Conference Paper (PDF Available) · October 2013 with 249 Reads ... Data connection (mobile IP connectivity) may be obtained from the Visited mobile ... Figure 4: Voice proxy for extending CAMEL call control from DSP to ARP Since ARP.
Roaming Unbundling - Challenges and Opportunities Rogier Noldus, Lennart Norell Ericsson {rogier.noldus, lennart.norell} @ericsson.com Abstract – The European Commission (EC) mandates that from July 1, 2014, Mobile network operators (MNO) shall offer the possibility to other parties, referred to as Alternative roaming provider (ARP), to offer ‘roaming services’. When a subscriber of a national MNO, referred to as Domestic service provider (DSP) in this context, travels abroad, that person should be entitled to receive voice, data, SMS and MMS from the ARP. Hereto, the enduser has to sign up with the ARP beforehand. Users shall also be entitled to use Local breakout (LBO) when traveling abroad. Data connection (mobile IP connectivity) may be obtained from the Visited mobile network operator (VMNO), through local GGSN / PDGw. Hereto, the end-user has to sign up with the local LBO operator. ARP and LBO present specific challenges for MNOs, but also opportunities for differentiation. The present paper provides overview of the architecture impact for achieving ARP and LBO.
I. Introduction
Figure 1: End-user charging whilst roaming Alternative roaming provider The new EU regulation stipulates that the subscriber should be able to get the services, when roaming inside one of the 27 EU countries, from the ARP. Specifically: the subscriber should be charged by the ARP, for the communication services used when abroad. This is reflected in Figure 2.
Current principle for roaming comprises the transfer of communication services subscription information from HLR or HSS in HMNO’s network to MSC/VLR or MME, respectively, in VMNO’s network. Communication services can be received whilst being abroad, using the mobile infrastructure of the VMNO. Charging the end-user for the communication services used abroad remains with the HMNO. Pre-paid or post-paid may be used for that purpose. The cost of using VMNO network infrastructure by HMNO subscriber is settled between the involved operators, either directly between HMNO and VMNO or through clearing house. So, effectively, the roaming subscriber remains a subscriber of the HMNO. This is reflected in Figure 1. The subscriber is charged by Home PLMN for the communication service received abroad. A portion of the charge is paid by HPLMN operator towards the Visited PLMN operator, in the form of accounting. Figure 2: end-user charging principle for ARP charging
Whereas the end-user is charged by the ARP for services received when roaming in EU territory, the DSP charges the ARP for the usage of the network by the (roaming) subscriber; i.e. accounting is applied between DSP and ARP. The charge levied by DSP to ARP comprises, but may not be limited to, the charges levied by VPLMN to DSP, for usage, by the roaming subscriber, of that VPLMN’s network. There may be multiple ARPs within one country, i.e. multiple companies offering roaming services to subscribers of any of the MNOs or MVNOs in that country. This leads potentially to a many-to-many relationship in a country (multiple DSPs, multiple ARPs). The applicability for ARP based charging for roaming subscriber is restricted to ‘regulated services’. This includes: -
calls established towards a destination inside European Union;
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terminating calls;
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SMS or MMS sent towards a destination inside European Union;
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Terminating SMS / MMS;
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Data bearer (GPRS/3G/4G) for internet services.
The current mechanism of communication establishment is not affected, including (not exhaustive) the use of MSC in foreign network, the invocation of CAMEL service(s), if applicable, the generation of CDRs and the transfer of TAP records to HPLMN. A further aspect of the preferred solution for ARP and LBO is that the end-user shall not be compelled to change UICC (‘SIM card’) and that the phone number (MSISDN) is not affected. Not changing the SIM card ensures that basic services and supplementary services are in principle unaffected. Also, UICC authentication is unaffected; the existing shared set of authentication information between UICC and HLR (or HSS for LTE access) is used. The ARP does not ‘own’ the subscription. The essential aspect of being charged by the ARP, for communication services received when abroad, is that the DSP has to expose a charging control interface towards the ARP, enabling the ARP to apply charging for the call. This is reflected in Figure 3.
Figure 3: Exposing charging control interface to ARP Different methods of exposing the charging control towards ARP are defined, which is described in a next section. Figure 3 provides limited view on the charging interface between DSP and ARP. Only the essential communication services (voice, data, SMS, MMS) are reflected. Local breakout A second flavour of receiving communication services from a different service provider than the HPLMN operator is LBO. LBO relates to mobile internet access only, i.e. no relation to MMS. In addition, LBO may be used independently of ARP. A roaming subscriber may use ARP, LBO or both. Unlike ARP, the LBO is offered by a local (in visited country) provider. Using LBO entails the establishment of a PDP Context or Data bearer using GGSN or PDGw, respectively, in the visited network. The selection of local GGSN / PDGw is facilitated by designated APN: euinternet. Note
Obtaining local data service from a provider other than the VMNO that the subscriber is registered with, is currently not considered, but may surface as a requirement in the future.
The charging of the local data connectivity is done from the LBO service provider, which may be an independent company, i.e. not the same company as the VMNO that the subscriber is registered with. The roaming subscriber signs up as customer of the LBO provider upon entering the country or beforehand, as appropriate. Data sessions established through LBO are hence exempt from charging by HMNO. Charging records related to data sessions established through LBO may (i) not be sent to HMNO or (ii) be sent to HMNO but not used for charging by HMNO. One essential aspect of LBO is the use of designated APN. The APN is used by the mobile terminal to
select the access point into the public IP data network. The SGSN or MME analyses the APN that’s provided by the terminal, at data bearer establishment, and selects the GGSN or PDGw respectively. Depending on the subscription profile and depending on SGSN/MME configuration, APN analysis results in selection of local GGSN/PDGw (in visited network) or home GGSN/PDGw (in home network). Main rationale of LBO is the avoidance of roaming data charges (and to prevent bill shock). The LBO capability as mandated by EU is a different form of LBO than the 3GPP LBO. -
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EU LBO: data connection is established locally and is charged by a local operator (LBO provider); designated APN is used. 3GPP LBO: data connection is established locally, but is still charged by HMNO. There is no specific definition of APN that may be used for this form of LBO.
When being an ARP subscriber and not having signed up at a LBO, the data connection in foreign network will be home routed, i.e. will not be LBO session. It is observed that, implicitly, WiFi also constitutes ‘local breakout’. The EU regulation on ARP and LBO does not pertain to WiFi. Roaming subscribers may, independent of LBO subscription, utilize local paid or unpaid WiFi connectivity. The GSM Association itself has also performed an analysis on the ARP and LBO regulation by the EC. The results of this analysis can be found in [3]. GSMA has concluded that the only viable options are Single IMSI and LBO, a conclusion that is shared by BEREC. Local breakout is strictly already defined for Voice over LTE (VoLTE). For guaranteeing the required quality of service, the data bearer that is established through LTE and Enhanced packet core (EPC; LTE and EPC are jointly referred to as Enhanced packet system, EPS) for a voice call needs to break out from the Packet data gateway (PDGw) in the visited EPS. The charging of a VoLTE call is, however, not based on data bearer level. The issue of LBO is, for the EU regulation context, applicable to non-VoLTE data services. II. Exposing charging capability by DSP A group of representatives from European operators and representatives from vendors, known as Technical Requirement Group (TRG), is devising architecture for realizing the roaming unbundling requirements. This work is being carried out on
behalf of BEREC (Body of European Regulator for Electronic Communication) [1]. Support is further received from, among others, the GSM Association [2]. Evaluation by GSMA of the guidelines that are drafted on behalf of BEREC can be found in [4]. Different options are considered for providing the ARP the ability to gain control of charging a communication service of a roaming subscriber. The options can be classified as follows: 1) Extend native network protocol from DSP towards ARP; 2) Provide charging API from DSP towards ARP. It’s crucial in this analysis to bear in mind that the main aim of roaming unbundling is to provide to ARPs the ability to perform charging for communication services of roaming subscribers. There is no requirement for providing call control capability to ARP. The architecture shall follow this principle. A. Extend native network protocol from DSP towards ARP This method entails the extending of the native network protocol, such as CAPv2 for call control or CAPv3 for SMS control, from DSP to ARP. But the actual method will differ per communication service and will depend on whether the roaming ARP subscriber is being charged through prepaid charging or through postpaid charging. Hence, we observe at least the following methods: -
CAPv2 for call control, forwarded from DSP towards ARP;
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CAPv3 for SMS control, forwarded from DSP towards ARP;
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Diameter based charging from DSP’s SMSC for SMS submission, forwarded towards ARP;
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Diameter based charging from DSP’s GGSN / PDGw, forwarded towards ARP;
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TAP files from visited network, for voice/data/SMS/MMS, forwarded towards ARP.
Figure 4 shows the ‘voice proxy’ which enables an ARP to gain control over a call by roaming subscriber.
The CAMEL dialogue mapping presents various intricate requirements, such as:
Figure 4: Voice proxy for extending CAMEL call control from DSP to ARP Since ARP based call control is applicable only for roaming ARP subscribers, the routing of CAMEL service invocation through voice proxy can be restricted to CAMEL service invocation coming from abroad. The voice proxy shall determine whether the calling subscriber is ARP subscriber and whether the call qualifies for being under ARP control. The conditions include: -
location: the call is established from a country in the EU;
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the destination of the call shall fall within the definition of ‘regulated service’; premium rate calls, free phone, for example, are not covered by ‘regulated services’;
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the destination of the call shall be within the EU.
Calls to short codes require further analysis by the voice proxy. Reason is that the short code may represent a regulated service, such as call to voice mail box, or may be represent an operator-specific service. The latter is normally exempt from ARP. A critical aspect of voice proxy is the ‘mapping of CAMEL dialogues’. Whereas Figure 4 provides limited view on the deployment of this solution, it does show that two CAMEL dialogues have to be interworked by interworking service logic. This is reflected in more detail in Figure 5.
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Screening of CAMEL operations; roaming unbundling aims for providing charging control to ARP, not call control. Hence, the voice proxy will impose restrictions on to which operations are permitted for use by ARP.
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Screening of parameters: the ARP may use Connect operation, but will not be entitled to connect the call to arbitrary destination. Hence, the Destination routing address in Connect will have to be analysed.
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Synchronisation of gsmSCF Basic call state model (BCSM) and gsmSSF BCSM (also in the case of CAP operation errors).
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Interworking between the respective TCAP dialogues, which may have different characteristics, such as pre-arranged end vs. basic end.
The capability of the voice proxy for mapping CAP dialogues does not comprise the entire capability set of the respective CAP version. Whereas charging operations of CAP shall be supported on the interface between DSP and ARP, support of call control operations on this interface is subject to agreement between DSP and ARP. If the voice proxy determines that the call does not qualify for ARP charging control, then the CAMEL service invocation will be extended to the DSP’s own charging system. Such extending may be done through SCCP based message relay, effectively taking the voice proxy out of the signaling path. The ARP has, just as the DSP, the obligation to prevent ‘double charging’ in the case of late call forwarding, i.e. call forwarding from the foreign PLMN. This is also known as ‘tromboning prevention’. In many PLMNs, this is accomplished through IN service logic that correlates terminating call control with forwarded call control. If an ARP gains control of a terminating call (for roaming ARP subscriber), then the ARP would likewise need to apply the roaming prevention service logic. The voice proxy handles, as its name implies, voice calls only. Similar method for extending the control over a communication service, from DSP to ARP, is defined for SMS, USSD and data session (incl. MMS). B. Provide charging API from DSP towards ARP
Figure 5: CAMEL interworking at voice proxy
The method of applying charging API towards ARP is grafted on the principle that all call control for
roaming subscriber remains with the DSP. The DSP provides the ARP charging control for calls that qualify for ARP charging. The ARP does not gain call control. This method is depicted in Figure 6.
Figure 6: Exposing Diameter towards ARP In this manner, the CAMEL service logic processing remains entirely with the DSP. There is no mapping of CAMEL dialogues involved. The on-line charging service logic may apply the charging service logic as normal, including accessing an external rating engine. The external rating engine holds the subscriber account information as well as the service logic and data to determine the cost of the call (or other action, like instructing the playing of an announcement when a call is not allowed to be established due to insufficient credit or because the destination is not allowed). When the on-line charging service logic has to be able to distribute the access to the rating engine between (i) the DSP’s own rating engine and (ii) the rating engine of one or more ARPs, then the on-line charging service logic needs to apply additional checks, before sending out the Diameter charging request, such as: -
is the served subscriber an ARP subscriber and if yes, which ARP;
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is the subscriber currently residing in ARP territory;
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does the call qualify for ARP based charging.
CAMEL service logic for on-line charging may in principle be subscriber-agnostic. The knowledge about the subscriber (subscription type, account
information) resides in the external rating engine. If the CAMEL service logic, however, has to decide whether to access its own rating engine or the rating engine of an ARP, it needs subscriber knowledge. One potential method for the CAMEL service logic to acquire that information might be differentiation in CAMEL subscription data. Specifically: the HLR may send different O-CSI to the visited network, with the contents of the O-CSI reflecting whether the subscriber is ARP subscriber. For example through differentiation in Service Key. This places additional requirement on subscription data provisioning in HLR. Another approach is to let the Diameter request, from CAMEL service logic towards rating engine traverse Diameter routing function (DRF). The CAMEL service logic may remain subscriberagnostic. The DRF contains logic and has access to subscriber data, to determine which rating engine shall handle this request. This is depicted in figure 7.
Figure 7: Diameter routing function The DRF does not need to contain the subscriber data, indicating whether or not a subscriber is an ARP subscriber, by itself. This data may reside in persistent data storage, such as HSS, with DRF keeping a local copy. When multiple DRFs are deployed, then each DRF contains a local copy of this data. According to this approach, the on-line charging service logic applies identical behaviour for calls that qualify for ARP charging and calls that do not qualify for ARP charging. This is a strong point in itself, as it means that the roaming subscriber gets consistent service when abroad, with only the rate of the call being affected (which is the primary aim of roaming unbundling). Any future enhancements to ARP policy, for example additional countries being marked as ARP territory, would then need to be implemented in the DRF only.
III. ARP for multitude of communication services Figure 8 provides more elaborate architecture for providing ARP based charging for different classes of communication services.
ARPs. Rationale of the MVNE is that all adaptation between DSP and ARP is concentrated in the MVNE infrastructure. Also, settlement of charging records between DSP and the ARP(s) can be taken care of by the MVNE. IV. Local breakout A subscriber that’s roaming abroad may use data services (internet access) through local data provider. This form of local data has two fundamental aspects: 1) the data connection is established locally, i.e. through GGSN of the visited network; 2) the charging of the data connection is done by local operator.
Figure 8: ARP for a multitude of operators The picture shows the on-line charging service logic and the various communication services enablers (SMSC, MMSC, GGSN). Each of these entities uses Diameter towards on-line charging system, OCS (charging & rating engine). The Diameter signaling is steered through Diameter routing function (DRF). DRF determines whether the communication qualifies for ARP based charging and selects the OCS accordingly. The usage of Diameter by the respective entities (charging service logic, SMSC etc.) differs. The respective OCS’s shall apply corresponding Diameter server handling, depending on whether the Diameter charging request relates to a voice/video call, an SMS, an MMS or relates to data transmission. 3GPP is in the process of ensuring that Diameter based (on-line) charging for circuit switched (CS) voice calls is standardised. With that standard in place transparent network architecture can be devised, based on Diameter for the various communication services, whilst minimizing the impact on core network and on application servers. Figure 8 shows Diameter charging interface from SMSC. In practical deployment, not all SMSCs may support such charging interface. Network adaptation may be applied in such case, e.g. in the form of a designated MAP SMS Gateway, through which the MAP signaling for SMS traverses and which applies the Diameter interworking. Not reflected in Figure 8 is the usage of service from an MVNO Enabler (MVNE). MVNE comprises network infrastructure that connects between the network of a DSP and the network(s) of one or more
The first aspect is not essentially new. Current 3GPP specifications of mobile data allows for selection of GGSN in visited network. The subscriber’s APN profile in HLR shall contain the designated APN for local breakout, namely ‘euinternet’. This APN shall have the parameter ‘Visited PLMN Address Allowed’ (VPAA) set to TRUE. VPAA=TRUE is a prerequisite for local GGSN selection. The euinternet APN expands, by APN analysis in visited network, into euinternet.mnc.mcc.gprs, following the rules of 3GPP TS 23.003. For expansion, and represents the LBO operator’s MNC and MCC respectively. The second aspect of LBO, namely charging the data connection by local operator, is fundamentally new. Figure 9 provides conceptual architecture of this form of LBO.
Figure 9: Local breakout LBO requires that the roaming subscriber has signed up at the LBO provider. This signing up at the LBO provider will typically be done when the subscriber has already entered the foreign country, whilst
signing up at an ARP is expected to be done before roaming abroad. The LBO provider will be one of the MNOs in the visited country. The SGSN is configured for establishing a local data connection for APN euinternet. The GGSN is configured for using Diameter based charging towards the MNO’s own On-line charging system (OCS). The aforementioned signing up procedure entails further that the subscriber becomes provisioned in the MNO’s OCS. The subscriber’s HMNO is not aware of the local data connection. The data does not traverse the HMNO’s GGSN and there are no TAP records sent to HMNO for the local data connection. (Practically, TAP records may be sent to HMNO, but then the TAP records shall be marked such that they will not result in charging by HMNO.) The subscriber that uses LBO is charged for voice, SMS and MMS by the HMNO, whilst data session, other than MMS, is charged by the local LBO. MMS charging is further dependent on APN policy of the operator, namely whether MMS uses a separate APN or uses the general internet APN. In the latter case, the GGSN would have to distinguish data packets for general internet services from data packets for MMS. Without that distinction by GGSN, MMS related data transfer is treated as general internet traffic. LBO may be used in combination with ARP. In that case, voice, SMS and MMS (if separate APN is used) are charged by ARP, whilst data is charged by visited MNO. One aspect of LBO is that the roaming subscriber needs to camp on the LBO provider’s network. When the subscriber signs up as LBO subscriber of Operator-X in the visited country, but camps on the mobile network of Operator-Y in that country, then the LBO will not function, since the subscriber is not provisioned in Operator-Y’s OCS. Data connections, whether they be established from Home PLMN or from foreign PLMN, may be subject to special data services offered by the Home PLMN operator. Specifically, these data services may be applied on the GGSN through which the data connection is established. One prominent example is the establishment of a VPN tunnel between GGSN and enterprise, as used for Blackberry subscribers. To use LBO in combination with such advanced feature places requirement on the local GGSN to be equally adapted for providing that service. When a particular advanced data service is dependent on subscription data, said adaptation will not be feasible, unless through special agreement between LBO operator and DSP.
Whereas LBO may constitute substantial saving for the roaming subscriber, some challenges are observed, including (but not limited to): -
APN setting in terminal: subscriber needs to set the APN when abroad and needs to revert to original APN when returning home. It was already earmarked as an advantage that ARP and LBO subscribers don’t need to change SIM card. Likewise, it should be aimed for that using the correct APN, when LBO applies, is automated in the terminal, for end-user convenience. A mobile App may help here.
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‘Data roaming’: many subscribers have this option in the phone set to ‘Off’. For using LBO, this option shall be set to ‘On’ (and back to ‘Off’ at some later point). Analogous to automated setting of APN, the switching On and Off of the data roaming option should ideally be automated and synchronized with LBO applicability. Here as well, a mobile App may mitigate this issue.
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‘Credit depletion’. When credit at the LBO operator has depleted, no further internet access will be possible. The subscriber may revert to using home-routed data connection (with associated cost) or replenish the credit at the LBO.
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Operators prefer to have a consistent data profile in HLR for their subscribers, whereby this data profile is sent to visited network, regardless of the country. Hence, APN profile containing euinternet APN could be sent to a country outside EU region. This should not lead to unexpected or unwanted behaviour in foreign network.
In addition, a subscriber that uses LBO abroad should preferably get an affirmative indication on the mobile phone’s display that the data connectivity is indeed ‘local’. VI. Conclusions Alternative roaming provider (ARP) and Local breakout (LBO), jointly referred to as Roaming Unbundling, are new concepts for providing roaming services to mobile network subscribers. Roaming Unbundling will be a regulatory capability to be provided by mobile network operators. Devising transparent and reliable network architecture for ARP and LBO is essential for safeguarding the investment
from MNOs, including the network itself, but also the roaming relations and interworking tests. Using Diameter as interface for providing charging capability to ARPs has the effect that call control, CAMEL handling, tromboning prevention etc. remains under control of the HMNO. It also allows for a harmonized charging interface between HMNO and ARPs. LBO may offer reduced data rates for roaming subscribers, but it’s essential that the practical use of LBO does not lead to confusion of subscribers, with respect to setting the APN in the terminal and setting the ‘Data roaming’ option. Also, unintended reverting back to home-routed data connection should be prevented, as that may result in bill-shock. A subscriber that signs up with an ARP or LBO remains in the first place a subscriber of his/her DSP. The basic services, like voice, SMS and data connectivity, and the supplementary services remain under control of the DSP and hence the DSP shall remain the party providing the guarantee of continuous service. The charging of these services when roaming may be in the hands of the ARP. Within this context, DSPs will safeguard the customer relationship and will ensure that the connecting of an ARP to their network will not comprise network stability and quality of service. References [1]
Body of European Regulator for Electronic Communication (BEREC); http://berec.europa.eu/
[2]
GSM Association; www.gsm.org
[3]
GSMA Europe Response to the BEREC Public Consultation on Roaming Regulation – Choice of Decoupling Method; http://www.gsma.com/ gsmaeurope/wp-content/uploads/2012/09/GSMA_ Europe_Response_to_BEREC_Consultation_on_ Decoupling-10Aug2012.pdf
[4]
GSMA Europe response to the BEREC consultation on BEREC Guidelines on the separate sale of regulated roaming services (Articles 4 and 5 of the Roaming Regulation); http://www.gsma.com/ gsmaeurope/wp-content/uploads/2013/06/GSMA_ Response_to_BEREC_Consultation_on_ Decoupling_Guidelines-3June2013.pdf
