The IMS Charging Module

Jason Penton

   Smile Communications
   <jason.penton@smilecoms.com>

Carsten Bock

   ng-voice GmbH
   <carsten@ng-voice.com>

Carlos Ruiz Diaz

   ng-voice GmbH
   <carlos@ng-voice.com>

   Copyright © 2013 Smile Communications

   Copyright © 2013 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. origin_host(string)
              4.11. origin_realm(string)
              4.12. destination_host(string)
              4.13. destination_realm(string)
              4.14. service_context_id_root(string)
              4.15. service_context_id_ext(string)
              4.16. service_context_id_mnc(string)
              4.17. service_context_id_mcc(string)
              4.18. service_context_id_release(string)

        5. Functions

              5.1. Ro_CCR(route_name, direction, charge_type, unit_type,
                      reservation_units)

        6. Statistics

              6.1. Initial CCRs (initial_ccrs)
              6.2. Interim CCRs (interim_ccrs)
              6.3. Final CCRs (final_ccrs)
              6.4. Sucessful initial CCRs (successful_initial_ccrs)
              6.5. Sucessful interim CCRs (successful_interim_ccrs)
              6.6. Sucessful 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. origin_hostparameter usage
   1.11. origin_realmparameter usage
   1.12. destination_hostparameter usage
   1.13. destination_realmparameter usage
   1.14. service_context_id_rootparameter usage
   1.15. service_context_id_extparameter usage
   1.16. service_context_id_mncparameter usage
   1.17. service_context_id_mccparameter usage
   1.18. service_context_id_releaseparameter usage
   1.19. Ro_CCR

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. origin_host(string)
        4.11. origin_realm(string)
        4.12. destination_host(string)
        4.13. destination_realm(string)
        4.14. service_context_id_root(string)
        4.15. service_context_id_ext(string)
        4.16. service_context_id_mnc(string)
        4.17. service_context_id_mcc(string)
        4.18. service_context_id_release(string)

   5. Functions

        5.1. Ro_CCR(route_name, direction, charge_type, unit_type,
                reservation_units)

   6. Statistics

        6.1. Initial CCRs (initial_ccrs)
        6.2. Interim CCRs (interim_ccrs)
        6.3. Final CCRs (final_ccrs)
        6.4. Sucessful initial CCRs (successful_initial_ccrs)
        6.5. Sucessful interim CCRs (successful_interim_ccrs)
        6.6. Sucessful 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
   2.2. External Libraries or Applications

2.1. Kamailio Modules

   The Following mouldes must be loaded before this module:
     * Dialog_ng
     * 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)

   3.1. Offline Charging (Rf)
   3.2. Online Charging (Ro)
   3.3. Online Charging (Ro): A practical example

   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):
   [charging1.png]

3.1. Offline Charging (Rf)

   For the offlinc 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:
   [charging2.png]

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. origin_host(string)
   4.11. origin_realm(string)
   4.12. destination_host(string)
   4.13. destination_realm(string)
   4.14. service_context_id_root(string)
   4.15. service_context_id_ext(string)
   4.16. service_context_id_mnc(string)
   4.17. service_context_id_mcc(string)
   4.18. service_context_id_release(string)

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 amout 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)

   This is the optional name of the origin host of the Diameter server
   (typically a Charging Server). If not set then realm routing is used.

   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.  origin_host(string)

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

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

   Example 1.10.  origin_hostparameter usage
...
modparam("ims_charging", "origin_host", "scscf.kamailio-ims.org")
...

4.11.  origin_realm(string)

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

   Default value is "ims.smilecome.com".

   Example 1.11.  origin_realmparameter usage
...
modparam("ims_charging", "origin_realm", "kamailio-ims.org")
...

4.12.  destination_host(string)

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

   Default value is 5s.

   Example 1.12.  destination_hostparameter usage
...
modparam("ims_charging", "destination_host", "ocs.kamailio-ims.org")
...

4.13.  destination_realm(string)

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

   Default value is "ims.smilecoms.com".

   Example 1.13.  destination_realmparameter usage
...
modparam("ims_charging", "destination_realm", "kamailio-ims.org")
...

4.14.  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 1.14.  service_context_id_rootparameter usage
...
modparam("ims_charging", "service_context_id_root", "calls@kamailio-ims.org")
...

4.15.  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 1.15.  service_context_id_extparameter usage
...
modparam("ims_charging", "service_context_id_ext", "ext2")
...

4.16.  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 1.16.  service_context_id_mncparameter usage
...
modparam("ims_charging", "service_context_id_mnc", "42")
...

4.17.  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 1.17.  service_context_id_mccparameter usage
...
modparam("ims_charging", "service_context_id_mcc", "262")
...

4.18.  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 1.18.  service_context_id_releaseparameter usage
...
modparam("ims_charging", "service_context_id_release", "262")
...

5. Functions

   5.1. Ro_CCR(route_name, direction, charge_type, unit_type,
          reservation_units)

5.1.  Ro_CCR(route_name, direction, charge_type, unit_type,
reservation_units)

   Perform a CCR on Diameter Ro interface for Charging

   Meaning of the parameters is as follows:
     * route_nameroute to be executed upon reception of charging requests
     * direction"orig"inating or "term"inating
     * charge_type"IEC" = Immediate Event Charging, "ECUR" - Event
       Charging with Unit Reservation or "SCUR" - Session Charging with
       Unit Reservation.
       (Note: At the moment only SCUR is supported)
     * unit_typeTypes of the unit to be requested
       (unused at the moment)
     * reservation_unitshow many units (at the moment seconds) should be
       reservated at the moment.

   This function can be used from REQUEST_ROUTE.

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

   Example 1.19. Ro_CCR
...
  xlog("L_DBG","Sending initial CCR Request for call\n");
  Ro_CCR("CHARGING_CCR_REPLY", "orig", "SCUR", "", "30");
}

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;
  }
...

6. Statistics

   6.1. Initial CCRs (initial_ccrs)
   6.2. Interim CCRs (interim_ccrs)
   6.3. Final CCRs (final_ccrs)
   6.4. Sucessful initial CCRs (successful_initial_ccrs)
   6.5. Sucessful interim CCRs (successful_interim_ccrs)
   6.6. Sucessful 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)

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. Sucessful initial CCRs (successful_initial_ccrs)

   Initial CCRs that ended with DIAMETER_SUCCESS response code.

6.5. Sucessful interim CCRs (successful_interim_ccrs)

   Interim CCRs that ended with DIAMETER_SUCCESS response code.

6.6. Sucessful 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.