How Broadband Works

Broadband Basics

Broadband is a term used to describe various types of high speed internet  which utilises phone lines, mobile networks and fibre-optic cables to transmit large amounts of data. There are different types of broadband:

  • ADSL Broadband is currently the most popular type in Ireland. It uses dedicated phone lines and is connected to the local exchange through copper wires. ADSL uses the phone socket in the wall and can also be used to make phone calls, as the plug in micro-filter separates the two signals.
  • Mobile Broadband uses mobile phone network masts on the 3G and 4G networks to provide high speed internet to devices capable of receiving this data, such as smart phones and USB dongles.
  • Fibre Broadband uses the same principals as ADSL, but instead uses fibre optic cables in place of copper. This gives higher speeds and more capacity to carry data (bandwidth). In many cases, fibre broadband is more reliable, as the new cables are free from degradation and are not affected by electromagnetic interference to the same extent.
  • Wireless Broadband is not a separate category; it is simply the conversion of an existing wired internet connection into a wireless signal. A computer or device can connect to the wireless signal, but the router it connects to will still have a physical cable connection.


The speed of a broadband package will determine how much you can do simultaneously online. High speed broadband is useful for those who may have multiple devices or use music or video streaming services.

Factors that affect broadband speed include:

  • Location – Urban areas typically have faster broadband connection although for ADSL and some types of fibre broadband, the distance from the telephone exchange also contributes to the speed you may get. You can check our fibre coverage map here or alternatively check to see if eir Fibre is available at your home using your home phone number here.
  • Connection Type – Fibre Broadband is currently the fastest on the market, followed by ADSL connections which are typically faster than mobile broadband connections.
  • Congestion - When the network you are using has congestion, your internet speeds are slowed down by many connections trying to use the network at the same time. Network congestion should only be temporary as it depends on the current usage of the entire network. If you find your internet is slow all the time, you may have speed issues. Data congestion may occur between your devices and your modem. We recommend that only 5 or less devices should be actively using the internet at one time, if you have more than this, you should be fine if some of those devices aren’t actively using the internet, or if they don’t need much data flow, such as normal browsing of the internet.

Contention Ratio is the number of users sharing the same data capacity. The lower the contention ratio the higher the quality of service. A 50:1 contention ratio means that up to 50 broadband customers are sharing the same bandwidth at any one time.


Cable broadband is nearly always the most reliable type of broadband. The phone line within a house or premises is connected to a nearby Network Terminal Unit (NTU) which in turn is connected to a local telephone exchange. Damage to this cabling due to development works or other events can cause broadband problems. Eir Fibre benefits from new fibre cabling between your local cabinet and the exchange, which helps to improve reliability. Factors that may affect the reliability of an ADSL line include:

  • Damage to cables
  • Degraded cables
  • Unpaid bill
  • Long distance between premises and telephone exchange

3G and 4G mobile broadband connections are only as reliable as a normal mobile phone service and can be suffer a drop in signal quality during peak times.