Calculate required WAN bandwidth for a branch office based on users and application mix.
Sizing a branch WAN link for every user's peak simultaneous demand would be wasteful, since not everyone is actively using the network at once — concurrency models the realistic peak busy-period usage (typically 60-80% for office environments) rather than the theoretical maximum. Fixed overhead accounts for always-on traffic like VoIP signaling, network monitoring, and background application traffic that doesn't scale directly with active user count. A headroom margin on top of the calculated requirement absorbs traffic bursts without saturating the link.
Required bandwidth
bw = users × concurrency% × per_user_Mbps + overhead
70-80% is a common planning figure for general office use, but bursty applications (all-hands video calls, backup windows) can push effective concurrency toward 100% for short periods — if those peak windows matter for your SLA, size for them explicitly rather than relying on an average concurrency assumption.
Sizing a link exactly to calculated peak demand leaves no margin for traffic bursts, new application rollouts, or growth — a 20% headroom buffer is a common rule of thumb to avoid an under-provisioned link degrading user experience the moment usage patterns shift slightly.
Significantly — a voice call may need under 100 Kbps, but HD video conferencing commonly needs 1.5-3+ Mbps per active participant (more for group calls with multiple video tiles), so a branch with heavy video conferencing use should raise the per-user Mbps input well above a voice/web-browsing baseline.