All You Need to Know About SIP URI


A SIP-URI or Session Initiation Protocol Uniform Resource Identifiers is a communications protocol. It comprises all the essential information to start and maintain a communication session with the parties involved in the call. In addition, it communicates who to call via SIP protocol. In simple words, SIP-URI is a user’s SIP number. It looks similar to an email address.

What is SIP?

The SIP or Session Initiation Protocol is a popular internet telephony protocol. It forms the foundation of all kinds of internet communication sessions. It is a technology that allows users to initiate sessions, manage to signal, and terminate the connection (IP calls and chats) as soon as the session ends. 

The technology was developed in 1996 by Mark Handley, Eve Schooler, Henning Schulzrinne, and Jonathan Rosenberg. Gradually, SIP became a popular technology to simplify real-time calls. It became uniform by the Internet Engineering Task Force (IETF) through RFC 3261.

SIP is usually identical to SIP trunking. Using this process, companies with SIP-enabled PBX can leverage the Internet to make or receive calls. Using a SIP trunk, a virtual phone line, businesses can reduce the costs of using a traditional PSTN phone system. 

How Does It Work?

SIP servers are used to initiate and terminate IP calls. Data packets are sent between endpoints in the call. These data packets generate a SIP request to the communication session. This request resembles an email. 

As soon as the participants receive the request or invite, they can click on the link provided in the invite to join the call. SIP generally uses Transmission Control Protocol (TCP) or UDP to accomplish this process. 

What is URI?

People often get confused between URI (Uniform Resource Identifiers) and URL (Uniform Resources Locator). However, both are quite different from each other. A URI is an identifier of a particular resource like a page, or book, or document. It can be categorized as a locator, a name, or both. On the other hand, a URL is a special kind of identifier that also tells users how to access it, like HTTPS, FTP, etc. It describes the primary access mechanism.

A URI is just an identifier, and a URL is an identifier that informs users how to get to their destination.

Syntax of URI

The syntax of URI is written as:

URI = scheme:[//authority]path[?query][#fragment]

Let’s look at each part or component in detail:

  • Scheme Component: The scheme component is a non-empty part followed by a colon (:). This part comprises a series of characters starting with a letter and followed by any combination of letters, period, digits, a hyphen, or plus. Some of the most common examples of schemes are FTP, HTTP, HTTPS, file, etc. One important thing to keep in mind regarding schemes is that these must be registered with the IANA (Internet Assigned Numbers Authority).
  • Authority Component: Authority component is an optional field that is led by (//). It usually comprises (a) an optional user info sub-component that may consist of a username and password, (b) a host sub-component that either includes an IP address or a registered name, (c) an optional port sub-component that is followed by a colon (:). 
  • Path: A path is an important part of URI that comprises several segments divided by a slash (/).
  • Query Component: It is another optional part of URI. It is usually preceded by a question mark (?). As the name suggests, a query component consists of a query string of non-hierarchical data.
  • Fragment Component: Another optional part in URI, the fragment component, is headed by a hash (#). This part consists of a fragment identifier that provides direction to a secondary resource.


A SIP URI is a system that connects a VoIP endpoint. Each VoIP SIP endpoint will have a similar SIP URI to connect to the particular distant peer. The URI comprises the address of the SIP device in the form of a DNS hostname. The DNS hostname includes the remote host, protocol, and destination number. 

It is quite easy to use SIP URI. To use a SIP phone for dialing a SIP address, users are just required to program the SIP address via the user portal. After programming the SIP address, users can utilize their phone address book to dial the SIP address. There are two ways to use SIP URI:

  • By using the outbound “click2call” command on the computer, which will ring the user’s phone and the receiving phone
  • By programming the telephone number into VoIP phone’s speed dial/super dial system. This will allow users to call the SIP address by pressing one or two digits. 


To conclude, the purpose of the SIP call is to eliminate the need for PSTN and use only the internet protocol. To leverage the benefits of SIP URI, users must subscribe to a professional service provider who can efficiently register their IP phone to their IP address. 

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