The Optus HFC Network
The Hybrid Fibre Coaxial or the ‘HFC’ is one of the access networks we use to reach you, our customers. We’ve got it in parts of Sydney, Brisbane and Melbourne, and it passes more than a million premises. HFC is an industry term for a broadband network utilising a combination of optical fibre and coaxial cables and the standard is known as DOCSIS. We often call it our “Cable Network”. You would recognise the network infrastructure as a thick black cable hanging a few meters below the street power cables.
The services offered using our HFC Network include Optus TV, Optus MeTV, Optus Fixed Broadband, LAT (Local Area Telephony) and LIP (Local Area Telephone over Internet Protocol).
Optus Fixed Broadband and LIP services connect into a modem known as an eMTA (embedded Multimedia Terminal Adapter). This is simply a cable modem and a telephone adapter all rolled into one smart device.
The eMTA interfaces the HFC network over a coaxial cable using a modulation scheme called QAM. These cables join up to an Optical Node. These nodes convert the coaxial electrical signals into optical signals for transport over greater distances. We use fibre technology as it allows us transfer more data over greater distances than the coaxial cable would.
Several nodes will converge onto into a CMTS and then uBR (Universal Broadband Router). The uBR is a massive Cisco Router and it’s the first IP device you see from your eMTA heading into the network.
Voice traffic splits and heads off into the Voice Network while data is forwarded by the uBR into the IP Network. From there it can reach almost anywhere in the world.
The Optus DSL Network
The Optus DSL Network is an alternative to the HFC Network. The DSL or Digital Subscriber Line is a family of technology which allows us to transmit high speed data over the existing copper wires in the ground. These copper wires were typically first used to provide plain old telephone service or POTS. The DSL variety we provide is called ADSL 2+ or Asymmetric Digital Subscriber Line 2+ (ITU G.992.5). ADSL 2+ provides for theoretical downstream speeds of up to 24Mbps, although this will vary depending on a number of factors.
The Optus DSL Network operates from more than 300 local exchanges providing services such as Optus MeTV, Optus Broadband (fixed) and Optus Home Phone. Your home phone connects directly via telephone wall socket and your internet service plugs into it via a modem. The modem converts the electric signals ready for transmission over the ULL back to our DSLAM in the exchange.
The ULL, or Unconditioned Local Loop, is the twisted pair copper wire between your home and the local exchange that we rent from Telstra to provide you with your service. The DSLAM or Digital Subscriber Line Access Multiplexer is a device that we’ve installed at your local telephone exchange. The DSLAM enables us to access the ULL so we can pump more data through. The DSLAM communicates with your modem, aggregates the traffic and sends it deeper into the Optus network. The next device we meet is called the Aggregator.
As you can probably guess, this device aggregates (or collects) traffic from many DSLAMs. The Aggregator splits up the voice traffic sending it off to the Voice Network; and the data traffic is sent onto the IP Network via an important piece of kit called the BRAS. The BRAS or Broadband Remote Access Server routes traffic between the IP Network and modem via the DSLAM. The BRAS is the first IP device you will see on your trace route (after your own device).
Once you’ve plugged into the Optus IP Network, the rest of the Internet is very much at your fingertips waiting for you to explore.