What is an EFM circuit?

Posted by SAS on Apr 18, 2016 02:05:00 PM

What is an EFM circuit?

EFM stands for Ethernet in the First Mile.  EFM refers to a type of circuit that uses multiple copper pairs to provide affordable but reliable, high speed IP connections for business sites. EFM can connect to the internet or to an IP VPN (or Ethernet) wide area network (WAN).

Most people are familiar with ADSL broadband, which offers an IP connection over a single 'phone line.  An EFM circuit  uses between 2 and 8 lines, which helps it deliver several major improvements over ADSL. Actually, its lines are referred to as Copper Pairs; they're the same wires that are used for phone lines, but  in EFM they're not used for calls. 

EFM offers several improvements over ADSL:

  • The use of up to 8 copper pairs allows EFM to offer speeds of up to 35Mbit/s
  • EFM  offers symmetric bandwidth - the same speed in both directions; upstream to the internet or WAN and downstream to the site.  This contrasts with ADSL which is geared up for browsing, with most of the bandwidth allocated to the downstream. 
  • EFM offers uncontended bandwidth.  You may know that ADSL's low cost comes in part from sharing the connection with other users, with contention ratios historically between 20:1 and 50:1.  Since EFM is uncontended, you're always guaranteed all of your bandwidth.
  • EFM offers circuit resilience.  If one of the Copper Pairs fails or degrades then the circuit can continue without it.  This makes EFM significantly more reliable than ADSL.

EFM is a great half-way house between low-cost DSL or Superfast and expensive Fibre Ethernet circuits.

For performance and reliability, fibre is always preferable to copper.  

  • Fibre Ethernet circuits support higher bandwidth and are more reliable than copper circuits, but this comes with a higher cost and longer lead time to install them.
  • Copper circuits are affected by electrical interference that causes intermittent or persistent errors and performance issues.
    The signal processing and re-transmission to overcome these errors also increases latency (the delay in sending and receiving data). This in turn reduces the performance of the circuit and slows down the applications and damages user experience.

Traditionally, businesses had the choice between a standard ADSL service and fibre-based Ethernet services. However, for some business sites, ADSL is not fast or reliable enough for their needs, whereas fibre-based Ethernet services are too expensive for them.

Happily, EFM sits right in-between ADSL and fibre Ethernet.  It is relatively cost effective, but offers good reliability and performance and a speedy installation.

EFM for Internet Access

A very common application for EFM is for  Business grade Internet Access, often called Dedicated Internet Access, or DIA.   For example, you can have dedicated internet access using our SASnet internet services. 

Real-time applications

It's important to ensure when you're looking at installing EFM circuits that will carry real-time applications such as SAP, Citrix and IP Telephony, that the circuit is delivered over a minimum of two pairs and with class of service (CoS). This will give better performance and resilience.

A common practice for some telco providers has been to reduce costs by offering lower speed EFM circuits on a single pair, and not providing CoS as an available option.

When ordering circuits for sites that will use real-time applications, always ensure that:

  • Your provider is using a minimum of  two copper pairs
  • Full details are on the order
  • CoS is an option (even if just for the future)

It will make all the difference!


Copper EFM circuits usually have quicker installation times than fibre circuits. So, if you've left it a bit late to order then a copper EFM circuit may just save your bacon as it only takes 30-45 days, rather than 90-180 days for fibre...!

What speeds can I get?

Just like ADSL, factors like your distance from the exchange will affect the speed you achieve. That said, it ranges from 1-10Mbit/s for an EFM 2 Pair service and 10-20Mbit/s for an EFM 4 Pair service. Some telco's offer more pairs, which gives a faster service further away from the exchange. 

Top tips: Key things to consider with EFM

There are several things you should look out for with EFM. A good managed network provider or network management service will cover all these things...so make sure you check that they do!

  • Ensure the number of pairs the service is delivered on is visible in your monitoring portal
  • During the on-boarding process, check the correct number of pairs is illuminated
  • Ensure that if an EFM circuit is being ordered for a real-time application customer, it's delivered over a minimum of 2 copper pairs. Even for low speed circuits!
  • A photograph that clearly shows the live status of the pairs on the customer premises equipment