A leased line for VoIP and cloud calling

Why calls need more than raw speed

A voice call uses very little bandwidth compared with a video meeting or a file upload. What it cannot tolerate is inconsistency. Three things spoil calls:

• Latency: the time it takes sound to cross the network. Too much and people talk over each other.
• Jitter: variation in that delay. Packets of speech arrive unevenly and the call sounds choppy or robotic.
• Packet loss: pieces of speech that fail to arrive, heard as gaps and clipped words.

On a shared broadband connection all three get worse when the network is busy, either because neighbours are busy on the same shared capacity or because someone in your own office starts a large upload. Upload is the weak point: calls send your voice up the line constantly, and broadband upload is often a fraction of its download. A leased line removes the shared element and gives you the same speed in both directions, which is why it is the usual foundation for a busy cloud phone system.

What BTnet brings to voice

BTnet has several features that help call quality, each described here as BT sets it out:

• Dedicated and uncontended. BT describes BTnet as 100% uncontended, so your bandwidth is not shared with other customers at busy times.
• Symmetrical bandwidth. Upload equals download, so outgoing voice has as much room as incoming. See symmetrical internet speeds.
• Voice prioritised. BT says BTnet is designed with voice in mind, naming its Cloud Voice and SIP services, and that voice traffic is given priority on its low-latency network.
• A latency commitment. BT's SLA sets an average round trip of 20ms or less across its UK core network, measured over each calendar month. See BTnet latency.
• An availability service level. BT sets a 100% availability service level with service credits under its terms. See the BTnet SLA.
• Static IPv4 addresses. Included as standard, which helps when a firewall rule or a supplier needs to recognise your office address. See static IP addresses.

None of this makes up for a line that is too small or a building network that treats calls like any other traffic, so the rest of this page covers sizing, your LAN and resilience.

BT Cloud Voice and SIP over BTnet

BT Cloud Voice is BT's hosted phone system: the system itself runs in BT's network and your desk phones and apps reach it over the internet. BT gives its BTnet leased line as one of the connections BT Cloud Voice can run over, alongside its business broadband and fibre, and names Cloud Voice among the voice services BTnet is built for. Forever Communications is an Authorised Supplier for BT and supplies BT Cloud Voice as well as BTnet, so we can plan the connection, the phones and the go-live date as one project.

If you keep your own phone system and connect it with SIP trunks, BT names its SIP services alongside Cloud Voice as voice traffic BTnet is designed for. Our sister site explains BT Cloud Voice SIP in more detail.

Many organisations are making this move now because of the PSTN switch-off, which replaces traditional phone lines with services that run over an internet connection. If the phones are moving to the internet, it is the right moment to look at the line they will depend on.

Planning bandwidth for calls

For BT Cloud Voice, BT's best practice guidance suggests allowing at least 120 kbps of upload bandwidth for every call that can be in progress at the same time, on top of your normal data use, and keeping voice and data together below 80% of the connection. The table simply multiplies BT's figure; it is arithmetic, not a measurement of your site.

Two things stand out. First, voice on its own rarely needs a large line, even for a busy contact team. Second, calls rarely run on their own: they share the line with video meetings, cloud apps, file sync, backups and cameras, and those decide the size. Count calls at your busiest hour, such as the morning rush on a sales or absence line, then add everything else using our bandwidth sizing guide. Our sister site covers the full BT Cloud Voice internet connection requirements, including BT's network assessment test.

Inside your building: network, settings and power

BT's responsibility for BTnet ends at the service management boundary: the LAN port of the managed router, or BT's network terminating equipment if you choose BTnet wires only. Everything after that point is your network, and it matters as much as the line:

• Prioritise voice on your network. Switches and routers should give voice traffic priority, often on its own network segment, so a large download in the next room does not affect calls.
• Check the cabling. BT's specification for BT Cloud Voice asks for at least CAT5e structured cabling.
• Set up the firewall for voice. On wires only, your own router or firewall handles calls; BT asks for settings such as SIP ALG to be switched off for BT Cloud Voice. See the BT Cloud Voice LAN and firewall guide.
• Power the phones and the network. Desk phones are often powered over Ethernet from a switch, so a power cut stops them unless the switches and router are on backup power.

If calls sound poor, the cause is often inside the building rather than on the line. A quick check of the LAN before go-live saves a lot of frustration later.

Keeping calls going if the line fails

A single line is a single point of failure. If the phone system matters, decide in advance what happens when the connection is down:

• Add a second BTnet line. BT offers failover, load-balancing and lower-speed back-up options for BTnet. See resilient BTnet.
• Divert calls. With BT Cloud Voice you can set calls to divert to mobiles or another site when phones cannot be reached, and key people can use the BT Cloud Voice app.
• Plan for emergency calls. BT points out that 999 and 112 calls over BT Cloud Voice depend on power and the connection, so keep another way of calling the emergency services, such as a mobile phone.

Resilience options, routes and power at your site are questions for the survey, and availability depends on your location and set-up. We can include them in your quote so you can see the difference.

How we help with voice and BTnet

We look at the line and the calls together:

• We can work out how many calls each site makes at its busiest time, and what else shares the line
• We can recommend a port speed and bearer with room to flex, and a plan that suits who manages your firewall
• We can include resilience in the quote so you can decide whether a second line is worth it
• We can supply BT Cloud Voice on the same project, and help time the phone go-live around the line's installation

Leased lines take longer to install than broadband. BT's help pages say installation can take up to 70 working days, depending on the survey, so start the line early if a phone move has a deadline. See BTnet lead times. Contact us to plan your calls and connection together.