SIP Trunk Integration for
Microsoft Teams

Once phone communication relied on underground copper wires and physical telephone lines, but now it is becoming increasingly digitised. One of the keys to this is SIP (Session Initiation Protocol) trunking. But what exactly is SIP trunking, what are the benefits, and how do you integrate it with Microsoft Teams?

What is SIP trunking?

What does SIP mean?

SIP by itself is a type of protocol you use for VoIP (Voice over Internet Protocol) communications, where you make and receive phone calls over the internet. A protocol is a computer science term for a set of rules or procedures for transferring data between electronic devices. So, this makes SIP a way to connect voice transfers to and from such devices. It does so by converting voice signals into data that can then be decoded. Although various protocols can be used in a VoIP system, SIP is the most common.

Direct Routing for Microsoft Teams
Why Is PSTN Calling Important?

What is trunking?

‘Trunking’ is a virtual link between a PBX (Private Branch Exchange) — a multiline telephone system typically used by businesses — and the standard phone network, which is called the PSTN (Public Switched Telephone Network). This is different to a channel. Whereas a trunk is what facilitates the connection between a PBX and a PSTN network, a channel is the lane in which communication happens. An unlimited number of channels can be configured from a single SIP trunk, and how many you’ll need depends on the number of simultaneous calls you’ll be making and receiving.


How does SIP trunking work?

A SIP trunk works through a SIP provider, which connects a company’s in-house PBX system to the PSTN. This allows companies to then use one network for both online and everyday voice calls, as well as to send things like images, videos and other files. All you need for SIP trunking is an internet connection with good bandwidth and speed.

Benefits of SIP trunks

Consolidated communications

A SIP trunk enables you to pay for data and voice transmissions across just one network, rather than separate ones. This will help your business cut costs because you won’t need to pay for multiple networks. What’s more, if you need to support a higher number of concurrent calls this can be achieved simply by adding more channels.

Cost savings

SIP trunks can also help you cut costs due to the fact you’ll use the internet to communicate instead of expensive physical phone lines. Long-distance and international calls will become local ones with SIP, making them cheaper, while SIP plans are broken down into a per-user recurring rate, reducing the possibility of hidden costs.

More agility

SIP technology helps your business to grow quickly considering you don’t need to wait for your local telecommunications company to implement any required changes. Adding new channels is incredibly easy, as is managing an entire phone system because there aren’t lots of legacy phones involved. Similarly, combining voice and data calls into one network helps to facilitate remote working.

Unified communications

Unified communications contain all of your communications channels (chat, file sharing, phone calls, video conferencing, email and more) within one platform. This has numerous benefits, including greater productivity, reduced costs and enhanced user experience. SIP can help you achieve this by moving all your communication channels to a data network.

Improved productivity

With a consolidated and unified communications system, your staff spend more time actually working than trying to figure out how to get in touch with somebody. In addition, SIP trunks give you access to call logs and reporting, helping you to measure usage and availability and better manage your team.

Greater reliability

With a traditional phone set up, an outage can spell huge trouble for your business. But with SIP trunking, an internet issue needn’t affect things as your service provider can reroute your calls to staff mobile devices or other offices. This makes it a lot more resilient than legacy systems.

SIP for Teams Direct Routing

Direct Routing is a solution that lets you place PSTN phone calls through Microsoft Teams. This improves your Teams experience in multiple ways, from making external calls easier and creating a single point of communications access, to centralising information and giving you full PBX functionality. SIP plays a vital part in this seeing as it’s the back-end technology that is most often used to make the integration connection with a Direct Routing solution.

What is the SBC’s role in Direct Routing?

Session Border Controllers (SBCs) convert IP packets to voice signals (and vice-versa) which are transmitted onto the PSTN. A session simply means communication between two parties, while the border here is the boundary between one part of a network and another, like a firewall, for instance. The SBC’s role is to allow information, calls and other media to enter a network from another, while also offering security against threats like Denial of Service (DoS) and Distributed DoS (DDoS) attacks. So, whereas SIP servers simply connect voice transfers, SBCs act as intermediaries between multiple networks, facilitating data flow management, while they can also help things be more secure.

For Direct Routing, the SBC will be situated at the network edge between the Microsoft Phone System and the provider’s PSTN network. Whenever individuals make calls via their Team-enabled devices, the data is transferred through the internet to the Phone System, before reaching the SBC. At this point, it will route the session data to the other user’s network after doing things like changing the message’s bandwidth to match the new network’s capabilities and applying security measures.

What do I need to make calls with Microsoft Teams?

Although you can use Microsoft Phone System and its Calling Plans to set up PSTN calling with Teams, this has clear shortcomings. For example, the features such as call recording, reporting or extensive call queue management are limited, making it hard to genuinely unify your communications.

This is why Direct Routing is a superior solution, offering complete PBX integration (including the features mentioned above), and endpoint and handset flexibility. Indeed, this gives it many advantages over Microsoft’s Calling Plans, helping you make the most of your communications system.

Callroute’s Direct Routing solution

Our Direct Routing solution gives you a free channel for life and flexible per-channel pricing, and enables your business to instantly make Teams your PBX. This is because we have autoconfigured our integration process, allowing companies to integrate their systems with Direct Routing a lot quicker than other providers.

Furthermore, as a business in the corporate telephony sector, we know better than most why reporting, security and calling features are so vital. With our Direct Routing solution, you can choose caller IDs, monitor call history, track user activity, view call data records (CDR’’s)and more.

Get in contact if you want to try our solution or find out more about how we can help your business.

Microsoft Teams

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SIP Trunking with other platforms

If Teams isn't your chosen business collaboration platform, we can still support you. At Callroute we also support Cisco Webex and Genesys Cloud CX. And if you want to integrate existing legacy equipment such as PBX's, we can help with that too. Discover our Callroute SIP Trunk integration solution for more information.

Cisco Webex
Genesys Cloud CX
Microsoft Teams


While you may require, say 50 SIP channels for the number of calls your business makes simultaneously, you only ever need one SIP trunk overall.

A PBX is simply a multiline telephone system typically used by businesses, while an SBC is what regulates and safeguards IP communications.

SBCs offer numerous benefits for Teams SIP trunking, including enhanced call quality and security, and significant routing capabilities.

Understand better how the modern telephony system works

Visit our modern telephony page to find out more about topics such as VoIP phone systems and the benefits of integrating different communication channels.