# How Many SIP Channels Do I Need? A Sizing Guide (2026)

> Work out how many SIP trunk channels you need from busy-hour calls and call length, with an Erlang B table, rules of thumb for offices, AI agents and IVRs, and bandwidth per call.

Source: https://edesy.in/blog/how-many-sip-channels-do-i-need-2026

**You need as many SIP channels as the most calls you will have at the same moment, plus a margin. Work it
out from busy-hour traffic: calls per hour times average minutes, divided by 60, gives erlangs. An Erlang B
table then gives channels for a blocking target. 200 calls an hour at 3 minutes needs 18 channels at 1%.**

> **Set your trunk's concurrent-call limit:** [Create a SIP trunk on Edesy](https://voice-app.edesy.in/?utm_source=edesy.in&utm_medium=blog&utm_campaign=how-many-sip-channels-do-i-need-2026) — per-minute billing, unanswered calls free.

## What a channel is (and isn't)

A SIP channel is one simultaneous call. Inbound and outbound share the same pool. Channels are not tied to
phone numbers or to people: 3 numbers and 40 staff can share a 12-channel trunk, and one number can carry 30
calls at once if the trunk allows it.

On a PRI line, channels come in fixed blocks of 30. On a SIP trunk the limit is a setting. On Edesy it is
the **max concurrent calls** field on each termination trunk. That makes sizing a planning question rather
than a hardware order. See [SIP trunk vs PRI line](https://edesy.in/blog/sip-trunk-vs-pri-line-india-2026) for the
background.

## Step-by-step: size your trunk

1. **Find your busiest hour.** Export call records from your PBX, dialer or contact center and count calls
   (inbound plus outbound) in the busiest hour of a normal busy week. Ignore one-off spikes, but note them.
2. **Find the average call length** in minutes for that hour, counting connected time only.
3. **Convert to erlangs:** busy-hour calls x average minutes / 60.
4. **Pick a blocking target.** 1% means one call in a hundred at peak finds every channel busy. Use 0.5%
   for sales or support lines where a lost call is expensive.
5. **Look up channels** in the table below or the [Erlang B calculator](https://edesy.in/tools/erlang-b-calculator).
6. **Add headroom** for growth and for calls you didn't see in the data (test calls, transfers that use two
   legs).

## Erlang B table: channels needed

We computed these with the standard Erlang B formula, the same one the calculator uses.

| Busy-hour calls | Avg length | Traffic (erlangs) | Channels at 1% | Channels at 0.5% |
|---|---|---|---|---|
| 20 | 3 min | 1 | 5 | 5 |
| 60 | 3 min | 3 | 8 | 9 |
| 100 | 4 min | 6.7 | 14 | 15 |
| 200 | 3 min | 10 | 18 | 19 |
| 300 | 4 min | 20 | 30 | 32 |
| 600 | 3 min | 30 | 42 | 44 |

Two things stand out. Small traffic needs proportionally more spare channels (1 erlang still needs 5
channels for 1% blocking). And a 30-channel PRI is exactly full at 20 erlangs: at 30 erlangs it would block
about 13% of busy-hour calls.

## Rules of thumb by use case

Erlang B assumes a blocked caller gives up. That is right for trunks, IVRs and bots, which answer calls
themselves. If callers wait in a queue for human agents, size agents with Erlang C first; see
[Erlang B vs Erlang C](https://edesy.in/blog/erlang-b-vs-erlang-c-lines-vs-agents-2026).

| Use case | How to size | Watch out for |
|---|---|---|
| Office PBX | Erlang B from busy-hour records; a rough start is 1 channel per 3 to 5 staff | Month-end or results-day peaks |
| Contact center | Agents with Erlang C, then channels = agents on calls + callers waiting in queue | Queue length at peak, not average |
| IVR or AI voice agent (inbound) | Erlang B on total call volume; every caller holds a channel | Call length grows when bots ask more questions |
| Outbound broadcast or AI campaign | Campaign max concurrent calls | Unanswered rings still hold a channel while ringing |
| Agent dialer (progressive/power) | Free agents x pacing (1.0, 1.5 or 2.0) + connected calls | Raising pacing raises channels in use |
| Transfers to mobiles | Count 2 channels per forwarded call | Both legs run through the trunk |

## Bandwidth per channel

Channels also need bandwidth. With G.711 (the codec Edesy trunks carry, A-law or u-law) plan for roughly
80 to 90 kbps each way per active call, including IP, UDP and RTP overhead.

| Simultaneous calls | Upload and download needed (approx.) |
|---|---|
| 5 | 0.5 Mbps each way |
| 10 | 1 Mbps each way |
| 30 | 2.7 Mbps each way |
| 50 | 4.5 Mbps each way |

Leave at least 30% spare, and keep large uploads (backups, video calls) from saturating the link during
business hours. Poor bandwidth shows up as choppy audio, not as blocked calls.

## What happens when you run out

When every channel is busy, the next call is rejected. Inbound callers usually hear a busy tone or a
network message; outbound attempts fail with a SIP error that your PBX or dialer logs. On Edesy, failed
calls carry a detailed outcome and the SIP response code in the call record and status callback, so you can
tell capacity failures apart from wrong numbers or unreachable phones.

## Setting it on Edesy

1. Create a termination trunk in [voice-app.edesy.in](https://voice-app.edesy.in/?utm_source=edesy.in&utm_medium=blog&utm_campaign=how-many-sip-channels-do-i-need-2026).
2. Note the **max concurrent calls** value on the trunk page and set the same number as **Maximum
   Channels** in your PBX, so the PBX stops before the trunk rejects.
3. For campaigns, set the campaign's max concurrent calls below the trunk limit, leaving room for inbound.
4. Ask support to raise the trunk limit when your sizing says you need more.

Billing does not change with the limit: calls are Rs 0.50/min with a 60-second pulse, unanswered calls free,
plus number rental (mobile Rs 499/mo, landline Rs 449/mo, toll-free Rs 999/mo), all excluding 18% GST.

More on the [SIP trunking page](https://edesy.in/sip-trunking) and in the [SIP trunking docs](https://edesy.in/docs/sip-trunking). Running an
AI agent? See [SIP trunks for AI voice agents](https://edesy.in/sip-trunk-for-ai-voice-agents).

## Common mistakes

- Sizing from daily totals instead of the busiest hour.
- Sizing by headcount for a contact center or campaign.
- Forgetting that a forwarded or transferred call uses two channels.
- Setting the PBX's channel limit higher than the trunk's, so calls fail at the trunk instead of queuing.
- Planning channels but not bandwidth.

[Create your trunk](https://voice-app.edesy.in/?utm_source=edesy.in&utm_medium=blog&utm_campaign=how-many-sip-channels-do-i-need-2026)
and start with the number the table gives you.

## Frequently Asked Questions

### What is a SIP channel?

One SIP channel carries one call at a time, in either direction. If your trunk allows 10 concurrent calls, the eleventh simultaneous call is rejected until one of the ten ends.

### How do I calculate the number of SIP channels?

Multiply busy-hour calls by average call length in minutes and divide by 60 to get traffic in erlangs. Then use an Erlang B table or calculator with a blocking target, such as 1%, to get the channel count. 200 calls an hour at 3 minutes each is 10 erlangs, which needs 18 channels at 1% blocking.

### Is one SIP channel per employee enough?

It is usually more than enough for an office, because people are not all on the phone at once. It is not enough for a contact center or an AI calling campaign, where nearly every seat or line is busy most of the time. Size those from traffic, not headcount.

### How much bandwidth does each SIP channel need?

With the G.711 codec, plan for roughly 80 to 90 kbps in each direction per active call including packet overhead. Ten simultaneous calls need around 1 Mbps upload and 1 Mbps download, plus headroom for everything else on the link.

### Do I pay for SIP channels on Edesy?

The published Edesy SIP trunk price is per minute: Rs 0.50/min with a 60-second pulse, unanswered calls free, plus number rental, excluding 18% GST. Each trunk has a max concurrent calls setting; contact support if you need it raised.

### How many channels does an outbound calling campaign need?

Set the campaign's max concurrent calls first, then make the trunk limit at least that number plus room for inbound and agent calls. For an agent dialer, lines in use are roughly free agents times the pacing ratio (1.0, 1.5 or 2.0 on Edesy) plus calls already connected.