How Does EFM Work? Here's How!
As an EFM provider, we're sometimes asked how EFM works. It works by bonding together multiple connections, with each connection sending electrical signals over voice-grade electrical wires, using a symmetric variant of DSL.
Data travels to and from the customer's site via the local telephone exchange - a building that could be located several miles away. The longer the cable distance between the customer's site and the local telephone exchange, the more the electrical signal degrades, causing the maximum data transmission speed to fall.
To compensate for distance-related reductions in speed, EFM wholeale network operators bond together several connections. In the UK, EFM providers routinely bond two to eight circuits together, multiplying the available bandwidth massively.
This bonding has an additional benefit. It increases connection resilience, as electical interference that might impact one circuit, might not impact some of the others.
Once the customer's electrical signals reach the telephone exchange, it encounters hardware known as a line card slotted into an MSAN - a multi-service access node, which then plugs into a switch. The signal then travels over the EFM provider's fibre-optic backhaul network to reach their real customer - typically a retail ISP selling services to business customers. That retail ISP will probably add additional services, including internet transit and peering and IP addressing.
More Specifics of How EFM Works In Practice
In the UK, the cable distance between the customer and the local exchange is typically up to 3900 meters.
The largest UK wholesale provider of EFM circuits uses either two or four circuits to deliver speeds of up to 20 Mbit/s.
Another major EFM provider bonds up to eight circuits to deliver speeds of up to 35 Mbit/s
When we talk of Ethernet First Mile we're really referring to services based on IEEE 802.3ah and ITU-T G.991.2 (G.SHDSL.bis).
When we talk of circuits, you should picture copper telephone lines that aren't being used for telephony. Phone lines aren't really a single line. They're two wires, as an electrical loop with current flowing through it needs to be created. As a result, EFM providers sometimes refer to using 'copper pairs.'
Different providers take different approaches to how they implement EFM. Some use line cards in different MSANs, for resilience. Others route all a customer's EFM circuits through a single MSAN.
Typically, EFM wholesale providers guarantees on the minimum connection speed their service will offer a given customer. The minimum speed is often significantly below the physical capacity the line is expected to deliver. For example, at our office in London, one provider estimates they can deliver 11 Mbit/s of connectivity, but they only guarantee 7 Mbit/s of that.
Discuss your EFM Options
If you're in the UK and your organisation is considering getting EFM, give us a call on 020 7847 4510. We'll be able to check EFM availability and give you an idea of the speeds available in your location.
