On a landline phone system, the number of lines determines the number of calls it can process. For IP-based phones, channels or trunks dictate how many simultaneous calls can be handled.
A trunk can be either inbound, outbound, or two-way. Many hosted PBX providers sell per user, at which point the type of trunk is irrelevant. That user will always have the ability to place and receive calls.
Unlike landline solutions, trunks are system-wide. They are not limited to a specific line or device. This means they are shareable among groups of users, which can save your business lots of money.
The number of channels is not the only thing that sets call capacity. In fact, the local network more often determines the maximum concurrent call volume. This term refers to anticipated and supported peak-call volumes.
Bandwidth & Codecs
Generally, the more bandwidth available, the more calls can occur at one time. To get the most out of a data connection, IP phones use codecs. Codecs compress audio data, making it less bandwidth intensive. The type of codecs used impacts how much bandwidth each simultaneous call requires.
For G.711, the standard codec, each call consumes roughly 0.1Mbsp. Therefore, ten simultaneous calls equals 1Mbsp. Based on your habits, multiply the maximum number of calls in progress by this metric. Then, consider what else competes for data (i.e. web browsing, emailing, and streaming). What does the total look like and does your current provider accommodate such traffic?
Calculate Expected Call Volumes
You should track your business’ peak hours for two reasons. First, peak hours indicate how many simultaneous calls need supporting. Second, it benchmarks the system and provides insights on when the phone system caps.
To estimate peak-hour call volumes, look at your monthly phone bills. Most invoices include an hour-by-hour outline, which makes it easy to pinpoint busy times. In the least, your bills should include an airtime overview for each line.
On a spreadsheet, circle the areas where your phone lines receive the most traffic. Add 20% to 40% to this figure to account for all other internet activity. Knowing your local threshold can help in the decision to acquire more or fewer channels.
In most landline environments, each user has a dedicated line. Hosted PBX does not work in this way. Instead, users can share banks of channels. Teledynamic provides guidelines for different company sizes.
- Companies with 100 employees or more need approximately 1 channel per 3 employees.
- Companies with 50 employees or fewer need:
- 4 channels per 2 phones;
- 6 channels per 5 to 10 phones;
- 12 channels per 25 phones;
- 23 channels per 50 phones.
As mentioned, per-user services often provide at least one two-way trunk per device. For this reason, you need not worry about maximum calling beside on your own network.