What is SIP?

Posted on: 2016-06-14 | Categories: SIP SIP Trunking

What is SIP? What does it mean? You will learn all about it in this post.

Entering the world of VoIP for the first time can seem daunting, what with all the technical jargon and acronyms. Even the name of the technology is an acronym! VoIP stands for Voice over Internet Protocol and what is confusing for most people is that it does not refer to a single thing specifically. It is also alternatively referred to as IP calling, Internet phone and various other terms.


VoIP is a loosely defined term that can refer to different technical implementations that all accomplish the same thing – sending voice calls over the Internet. Transmitting voice calls over the Internet is not as easy as it appears to be at first glance and there is a lot of data conversion and routing going on behind the scenes.

VoIP can refer to a whole bunch of different deployments. For instance Skype is one of the most popular consumer level VoIP systems. There are phone companies like Vonage and MagicJack which also offered VoIP hardware/service aimed at households. Enterprise grade hosted VoIP services are in a class of their own when it comes to features, pricing and functionality.

What are protocols in computing?

But to actually implement VoIP, computing protocols are necessary. A protocol is defined as a standard that can be used to define how data is exchanged, formatted or transmitted over the network whether it is the Internet, intranet or a corporate LAN. Protocols are commonly and extensively used in computing for everything from VoIP to email.

For instance, the HyperText Transfer Protocol (HTTP) is a standard that transmit data over the Internet. The Simple Mail Transfer Protocol (SMTP) is another well-known standard that is used to transmit email messages from one client to another. Each protocol may have its own method that defines how the data should be shared, formatted, checked for errors, what to do with the data when it is received etc.

Protocols are the technical underpinnings for most computing technologies and they’re often created, maintained or developed by specific organizations.

What is SIP?

As you might have guessed, SIP is simply a protocol that is used for deploying VoIP. SIP stands for Session Initiation Protocol and is used for voice/video calls and instant messaging on the Internet. Contrary to popular thought, SIP alone is not sufficient to deploy VoIP. It is often used in conjunction with many other protocols including SDP, RTP and SRTP among others.

The reason for much of the confusion between SIP and VoIP is simply because it is the most popularly used protocol by enterprises, vendors, manufacturers of VoIP equipment etc. In everyday conversations, a lot of people use SIP and VoIP interchangeably even though they mean and refer to entirely different things.

What does SIP do?

The main purpose of SIP is to set up and terminate calls on the Internet. These calls can be purely voice or include video streams as well. The SIP protocol defines how messages will be exchanged between the two endpoints and establishes the other parameters of the call. It is important to note that SIP itself does not carry any media between the two – or multiple – users. Other protocols are used for this purpose.

When a call is initiated, SIP requests are exchanged between the endpoint and the server. These messages determine how and whether the call goes through. This is also how endpoints communicate that they are busy or available for calls. For instance, a particular endpoint may respond to a request by saying that the user is unavailable or busy.

Why is SIP so popular?

SIP is an open source and nonproprietary protocol, which is one of the many reasons for its popularity. Even though Skype is a popular consumer VoIP platform, it is considered to be a closed source network because it does not utilize SIP or other open formats. The technology behind Skype is closed source and proprietary which is why Skype users can only communicate with other Skype users.

On the other hand, deployments which utilize SIP do not restrict users in a similar manner. As long as the system is compatible with the SIP protocol, users can make and receive calls between one another. The SIP code is easily available to anyone and the protocol can be implemented without having to pay licensing fees to a single company. Due to this, most equipment manufacturers and vendors utilize SIP for providing VoIP services.

For instance, if an organization wants to deploy its own VoIP solution for voice calling they are most likely to utilize SIP. As long as any equipment or hardware they purchase supports the protocol, it will be compatible with other components on the network. This reduces problems due to incompatibility and makes the entire ecosystem interoperable.

Just as how knowledge of the SMTP protocol is not needed to send and receive emails, most users don’t have any idea about SIP. However for those who are in charge of implementing VoIP, understanding SIP is essential.