What IsSIP Registration?

A Session Initiation Protocol or SIP registration refers to the process of linking an endpoint device (an IP phone) with a service provider’s network (a contact address).

This validates that the phone can make and receive VoIP (Voice over IP) calls. Once the endpoint sends a SIP register to the registrar, the latter confirms the request and stores the connection in the domain’s network (the location server). The registration changes several times throughout the day to prevent fraudulent activity. Besides voice calls, SIP also supports video conferencing, media distribution, and instant messaging

How Does SIP Registration Work?

The SIP registration process consists of several components. These include the SIP registrar, the endpoint, and the AOR (Address of Record). Also referred to as IP phones, SIP endpoints are all over the internet and most of them don’t contain an IP address. This requires each endpoint to register an IP address and port number with a registrar in order to be available to other endpoints. A SIP register message forms a link between the endpoint device and an AOR, which appears as sip:user@domain.

As per the SIP standard, the process begins automatically after a user sets up an IP phone. SIP registrations expire periodically with timeouts depending on the SIP device vendor. IP phones need to renew the registration before the connection expires. Therefore, most of them automatically re-register halfway through each period. 

Benefits of SIP Registration


An ordinary PSTN (public switched telephone network) phone number can only enable making and receiving calls from the phone’s location. With a SIP endpoint, employees can reach each other whether they are in the office or working remotely.

Agility and Scalability

SIP technology allows companies to add numbers with ease whenever needed. They can use each of those numbers to make and receive an unlimited number of calls, whether local or long-distance. Businesses can also drop a number when they no longer need it, and they only pay for what they use.


SIP lines tend to be affordable; in most cases, you only pay a minimal monthly fee for outgoing voice calls. And it is only a fraction of the cost that you would otherwise pay for calls on leased lines.

Virtual Presence

Companies can use SIP numbers with any area code and exchange available. This means being able to appear local to customers who prefer dealing with local businesses, regardless of where your office is based.


As opposed to working with phone companies, which can be inconvenient, SIP technologies are less time-consuming and easier to manage.

Elements of SIP Registration

  • SIP endpoint (or user agent): The SIP entity that the user interacts with. This can be a softphone application, a SIP handset, or any device with a microphone and speakers

  • SIP AOR: The SIP address that identifies the user and consists of a username and a domain name

  • SIP registrar server: The server that accepts SIP register requests and keeps a database of a user’s registrations

  • Binding table: A table that includes data such as ports, IP addresses, and phone numbers

  • Location server (or domain network): Where the SIP registrar stores the connection data

  • IP authentication: A check that the SIP registrar does to validate the user’s details

  • Redirect S\server: The server that consists of alternative locations where the call can be directed (that is to say where the user can be reached)

SIP Register Examples

A Failed SIP Register

A failed SIP register example involves getting “401 unauthorized” as a response for all the requests. The first response is due to insufficient information about the endpoint (or the user agent). At this point, the SIP endpoint makes another “register” request. Getting another “401 unauthorized” indicates a configuration issue or that the username and password are incorrect. The registration will not be successful until the registrar server obtains the proper parameters and has the SIP AOR on file—only then will VoIP calls be available. 

A Successful SIP Register

In a successful SIP register example, the initial response to a register would also be “401 unauthorized.” The reason for this is that the SIP registrar server requires more information about the SIP endpoint. That is when the endpoint sends another “register” message. The response, in this case, would now be “200 OK.” This indicates that the SIP registration is a success and the phone number can support VoIP termination

SIP Registration With Dexatel

As a mobile communications provider, Dexatel offers a VoIP service that includes voice calls, flash calls, and application-to-person calls. This service is supported by a SIP, allowing businesses to carry out flexible, convenient, and cost-efficient communications on both internal and external fronts. This form of technology is similar to the SMPP (short message peer-to-peer) protocol for SMS, which enables users to communicate via SMS over the internet.