WIN to CAMEL Conversion Methodology for Inter-Standard ... · PDF fileWIN to CAMEL Conversion Methodology for Inter-Standard Roaming for Subscribers on Real Time Charging Rajarshi

WIN to CAMEL Conversion Methodology for Inter-Standard Roaming for Subscribers on Real Time Charging

Rajarshi Sanyal

Engineering and Operations Expert – Roaming and Signalling Belgacom International Carrier Services (BICS)

[email protected]

Abstract Migration of the CDMA and GSM networks worldwide to LTE is a long drawn process. Even after

migration, the 2G/3G and the CDMA Networks will coexist and will prevail for years. So enabling roaming between CDMA and GSM network is an unending endeavour. As per CDG (CDMA Development Group) there are presently 560 million plus CDMA subscribers worldwide. While there is a defined standard for basic Inter-standard Roaming for actuating ANSI 41 to MAP conversions, the methodology for actuating a protocol conversion between CAMEL (GSM) to WIN (CDMA) is still not defined. CAMEL and WIN are the key protocols for Real Time Charging for prepaid customers. So the inter conversion of these two protocols is a must for the success of Inter standard roaming. This paper attempts to set out the technology for realising both way Interworking between WIN and CAMEL protocols to facilitate roaming for the prepaid customers and thereby enhance the roaming penetration.

Keywords: WIN, CAMEL, ANSI 41, MAP, IIF-G, CDG

1. Introduction

In the present mobile communication landscape we envisage roaming across 4 access topologies. They are :

1. LTE 2. WiFi 3. GSM/UMTS 4. CDMA

Enabling roaming between these different technologies faces some key challenges :

1. Basic Protocol Conversion at the core network : MAP (GSM) IS41(CDMA)[4] DIAMETER (LTE) RADIUS(WiFi).

2. Managing authentication across the domains 3. Enabling voice (SS7/TDM SIP/RTP) and data roaming (GTP MIP PMIP) 4. Protocol conversions for real time charging.

The challenges of interoperability, roaming and real time charging between LTE and GSM Networks have been addressed in [7]. In this paper, we address the 4th issue. We set out the technology for enabling roaming between CDMA and GSM for the subscriber which are charged in real time based on Intelligent Network protocols. Below are the protocol standards across the 2 domains. For CDMA:

IS-826 commonly referred to as WIN (Wireless intelligent Network) [5] IS-848 (mainly for Location Based Services with some application in real time charging) [6]

For GSM:

CAMEL (Customised Application for Mobile Enhanced Logic) Phase I,II,III,IV

WIN to CAMEL Conversion Methodology for Inter-Standard Roaming for Subscribers on Real Time Charging Rajarshi Sanyal

Journal of Communications and Information Sciences(JCIS) Volume3. Number2. April. 2013 doi: 10.4156/jcis.vol3.issue2.3

Standard do exist that’s defines roaming principles between GSM and CDMA for postpaid : J-STD-038 [1] from IFAST. However standards do not exist to enable GSM CDMA roaming for prepaid customers, hence we address this topic in this paper. In Figure 1, we demonstrate the high level process to intercept a call leg at the Service Switching Functionality in the Telecom Switch A where we have an incumbent call from A party. The call is put on hold while the Switch invokes a query towards the AAA database for authentication and authorisation. In case this yields a positive result, the call is terminated to Switch B.

Fig 1.Basic IN call leg

1.1. Key Issues for protocol conversion between WIN and CAMEL.

The primary issues to actuate protocol conversion between WIN and CAMEL are as follows:

– Different philosophies for call control o In GSM call control is actuated by SCP. It periodically invokes CAMEL Apply Charging

messages towards the SSP intimating the Maximum call duration. o In CDMA SCP just enquires from the SSP by Call Control Directive (CCDIR) messages whether

the call is alive or not. The SSP enjoys the driving seat – State machine concepts have deviations o CAMEL is based on Dialogues. We have TCAP Begin / Continue / End. Camel can support both

SCCP Protocol Class 0 (without sequence control) and SCCP Protocol Class 1 messages.UDT and XUDT are both supported

o In WIN (and especially in CDMA) , there are no dialogues. We have only the query and the response. Only SCCP Protocol Class 0 messages are supported.XUDTs are not supported in CDMA.

– Late call forwarding related rules are different [8]

o In GSM : forwarded leg is tromboned from the visited MSC (unless there are optimal routing solutions).

o In CDMA: third leg is always anchored from GMSC. – Trigger download o In CAMEL: Only SCP address is downloaded during the Location update process. o In WIN: The entire list of Originating triggers are downloaded and armed during the Registration

process in the parameter ‘Trigger Address List’. SCP address is also downloaded. – Routing issues o In CAMEL: 2 way Global Title (GT address in both SCCP calling and called party) are used.

TT=0 is always used. o In WIN: PC/SSN based routing or 1 way GT are still being in use is some countries. Different TTs

are used for various numbering plans and adjuncts. CAMEL [3] and WIN inter conversion can be actuated by the Inter standard and Interworking Function Gateway (IIF-G). The IIF-G standards for basic MAP[2] to ANSI 41 conversion are defined in the


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Table 1: Mapping for CDMA and GSM parameters GSM Message Parameter CDMA Message Parameter

MAP_INSERT_ SUBSCRIBER_DATA

O-CSI registration notification_rr

Orig_Attmpt_Auth, Call_Rout_Add_Av, O_Answer/O_Disconnect in the TAL (Trigger address list)


T-CSI registration notification_rr

*NIL


SMS CSI registration notification_rr

**NIL


SCF Address, E.164

registration notification_rr

SCP Point Code (IIF-G SCP Emulator)


Win Operations Capability …CCDIR \ Connect Resource

In GSM CAMEL scenario, IN triggers are sent to the SCP by the Originating MSC. Hence

termination triggers should not be sent to the CDMA Serving MSC.

There is no parameter equivalent to SMS_CSI in CDMA, hence for any SMS_MO / SMS-MT cases to the inroaming GSM subscriber the IIF G GSM MSC Emulator shall communicate first with the GSM SCP based on the SMS_CSI received.

The call flow explaining the mapping of the Registration Notification (ANSI 41) to GSM MAP is

shown in the diagram in Fig 3.

Registration call flow

MSCGSM

VPLMN HLRIIF G

REGNOT [MIN, ESN, MSCID, SenderIN

MAP_LOCUPDT [IMSI, MSCISDN of IIF MSC Emulator]

MAP_INS_SUB_DATA [IMSI, SUB PROFILE, O/T CSI FLAG, SCF ISDN ]

map_ins_sub_data_ack

map_loc_updt_ack [ MSISDN, HLRISDN, Supplementary Service Info]

regnot_rr [MDN, HLRID (IIF), Profile with TAL]

Fig 3. Mapping GSM Location Update and CDMA Registration Notification


2.1 Call Origination of GSM in CDMA Network

CDMA MSC on encountering WIN Call Origination triggers for the subscriber, routes ORREQ/ANLYZD/OANS/ODISC messages to IIF SCP Emulator based on the IIF Point code / IIF E.212 Address received in the Trigger Address List of regnot_rr message. IIF SCP Emulator shall convert the IS-826 messages received from CDMA Network to the appropriate GSM CAMEL messages. Origination call flow for a CAMEL GSM Subscriber in CDMA network is shown in Fig 4.

Fig 4. Voice Call Origination of GSM in CDMA Network

Once the call origination request (IDP) is validated by the GMS SCP, it sends RRBE message

followed by APPLY_CHARGING MESSAGE with the allowed call duration. SCP sends periodic Apply Charging message to the serving MSC to update the allowed talk time till the subscribers account expires.

IIF SCP Emulator on receiving a positive acknowledgement from the GSM SCP with allowed call duration should formulate an orreq_rr message with Action code = ‘Continue Processing’.


IIF SCP Emulator shall respond to the ANLYZD message with positive acknowledgement since the call origination is already validated by the GSM SCP. So the IIF-G shall respond with Continue Processing for all ANLYZD message invoked by the CDMA MSC.

IIF SCP Emulator shall validate the existence of the call context in the MSC by sending CCDIR

message periodically every 30 second. IIF SCP Emulator shall send CCDIR message with Action Code = Disconnect call once the

allowed call Duration for the subscriber expires.

2.2 Call Termination for a GSM Subscriber in CDMA Network

In GSM CAMEL scenario, IN triggers are sent to the SCP by the Originating MSC. Hence termination triggers are not be sent to the CDMA Serving MSC.For the same reason the serving CDMA MSC would not send any trigger to IIF G SCP.For a termination call GSM MSC/GMSC sends MAP_SRI message to GMS HLR with O/T CSI Suppress Flag disabled to obtain the CAMEL capabilities and the SCP address. The GSM HLR as part of the call processing sends MAP_PSI (Provide Subscriber Info) to serving MSC, querying the subscriber status and location. IIF-Gateway shall invoke a POSREQ (IS_848) message to the serving CDMA MSC to obtain the location and status of the GSM subscriber. POSREQ message shall be routed on 1way GTT with the MSCIN and TT=2 or on to MSC PC. The originating GSM MSC on receiving the CAMEL capabilities and SCP address communicates with the GSM SCP for authorizing the call. Once the call origination is authorized, the originating MSC/GMSC sends MAP_SRI to GSM HLR with O/T CSI Suppress Flag enabled, GSM HLR further invokes MAP_PRN to IIF_Gateway to obtain the MSRN. IIF-G HLR Emulator shall formulate a ROUTERQ message with the IMSI converted to the corresponding MIN, and shall route the message to serving MSC to obtain the TLDN. The TLDN received in the route_req response message shall be converted to MSRN and shall be forwarded to the GSM HLR. After the call is setup through ISUP messages, no MAP messages are sent to IIF-G and also no IS 41/826/848 messages are to be conveyed between IIF-G and CDMA network. The end to end call flow is in Fig.5.

G S M G M S C I I F

G a t e w a yG S M S C P

G S M H L R

I A M M A P P S I

m a p p s i ( L o c , s u b s t a t u s )

M A P S R I ( O / T C S IS u p p r e s s =

F a ls e )

m a p s r i ( O / T c a p a b i l i t i e s ,S C P E . 1 6 4 A d d r e s s )

I D P ( D P 1 2 ) ( s e r v i c e k e y , c a l l e d p a r t y n o , c a l l i n gp a r t y n o )

R R B E ( T A n s / T N o A n s : D P 1 4 , 1 5 )

R R B E ( T D is c o n n e c t : D P 1 7 )

A p p ly c h a r g in g ( m a x c a l l d u r a t i o n )

M A P S R I ( O / T C S IS u p p r e s s = T r u e )

S p e e c h

M A P P R N

m a p p r n ( m s r n )m a p s r i ( m s r n )

A C M

E R B E ( T A n s : D P 1 5 )

R E L

E R B E ( T D is : D P 1 7 )

C A P R e le a s e

A p p l C h a r g i n g ( C a l l r e s u l t , d u r a t i o n )

R E L

R L C R L C

A N M

A C M

A N M

C D M AM S C

P O S R E Q [ P O S C O D E , M I N ]

p o s r e q _ r r [ S T A T U S ,L O C A T I O N I N F O ]

I A M

R O U T R E Q [ M I N , M S C I N ]

R o u t e r e q [ T L D N ]

Fig 5. Voice call Termination Call Flow


2.3 SMS Transactions for a GSM CAMEL Inroamer

SMS_MO related signalling between GSM SCP and IIF_G GSM MSC Emulator shall be based on CAMEL phase 3[3]. 1) When the GSM inroamer originates a SMS, the message first reaches his serving MSC, which

invokes SMDPP message with bearer data to CDMASTP, the CDMASTP further routes the message to IIF CDMA SMSC Emulator.

2) IIF SMSC Emulator on receiving the SMDPP_MO message from CDMA MSC shall check the subscriber’s profile. If the subscriber is a CAMEL subscriber and if the profile is having SMS-CSI flag set, then the IIF-G GSM MSC emulator shall invoke an IDP_SMS message to the GSM SCP.

3) IIF G MSC Emulator based on the response from the SCP shall invoke Forward_SM_MO to the

GSM SMSC. If there is no positive acknowledgement from the SCP then the SMS should not be forwarded to the GSM SMSC.

Call flow for a SMS_MO is provided in Fig 6.

MSCGSM

VPLMN SCP

IIF G

SMDPP_MO [MIN,A Party MDN, B party MDN]IDP_SMS [Service Key, B party MSISDN, A

party MSISDN, IMSI]

RRSMSE [Submitted / Failed]

ERSMSE [Submitted/Failure]

GSM VPLMN SMSC

Forward_SM_MO [A party IMSI, B party Number, A party MSISDN]

forward-sm_mo[Ack]

ReleaseSMS

smdpp_mo_ack

Fig 6. SMS Mobile Originating Call Flow

2.4 SMS_MT for a GSM Inroamer in CDMA Network

SMS_MT related signalling between GSM SCP and IIF_G GSM MSC Emulator shall be based on CAMEL phase 4.

1. When there is a SMS to be delivered to a GSM inroamer, then the IIF-G GSM MSC Emulator receives Forward_SM_MT message from the GSM SMSC.

2. IIF-G GSM MSC Emulator shall communicate with the GSM SCP if the subscriber is provisioned with a CAMEL based SMS terminating service (this information comes in SMS_CSI at the time of registration). The signalling between IIF-G GSM MSC Emulator and GSM SCP for SMS_Termination shall be based on CAMEL phase 4 specification

3. IIF-G shall initiate SMS Termination process with the CDMA MSC only after receiving a positive response from the GSM SCP.

4. IIF-G CDMA SMSC Emulator after receiving a positive response from GSM SCP shall formulate SMDPP_MT message with the B party IMSI and MSISDN changed to the corresponding MIN and MDN. The message shall then be routed to the CDMA Serving MSC.

5. Call flow is in Fig 7.


MSCGSM

VPLMN SCP

IIF G

IDP_SMS [Service Key, B party MSISDN, A party MSISDN, B party IMSI]

RRSMSE [Submitted / Failed]

ERSMSE [Submitted/Failure]

GSM VPLMN SMSC

ReleaseSMS

smdpp_mt_rr

Forward_SM_MT [B party IMSI, B party MSISDN, A party MSISDN

SMDPP_MT(Bparty, B party MIN, A party Number]

Fig7. Call flow for SMS_MTs provided below.

3. CDMA WIN Subscriber roaming in the GSM Network

3.1 Registration of the CDMA subscriber in the GSM CAMEL Network

When a Location Update happens for the CAMEL subscriber, the following parameters are

downloaded in the GSM VLR with the. O \ T CSI Flag, SMS CSI flag SCF Address – This is the E.164 Address assigned to the SCP, which serves the subscriber. When a Registration Notification happens for a WIN subscriber, the following parameters are downloaded as a part of the Trigger Address List. Originating Triggers : Origination_Attempt_Authorized, Calling_Routing Address_Available,

O_Answer \ O_Disconnect TerminatingTriggers: Initial_termination,Location, Called_Routing_Address_Available,

T_Answer \ T_Disconnect Win Operations Capability …CCDIR \ Connect Resource. Point Code of the SCP. Registration call flow

This section explains the Registration of a WIN (CDMA) subscriber in GSM Network


GSM MSC CDMA HLRIIF G

REGNOT [MIN, ESN, MSCID, SenderIN

MAP_LOCUPDT [IMSI, MSCISDN of IIF MSC Emulator]

MAP_INS_SUB_DATA [IMSI, SUB PROFILE, O/T CSI FLAG, SCP ISDN(E.164 address) ]

map_ins_sub_data_ack

map_loc_updt_ack [ MSISDN, HLRISDN, Supplementary Service Info]

regnot_rr [MDN, HLRID (IIF), Profile with *TAL(PC of SCP)]

IIF-G on receiving the SCP PC in regnot response, maps the SCP PC to E.164

SCP Address as required for GSM addressing.

Fig 8: Mapping a MAP Location Update with CDMA (ANSI) Registration Notification

Triggers downloaded in the Trigger Address List (TAL) are Origination_Attempt_Authorized, Calling_Routing Address_Available, O_Answer \ O_Disconnect,T_Answer and T_Disconnect. When the CDMA subscriber registers in the GSM network, the GSM MSC forwards the

MAP_LOCATION_ UPDATE to the IIF-G, which in turn Invokes the REGNOT towards the HLR.

The HLR , in return to the REGNOT , downloads the TAL (The SCP PC and the Triggers in the IIF-G).

Triggers downloaded in the TAL are Origination_Attempt_Authorized, Calling_Routing Address_Available, O_Answer \ O_Disconnect,T_Answer and T_Disconnect. The IIF-G, while invoking INSERT_SUBSCRIBER_DATA message to the GSM MSC, it has to

populate an E.164 address of the SCP in SCF address field in INSERT_SUBSCRIBER_DATA message .Hence the IIF-G on receiving PC of the SCP in the regnot_rr , maps the SCP Point Code to a E.164 number as required in GSM network.

For Successful Registration of WIN Subscriber in GSM Network, IIF-G shall map the parameters coming in the regnot_rr message, stores in a dynamic table and formulates the GSM MAP_INSERT_SUBSCRIBER _DATA according to Table 2. The call flow is provided in Fig 8.

Table 2 : Mapping for the parameters related to the Location Update process

GSM Message Parameter CDMA Message Parameter MAP_INSERT_ SUBSCRIBER_DATA

O-CSI registration notification_rr

Orig_Attmpt_Auth, Call_Rout_Add_Av, O_Answer/O_Disconnect in the TAL


NIL registration notification_rr

T_Answer,T_Disconnect(If the subscriber is roaming)


SCF Address, E.164


SPC of SCP

3.2 Call Origination of CDMA WIN Subscriber in GSM Network

For a CDMA WIN subscriber roaming in GSM network, it is proposed that the CDMA SCP should

function as a dual stack SCP (GSM and CDMA). If the CDMA subscriber is latched in the GSM network and is making an Originating call, then the CAMEL triggers (from the GSM network) can come directly to the CDMA SCP. Hence the message need not be taken through the IIF-G, thereby reducing the number of transactions considerably.

The IIF‐G

should house

a Table which

maps the Point

code of SCP


Mobile Origination call flow for a CDMA subscriber in GSM network is shown below.

Fig 9 .Call Origination of GSM in CDMA Network

The SSP (GSM MSC) invokes an IDP to CDMA STP, which does Intermediate GT, and forwards the IDP to the CDMA SCP. The Message is invoked by the GSM MSC based on the SCP Address (E.164)forwarded by the IIF-G in the MAP_INSERT_SUBS_DATA during registration of the CDMA Subscriber in GSM Network.

On Receiving the IDP, the CDMA DUAL Stack SCP , invokes the RRBE

(O_ANS,NO_ANS,O_DISC) followed by APPLY_CHARGING message with allowed call duration .

SCP sends periodic Apply Charging message to the serving MSC to update the allowed talk time till the subscribers account expires.

Note: In case the SCP at CDMA is not Dual Stack (GSM/CDMA) IIF G needs to actuate protocol conversion (IDP to ORREQ and then the subsequent messages)

3.3 Call Termination to a CDMA Subscriber in GSM Network

For call termination to a CDMA WIN subscriber roaming in GSM network , it proposed that the

HLR shall download all the termination triggers ( Initial_Termination, Location and Called_Routing_Address_Available , T_ANSWER , T_DISCONNECT) in the GMSC in response to the first LOCREQ. The GMSC should be able to invoke TANSWER and TDISCONNECT depending on the ISUP ANM and the ISUP REL arriving at the GMSC respectively. The following sections explain the same in details. In CDMA WIN network, the Termination triggers , Initial_Termination, Location and Called_Routing_Address_Available are armed in the G-MSC and the T_Answer and T-Disconnect triggers are armed in the Serving –MSC(Serving B-party).


In a G-MSC that if the T_Answer and T_Disconnect triggers are armed dynamically in the locreq_rr, then the GMSC is able to invoke the TANSWER and TDISCONNECT according to the ISUP Answer and Release messages. Call flow is provided in Fig 9.

3.4 Termination Call Flow

When a Terminating call arrives for a CDMA WIN subscriber roaming in GSM Network, the

Sequence of events which occurs is as follows: The G-MSC detects the Mobile Termination triggers and sends a LOCREQ to the HLR associated

with the MS, this association is made through the Dialed MS address digits

The HLR sends the locreq to the G-MSC with the TRIGADDRLIST parameter set to indicate the Initial_Termination, Location and Called_Routing_Address_Available , *T_ANSWER , *T_DISCONNECT triggers shall be armed. TAL comprises of Initial_Termination, Location and Called_Routing_Address_Available , T_ANSWER , T_DISCONNECT.

The TAL also consists of the Point Code of CDMA SCP. The G-MSC MSC detects the Initial_Termination trigger and sends an ANLYZD (On PC/SSN ) to

the SCP indicated in the TRIGADDRLIST parameter. The TRIGTYPE parameter is set to indicate the Initial_Termination trigger is detected .

The SCP determines the called subscriber has PPC active and that the account balance is above the threshold level. The SCP sends an anlyzd to the Originating MSC. The DMH_SVCID parameter is set to indicate that PPC was invoked.

The Originating MSC detects the Location trigger and sends a LOCREQ to the HLR. The

TRIGTYPE parameter is set to indicate the Location trigger was encountered. The HLR determines call processing shall continue and sends a ROUTREQ to the IIF-G with the

MIN of CDMA Subscriber. The IIF-G converts the MIN to IMSI and forwards the MAP_PRN message to the GSM MSC . The GSM MSC allocates MSRN in the map_prn , which is converted to TLDN by the IIF-G and

forwarded to CDMA MSC.

The call flow is provided in Fig 10.


o

o o

. 4.

[1][2][3][4][5][6][7]

[8][9]

The HLR sesubscriber.

On receiving

When the CT_DISCONN

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WIN to CAMEL Conversion Methodology for Inter-Standard ... · PDF fileWIN to CAMEL Conversion Methodology for Inter-Standard Roaming for Subscribers on Real Time Charging Rajarshi