The IMS Charging Module

Jason Penton

Smile Communications

Carsten Bock

ng-voice GmbH

Carlos Ruiz Diaz

ng-voice GmbH

Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Understanding Charging in the IP-Multimedia-Subsystem (IMS)
3.1. Offline Charging (Rf)
3.2. Online Charging (Ro)
3.3. Online Charging (Ro): A practical example
4. Parameters
4.1. hash_size(int)
4.2. interim_update_credits(int)
4.3. timer_buffer(int)
4.4. ro_forced_peer(string)
4.5. ro_auth_expiry(integer)
4.6. ro_auth_expiry(integer)
4.7. cdp_event_latency(integer)
4.8. cdp_event_threshold(integer)
4.9. cdp_event_latency_log(integer)
4.10. single_ro_session_per_dialog(integer)
4.11. origin_host(string)
4.12. origin_realm(string)
4.13. destination_host(string)
4.14. destination_realm(string)
4.15. service_context_id_root(string)
4.16. service_context_id_ext(string)
4.17. service_context_id_mnc(string)
4.18. voice_service_identifier(string)
4.19. voice_rating_group(string)
4.20. video_service_identifier(string)
4.21. video_rating_group(string)
4.22. service_context_id_mcc(string)
4.23. service_context_id_release(string)
4.24. custom_user_avp (avp string)
5. Functions
5.1. Ro_CCR(route_name, direction, reservation_units, domain, incoming_trunk_id, outgoing_trunk_id
5.2. Ro_set_session_id_avp()
6. Statistics
6.1. Initial CCRs (initial_ccrs)
6.2. Interim CCRs (interim_ccrs)
6.3. Final CCRs (final_ccrs)
6.4. Successful initial CCRs (successful_initial_ccrs)
6.5. Successful interim CCRs (successful_interim_ccrs)
6.6. Successful final CCRs (successful_final_ccrs)
6.7. Failed initial CCRs (failed_initial_ccrs)
6.8. Failed interim CCRs (failed_interim_ccrs)
6.9. Failed final CCRs (failed_final_ccrs)
6.10. CCRs average response time (ccr_avg_response_time)
6.11. CCRs responses time (ccr_responses_time)
6.12. CCRs requests, which ended with a timeout (ccr_timeouts)
6.13. Billed seconds (billed_secs)
6.14. Killed calls (killed_calls)

List of Examples

1.1. hash_sizeparameter usage
1.2. interim_update_creditsparameter usage
1.3. timer_bufferparameter usage
1.4. ro_forced_peerparameter usage
1.5. ro_auth_expiryparameter usage
1.6. ro_auth_expiryparameter usage
1.7. cdp_event_latencyparameter usage
1.8. cdp_event_thresholdparameter usage
1.9. cdp_event_latency_logparameter usage
1.10. single_ro_session_per_dialogparameter usage
1.11. origin_hostparameter usage
1.12. origin_realmparameter usage
1.13. destination_hostparameter usage
1.14. destination_realmparameter usage
1.15. service_context_id_rootparameter usage
1.16. service_context_id_extparameter usage
1.17. service_context_id_mncparameter usage
1.18. voice_service_identifierparameter usage
1.19. voice_rating_groupparameter usage
1.20. video_service_identifierparameter usage
1.21. video_rating_groupparameter usage
1.22. service_context_id_mccparameter usage
1.23. service_context_id_releaseparameter usage
1.24. custom_user_avpparameter usage
1.25. Ro_CCR
1.26. Ro_set_session_id_avp

Chapter 1. Admin Guide

Table of Contents

1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Understanding Charging in the IP-Multimedia-Subsystem (IMS)
3.1. Offline Charging (Rf)
3.2. Online Charging (Ro)
3.3. Online Charging (Ro): A practical example
4. Parameters
4.1. hash_size(int)
4.2. interim_update_credits(int)
4.3. timer_buffer(int)
4.4. ro_forced_peer(string)
4.5. ro_auth_expiry(integer)
4.6. ro_auth_expiry(integer)
4.7. cdp_event_latency(integer)
4.8. cdp_event_threshold(integer)
4.9. cdp_event_latency_log(integer)
4.10. single_ro_session_per_dialog(integer)
4.11. origin_host(string)
4.12. origin_realm(string)
4.13. destination_host(string)
4.14. destination_realm(string)
4.15. service_context_id_root(string)
4.16. service_context_id_ext(string)
4.17. service_context_id_mnc(string)
4.18. voice_service_identifier(string)
4.19. voice_rating_group(string)
4.20. video_service_identifier(string)
4.21. video_rating_group(string)
4.22. service_context_id_mcc(string)
4.23. service_context_id_release(string)
4.24. custom_user_avp (avp string)
5. Functions
5.1. Ro_CCR(route_name, direction, reservation_units, domain, incoming_trunk_id, outgoing_trunk_id
5.2. Ro_set_session_id_avp()
6. Statistics
6.1. Initial CCRs (initial_ccrs)
6.2. Interim CCRs (interim_ccrs)
6.3. Final CCRs (final_ccrs)
6.4. Successful initial CCRs (successful_initial_ccrs)
6.5. Successful interim CCRs (successful_interim_ccrs)
6.6. Successful final CCRs (successful_final_ccrs)
6.7. Failed initial CCRs (failed_initial_ccrs)
6.8. Failed interim CCRs (failed_interim_ccrs)
6.9. Failed final CCRs (failed_final_ccrs)
6.10. CCRs average response time (ccr_avg_response_time)
6.11. CCRs responses time (ccr_responses_time)
6.12. CCRs requests, which ended with a timeout (ccr_timeouts)
6.13. Billed seconds (billed_secs)
6.14. Killed calls (killed_calls)

1. Overview

This module contains all methods related to the IMS charging control functions performed by an network element (e.g. a S-CSCF) over the Ro interface. This module is dependent on the CDP (C Diameter Peer) modules for communicating with a Charging-Server as specified in 3GPP specification TS xx.xxx.

Please also refer to RFC 4006 (Diameter Credit-Control Application)

2. Dependencies

2.1. Kamailio Modules

The Following modules must be loaded before this module:

  • ims_dialog

  • TM - Transaction Manager

  • CDP - C Diameter Peer

  • CDP_AVP - CDP AVP Applications

2.2. External Libraries or Applications

This modules requires the internal IMS library.

3. Understanding Charging in the IP-Multimedia-Subsystem (IMS)

Before each service usage, the charging system must be asked for permission (credit authorization). The charging server must make a decision: Either authorize or deny the session. For postpaid scenarios this is fairly easy: The charging-server only needs to collect the usage data for processing it at the end of the month. As no realtime account updating is needed, this is often called "offline-charging". For prepaid scenarios the charging server needs to know the user's account balance and it will need to update the account in real-time. This is often referred to as "online-charging".

Question: What is the double of the Radius? Answer: It's the Diameter!

As quite often, we use the Diameter-Protocol to do the Charging in the IMS. And as quite often, IMS uses a huge bunch of acronyms to describe the different interfaces: We call the diameter-interface for offline-charging the "Rf"-interface and the interface for online charging the "Ro"-interface.

Each system, that needs this credit authorization, have to be equipped with a proper charging trigger, a so-called charging-trigger-function (CTF) in order to communicate with the charging-server (also called charging-function):

3.1. Offline Charging (Rf)

For the offline charging (Rf), we have the following two diameter-messages:

  • ACR - Accounting Request

  • ACA - Accounting Answer

Each request can have the following Accounting-Record-Type:

  • START_RECORD - used to start an accounting session, typically when the application receives a SIP 200 OK acknowledging an initial SIP INVITE.

  • INTERIM_RECORD - used to update a session, for example, in the case of SIP RE-INVITE and/or UPDATE in the current SIP dialog.

  • STOP_RECORD - used to stop an accounting session, for example, when the application receives a SIP BYE message.

  • EVENT_RECORD - used for event-based accounting, e.g. a short message or similar

3.2. Online Charging (Ro)

For online charging (Ro), this get's a little bit more complicated. The charging function needs to perform credit control before allowing resource usage. The prepaid subscriber needs to exist in the charging-server and all activities must be monitored by the charging-server. We must distinguish between the following two cases:

  • Direct debiting - the amount is immediately deducted from the user's account in one single transaction. This could be for example a SMS or the ordering of a movie in case of Video-on-Demand.

  • Unit reservation - an amount is reserved by the charging-server. This is done, because the charging-server does not know yet, how many units are needed to provide the service. During the session, the used amount may be deducted and more units can be requested; at the end of the session the used sessions are reported in the final request. These sessions could be typically a voice- or video-call or a Pay-TV session, if you pay per usage.

As a result, we have the following three scenarios:

  • Immediate Event Charging (IEC) - used for simple Event-based charging

  • Event Charging with Unit Reservation (ECUR) (of type Event-based charging)

  • Session Charging with Unit Reservation (SCUR) (of type Session-based charging)

3.3. Online Charging (Ro): A practical example

But how does it look in reality? Let us make a more practical example:

Let us assume we have a subscriber, who has sufficient credit for 75 seconds of talking. The subscriber initiates a call; as we do not know, how long the call will take, we start with requesting credit for 30 seconds (CCR-Request, we could request any duration, e.g. 2 hours, but it would probably block other calls if we reserve all the required credit).

The call proceeds, so after 30 seconds we send another CCR-Request with the indication that we used the reserved 30 seconds and that we request another 30 seconds. We reduce the account of the subscriber by 30 seconds, so he has a credit of 45 seconds. Since 45 seconds is more than the requested 30 seconds, this second request can also easily be accepted and another 30 seconds can be granted. After this request, the account is at 45 seconds and we still (or again) have 30 seconds reserved.

Meanwhile the subscriber initiates a second call. We try to request again 30 seconds from the charging-server, but as our account is at 45 seconds of speaking time and since we reserved another 30 seconds for the first call, we can only grant 15 seconds for the second call. The last 15 seconds are now reserved for this subscriber; we have 45 seconds on the account of which 45 seconds are reserved.

Now the first call gets terminated: We only used 20 seconds from the granted 30 seconds. So we decrease the account of the subscriber by 20 seconds and we reduce the amount of reserved units by 30. We have 25 seconds in the account and we have still reserved 15 seconds for the second call.

As the second call is still proceeding, we will try to request another 30 seconds and we indicate, that we used the granted 15 seconds. The account is deducted by 15 seconds (the used units) and we can grant another 10 seconds for the second call, as this is the remains on the account.

After 10 seconds, no more units can be granted, so the call is teared down.

The following diagram is a graphical representation of the above example:

4. Parameters

4.1. hash_size(int)

The size of the hash table internally used to keep the Diameter-Ro-Session. A larger table is much faster but consumes more memory. The hash size must be a power of two number.

IMPORTANT: If Ro-Session's information should be stored in a database, a constant hash_size should be used, otherwise the restoring process will not take place. If you really want to modify the hash_size you must delete all table's rows before restarting the server.

Default value is 4096.

Example 1.1. hash_sizeparameter usage

...
modparam("ims_charging", "hash_size", 1024)
...

4.2. interim_update_credits(int)

How much credit should be requested interim request? At the start of the call, we request the amount of seconds as per Command. For each interim request, we would request credit for "interim_update_credits".

Default value is 30.

Example 1.2. interim_update_creditsparameter usage

...
modparam("ims_charging", "interim_update_credits", 600)
...

4.3. timer_buffer(int)

How many seconds before expiry of our credit should we request more credit?

Default value is 8.

Example 1.3. timer_bufferparameter usage

...
modparam("ims_charging", "timer_buffer", 10)
...

4.4. ro_forced_peer(string)

FQDN of Diameter Peer (OCS) to use for communication (CCR). 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 is ''.

Example 1.4. ro_forced_peerparameter usage

...
modparam("ims_charging", "ro_forced_peer", "ocs.ims.smilecoms.com")
...

4.5. ro_auth_expiry(integer)

This is the expiry length in seconds of the initiated Diameter sessions.

Default value is 7200.

Example 1.5. ro_auth_expiryparameter usage

...
modparam("ims_charging", "ro_auth_expiry", 14400)
...

4.6. ro_auth_expiry(integer)

This is the expiry length in seconds of the initiated Diameter sessions.

Default value is 7200.

Example 1.6. ro_auth_expiryparameter usage

...
modparam("ims_charging", "ro_auth_expiry", 14400)
...

4.7. cdp_event_latency(integer)

This is a flag to determine whether or slow CDP responses should be reported in the log file. 1 is enabled and 0 is disabled.

Default value is 1.

Example 1.7. cdp_event_latencyparameter usage

...
modparam("ims_charging", "cdp_event_latency", 1)
...

4.8. cdp_event_threshold(integer)

This time in milliseconds is the limit we should report a CDP response as slow. i.e. if a CDP response exceeds this limit it will be reported in the log file. This is only relevant is cdp_event_latency is enabled (set to 0).

Default value is 500.

Example 1.8. cdp_event_thresholdparameter usage

...
modparam("ims_charging", "cdp_event_threshold", 500)
...

4.9. cdp_event_latency_log(integer)

This time log level at which we should report slow CDP responses. 0 is ERROR, 1 is WARN, 2 is INFO and 3 is DEBUG. This is only relevant is cdp_event_latency is enabled (set to 0)

Default value is 0.

Example 1.9. cdp_event_latency_logparameter usage

...
modparam("ims_charging", "cdp_event_latency_log", 1)
...

4.10. single_ro_session_per_dialog(integer)

This tells the module whether it should do a single ro session per dialog no matter how many times Ro_send_CCR is called from the config file or initiate an ro session each time Ro_send_CCR is called. It is useful for IMS charging where you might want to charge for on-net originating and off-net originating calls but always have only a single ro session.

Default value is 0.

Example 1.10. single_ro_session_per_dialogparameter usage

...
modparam("ims_charging", "single_ro_session_per_dialog", 1)
...

4.11. origin_host(string)

Origin host to be used in Diameter messages to charging-server.

Default value is "scscf.ims.smilecoms.com".

Example 1.11. origin_hostparameter usage

...
modparam("ims_charging", "origin_host", "scscf.kamailio-ims.org")
...

4.12. origin_realm(string)

Origin Realm to be used in Diameter messages to charging-server.

Default value is "ims.smilecome.com".

Example 1.12. origin_realmparameter usage

...
modparam("ims_charging", "origin_realm", "kamailio-ims.org")
...

4.13. destination_host(string)

Destination host to be used in Diameter messages to charging-server.

Default value is 5s.

Example 1.13. destination_hostparameter usage

...
modparam("ims_charging", "destination_host", "ocs.kamailio-ims.org")
...

4.14. destination_realm(string)

Destination realm to be used in Diameter messages to charging-server.

Default value is "ims.smilecoms.com".

Example 1.14. destination_realmparameter usage

...
modparam("ims_charging", "destination_realm", "kamailio-ims.org")
...

4.15. service_context_id_root(string)

This defines a root-element of the Service-Context-Id AVP used in the diameter-message

The Service-Context-Id AVP is of type UTF8String (AVP Code 461) and contains a unique identifier of the Diameter credit-control service specific document that applies to the request (as defined in section RFC 4006 4.1.2). This is an identifier allocated by the service provider, by the service element manufacturer, or by a standardization body, and MUST uniquely identify a given Diameter credit-control service specific document. The format of the Service-Context-Id is:

"service-context" "@" "domain" service-context = Token

The Token is an arbitrary string of characters and digits.

'domain' represents the entity that allocated the Service-Context-Id. It can be ietf.org, 3gpp.org, etc., if the identifier is allocated by a standardization body, or it can be the FQDN of the service provider (e.g., provider.example.com) or of the vendor (e.g., vendor.example.com) if the identifier is allocated by a private entity.

Service-specific documents that are for private use only (i.e., to one provider's own use, where no interoperability is deemed useful) may define private identifiers without need of coordination. However, when interoperability is wanted, coordination of the identifiers via, for example, publication of an informational RFC is RECOMMENDED in order to make Service-Context-Id globally available.

Default value is "32260@3gpp.org".

Example 1.15. service_context_id_rootparameter usage

...
modparam("ims_charging", "service_context_id_root", "calls@kamailio-ims.org")
...

4.16. service_context_id_ext(string)

This defines the extension of the Service-Context-Id AVP used in the diameter-message.

Default value is "ext".

Example 1.16. service_context_id_extparameter usage

...
modparam("ims_charging", "service_context_id_ext", "ext2")
...

4.17. service_context_id_mnc(string)

This defines Mobile-Network-Code (MNC) of the Service-Context-Id AVP used in the diameter-message.

Default value is "01".

Example 1.17. service_context_id_mncparameter usage

...
modparam("ims_charging", "service_context_id_mnc", "42")
...

4.18. voice_service_identifier(string)

This defines the service identifier to be used for charging voice.

Default value is "1000".

Example 1.18. voice_service_identifierparameter usage

...
modparam("ims_charging", "voice_service_identifier", "1000")
...

4.19. voice_rating_group(string)

This defines the rating group to be used for charging voice.

Default value is "100".

Example 1.19. voice_rating_groupparameter usage

...
modparam("ims_charging", "voice_rating_group", "100")
...

4.20. video_service_identifier(string)

This defines the service identifier to be used for charging video.

Default value is "1001".

Example 1.20. video_service_identifierparameter usage

...
modparam("ims_charging", "video_service_identifier", "1000")
...

4.21. video_rating_group(string)

This defines the rating group to be used for charging video.

Default value is "200".

Example 1.21. video_rating_groupparameter usage

...
modparam("ims_charging", "video_rating_group", "100")
...

4.22. service_context_id_mcc(string)

This defines Mobile-Country-Code (MCC) of the Service-Context-Id AVP used in the diameter-message.

see https://en.wikipedia.org/wiki/Mobile_country_code_(MCC) for details.

Default value is "001".

Example 1.22. service_context_id_mccparameter usage

...
modparam("ims_charging", "service_context_id_mcc", "262")
...

4.23. service_context_id_release(string)

This defines Release of the Service-Context-Id AVP used in the diameter-message.

Default value is "8" (Release 8).

Example 1.23. service_context_id_releaseparameter usage

...
modparam("ims_charging", "service_context_id_release", "262")
...

4.24. custom_user_avp (avp string)

When this parameter is set and the contents of the AVP is not empty, the User-AVP in the Ro-Charging-Request will be based on the this parameter rather than on the P-Asserted or From-Header.

This parameter allows you to setup an AVP with which you can customise the user to be used in the Diameter-Request.

Default value: if not set, P-Asserted-Identity with a fallback to the From-Header is used.

Example 1.24. custom_user_avpparameter usage

...
modparam("ims_charging", "custom_user_avp", "$avp(from_user)")
...

5. Functions

5.1. Ro_CCR(route_name, direction, reservation_units, domain, incoming_trunk_id, outgoing_trunk_id

Perform a CCR on Diameter Ro interface for Charging

Meaning of the parameters is as follows:

  • route_name route to be executed upon reception of charging requests

  • direction "orig"inating or "term"inating

  • reservation_units how many units (at the moment seconds) should be reserved at the moment.

  • domain Logical domain within registrar.

  • incoming_trunk_id Identifies the trunk group from which this originates.

  • outgoing_trunk_id Identifies the trunk group where this will be terminated.

This function can be used from REQUEST_ROUTE.

This method is executed asynchronously. See example on how to retrieve return value.

Example 1.25. Ro_CCR

...
  xlog("L_DBG","Sending initial CCR Request for call\n");
    Ro_CCR("RO_ASYNC_TERM_REPLY", "term", 30, "1", "1");
}

route[CHARGING_CCR_REPLY] 
  xlog("L_DBG","cca_return code is $avp(s:cca_return_code)\n");
  switch ($avp(s:cca_return_code)) {
    case 1: #success
        xlog("L_DBG", "CCR success - will route message\n");
        route(Finalize_Orig);
        break;
    case -1: #failure
        xlog("L_ERR", "CCR failure - error response sent from module\n");
        sl_send_reply("402","Payment required");
        break;
    case -2: #error
        xlog("L_ERR", "CCR error - error response sent from module\n");
        sl_send_reply("500", "Charging Error");
        break;
    default:
        xlog("L_ERR", "Unknown return code from CCR: [$avp(s:cca_return_code)] \n");
        break;
  }
  exit;
  }
...

5.2. Ro_set_session_id_avp()

Sets the Ro session ID to an AVP for use in the config file

This function can be used from REQUEST_ROUTE or ONREPLY_ROUTE.

Example 1.26. Ro_set_session_id_avp

...
            Ro_set_session_id_avp();
            xlog("L_DBG","Ro session AVP has been set: $avp(ro_session_id)\n");
...

6. Statistics

6.1. Initial CCRs (initial_ccrs)

The number of initial CCRs, i.e., the CCRs that were sent for the initial INVITEs.

6.2. Interim CCRs (interim_ccrs)

The number of CCRs sent within established sessions.

6.3. Final CCRs (final_ccrs)

The number of CCRs sent to terminate a session.

6.4. Successful initial CCRs (successful_initial_ccrs)

Initial CCRs that ended with DIAMETER_SUCCESS response code.

6.5. Successful interim CCRs (successful_interim_ccrs)

Interim CCRs that ended with DIAMETER_SUCCESS response code.

6.6. Successful final CCRs (successful_final_ccrs)

Final CCRs that ended with DIAMETER_SUCCESS response code.

6.7. Failed initial CCRs (failed_initial_ccrs)

Initial CCRs that ended with no DIAMETER_SUCCESS response or with some other error during processing.

6.8. Failed interim CCRs (failed_interim_ccrs)

Interim CCRs that ended with no DIAMETER_SUCCESS response or with some other error during processing.

6.9. Failed final CCRs (failed_final_ccrs)

Final CCRs that ended with no DIAMETER_SUCCESS response or with some other error during processing.

6.10. CCRs average response time (ccr_avg_response_time)

Average CCA arrival time in milliseconds.

6.11. CCRs responses time (ccr_responses_time)

Total CCA arrival time in milliseconds.

6.12. CCRs requests, which ended with a timeout (ccr_timeouts)

Number of CCR-Requests, which ran into an timeout.

6.13. Billed seconds (billed_secs)

Number of seconds billed in total.

6.14. Killed calls (killed_calls)

Number of calls that were killed due to lack of credit.