# Creating a SIP Domain

A "SIP Domain" represents a domain name to which users can register. It also defines registrars from which the SBC forwards registration requests.

The creation of SIP domains is performed as follows:

\
1\. Select SIP Domain in the navigation panel

<figure><img src="https://docs.telcobridges.com/w/images/4/48/Create_SIP_DomainNavMenu.png" alt=""><figcaption></figcaption></figure>

\
2\. Click Create New SIP Regisration Domain

<figure><img src="https://docs.telcobridges.com/w/images/1/1e/Create_SIP_Domain.png" alt=""><figcaption></figcaption></figure>

\
3\. Configure the SIP Registration Domain

<figure><img src="https://docs.telcobridges.com/w/images/2/2f/Create_SIP_Domain1.png" alt=""><figcaption></figcaption></figure>

* Enter a configuration Name for this domain.
* Enter a Domain Name for the SIP Registration Domain. A domain can be a FQDN or an IP address.
* Set the number Maximum Registered Users for this domain
* Set the Expires value used by SBC when the remote device doesn't supply one (Default Contact Expiration)
* Select Routing Method the system will use to route calls to registered users (if enabled in routing scripts).
  * Register source: Sends SIP Invite to the registering source IP address.
  * Contact: Sends SIP Invite to the 'contact' from the Register message.
* Set the Default Contact Expiration, this value will be used when no *Expires* value is supplied by the user agent.
* Set the Minimum Contact Expiration, this is the minimum *Expires* value that can be supplied by a user agent. Lower values will be rejected with a 423 'Interval too brief' response.
* Set the Maximum Contact Expiration, this is the maximum *Expires* value that can be supplied by a user agent. Higher value are replaced by this parameter.
* Forwarding Parameters:
  * Select the Registration Forwarding Mode to the registrar:
    * Contact Remapping: Changes the user and the IP address.
    * Contact Passthrough: Doesn't change anything. Enables devices to be contacted directly without going through the SBC.
  * Set Minimum Registrar Expiration, this is the minimum *Expires* value sent by the SBC to the registrar. If a user agent 'Expires' value is greater than this parameter, the SBC will do rate adaptation between the user agent and the Registrar.
  * Set Maximum Pending Register Forward, the maximum number of simultaneous pending register requests allowed for this domain. New REGISTER requests are being refused passed this threshold.
  * Set Maximum Simultaneous Register Forward, the maximum number of simultaneous active register requests allowed for this domain. New REGISTER requests are being refused passed this threshold.
  * Select the Registration Registrar Selection Mode to the registrar:
    * Active/Standby: The active registrar is the one with status up and the lowest priority (automatic fallback).
  * Enable the Forward After Switchover: After a switchover, the first register refresh request from each user will be forwarded to the active registrar.
* Click Create

\
4\. Verify that the Sip registration domain was successfully created message appears

<figure><img src="https://docs.telcobridges.com/w/images/c/c9/Create_SIP_Domain2.png" alt=""><figcaption></figcaption></figure>

<figure><img src="https://docs.telcobridges.com/w/images/4/4d/Create_SIP_Domain3.png" alt=""><figcaption></figcaption></figure>

4.a. You can create and update the SIP Registration Domain with RESTful API. Please check the following link:

{% content-ref url="../../../tools-tips-and-tricks/restful-api/prosbc-restful-api-sip-domain" %}
[prosbc-restful-api-sip-domain](https://prosbcdocs.telcobridges.com/tools-tips-and-tricks/restful-api/prosbc-restful-api-sip-domain)
{% endcontent-ref %}

\
5\. Create one or multiple SIP registrars for the SIP domain

* Click the SIP domain that was just created
* Click Create New SIP Registration Registrar

<figure><img src="https://docs.telcobridges.com/w/images/a/a5/Create_SIP_registrar.png" alt=""><figcaption></figcaption></figure>

\
6\. Enter the name of SIP Registration Registrar

* Select a NAP
* Click Create

<figure><img src="https://docs.telcobridges.com/w/images/d/df/Sip5.png" alt=""><figcaption></figcaption></figure>

6.a. You can create and update SIP Registration Registrar with RESTful API. Please refer to the following link:

{% content-ref url="../../../tools-tips-and-tricks/restful-api/prosbc-restful-api-sip-domain-registrar" %}
[prosbc-restful-api-sip-domain-registrar](https://prosbcdocs.telcobridges.com/tools-tips-and-tricks/restful-api/prosbc-restful-api-sip-domain-registrar)
{% endcontent-ref %}

Multiple registrars (registration redundancy) Multiple registrars can be created per domain, for redundancy.

* Registrars are ordered by priority
* Users' registration requests are forwarded to the available registrar with the highest priority in the list
* SIP 'options' polling is used to determine which registrars are available or not

<figure><img src="https://docs.telcobridges.com/w/images/d/de/Multiple_registrars.png" alt=""><figcaption></figcaption></figure>

\
Create routes for registered users

In most cases, FreeSBC will route SIP calls (SIP Invite) to registered users. This is done by [creating appropriate routes](https://prosbcdocs.telcobridges.com/configuration-details/configuration-by-use-case/sip-registration-forwarding).