What Is Session Initiation Protocol (SIP)?
When you communicate with another person online, you need a reliable technological foundation through which to communicate. Session Initiation Protocol (SIP) is a common VoIP protocol that helps initiate online communications and phone calls over Internet connections. In this article, we'll discuss SIP, how it works, and the benefits of using SIP.
What is SIP?
SIP stands for Session Initiation Protocol. It’s a method of VoIP (Voice over Internet Protocol) that initiates, or enables, messages to be sent between two endpoints over the Internet. Session Initiation Protocol allows for many types of information to be exchanged over the Internet, including voice, video, instant messaging, and even media files. It’s a flexible protocol that essentially works to set up multimedia transfers between people in real time.
In order to fully understand Session Initiation Protocol, it’s helpful to break down each word:
- A session is a period of time in which two devices exchange information over the Internet. Think of a session as a video conferencing call or instant messaging chat.
- Initiation refers to starting a session, keeping the session online, and ending the session. It's comparable to pressing the "call" and "end" buttons. SIP handles the technological processes that take place when you click those buttons.
- Protocol is a computing term that essentially means a set of rules that control the exchange of information between devices. It is a means to ensure that devices understand each other and can communicate clearly over the Internet.
Taking all three terms together gives you a protocol that lets you initiate live communication sessions with others over the Internet.
How does SIP work?
Session Initiation Protocol operates on the application layer of the OSI model. It's a response-request protocol, meaning responses and requests are the names of message protocols sent between devices.
The protocol organizes the structure for the communications, including the endpoints used, the media and parameters, and the consent for communication. Once everything is established, the Session Initiation Protocol receives requests from a client. It then receives a response from a server, facilitating communications between the clients and servers.
What is SIP calling and how does it work?
SIP calling is the process by which voice calls are transmitted via an Internet or WiFi connection. Session Initiation Protocol involves two-way communication whereby one device sends a request and the other device receives the request and responds. It works by coding the requests and running automatic checks upon initiating the call as well as throughout the call.
It checks that:
- the recipient maintains an Internet connection
- the recipient is available to receive a communication
- the recipient's device is compatible
Session Initiation Protocol then ends the connection between the two parties when either party hangs up. You can purchase dedicated SIP phones for using Session Initiation Protocol communication methods.
Functions of SIP
Though its general purpose is controlling multimedia communication sessions, here are five key functions of Session Initiation Protocol.
Session establishment
SIP sets up sessions between participants by sending an invite request to participants, sharing details about media types and format supported, and agreeing on session parameters.
Session modification
During active communication sessions, SIP lets participants change the session parameters by adding media streams, changing codecs, or adjusting the bandwidth.
Session termination
SIP also ends sessions when a participant sends a BYE request. Once that’s sent, other participants send acknowledgments to confirm the termination, and SIP ends the session and releases the allocated resources.
Call routing and proxy services
SIP works with proxy servers, which route SIP requests and responses between clients and servers.
User location and registration
SIP uses location services to discover the current IP address and port of a user, which lets calls go to the correct location. It does this through a SIP registration process. Users send REGISTER requests to a SIP registrar server, which keeps a database of users’ contact information for future initiated requests.
Session Initiation Protocol is responsible for supporting the establishment, modification, and termination of multimedia communication sessions. However, as seen through these functions, it can also perform call routing and work with proxy services.
What is SIP trunking?
SIP calling is primarily made possible by Session Initiation Protocol trunks. Though it may seem difficult to understand what a SIP trunk is, think of it this way: they’re essentially digital phone lines that allow users to make and receive calls from anyone with a phone number, whether digital or landline.
Instead of a traditional line that uses a physical PBX (Private Branch Exchange), it uses a cloud-based system called an IP PBX system to connect your physical phones to the Internet. PRI (Primary Rate Interface) lines also use PBX communication; however, Session Initiation Protocol is still the better choice, as it offers greater flexibility for the user.
SIP trunking is a huge technological advancement as it allows businesses to replace their traditional phone lines with "virtual" phone lines. It works using a packet switch network where communications turn into digital packets and travel across a network.
SIP vs. VoIP
SIP and VoIP are separate protocols, but they work in conjunction with one another.
VoIP enables the transmission of voice communication over the Internet. It includes numerous different protocols, codes, and technologies, all which help translate voice signals into digital data to transmit across networks.
Session Initiation Protocol is a signaling protocol that establishes, modifies, and ends communications sessions like VoIP calls or instant messages. It’s one of the several signaling protocols used in VoIP systems.
Essentially, VoIP is the underlying technology that allows for voice calling over the Internet. Session Initiation Protocol is a specific element of VoIP that enables the initiation of calls and maintains the connection throughout.
Why use SIP calling?
There are many benefits of SIP calling that users can’t get with traditional phone systems. Here are a few benefits of the system.
Flexibility
SIP calls, as opposed to traditional calls, occur on a wide array of devices, from mobile devices to tablets and laptops. This allows employees to access their business phone lines from anywhere, which is especially important as more businesses begin to work remotely.
Scalability
Because SIP operates on the Internet, it boasts a much higher data capacity than traditional copper telephone lines. This means that calling up operations is as simple as clicking a button as all the data operates on the cloud. Traditional phone lines would require the installation of additional copper lines.
Easy to implement
Whether a business has an existing system with desk phones or not, SIP systems are quite easy to implement because they are virtual. Furthermore, implementing a Session Initiation Protocol system involves digitizing an existing physical phone system.
Reliability
Because SIP doesn't rely on built-in hardware, it's much more reliable than traditional phone lines. With traditional phone lines, many things can go wrong, from the PBX to the copper lines themselves. Though with any software, there's always a chance of failure, SIP calling minimizes those chances.
Affordability
With SIP, you have only installation, hardware, and maintenance costs. With most Session Initiation Protocol service providers, you only pay for what you use. SIP trunk pricing differs from provider to provider, but all provide cost savings compared to traditional phone lines.
Session Initiation Protocol is a clear winner when it comes to modernizing business’ phone systems. SIP trunk services offer much greater flexibility, allowing businesses to communicate and do business more efficiently in the ever-changing technological landscape.
Frequently asked questions
What does SIP stand for?
SIP stands for Session Initiation Protocol.
What does SIP mean in front of a phone number?
If you see SIP in front of a phone number, it means that the line uses Session Initiation Protocol to connect to others and make calls.
Can Session Initiation Protocol calls be traced?
Yes, it's possible for Session Initiation Protocol calls to be traced, although it's not like tracing a traditional call. These calls are more difficult to trace and detect due to caller ID spoofing.
