SIP Line vs SIP Trunk: How are They Different?


Do you remember how the phone bill can easily pile up if you make international calls pre-internet? If you aren’t at that age yet, then perhaps you remember how you need to get to your home phone to talk to your friends.

That’s essentially what it was like before to make calls using now-antiquated phone lines: expensive and inconvenient.

But through the services provided by companies like, your business can save on the costs of communication. This is what SIP line and trunk can do for you.

Before we discuss their difference in detail, you should know what SIP is to begin with.

Understanding Session Initiation Protocol (SIP)

Session Initiation Protocol or SIP creates connections and makes teamwork location independent. It is the reason communication over the internet is possible. Through its configuration, you can create, change, or end communications done over the internet.

So in itself, SIP doesn’t provide internet communication. What it does is provide functions that allow you to know the:

  • Location of the user. This is done through a device registration process (laptop, mobile phone, etc.) in the network.
  • Availability of the user. SIP determines this when you choose to respond or not respond to a call. If you have many devices registered, SIP will try other devices for your availability.
  • User communication capabilities. Your communication modes are limited by the type of device you’re using. SIP also uses this information to encrypt and decrypt your data.
  • Setting up communication. When someone tries to contact another person in the network through a call, SIP allows you to establish it.
  • Managing the communication session. With this, you can transfer devices or change from voice to video or vice versa without any hassle.

Most of the time, it’s confused with Voice over Internet Protocol (VoIP). But what you just have to know is VoIP is a type of internet call while SIP is what makes VoIP and other internet communications happen.

What is a SIP line?

A SIP line is what is established when you communicate using the internet – whether that’s voice, video, or instant messaging. Think of it as your home phone (if you still have one) where you can call only one person at a time.

It’s very rare that a company only needs one SIP line. The exact number needed will depend on many factors such as:

  • Time zones where your employees work
  • How heavily reliant on communication your operations are
  • How many lines are used at a time
  • The nature of the business (call centers would need more lines than a construction agency)

What is a SIP trunk?

And because one line rarely is sufficient, the SIP trunk fills the gap. You can imagine a SIP trunk as an online version of your phone lines.

From its name, you can see it as the trunk of a tree which holds many branches where every branch is an SIP line that lets you communicate to another device.

With a SIP trunk, you can send and receive different types of data from people registered within the network – no matter where they are in the world. Using this modern technology has the following benefits:

  • You only need your internet connection to be reliable. Investing in costly equipment isn’t needed.
  • It’s much cheaper. International calls won’t burn a hole in your pocket. And domestic calls and calls within the network are free.
  • It’s more scalable. If you want to add SIP lines, doing so would entail simply informing the service provider. The same goes should you decide to scale down.
  • It’s more dependable. If you register multiple devices, your call can be forwarded to another device if you can’t be reached on your primary device.

So how are they different?

The SIP trunk operates at a much larger scale than your SIP line. To elaborate, there are two main differences which can help you decide what is right for you:


Your SIP trunk is comprised of SIP lines. This means that the former has a larger capacity.

And why does this matter? Because you have to decide the capacity of the SIP trunk. So if you have 100 employees, it doesn’t mean you need 100 lines.

Knowing how many lines are used simultaneously can help you decide.


Because it only has the capacity of a single call, a SIP line is much cheaper. The more calls you need to do simultaneously, the bigger the SIP trunk you need.

And the bigger it is, the costlier it’s going to be. But as much as you want to keep costs down, make sure that what you’re getting is enough to keep communication efficient.

Which is better?

Do you know how they say that the sum is greater than its parts? Following this logic, a SIP trunk is better – the tree is better than the branch.

The SIP trunk is able to hold many and simultaneous communication lines. On the other hand, a SIP line may only support one. And for a growing business, having only one line isn’t enough to handle customer support and internal communication.

So unless you need it for personal use, we strongly recommend SIP trunk for you to have smart and efficient business communication. It simplifies communication, making everyone’s job much easier to do.