In short
A backup leased line is a second line kept in reserve for when the main one fails. BT's back-up option for BTnet provides a secondary access line at a lower speed than the primary. It suits sites that need essential services to keep running during a fault but can accept reduced speed until the main line is restored.
Get a quote for BTnet with a back-up line
Tell us roughly how many users or sites you have and we will reply by email with options and a quote.
What BT's back-up option is
In BT's service schedule for BTnet, back-up is one of three resilience options. It provides a secondary access line at a lower speed than your primary line, as a back-up route into BT's network. Like the other options, BT's terms ask you to connect the equipment for the back-up line to the same segment of your LAN as the equipment for the primary line, so your devices can reach either.
The difference from failover and load balancing is the deliberate trade: less speed during a fault in exchange for a lower-cost second line. Which options you can have depends on your configuration, routing, speed and site, and is confirmed at quote.
BT's terms describe BTnet bandwidth as uncontended and symmetrical. The back-up line is the second access line in that service, running at a lower speed than the primary; its speed and set-up are confirmed in your quote.
When a back-up line is enough
A back-up line makes sense when an outage would hurt, but running at reduced speed for a while would not. That describes many sites:
- Offices where calls and email matter most, and large uploads or downloads can wait
- Shops, branches and surgeries that need booking, stock or clinical systems and calls to keep going
- Hospitality sites where staff systems must stay up, even if guest Wi-Fi is limited for a while
- Sites with a big primary line sized for peaks, where essentials need only a fraction of it
If your site needs to carry on close to normal, look at failover with a similar-sized second line. If you would rather put both lines to work every day, see load balancing. Our resilient BTnet hub compares all three.
Plan what must keep working
The key step with a back-up line is deciding, before a fault, what it must carry. Work through it in this order:
- List the essentials. Calls, the systems you trade on, remote access for key staff, building systems that report to the cloud.
- Estimate what they need at the same time. Count simultaneous calls and video meetings, and the cloud apps people use at once. Our bandwidth guide shows how to build that list.
- Upload as well as download. Calls, video and cloud sync need upload capacity. BT's terms describe BTnet bandwidth as symmetrical, so size the back-up line for the heavier of the two directions.
- Decide what can pause. Backups, software updates, large file transfers and guest Wi-Fi are the usual candidates.
- Set priorities on your network. Quality of service on your router or firewall keeps calls and key apps ahead of everything else while you are running on the back-up line.
- Choose the back-up speed. Size it for the essentials, with some headroom, and confirm the speed in your quote.
A note on card payments
If card payments are on your list, plan them carefully. Card payment security is governed by the payment card industry's PCI DSS standard and by your payment provider's requirements, and needs its own controls whichever line is in use. See leased lines for retail and ask us before you plan payments around BTnet.
An illustrative example
Every site is different, so this shows the thinking rather than figures. Take a branch office with a reception desk, a small team on a cloud phone system, a booking system in the cloud, Microsoft 365, CCTV and guest Wi-Fi in the waiting area.
| Traffic | On the back-up line? | Why |
|---|---|---|
| Phone calls | Yes, with priority | Customers need to reach the branch |
| Booking system | Yes | The branch cannot trade without it |
| Email and Microsoft 365 | Yes | Light, steady use that staff rely on |
| CCTV cloud uploads | Reduced or buffered | Keep what your obligations require; let the rest catch up later |
| Large file transfers and updates | No | Can wait until the main line is back |
| Guest Wi-Fi | No, or tightly limited | Frees capacity for the essentials |
The back-up line in this example is sized for the rows marked yes, with headroom, rather than for everything the main line carries on a busy day. That is what keeps the cost of the second line in proportion while protecting the work that matters. If you want help with the sizing, we can review your list with you before you order.
What a back-up line does not do
A back-up line protects you against a fault on the main access line. It does not protect against a power cut at your site, a failure of your own router or firewall, a fault on your office network or Wi-Fi, or an outage at a cloud service you depend on. Plan for those separately, and keep a record of both lines' references so a fault on either can be reported to BT quickly.
Not sure which option fits? Ask us
Tell us what you need and we will recommend the right option for your organisation, with a quote.
What to check before you order
A back-up line only helps if it is still working when the main line is not. The same questions apply as for any resilient design:
- Separate routes and entry points. Ask what route separation is possible; it is confirmed at the site survey.
- Power. Where BT's equipment is on site, BT's terms make a secure, continuous power supply and back-up power your responsibility. Lines and equipment sharing one power supply go down together.
- Your edge equipment. On BTnet wires only, one firewall in front of both lines is still one device that can fail.
- Static IPs and VPNs. Plan how remote access, allow-listed services and site-to-site tunnels behave on the back-up line. See static IP addresses on BTnet.
- Testing. Agree how to test the back-up so you know the essentials work on it before a real fault.
Cost, contract and the SLA
A lower-speed back-up line can cost less than a like-for-like second line, because it runs at a lower port speed. It is still a second access line, though, so under BT's terms service introduction charges apply per bearer where resilience uses dual access bearers, including the back-up line, as do cancellation charges if the order is cancelled before the service goes live. We do not publish prices; the factors are on BT leased line cost, and your quote shows the resilient design in one place.
If a qualifying incident hits a resilient service, BT's terms say BT applies the availability credit at the impacted site. The claim steps are on the BTnet SLA page.
Tell us what has to keep working at your site and we will help you size a back-up line around it. Contact us for a quote.
Why buy BTnet from Forever Communications
Forever Communications is part of Forever Group and an Authorised Supplier for BT. We supply BTnet, BT's dedicated leased line internet service, to businesses, schools, charities and public sector organisations, and we help with each step from first enquiry to go-live.
- The right BTnet option for you: we help you choose a speed, bearer, router and resilience option that fits how your sites actually work, from BTnet plans to BTnet speeds
- A clear quote: BTnet is priced per site, so we check availability at your address and set out what is included; see leased line cost
- Installation managed with you: we explain the survey, any wayleave or construction steps and the installation process, and keep you updated on progress
- Connected services in one conversation: phones with BT Cloud Voice, Wi-Fi, firewalls and backup lines, so the whole set-up is planned together
- Help after go-live: we can help with faults, changes and upgrades, with the support arrangements confirmed in your quote
BTnet is a business service. Service levels, lead times and features are BT's and are confirmed at order.
Frequently asked questions
What is a backup leased line?
A second line kept for when the main line fails. BT's back-up option for BTnet is a secondary access line at a lower speed than the primary, so essential services can keep running during a fault.
Is a backup line cheaper than failover?
It can be, because the back-up line runs at a lower speed than the primary. Charges still apply per bearer for the second line under BT's terms. Ask us for a quote that shows both options.
How fast should my backup leased line be?
Fast enough for what must keep working at the same time: calls, key cloud apps and remote access, with some headroom. List the essentials first, then size the line to them.
Is a backup line the same speed in both directions?
BT's terms describe BTnet bandwidth as symmetrical, the same upload and download speed. The back-up line runs at a lower speed than the primary, and its exact speed and set-up are confirmed in your quote.
Does a backup line keep my phones working?
It can carry calls if it has enough capacity and your network gives calls priority. Plan for the number of calls you need at the same time when you choose the back-up speed.
Still have a question about BTnet with a back-up line?
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