IMS Usrloc PCSCF Module

Jason Penton

Smile Communications

Edited by

Richard Good

Smile Communications

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
3.1. default_expires (int)
3.2. default_expires_range (int)
3.3. min_expires (int)
3.4. max_expires (int)
3.5. subscription_default_expires (int)
3.6. subscription_expires_range (int)
3.7. subscription_min_expires (int)
3.8. subscription_max_expires (int)
3.9. user_data_dtd (string)
3.10. user_data_xsd (string)
3.11. support_wildcardPSI (int)
3.12. scscf_name (string)
3.13. store_profile_dereg (int)
3.14. cxdx_dest_realm (string)
3.15. cxdx_forced_peer (string)
3.16. append_branches (integer)
3.17. method_filtering (integer)
3.18. user_data_always (integer)
3.19. error_reply_code (int)
4. Functions
4.1. save(async_reply_route, domain)
4.2. lookup(domain)
4.3. lookup_path_to_contact(uri)
4.4. unregister(domain)
4.5. assign_server_unreg(aysnc_reply_route, domain, direction)
4.6. impu_registered(domain)
4.7. term_impu_registered(domain)
4.8. reg_fetch_contacts(domain, uri, profile)
4.9. reg_free_contacts(profile)
4.10. can_subscribe_to_reg(domain)
4.11. subscribe_to_reg(domain)
4.12. can_publish_reg(domain)
4.13. publish_reg(domain)
5. RPC Commands
5.1. regscscf.dereg_impu
6. Statistics
6.1. registered contacts
6.2. impus
6.3. expired contacts
2. Frequently Asked Questions

List of Examples

1.1. Set default_expires parameter
1.2. Set default_expires_range parameter
1.3. Set min_expiresparameter
1.4. Set max_expiresparameter
1.5. Set subscription_default_expires parameter
1.6. Set subscription_expires_range parameter
1.7. Set subscription_min_expiresparameter
1.8. Set subscription_max_expiresparameter
1.9. Set user_data_dtdparameter
1.10. Set user_data_xsdparameter
1.11. Set support_wildcardPSIparameter
1.12. Set scscf_nameparameter
1.13. Set store_profile_deregparameter
1.14. Set cxdx_dest_realmparameter
1.15. Set cxdx_forced_peerparameter
1.16. Set cxdx_forced_peerparameter
1.17. Set cxdx_forced_peerparameter
1.18. Set user_data_alwaysparameter
1.19. Set error_reply_code parameter
1.20. save usage
1.21. lookup usage
1.22. lookup usage
1.23. unregister usage
1.24. impu_registered usage
1.25. term_impu_registered usage
1.26. reg_fetch_contacts usage
1.27. reg_free_contacts usage
1.28. can_subscribe_to_reg usage
1.29. subscribe_to_reg usage
1.30. can_publish_reg usage
1.31. publish_reg usage

Chapter 1. Admin Guide

1. Overview

This module contains REGISTER processing logic for the S-CSCF. The 'storage engine' of this module is provided by the ims_usrloc_scscf module:

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • CDP

  • CDP_AVP

  • TM

  • ims_usrloc_scscf

2.2. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio with this module loaded:

  • LibXML2 - used for parsing the XML Subscription information obtained from the HSS (Home Subscriber Server)

3. Parameters

3.1. default_expires (int)

If the processed message contains neither Expires HFs nor expires contact parameters, this value will be used for newly created S-CSCF usrloc records. The parameter contains number of second to expire (for example use 3600 for one hour). If it is set to a lower value than the min_expires parameter then it will be ignored. This parameter can be modified via ser config framework. A random value in a specific interval can be selected by using the default_expires_range parameter

Default value is 3600.

Example 1.1. Set default_expires parameter

...
        modparam("ims_registrar_scscf", "default_expires", 3600)
...

3.2. default_expires_range (int)

This parameter specifies that the expiry used for newly created S-CSCF usrloc records are not fixed(when default_expires applies), but a random value in the intervalrdq [default_expires-default_expires_range%, default_expires+default_expires_range%]. The value is between 0 and 100 and represent the maximum percentage from default_expires that will be subtracted or added when computing the value. Default in 0, meaning default_expires is left unmodified. This parameter can be modified via ser config framework.

Default value is 0.

Example 1.2. Set default_expires_range parameter

...
        modparam("ims_registrar_scscf", "default_expires_range", 30) # +- 30% from default_expires
...

3.3. min_expires (int)

The minimum expires value of a Contact, values lower than this minimum will be automatically set to the minimum. Value 0 disables the checking. This parameter can be modified via ser config framework.

Default value is 60.

Example 1.3. Set min_expiresparameter

...
        modparam("ims_registrar_scscf", "min_expires", 1800)
...

3.4. max_expires (int)

The maximum expires value of a Contact, values higher than this maximum will be automatically set to the maximum. Value 0 disables the checking. This parameter can be modified via ser config framework.

Default value is 0.

Example 1.4. Set max_expiresparameter

...
        modparam("ims_registrar_scscf", "max_expires", 3600)
...

3.5. subscription_default_expires (int)

If the processed message contains neither Expires HFs nor expires contact parameters, this value will be used for newly created subscriptions. The parameter contains number of second to expire (for example use 3600 for one hour). If it is set to a lower value than the subscription_min_expires parameter then it will be ignored. A random value in a specific interval can be selected by using the subscription_expires_range parameter

Default value is 3600.

Example 1.5. Set subscription_default_expires parameter

...
        modparam("ims_registrar_scscf", "subscription_default_expires", 3600)
...

3.6. subscription_expires_range (int)

This parameter specifies that the expiry used for newly created subscriptions are not fixed(when subscription_default_expires applies), but a random value in the interval [subscription_default_expires-subscription_expires_range%, subscription_default_expires+subscription_expires_range%]. The value is between 0 and 100 and represent the maximum percentage from subscription_default_expires that will be subtracted or added when computing the value. Default in 0, meaning subscription_default_expires is left unmodified.

Default value is 0.

Example 1.6. Set subscription_expires_range parameter

...
        modparam("ims_registrar_scscf", "subscription_expires_range", 30) # +- 30% from subscription_expires_range
...

3.7. subscription_min_expires (int)

The minimum expires value of a subscription, values lower than this minimum will be automatically set to the minimum. Value 0 disables the checking.

Default value is 10.

Example 1.7. Set subscription_min_expiresparameter

...
        modparam("subscription_min_expires", "min_expires", 1800)
...

3.8. subscription_max_expires (int)

The maximum expires value of a subscription, values higher than this maximum will be automatically set to the maximum. Value 0 disables the checking.

Default value is 1000000.

Example 1.8. Set subscription_max_expiresparameter

...
        modparam("ims_registrar_scscf", "subscription_max_expires", 3600)
...

3.9. user_data_dtd (string)

DTD to check the user data received in SAA (Server Assignment Answer).

Default value is NULL (none).

Example 1.9. Set user_data_dtdparameter

...
        modparam("ims_registrar_scscf", "user_data_dtd", "/usr/local/etc/kamailio/CxDataType_Rel7.dtd")
...

3.10. user_data_xsd (string)

XSD to check the user data received in SAA (Server Assignment Answer).

Default value is NULL (none).

Example 1.10. Set user_data_xsdparameter

...
        modparam("ims_registrar_scscf", "user_data_xsd", "/usr/local/etc/kamailio/CxDataType_Rel7.xsd")
...

3.11. support_wildcardPSI (int)

indicate support for wildcard PSI is subscription profile (SAA)

Default value is 0.

Example 1.11. Set support_wildcardPSIparameter

...
        modparam("ims_registrar_scscf", "support_wildcardPSI", 1)
...

3.12. scscf_name (string)

The name of the S-CSCF

Default value is sip:scscf.ims.smilecoms.com:6060.

Example 1.12. Set scscf_nameparameter

...
        modparam("ims_registrar_scscf", "scscf_name", "sip:scscf2.ims.smilecoms.com:6060")
...

3.13. store_profile_dereg (int)

Should the subscription profile be stored on de-registration

Default value 0.

Example 1.13. Set store_profile_deregparameter

...
        modparam("ims_registrar_scscf", "store_profile_dereg", 1)
...

3.14. cxdx_dest_realm (string)

Destination realm to be used in Diameter messages

Default value "ims.smilecoms.com"

Example 1.14. Set cxdx_dest_realmparameter

...
        modparam("ims_registrar_scscf", "cxdx_dest_realm", "my.domain,org")
...

3.15. cxdx_forced_peer (string)

FQDN of Diameter Peer (HSS) to use for communication (SAR). If you use this, the routing defined in your diameter xml configuration file (CDP) will be ignored and as a result you will lose the benefits of load balancing and failover.

Default value NULL (none)

Example 1.15. Set cxdx_forced_peerparameter

...
        modparam("ims_registrar_scscf", "cxdx_forced_peer", "hss.ims.smilecoms.com")
...

3.16. append_branches (integer)

The parameter controls how lookup function processes multiple contacts. If there are multiple contacts for the given username in usrloc and this parameter is set to 1, Request-URI will be overwritten with the highest-q rated contact and the rest will be appended to sip_msg structure and can be later used by tm for forking. If the parameter is set to 0, only Request-URI will be overwritten with the highest-q rated contact and the rest will be left unprocessed. This parameter can be modified via Kamailio config framework.

Default value is 0 (disabled)

Example 1.16. Set cxdx_forced_peerparameter

...
        modparam("ims_registrar_scscf", "append_branches", 1)
...

3.17. method_filtering (integer)

Tells if the contact filtering based on supported methods should be performed during lookup. It's enabled only if it has a non zero value.

Default value is 0 (disabled)

Example 1.17. Set cxdx_forced_peerparameter

...
        modparam("ims_registrar_scscf", "method_filtering", 1)
...

3.18. user_data_always (integer)

If specified this will make the S-CSCF always request user data from HSS.

Default value is 0 (disabled)

Example 1.18. Set user_data_alwaysparameter

...
        modparam("ims_registrar_scscf", "user_data_always", 1)
...

3.19. error_reply_code (int)

In certain error conditions, the S-CSCF may not be able to process the request (e.g. in case of database failures). Per default and according to the Specs, the S-CSCF would return a 500 error in this case. However, according to the SIP-Specs for DNS-SRV, this won't trigger a failover, which may be desired.

This parameter let's you override the default 500 with another return-code (e.g. 503) in order to get the desired behaviour.

Default value is 500.

Example 1.19. Set error_reply_code parameter

...
        modparam("ims_registrar_scscf", "error_reply_code", 503)
...

4. Functions

4.1. save(async_reply_route, domain)

The function processes a REGISTER message. It can add, remove or modify usrloc records depending on Contact and Expires HFs in the REGISTER message. On success and when called from the REQUEST_ROUTE, 200 OK will be returned listing all contacts that are currently in usrloc. On an error, error message will be sent with a short description in reason phrase. In case of internal errors the function will return FALSE, otherwise a force to exit the cfg is file is actioned by returning 0 (asynchronous processing)

Meaning of the parameters is as follows:

  • async_reply_route- the route to execute after the save has completed. This is required because the save function is executed asynchronously (Diameter).

  • domain- Logical domain within registrar.

This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE

Example 1.20. save usage

...
if (!impu_registered("location")) {
   save("PRE_REG_SAR_REPLY","location");
}
...

4.2. lookup(domain)

This function extract the IMPU from the Request-URI and tries to find all registered contacts in usrloc. If there are no such contacts, -1 is returned. If there are, Request-URI will be rewritten with the contact that has the highest q value. The rest of the contacts will be appended to the sip msg structure (if append_branches is set) and can be later used by TM module for forking for example...

If the method filtering option is enabled, the lookup function will only return contacts that support the method of the request being processed (see allows header)

Meaning of the parameters is as follows:

  • domain - Logical domain within registrar.

Return codes:

  • -1 - Not found

  • -2 - Found, but method not allowed (check Allows header for INVITE, MESSAGE, etc).

  • -3 - Error occurred internally during processing

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE

Example 1.21. lookup usage

...
lookup("location");
switch ($retcode) {
    case -1:
    case -3:
        sl_send_reply("404", "Not Found");
        exit;
    case -2:
        sl_send_reply("405", "Not Found");
        exit;
};
...

4.3. lookup_path_to_contact(uri)

This function take a URI and tries to find the contact in usrloc. If the contact is found and has a path set, then a path header is added to the SIP message so it can be loose routed.

Meaning of the parameters is as follows:

  • uri - URI of contact to lookup

Return codes:

  • 1 - Success

  • -1 - Failure

This function can be used from REQUEST_ROUTE, FAILURE_ROUTE

Example 1.22. lookup usage

...
lookup_path_to_contact($ruri);
...

4.4. unregister(domain)

This function will remove all bindings for the IMPU found in the Request-URI.

Meaning of the parameters is as follows:

  • Domain- Logical domain within registrar.

This function can be used in REQUEST_ROUTE, FAILURE_ROUTE

Example 1.23. unregister usage

...
unregister("location");
...

4.5. assign_server_unreg(aysnc_reply_route, domain, direction)

TBD

used in REQUEST_ROUTE

4.6. impu_registered(domain)

This function checks if the IMPU in the To header is registered in usrloc.

Meaning of the parameters is as follows:

  • domain- Logical domain within registrar.

Return codes:

  • 1 - True, IMPU exists in registered state in usrloc

  • -1 - False, IMPU not registered

This function can be used in REQUEST_ROUTE, FAILURE_ROUTE

Example 1.24. impu_registered usage

...
impu_registered("location");
switch ($retcode) {
    case -1:
        sl_send_reply("404", "Not Found");
        exit;
    case 1:
        #true, continue with normal processing
};
...

4.7. term_impu_registered(domain)

This function checks if the IMPU in the Request-URI is registered in usrloc.

Meaning of the parameters is as follows:

  • domain- Logical domain within registrar.

Return codes:

  • 1 - True, IMPU exists in registered state in usrloc

  • -1 - False, IMPU not registered

This function can be used in REQUEST_ROUTE, FAILURE_ROUTE

Example 1.25. term_impu_registered usage

...
term_impu_registered("location");
switch ($retcode) {
     case -1:
          sl_send_reply("404", "Not Found");
          exit;
     case 1:
          #true, continue with normal processing
};
...

4.8. reg_fetch_contacts(domain, uri, profile)

The function fetches the contacts for 'uri' from table 'domain' to pseudo-variable $imssulc(profile) [imssulc = ims scscf ulc].

Meaning of the parameters is as follows:

  • domain - Name of table that should be used for the lookup of contact addresses.

  • uri - The SIP URI address of the user which to fetch the contact addresses for. It can contain pseudo-variables that are evaluated at runtime.

  • profile - Name of $imssulc pseudo-variable profile that will store the fetched contacts. It is a static string.

This function can be used in REQUEST_ROUTE, FAILURE_ROUTE

Example 1.26. reg_fetch_contacts usage

...
reg_fetch_contacts("location", "$ru", "callee");
reg_fetch_contacts("location", "sip:user@kamailio.org", "caller");
...

4.9. reg_free_contacts(profile)

The function frees the contacts from pseudo-variable $ulc(profile). Should be called to release the content of a profile. Anyhow, fetching a new contact addresses set over a profile will release any existing data in that profile.

Meaning of the parameters is as follows:

  • profile - Name of $imssulc pseudo-variable profile that stores the contacts. It is a static string.

This function can be used in REQUEST_ROUTE, FAILURE_ROUTE

Example 1.27. reg_free_contacts usage

...
reg_free_contacts("callee");
...

4.10. can_subscribe_to_reg(domain)

This function checks to see that a SUBSCRIBE request is authorised to subscribe to the particular identity. Only 3 entities can subscribe:

  • The user agent to it's own state

  • The P-CSCF specified in the path header for that user

  • Application Server (AS) not yet implemented

Meaning of the parameters is as follows:

  • domain - Logical domain within registrar.

This function can be used in REQUEST_ROUTE

Example 1.28. can_subscribe_to_reg usage

...
if (can_subscribe_to_reg("location")){
     $var(ret)= subscribe_to_reg("location");
}
...

4.11. subscribe_to_reg(domain)

Save the subscription to the REG event for the UAC or the appropriate P-CSCF (in the path to the UAC).

Meaning of the parameters is as follows:

  • domain - Logical domain within registrar.

This function can be used in REQUEST_ROUTE

Example 1.29. subscribe_to_reg usage

...
if (can_subscribe_to_reg("location")){
     $var(ret)= subscribe_to_reg("location");
}
...

4.12. can_publish_reg(domain)

This function checks to see that a PUBLISH request is authorised to publish for a particular identity. Only 3 entities can publish:

  • The user agent to it's own state

  • The P-CSCF specified in the path header for that user

  • Application Server (AS) not yet implemented

Meaning of the parameters is as follows:

  • domain - Logical domain within registrar.

This function can be used in REQUEST_ROUTE

Example 1.30. can_publish_reg usage

...
if (can_publish_reg("location")){
    $var(ret)= publish_reg("location"); 
}
...

4.13. publish_reg(domain)

Save the publish to the REG event for the UAC or the appropriate P-CSCF (in the path to the UAC).

Meaning of the parameters is as follows:

  • domain - Logical domain within registrar.

This function can be used in REQUEST_ROUTE

Example 1.31. publish_reg usage

...
if (can_publish_reg("location")){
    $var(ret)= publish_reg("location"); 
}
...

5. RPC Commands

exported RPC commands.

5.1. regscscf.dereg_impu

Initiate network de-register of IMPU

6. Statistics

Exported statistics are listed in the next sections.

6.1. registered contacts

Number of AOR contacts in registered state - cannot be reset.

6.2. impus

Number of IMPUs - cannot be reset.

6.3. expired contacts

Number of expired contacts - can be reset.

Chapter 2. Frequently Asked Questions

2.1. Where can I find more about Kamailio?
2.2. Where can I post a question about this module?
2.3. How can I report a bug?

2.1.

Where can I find more about Kamailio?

Take a look at https://www.kamailio.org/.

2.2.

Where can I post a question about this module?

First at all check if your question was already answered on one of our mailing lists:

E-mails regarding any stable Kamailio release should be sent to and e-mails regarding development versions should be sent to .

2.3.

How can I report a bug?

Please follow the guidelines provided at: https://github.com/kamailio/kamailio/issues.