable, low latency. If you have FTTP, you can take full advantage of any speed tier your ISP offers.
HFC — Hybrid Fibre Coaxial
Fibre runs to a neighbourhood node, then uses the old Foxtel cable network to your home. Can achieve 100–1000Mbps but is shared infrastructure — speeds can degrade in the evening when the whole street is streaming. Very common in Melbourne's inner suburbs.
FTTC — Fibre to the Curb
Fibre runs to a small box on your street (the "Distribution Connection Device"), then uses existing copper phone line for the last 50–100 metres. Faster and more reliable than FTTN. Most homes can achieve 100Mbps+ plans.
FTTN — Fibre to the Node
Fibre runs to a large green cabinet in your street, then uses copper phone line for the last few hundred metres to a kilometre. Speed is heavily dependent on the length and condition of that copper. Homes further from the node may only achieve 25–50Mbps in practice. The most problematic NBN technology.
Fixed Wireless
Used in regional and semi-rural areas where fibre isn't economically viable. A signal from a tower connects to an antenna on your home. Can be excellent or inconsistent depending on tower congestion and distance.
How to Check Your Connection Type
Log into your ISP's account portal, or visit the NBN Co website (nbn.com.au) and enter your address for a technology check. If you have FTTN and are getting slow speeds, you may be eligible for an upgrade under NBN Co's upgrade programme — worth checking.