In short: BT Cloud Voice needs a business internet connection with enough spare upload bandwidth for the calls you make at the same time, a sound office network with at least CAT5e cabling, and a pass on BT's network assessment test before ordering. Full fibre is not always needed, but busy sites benefit from business fibre or a leased line.
What BT Cloud Voice needs from your connection
BT Cloud Voice is a hosted phone system: the phone system itself lives in BT's network, and your desk phones and apps reach it over the internet. BT's minimum specification asks for three things:
- A compatible business internet connection with enough bandwidth for your voice and data together. BT gives its own business broadband, business fibre and BTnet leased line as examples, but other business connections can be used if they are set up correctly.
- A suitable local area network (LAN) inside your building, with a minimum of CAT5e structured cabling.
- A BT Cloud Voice device or app for each user, plus access to the BT Cloud Voice Business Portal for anyone who manages settings.
BT's best practice guide says the service is designed to run over broadband, fibre broadband and leased lines, and through the BT Cloud Voice app on a mobile. It is not intended for other kinds of access, so it is worth checking before you plan around, for example, a shared building network you do not control.
Fibre is not always required. A standard business broadband line can work well for a small team, provided it has the bandwidth and stability the network assessment asks for.
How much bandwidth do you need?
Voice calls do not use much bandwidth, but they are sensitive to delay and to other traffic competing for the line. The number that matters most is your upload speed, because that is usually the smaller figure on a broadband line.
BT's rule of thumb is to allow at least 120 kbps of upload bandwidth for each call you expect to be on at the same time, on top of what your data already uses. BT also recommends using no more than 80% of the connection for voice and data together, so there is always headroom. The figures below simply multiply BT's rule of thumb; your network assessment result is what counts.
| Calls at the same time | Extra upload to allow (BT rule of thumb) |
|---|---|
| 2 | At least 240 kbps |
| 5 | At least 600 kbps |
| 10 | At least 1.2 Mbps |
| 20 | At least 2.4 Mbps |
Size for your busiest hour, not an average day. Think about the morning rush on a sales line, or a school absence line at 8am. Video meetings, cloud backups and large uploads all compete for the same upload bandwidth, so a line that looks fast on a download speed test can still struggle. If you add users or make other changes that use more bandwidth later, BT asks to be told so the connection can be checked again.
The network assessment test
Before BT Cloud Voice can be ordered, your site needs to pass BT's network assessment test. It checks your LAN, your broadband connection and the path to BT's voice network by simulating calls from a computer on your network to the BT Cloud Voice service, then reports whether your connection can carry the number of calls you need.
- Use a computer plugged into the router with an Ethernet cable. The test cannot be run over Wi-Fi.
- Open the test link in Firefox, Chrome, Safari or Edge and enter how many calls you expect to make or take at the same time.
- Download and run the small test app the page asks for.
- Leave the page open. The test usually takes about three minutes and you can carry on working while it runs.
- Read the results: jitter, packet loss, round trip time (RTT), a mean opinion score (MOS) for overall voice quality, and the bandwidth usable for voice.
The bandwidth figure will always be lower than a general speed test shows, because it measures what is really usable for calls. The test also needs a few ports open on your firewall and SIP ALG switched off on the router; if the ports are closed it fails within seconds. Our LAN and firewall guide explains both. If you do not pass, BT's suggested fixes are stopping big downloads during the test, checking cables and ports, restarting routers, updating software, using quality of service to prioritise voice and replacing old or faulty hardware. If it still fails on quality or bandwidth, the connection itself needs attention from your access provider.
Broadband or leased line?
| Connection | Suits | Things to know |
|---|---|---|
| Business broadband (copper or part fibre) | Small offices with a handful of simultaneous calls | Upload speeds are modest; check the assessment result carefully |
| Business full fibre broadband | Most small and medium offices | Much higher upload speeds; still a shared, contended service |
| Leased line (such as BTnet) | Larger sites, call centres, busy multi-site offices | Dedicated, uncontended bandwidth with a service level agreement |
BT's own guidance points to its business fibre broadband or a BTnet leased line for the best results. On a BT connection, BT's business hubs prioritise voice traffic and have SIP ALG switched off, and you have one supplier for both voice and access. On a non-BT connection, the access service, router and any firewall must be set up for SIP and voice traffic before BT Cloud Voice is connected, and you deal with your access provider if the fault turns out to be on the connection.
We can supply BT connectivity through our sister site: see BT Business Broadband and BTnet leased lines.
Resilience, backup and 999 calls
If the internet connection or the power fails, desk phones on that site cannot make or take calls. Plan for it:
- Set a Not Reachable divert so that if a phone cannot be reached, calls go to a mobile or another site. See how to divert calls.
- Use the BT Cloud Voice app on mobiles, so key people can still take calls on the business number over mobile data.
- Consider a backup connection for busy sites, such as a second line or a router with mobile-data backup.
- Put routers and PoE switches on a UPS if phones must keep working through short power cuts.
BT is clear that 999 and 112 calls depend on your LAN, internet connection and power. You might not be able to make emergency calls during a power or network failure, or when using the service through an app on a mobile. Keep another way of calling the emergency services, such as a mobile phone. BT also holds each site's address for emergency services, so tell us if a site moves.
Number porting tip: BT says it cannot port a number from the phone line that carries your broadband, because porting it would stop that line and the broadband working. The options are to move the broadband to a different line before installation, or to divert the old number to BT Cloud Voice. We check this in advance and plan the order of work. Read more in numbers and porting.
How Forever Communications Limited checks your connection
As a BT Business Partner, Forever Communications Limited checks the network side before anything is ordered:
- We work out how many calls each site makes at its busiest time
- We arrange the network assessment test and go through the results with you
- We review your router, firewall, switches and cabling against BT's guidance
- We recommend whether your current connection is enough, or whether an upgrade or backup makes sense
- We plan the go-live so the number port happens only once the phones are working
See switching to BT Cloud Voice for the full process, or Contact us to book a connection check.
Network and call quality guides
Why buy BT Cloud Voice from Forever Communications Limited
Forever Communications Limited is part of Forever Group and a BT Business Partner. We supply, set up and support BT Cloud Voice for UK businesses, schools, charities and public sector organisations, from a handful of users to multi-site teams.
- A named partner who plans your numbers, call flows, user feature packs and handsets with you
- Number porting managed for you, timed to avoid downtime
- Connectivity checked first, so call quality is right from day one, with BT business broadband and BTnet available if you need it
- Help with the digital switchover, including alarms, lifts, card terminals and other analogue lines
- Training and ongoing support for the apps, Microsoft Teams integration, moves, adds, changes and faults
BT Cloud Voice is a business service. We do not sell consumer or home phone products.
Want a BT Cloud Voice quote for your business?
Tell Forever Communications what you need and we will come back to you by email with options, not a hard sell.
Contact usFrequently asked questions
Do I need fibre broadband for BT Cloud Voice?
Not always. BT Cloud Voice works over business broadband, fibre broadband and leased lines, as long as the connection has enough bandwidth and passes BT's network assessment test. Full fibre or a leased line gives more headroom for busy sites.
How much bandwidth does BT Cloud Voice use per call?
BT's rule of thumb is at least 120 kbps of upload bandwidth for each simultaneous call, on top of your normal data use, while using no more than 80% of the connection for voice and data together.
Can I use BT Cloud Voice on a non-BT internet connection?
Yes. Your access service, router and firewall must be set up for SIP and voice traffic, with SIP ALG turned off, before BT Cloud Voice is connected. If there is a fault on the connection itself, you deal with your access provider.
What is the BT Cloud Voice network assessment test?
It is a test of about three minutes, run from a computer wired to your router, that simulates calls to BT Cloud Voice and reports jitter, packet loss, round trip time, a voice quality score and usable bandwidth. Your site must pass it before you order.
Will BT Cloud Voice work in a power cut?
Desk phones need power and a working connection, so they stop in a power cut unless your router and switches are on backup power. Calls can be diverted to mobiles, and the mobile app can be used, but 999 calls may not work over the app during a failure.