Lý thuyết CAMEL trong mạng NGN

Prepaid subscription with roaming • The initial driving force behind CAMEL was to give mobile users with prepaid accounts the ability to bil ih id h bili roam to other networks • Many operators implement their prepaid accounts on a service node with a specialized database for the prepaid accounts • When a prepaid subscriber places a call, the MSC , consults the service node for a credit check, and the service node will respond by granting a certain connection time based on the remaining credit • If there is no credit, the service node will tell the MSC to refuse the call call • Such prepaid implementations b d on service h d l based nodes or local IN systems not allow the subscriber to place calls i other networks, b ib l ll in h k because there is no standardized interface that lets the MSC i a visited network consult a l h SC in ii d k l service node in the home network • CAMEL provides a solution because it lets the CAMEL provides a solution, because it lets the  MSC in the visited network consult the SCF in  the home network the home network Prepaid roaming with CAMEL Procedure • When the roaming subscriber tries to make an  outgoing call in a visited network, the VLR first  checks for the presence of O‐CSI checks for the presence of O CSI • If O‐CSI is found, the call requires CAMEL treatment  If O CSI is found the call requires CAMEL treatment and the SSF starts the O‐BCSM.  • The O‐CSI contains a trigger for the prepaid service at the Collected Info detection point Collected_ – The BCSM encounters this detection point after the user has dialed the destination number, and triggers the prepaid service in the SCF d h • The service logic program for the prepaid  service first checks the current credit of the  service first checks the current credit of the subscriber’s prepaid account and instructs  the SSF to allow the call to proceed for a  the SSF to allow the call to proceed for a limited amount of time.  – The amount of time that the SCF allows the SSF The amount of time that the SCF allows the SSF  for the call can depend on the visited network  location, the destination of the call, and tariff  , , tables for the visited network.  • The O‐BCSM starts a timer and completes the call Upon call expiration of the allowed time, the SSF sends another trigger to the SCF gg • As a result, the SCF updates the credit of the prepaid account and checks again whether the remaining credit is sufficient – If there is sufficient credit to continue the procedure, steps and are repeated d d • If there i i ffi i h is insufficient credit, as i the example i Fi di in h l in Figure, the SCF clears the call GPRS Core Network • The General Packet Radio Service (GPRS) system  is used by GSM mobile phones, the most  common mobile phone system in the world, for  common mobile phone system in the world for transmitting IP packets.  • The GPRS core network is the centralized part of  the GPRS system.  • It also provides support for WCDMA based 3G networks.  networks • The GPRS core network is an integrated part of The GPRS core network is an integrated part of  the GSM network switching subsystem General support functions • The GPRS core network provides mobility management,  session management and transport for Internet Protocol  session management and transport for Internet Protocol packet services in GSM and WCDMA networks.  • The core network also provides support for other additional  functions such as billing and lawful interception • Like GSM in general, GPRS module is an open standards  driven system. The standardization body is the 3GPP driven system The standardization body is the 3GPP PDP Context Activation in 2.5G PDP Context Activation in 5G • • C1 :DP for CAMEL_GPRS_PDP_Context_Establishment C2 :DP for CAMEL_GPRS_PDP_Context_Establishment_Acknowledgement MS BSS 2G-SGSN 2G SGSN 2G-GGSN 2G GGSN Activate PDP Context Request C1 Security Functions Invoke Trace Create PDP Context Request Create PDP Context Response BSS Packet Flow Context Procedures C2 Activate PDP Context Accept 50 PDP Context Activation in 3G PDP Context Activation in 3G • • C1 :DP for CAMEL_GPRS_PDP_Context_Establishment C2 :DP for CAMEL_GPRS_PDP_Context_Establishment_Acknowledgement MS UTRAN 3G-SGSN 3G SGSN 3G-GGSN 3G GGSN Activate PDP Context Request C1 Create PDP Context Request Create PDP Context Response Radio Access Bearer Setup Invoke Trace Update PDP Context Request Update PDP Context Response p p C2 Activate PDP Context Accept 51 SGSN Routing Update • A GPRS IN customer may roam to a new service area (within the same SGSN or belonging to a new SGSN) while involved in a GPRS dialogue , which is called SGSN Routing Area Update • When the roaming occurs within a SGSN it is called SGSN, Intra‐SGSN Routing Area Update, which would make no effect on IN service execution because the gprsSSF is implemented on SGSN; otherwise it is an Inter‐SGSN Routing Area Update 52 SGSN Routing Update • The old attached GPRS session would be detached from  the old SGSN and attached to the new SGSN once a GPRS  customer roams to a new SGSN, and  SGSN d • the activated PDP contexts would be handed over to the  new SGSN and reestablished there at the same time.  new SGSN and reestablished there at the same time • The gsmSCF should be informed about the transition The gsmSCF should be informed about the transition  using defined DPs and CAP messages if the customer is  currently involved in a GPRS IN service instance.  – The gsmSCF is responsible for continuing the service while  making the transition transparent to the customer.  53 SGSN Routing Update • I CAMEL3 th ld GPRS di l In CAMEL3 the old GPRS dialogue between the gsmSCF and the old  b t th SCF d th ld gprsSSF (on the old SGSN) should be closed, at the same time a new  GPRS dialogue between the gsmSCF and the new gprsSSF (on the  new SGSN) would be opened SGSN) ld b d • This is different from the GSM IN system where the CAMEL  relationship would be maintained all through the service execution  due to Anchor MSC which would be the same during a call even if a  due to Anchor MSC which would be the same during a call even if a roaming occurs.  • Though the GPRS dialogue is not the same in case of interSGSN g p , p Routing area update, the service is not disturbed from the point of  view of the GPRS customer involved.  54 Charging • The difference between the GPRS IN system and the GSM The difference between the GPRS IN system and the GSM  IN system is that charging may be on data volume in the  GPRS IN system.  • Adding new charging function to the gsmSCF is required  while maintaining the conventional service execution  while maintaining the conventional service execution mechanism.  • R l i Real‐time charging on simultaneous PDP contexts is  h i i l PDP i virtually the most difficult problem regarding charging.  • In particular, when the customer whose account is not  obeyed to overdraw  (a PPS customer) has more than one  activated PDP contexts at one time, the gsmSCF should  activated PDP contexts at one time the gsmSCF should always ensure the account balance positive while providing  duration/volume as much as possible to the customer.  55 Charging • The basic way for charging is a “request/assign” process, that is, • prior to the actual data transfer a new activated PDP transfer, context must ask for some duration/volume from the gsmSCF which then assigns fixed duration/volume (called a unit) to the PDP context according to related account balance and the customer’s status, such as the number of activated PDP contexts for him • When the assigned threshold is reached, the PDP context must apply again which invokes another again, “request/assign” process • The PDP context must return the remaining duration/volume t th account while fi i h d d ti / l to the t hil finished 56 CAMEL procedures for charging  activities Procedure ssf -> scf > ApplyChargingGPRS scf ->ssf >ssf - ApplyChargingReportGPRS l h - InitialDPGPRS - ContinueGPRS C G S - EventReportGPRS - RequestReportGPRSEvent G S - 57 CAMEL PREPAID SERVICE • The Prepaid Service (PPS) permits the GSM/UMTS service provider to collect subscriber charges before the telephony resources are actually utilized • The caller's mobile charges are debited from the subscriber's account in realtime • On originating of a call, the service provider may choose to i f inform the subscriber of their remaining allocated time h b ib f h i i i ll d i prior to the call proceeding 58 CAMEL PREPAID SERVICE • A Service Control Point (SCP) acts as a centralized database within a network and performs IN service call network, processing function • The SCP call handling uses the TCAP protocol service that provides reliable transaction associations between SCPs and SSPs • The SS i the MSC i the CA L services h SSP is h SC in h CAMEL i 59 CAMEL PREPAID SERVICE A typical PPS normal call flow are as follows The mobile station (MS), calling party, places a call using  PPS Service The MSC/SSP triggers on the calling party MSISDN, and  queries the SCP.  The SCP retrieves the subscriber's profile (using the  Calling Party MSISDN), applies appropriate tariffs,  Calling Party MSISDN) applies appropriate tariffs through tariff screening of the Called Party Number and  converts the account balance into maximum call  duration duration 60 CAMEL PREPAID SERVICE The SCP requests the MSC/SSP to arm events and to continue the call as dialed The SCP sends the Prepaid Call Tariff information to the SSP to indicate the subscribers current account balance and the call's flat and balance, call s variable rate CAMEL PREPAID SERVICE The MSC/SSP receives an answer indication, and notifies the SCP with an event response The SCP begins changing for the call by decrementing the subscriber's SCP balance information at each debit interval For each debit interval an event record i generated d is d Service Call flow 62 CAMEL PREPAID SERVICE • There is a need for MSC/SSP to send Terminating  Information to the SCP, the TCAP message flow Information to the SCP the TCAP message flow Service Message Flow 63