The Technology

This page will outline the types of technology deployed in my area as well as work through some of the technical terminology that seems to baffle those of us less technically minded. I will start with the basics and work my may up to how these concepts are at work in Gungahlin.


In its purest sense “broadband” refers to a wide set of frequencies used to deliver information, or a broad bandwidth. In the context of Internet access it has become a label for a number of technologies that deliver high volume data connections. Asymmetric Digital Subscriber Line (ADSL), Cable and Fibre Optic are commonly referred to as broadband services. Conversely there are services referred to as narrow band, the most notable being dial up connections via a traditional telephone modem.

Additional information on the term broadband and its use can be found here

Broadband availability in Gungahlin

To my knowledge all suburbs in the greater Gungahlin area only have access to one broadband technology – ADSL. The only exception to this seems to be the suburb of Forde and some stage releases in the Suburb of Franklin who can get Fibre to the Premises (FTTP).

Forde and Franklin are some of the newest land releases in north Canberra and FTTP access is provided by Transact an ACT based provider. Information on FTTP can be found on the Transact Fibre to the Premises Webpage

What is ADSL?

ADSL is an acronym for Asymmetric Digital Subscriber Line. It is a method of delivering high speed Internet connectivity to a premises using copper phone lines. The ADSL connection can share the same pair of copper wires as your land line phone or can be placed on a separate phone line. The technology works on the principal that you can have two separate signals sharing the same set of wires as long as the signals don’t interfere with one another.

When an ADSL service shares the same line as an acoustic telephone line some noise can be heard. This is removed by a “filter” device which blocks the ADSL frequency from reaching the phone. As the transmition of a voice is being sent on a separate set of frequencies than the ADSL signal no distortion or alteration can be detected during a call.

ADSL works over copper wire lengths of up to approximately 5km. Some have experienced issues well under this distance while others have managed to get services at distances futher that 5km. The limitation is based on the strength of the ADSL signal and other influencers like interference. The futher the distance the signal travels the weaker the signal becomes until a connection can not be supported. The condition of the copper wires, age and environmental issues all affect the performance.

ADSL2 and ADSL2+ are essentially the same technology but an improved implementation. ADSL 2 increases the maximum possible download bandwidth to 24megabit per second. ADSL 2+ increases the range of ADSL2 to improve the reach of the service.

ADSL requires a complete copper circuit between your modem/router and the telco termination device called a Digital Subscriber Line Access Multiplexer or DSLAM for short. A DSLAM usually resides inside a Telstra exchange building and acts as the bridge between the copper phone line and the network backbone.

What is a RIM?

Up until late 2005 ADSL in Gungahlin was limited to only a lucky few who had direct copper connectivity to Crace exchange. A significant percentage of residences were connected to Crace exchange via Remote Integrated Multiplexers (RIM). A RIM works as a consolidation point for around 200 phone lines which are within the same area as the houses it services. From this point all the lines are transmitted onto fibre optic cable and sent to the exchange.

RIMs provided telecommunications companies with a cost effective solution to laying cables in new land developments and estates. One of the largest expenses for a telecommunications company is the cost of purchasing and laying hundreds of copper cables along numerous kilometers of trenches. By placing RIMs in strategic locations within a development the investment in copper is minimised and only a small number of fibre optic cables are required to be layed back to an exchange.

The practice of deploying RIMs was widely used in the 1980’s and 1990’s and still continues today.


In late 2005 Telstra started a roll out of a series of upgrades to the RIM infrastructure within the greater Gungahlin area. This upgrade enabled residents who were connected to a RIM to access ADSL broadband services. The upgrade took nearly three years to complete with the majority of RIMs in north Canberra upgraded in between August 2006 through to March 2008.

The upgrades replaced some of the RIM infrastructure with a new device called a Customer Multiplexer (CMUX). There are various versions and sizes of CMUX’s available, the version retrofitted into the existing RIM cabinets is known as a mini-CMUX.

A CMUX provides all the services of a RIM, with the addition of termination of ADSL connectivity. A CMUX can operate as a mini DLSAM, terminating ADSL on the copper connection within a residential area. It then uses the fibre optic path to the exchange like a backbone network link.

A great resource which explains these technologies further can be found here on the Whirlpool forums

As of mid 2008 nearly all the greater Gungahlin area had access in one form or another to ADSL.

Then what happened?

Telstra had completed its upgrade of all the RIM infrastructure to the mini-CMUX and people applied for ADSL in droves. As thousands of people had waited for such a long time for broadband in northern Canberra many people took advantage of the new technology.

It is my opinion, and my opinion only that Telstra failed to consider what these RIM upgrades would mean to the rest of the network. This failure in forethought and planning is the reason why the curent performance is unacceptable.

Let me explain why.

Crace exchange has one of the highest numbers of RIM/CMUX devices connected to it in the country. There are currently 75  RIM cabinets across the north of Canberra that all connect back to a single exchange. There are also numerous mobile phone towers and other services like Integrated Services Digital Network (ISDN) that also terminate at Crace exchange.

The Gungahlin area is one of the highest population growth areas in Canberra with approximately 38,000 people (reference). According to the Australia Bureau of Statistics 3 of the top 4 suburbs for population growth within the ACT for 2007-2008 are within the Gungahlin area;

  • 1st Harrison 73.2% growth
  • 3rd Gungahlin 13.6% growth
  • 4th Amaroo  4.2% growth                        (reference)

In performing the upgrade Telstra enabled 38,000 people who were on narrow band dial up internet to use broadband services in a short period of time. The volume of data that is now being moved through Crace exchange has increased in volume by possibly 35 times more than before.

The basic math.

  • dial up typical maximum speed 56kb/s or 56,000 bits per second
  • ADSL average line speed 2mb/s or 2,000,000 bits per second (approximation)

2,000,000 divided by 56,000 = 35.714

Sure there are a few assumptions being made here but it illustrates my point. The impact of these upgrades should have been obvious to Telstra and should have been catered for. This is the reason for the congestion – devices or links within Crace exchange are not capable of delivering the bandwidth enabled for the residents of Gungahlin.

I will put this into a different context people may be more familiar with.

It is analogous to the Roads and Traffic Authority widening the Sydney Harbour Tunnel  from 2 lanes to 70 in each direction but only leaving the original number of toll boths open. Sure all the traffic will move at incredible speeds through the tunnel, but it comes to a complete standstill while trying to pass through the bottleneck that is the toll booths.

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