How to pick a SIP trunk for a 50-seat call center

Fifty seats is the size where a call center stops being a side project and becomes infrastructure. A trunk that worked for ten agents starts to show its limits: busy signals at peak, choppy audio when the dialer ramps up, and invoices nobody can explain. This guide walks through the decisions that matter most.

1. Size your concurrent channels, not your seat count

A channel is one simultaneous call. Inbound teams rarely have every agent talking at once, so a 50-seat inbound floor might peak at 35 to 40 channels. Outbound teams running predictive dialers are the opposite: the dialer places more calls than there are agents to absorb no-answers, so plan for 1.5 to 3 channels per agent.

• Inbound only: roughly 0.7 to 0.8 channels per seat at peak
• Blended: around 1 to 1.2 channels per seat
• Predictive outbound: 1.5 to 3 channels per seat depending on your dial ratio

2. Check calls-per-second, not only channels

Dialers burst. When a campaign starts, the system may try to launch dozens of calls in the same second. Many trunks cap calls-per-second (CPS) much lower than their channel limit. If your CPS is too low you will see failed calls even though plenty of channels are free.

3. Pick codecs with your bandwidth in mind

G.711 sounds great but uses around 87 kbps per call with overhead. G.729 uses roughly a third of that. For 50 agents on a modest office connection, G.729 or Opus can be the difference between clear calls and constant complaints.

4. Compare rates the way finance will

The headline per-minute price is only part of the cost. Billing increments matter: a 60/60 plan charges a full minute for a 10-second call, while 6/6 charges in six-second blocks. For short outbound calls this can change your bill by 30 percent or more.

5. Insist on visibility

You should be able to see live calls, filter call logs and export them without asking support. If a provider cannot show you answer status and duration per call, you cannot manage campaign quality.

A short checklist

1. Peak concurrent channels and CPS limits that fit your dialer
2. Codec support that matches your bandwidth
3. Billing increments that suit your average call length
4. Self-service lines, caller ID and password rotation
5. Live calls view and exportable call logs
6. Prepaid or capped billing to limit fraud exposure