What Is SIP Calling and SIP Trunking?

What is SIP?


Session Initiation Protocol (“SIP”) is a communication protocol used to initiate, modify and terminate interactive user sessions. It supports multimedia communications, including voice, video, and messaging. It is widely used in VoIP implementations. It is not necessary for all VoIP implementations but is required to support some advanced features such as device mobility.

To be a little technical, SIP is an application-layer protocol that defines how the devices involved in a conversation exchange information with each other to set up and control a session.

Overall, SIP is a powerful and flexible protocol that enables a wide range of communication services and applications, including voice and video conferencing, instant messaging, and multimedia collaboration tools.

SIP is made up of two main sub-protocols, SIP Calling and SIP Trunking. They are often confused but support different SIP concepts.

SIP Calling

SIP Calling

SIP Calling is a specialised SIP protocol that enables communications between two or more participants. It establishes an Internet link between devices, initiates the call, including any encryption requirements, and terminates the communications session.  It supports voice, data, and messaging.

To make a SIP call, users need a device that supports SIP, such as a SIP-enabled phone, softphone app, or PBX system. They also need to have a SIP account from a SIP service provider, which can provide them with a phone number, calling plan, and other features. The SIP account information is usually provided by the corporate VoIP system, or by the SIP module in a SIP-enabled PBX system.

Once the user has a SIP account and device, they can initiate a call by entering the destination phone number or SIP address. The SIP device sends a request to the SIP server to establish a connection with the destination device. If the connection is successful, the two devices can exchange voice or video data packets to complete the call.

SIP calling offers many benefits, including cost savings, greater flexibility, and advanced calling features. It also enables users to make and receive calls from anywhere with an Internet connection, which is especially useful for remote workers, travellers, or people who need to communicate across different locations.

Implementations of the SIP Calling Protocol on smart devices make the smart device a VoIP-capable device. Users connected to a corporate WiFi network can use their smart device as a VoIP handset. In large sites, such as a campus, users can be contacted on their internal extension number, and make calls wherever they are.

SIP Trunking

SIP Trunking

SIP Trunking, like SIP Calling, is used to manage Internet-based communications using the SIP protocols. The difference is that it acts as an interface between an existing internal PBX and the Internet. Organisations can use their existing phone system to make and receive calls without changing their infrastructure, but over the Internet rather than existing PSTN lines.  That can be a major cost saving for organisations, particularly those that make long-distance and International calls.

To set up SIP trunking, businesses need a SIP-enabled PBX system and a SIP service provider. The provider will assign a range of phone numbers, which can be used by employees to make and receive calls over the Internet. The provider will also handle the routing of calls between the PBX system and the public switched telephone network (PSTN), which allows for calls to be made to non-SIP devices, such as traditional landline phones.

In summary, in normal operation the SIP service provider acts as a virtual phone line, allowing businesses to make and receive calls using their existing PBX system. This eliminates the need for the maintenance of the expensive hardware and infrastructure associated with traditional phone systems and can significantly reduce communication costs.

SIP trunking also offers greater flexibility and scalability than traditional phone systems, allowing businesses to easily add or remove phone lines as needed. It also provides advanced features such as call routing, caller ID, and call recording.

Overall, SIP trunking is a cost-effective and flexible solution for businesses that want to modernize their communication systems and take advantage of the benefits of VoIP technology.

Final Thoughts

SIP is a viable option for businesses seeking to reduce their communications costs, while at the same time improving service levels, and internal operational efficiencies. Whether they opt for a full-blown VoIP system incorporating SIP trunking, or a simpler VoIP-based SIP Calling implementation, depends on their individual corporate development plans.