Impact of the LTE Migration for MVNOs A Whitepaper Converting Diameter to SS7 protocols (CAMEL/SOAP/RADIUS/WIN/GSM MAP) and other proprietary protocols October 2012 By Dan Wonak Director of Marketing Abstract: Wireless operators around the world are upgrading their networks to LTE. This means not just the addition of new network elements like the P- Gateway and the S-Gateway, but also a fundamental change to the underlying signaling from SS7 to Diameter. Mobile virtual network operators (MVNOs) who typically have their own billing system and policy controller framework depend on the mobile network operators (MNOs) to provide them the underlying wireless network infrastructure. They need to communicate with each other via standardized (or proprietary) interfaces and are significantly impacted by this migration to LTE. A Diameter Protocol Converter can convert, not just between disparate diameter variants, but also to SOAP/SS7 and other proprietary interfaces and assist MVNOs manage the migration to LTE.
Introduction A mobile virtual network operator (MVNO) or (in the United Kingdom) mobile other licensed operator (MOLO) is a wireless communications services provider that does not own the radio spectrum or wireless network infrastructure over which the MVNO provides services to its customers. An MVNO enters into a business agreement with a mobile network operator to obtain bulk access to network services at wholesale rates, and then packages this with their own branding and marketing clout. In this way, the MVNO can offer subscribers a competitive service at competitive prices. An MVNO may use its own customer service and billing support systems and its own customer service, marketing and sales personnel or it may employ the services of a mobile virtual network enabler (MVNE) to provide these functions. An existing MVNO or MVNE will have its billing support system (BSS) and possibly policy management based on 2G/3G signaling technology, which uses protocols such as RADIUS, SOAP and CAMEL, whereas 4G billing systems are based on the Diameter protocol. Migration to LTE will require either the billing system to be upgraded to accommodate the Diameter as well as the legacy protocols or alternatively the use of a protocol converter that will convert from legacy to Diameter protocol. Today s mobile networks by their design and nature contain dynamic subscriber states so static routing models don t work. The Diameter Signaling Controller (DSC) can provide real-time routing decisions to minimize inefficient and costly routing processing. The DSC can enable either backwards or forwards compatibility of 3G to 4G network and BSS infrastructure, translating and converting protocols to simplify migration and integration as well as roadmap changes to either side of the architecture. LTE Legacy Interworking for the MVNO The Diameter protocol is ubiquitous in the LTE core network and is the standard for all aspects of policy, charging and subscription management. Diameter is based on RADIUS but has been enhanced to support failover, transmission security, reliable transport, agent support, server initiated messages, capability negotiation, peer discovery and configuration. It is also expandable with command codes (CC) and additional attributevalue pairs (AVP). The base Diameter protocols have been defined by the Internet Engineering Task Force (IETF) and these have been extended using additional CCs and AVPs by the GSMA, 3GPP and 3GPP2 to support interfaces between Evolved Packet Core (EPC) network elements. The standards bodies anticipated a number of potential issues in the transition to 4G and have defined certain signaling functions that are essential for the successful migration to 4G. These include the 3GPP Interworking Function (IWF) for Diameter- MAP: TS 29.305 and the IETF Diameter Translation Agent (TLA): RFC 3588. These and www.diametriq.com 2/8
other functions are included in a new network element the industry is calling the Diameter Signaling Controller (DSC). A typical MVNO will most likely need to maintain its 3G billing system while adding 4G services and customers. This means that they will be connecting to both 3G and 4G network elements, which use different signaling protocols. A DSC positioned between the PCRF and different vendor network elements such as PCEFs, OCSs, BRAS, SCPs and MSCs can provide translation and mapping of vendor variant Diameter protocols such as Rf, Ro, Rx, Tx, Ty, Gy, and Gx to enable seamless integration. Because network vendors interpret standards differently, and often provide proprietary extensions as a differentiator, no standard is implemented identically from vendor to vendor or even from release to release. To address this challenge the DSC can provide asynchronous translation and conversion of real time session signaling between network elements providing a central interconnect function serving to normalize communication. A DSC serving as a Diameter Interworking Function (IWF) provides the interworking capability for Diameter and SS7 protocols. However, support for MAP to and from Diameter (S6a, S6d, S13, S13 to GSM MAP and ANSI-41 MAP) and CAP or WIN to or from Diameter (Gy, Ro to CAP and IS-826 WIN) is required to accommodate roaming with operators that have not yet transitioned to 4G. Figure 1: The Diameter Interworking Function (IWF) The Evolved Packet Core (EPC) uses Diameter for access to the HSS, EIR and OCS. When the EPC is deployed in a PLMN there may be a need to use existing legacy elements like the HLR, EIR and Prepaid SCP with SS7. Conversely, when the HSS, EIR and OCS are deployed or upgraded to use Diameter there may be a need for them to be used by legacy elements using SS7. In both cases there is a need for an interworking function (IWF) between Diameter and SS7. Additionally, the correct instance of the HLR/EIR and Prepaid SCP needs to be selected. For this the 3GPP defines a subscriber location www.diametriq.com 3/8
function (SLF). The 3GPP also defines an IWF between Diameter and MAP, although there is no corresponding standard for Diameter to CAP. The DSC can be deployed in the EPC to act as a SLF and IWF at the same time. When the MME, SGSN and PCEF use Diameter, the DSC selects the correct instance and converts the Diameter signaling messages (S6a, S6d, S13 and Gy) to SS7 (Gr, Gf and Ge) and sends them to the HLR/EIR or Prepaid SCP. The DSC then converts the SS7 responses back to Diameter signaling messages (see figure below). When the SGSN uses the SS7 protocol, the DSC selects the correct instance and converts the SS7 signaling messages (Gr and Ge) to Diameter signaling messages (S6a, S6d and Gy) and sends them to the HSS or OCS and converts the Diameter responses back to SS7. The DSC may be deployed in a distributed or centralized configuration and optionally in a non-collocated geographically redundant configuration for disaster recovery. The use of the DSC allows for easy transition from legacy networks to the EPC within a PLMN (see figure below). www.diametriq.com 4/8
If an MVNO is operating with existing 3G legacy elements like the HLR, EIR and Prepaid SCP using SS7 and one of its subscribers roams into a network where an EPC has been deployed, then signaling from the V-PLMN uses Diameter messages and the H-PLMN uses SS7. Conversely, if the EPC has been deployed in a PLMN and one of its subscribers roams into a network where EPC has not been deployed, then signaling from the V- PLMN will use SS7 and the H-PLMN supports the HSS and OCS that use Diameter signaling. In both cases there is a need for an IWF between Diameter and SS7. Also, the correct instance of the HLR/EIR, Prepaid SCP, HSS or OCS needs to be selected. The 3GPP defines an IWF between Diameter and MAP, but there is no corresponding standard for Diameter to CAP. Here the 3GPP defines a Diameter routing agent (DRA) selection function. Additionally, there is a need to provide border security and topology hiding at the edge of both the visited and home PLMNs. The GSMA defines the Diameter edge agent (DEA) to perform this function. A DSC can be deployed in the EPC to act as a DEA, DRA and IWF at the same time. When the MME, SGSN and PCEF use Diameter the DSC selects the correct instance and converts the Diameter signaling messages (S6a, S6d, S13 and Gy) to SS7 (Gr, Gf and Ge) and sends to the HLR/EIR or Prepaid SCP. The DSC then converts the corresponding SS7 responses back to Diameter signaling messages (see figure below). When the SGSN uses the SS7 protocol, the DSC selects the correct instance of the protocol and converts the SS7 signaling messages (Gr, Ge and Gf) to Diameter signaling messages (S6a, S6d and Gy). The DSC then appropriately converts the Diameter-based HSS or OCS signaling messages to SS7 (see figure below). www.diametriq.com 5/8
The DSC may be deployed in a distributed or centralized configuration and optionally in a geographic redundant configuration for disaster recovery. The use of the DSC allows for easy transition from for roaming between PLMN with and without an EPC. Diametriq s Unique Protocol Translation Function One of the key features of Diametriq s DSC, the Diameter Routing Engine (DRE), is to allow seamless Diameter-to-any-protocol translation. This function is performed by the Network Interface Module, which allows any Diameter variant to be defined in the data dictionary. www.diametriq.com 6/8
Once defined in the dictionary, this allows the transformer module to receive diameter messages that conform to the specified syntax. This works in conjunction with the Transformation Modules. Transformation Modules are pluggable code segments that define the translation between different protocol variants or completely different protocols. Using the protocol translation function, the DRE can easily convert between various flavors of Diameter, Diameter-to-SS7, Diameter-to-RADIUS, Diameter-to-SOAP or Diameter to any proprietary variant. Summary and Conclusion The challenges to an MVNO handing both 2G and 3G signaling and migrating to 4G simultaneously can be daunting. An effective solution is to use a properly scaled and reliable DSC. Diametriq offers the Diameter Routing Engine (DRE) which provides interworking as well as load balancing and roaming that can be customized to an MVNO s specific requirements. The platform is flexible and is designed to meet the demands of MVNOs transitioning to 4G network technology. About Diametriq Diametriq, offering LTE control signaling solutions to meet the needs of LTE network operators, was built on the assets of IntelliNet Technologies, a wireless solutions company founded in 1992. The company s application enabled Diameter Routing Engine (DRE) addresses traffic management, interoperability and service migration issues. The DRE includes a Diameter Routing Agent (DRA), Diameter Edge Agent (DEA), a Subscription Locator Function (SLF) and a Diameter Interworking Function (IWF). For more information, visit www.diametriq.com. www.diametriq.com 7/8
Acronym Reference Description BRAS IETF Broadband Remote Access Server DEA GSMA Diameter Edge Agent DPI General Deep Packet Inspection DRA 3GPP Diameter Routing Agent DRE Diametriq Diameter Routing Engine DSC General Diameter Signaling Controller EPC 3GPP Evolved Packet Core Ge 3GPP Interface between gprsssf (SGSN) to gsmscf (SCP) Gf/Gr 3GPP Interface between SGSN and EIR/HLR GGSN/SGSN 3GPP Gateway/Serving GPRS Support Node Gx/Gxc 3GPP Interface between P-GW/S-GW and PCRF Gy/Gz 3GPP Interface between OCS/OFCS and PCEF H-PLMN/V-PLMN 3GPP Home/Visitor Public Land Mobile Network HLR 3GPP Home Location Register HSS 3GPP Home Subscriber Server MAP 3GPP Mobile Application Part MME 3GPP Mobile Management Entity MSC/GMSC 3GPP Mobile Switching Center or Gateway-MSC OCS/OCFS 3GPP On-line/Off-line Charging System P-GW/S-GW 3GPP PDN/Serving Gateway PCEF 3GPP Policy and Charging Rules Enforcement PCRF 3GPP Policy and Charging Rules Function PDG/ePDG 3GPP Packet Data Gateway Evolved PDG PDN 3GPP Packet Data Network RADIUS IETF Remote Authentication Dial In User Service Ro/Rf 3GPP Interface between the CSCF and OCS/OFCS Rx 3GPP Interface between the CSCF and PCRF S13/S13 3GPP Interface between MME/SGSN and EIR S6a/S6d 3GPP Interface between MME/SGSN and HSS S9 3GPP Interface between the H-PCRF and V-PCRF Sh/Si/Dh 3GPP Interface between the AS/IM-SSF and HSS/SLF SCP IETF Service Control Point SLF 3GPP Subscription Location Function www.diametriq.com 8/8