What UCaaS bandwidth requirements should businesses plan for?

Microsoft's network preparation guide for Teams is a useful model because it gives separate figures for audio, video and screen sharing, and separate figures for each direction. Its recommended rates for meetings are the ones we use below.

In these rates the video allowance is far larger than the audio one. A device in a video meeting is allowed about 43 times the upload of a device on an audio call. So on Teams, the number of people on camera at once moves the total much more than the number of people on the phone.

Microsoft also publishes a minimum and a "best performance" figure for each row. Its minimums are 10 kbps for audio, and 150 kbps up and 200 kbps down for meeting video at low resolution. The guide says actual use varies with video layout, resolution and frame rate, and that Teams puts audio quality ahead of video quality when bandwidth is short. So treat the recommended rates as a planning allowance for good quality. A call doesn't fail the moment a connection drops below them.

These figures belong to Teams. Another service uses its own audio and video technology and publishes its own numbers. Twilio's documentation for its SIP trunking service, for instance, tells customers to allow 100 kbps for each simultaneous call, a figure it ties to one audio format, G.711, plus room for overhead. That's about 1.7 times Microsoft's audio figure, and each is right for the service it describes. Use the rates your own provider gives you. We explain where audio figures like these come from in how much bandwidth a VoIP call uses.

The number to multiply is the count of devices active at the same moment. It isn't the number of licenses you bought, because a license says who is able to call and nothing about who is calling right now.

Microsoft's guide adds a detail that's easy to miss. Its rates are per endpoint, which means per device. Typically that's one per person, but someone who joins a meeting on a computer and a mobile device at once counts as two.

Your own history is the place to start for the count. If your current phone system or carrier reports peak simultaneous calls, use that figure, and look at your calendar for the large recurring meetings that overlap. Where you have no history, pick an estimate, write it down, and revisit it after the first month of real use.

Suppose a 40-person office uses Teams. Suppose that at its busiest moment, 8 devices are in video meetings and 10 other devices are on audio-only calls, all at once. Using Microsoft's recommended rates:

• Video upload: 8 × 2,500 kbps = 20,000 kbps
• Video download: 8 × 4,000 kbps = 32,000 kbps
• Audio in each direction: 10 × 58 kbps = 580 kbps

That comes to 20,580 kbps up and 32,580 kbps down, or about 20.6 Mbps and 32.6 Mbps. The ten audio calls are less than 3 percent of the upload total. Two additional devices joining on video would add 5 Mbps of upload and 8 Mbps of download.

The example makes modeling choices of ours. It applies the video allowance once to each of the eight video devices and adds no separate audio allowance for them. It also leaves screen sharing out. An office whose meetings regularly share screens should model that separately with the screen sharing row, for the number of devices it expects to be in those meetings at once.

Calls share the connection with everything else the office does. Suppose the firewall's traffic report shows the office already using 15 Mbps up and 60 Mbps down at that time for cloud backups, file sync and ordinary browsing. The totals become 35.6 Mbps up and 92.6 Mbps down.

Then comes the margin. Suppose this office adds 25 percent to cover growth and an unusually busy day. That percentage is our assumption for the example, and a business expecting to hire or to hold more video meetings has reason to choose more. With it, the planning figures are about 44.5 Mbps up and 115.7 Mbps down.

Check each figure against the matching side of the internet plan. Suppose the office has a plan rated at 300 Mbps down and 30 Mbps up. Download has room to spare, and upload falls about 14.5 Mbps short. A plan can pass in one direction and fail in the other, which is why the two totals stay separate all the way through.

Teams administrators can run the same exercise in Microsoft's Network Planner. The guide describes it as a tool that calculates network requirements for each physical location from your network details and Teams usage.

The same arithmetic applies on any UCaaS service, with that provider's rates in place of Microsoft's. The mix of uses is the part that differs from office to office.

Atlantech Online's UCaaS page lists several ways a person can use its hosted service: a softphone tied to the business dial plan, mobile apps for Android and iOS, high-definition video conferencing, and desktop and file sharing. Each one loads a connection differently. A voice call on the softphone is audio. A video conference with a shared desktop adds screen sharing traffic to the video. A call on the mobile app uses the office connection when the phone is on office Wi-Fi, and the cellular network when the phone is on mobile data.

So two offices with the same plan and the same number of users can need different circuits. One that mostly answers the phone is sized by its audio calls. One that runs client meetings on camera is sized by its video. The Teams rates above don't transfer to another provider's service, so for a hosted plan like Atlantech's the sizing uses the rates that provider supplies.

Remote staff need the same care about which connection carries what. A person working from home sends their calls over their home connection, so those calls stay out of the office total. That changes if their traffic is routed through the office over a VPN, because then it passes through the office circuit too. Microsoft's guide recommends letting Teams traffic bypass the VPN. Its reasons are that VPNs typically aren't designed for real-time media and that the detour adds delay. We go further into the home side in how to set up UCaaS for a remote team.

A connection can pass this arithmetic and still deliver poor calls. The arithmetic measures volume, and calls also depend on timing. Microsoft's guide lists calls that cut out and voices that sound robotic as possible signs of jitter or packet loss, and it treats insufficient bandwidth as a separate cause. We cover those symptoms in common UCaaS call quality problems.

On a network you manage, Quality of Service, or QoS, is the tool Microsoft recommends. It prioritizes voice and video packets over other traffic. The guide says to implement it on all segments of a managed network, including a network with adequate bandwidth, so that unexpected network events don't hurt call quality. Its reach is the path you control. It makes no promise about a home network or the public internet beyond your equipment.

Wi-Fi is the last item to plan for. Microsoft notes that Wi-Fi networks aren't necessarily designed or configured for real-time media, and that access point placement and the choice of frequency band both affect call quality. An office can buy a circuit that clears every figure above and still have poor calls in the conference room at the far end of the floor, because the weak link there is the wireless hop inside the building.