May 2010 | Volume 2/Number 3
Feature Story
Service Brokering on the LTE NetworkBy Jose Deras The 4G networks are coming. Many communications service providers have now officially announced their LTE plans, and some have even begun LTE rollouts. But we are still at the infancy, and there’s a larger wave of network upgrades and new handsets that will certainly transform mobile broadband as we know it. Of course there are options on how to move forward with voice delivery architectures. The backdrop of which is the general agreement that current 2G and 3G networks will be in place for some time to come, and therefore CSPs must take into account not only how their networks will evolve, but how to support roaming and handovers across multiple CSPs. In addition, the expectation is that current 2G/3G subscribers will be the first to migrate to 4G as CSPs provide upgrade incentives. That creates that additional burden of providing feature and service parity as part the upgrade as subscribers will expect their current call feature sets to behave the same once they upgrade. Among the most studied options for voice delivery are: 3GPP IMS (One Voice) The obvious long-term solution for voice and SMS delivery is based on a migration to IMS, leveraging industry know-how gained as part of the development of UMTS. Deployment of IMS-based LTE voice has been documented since IMS Release 8, and it’s viewed as the preferred long-term solution for voice evolution. At the 2010 Mobile World Congress, several manufacturers and service providers stated support for an initiative called One Voice, which specifies an IMS voice and SMS profile, as well as the minimum mandatory feature set. Moving to IMS has the obvious advantage of commoditizing a large portion of the network, bringing with it all the benefits discussed for several years now. 3GPP Circuit Switched FallBack In addition to IMS, 3GPP also has proposed using a technique called Circuit Switched FallBack or CSFB (standardized under 3GPP specification 23.272), whereby the handset normally operates in 4G (LTE) mode when accessing data services and idle, but switches to a 2G or 3G radio when it is informed of an incoming call, or an outgoing call is placed, or for circuit-switched applications such as SMS. The handsets therefore are dual-mode, supporting 2/3G for voice and 4G for data services. A mechanism to inform the handset via 4G (IP data path) that a call is inbound is utilized, but there is some concern regarding longer call set-up times instigated by the necessity of switching radios. Voice over LTE Generic Access Another option that has been put forth is Voice over LTE Generic Access (VoLGA), supported by an industry consortium known as the VoLGA Forum. VoLGA proposes utilizing the IMS-based LTE radio access network, but maintains the circuit-switched network (either GSM or CDMA based) by introducing a network element known as the VANC (VoLGA Access Network Controller). This solution is positioned as an interim approach prior to a full IMS deployment, specifically for voice and SMS delivery. Proprietary Solutions Other options do exist, such as upgradable IP-enabled MSCs, but those tend to be tied to a specific vendor architecture and may be best approached by current customers. To be clear, these architecture options address how to marry the packet-switched LTE radio network with the service operator core network for the purpose of delivering voice. What is not immediately apparent is how the CSP delivers voice applications, such as find me/follow me, voice VPN, CRBT and all the critical revenue generating add-ons that subscribers use and would expect to migrate to LTE. Regardless of the architecture chosen, CSPs will be faced with application delivery challenges created by the transition in LTE to packet based voice. Today’s voice services are predominantly delivered via service control points or intelligent network application servers that rely on IN protocols (such as INAP and CAMEL) for complex call control. Those services tend to be highly stable and profitable and also highly customized, and are therefore not easily moved to SIP-based application servers. Recreating the functionality of deployed IN-based applications requires an exhaustive survey, documentation, and duplication of used features and capabilities, a task that may not be easily achieved. CSPs will need to deliver these same services (down to feature sets and even quirky behavior) on LTE subscribers to ensure migrated users have the same level of service and experience. As CSPs evolve their networks for LTE, the resulting networks present tremendous challenges in voice services and application delivery. It’s the same challenge faced in migrations to NGN and IMS. Realizing this opportunity, the telecom software industry has come forward with a purpose-built network element: the service broker, a solution specifically designed to overcome network architecture challenges and ensure voice service delivery from any network domain to any other network domain. Service brokers are placed between the application layer and the control layer, with the purpose of delivering and extending the reach of applications to all network domains of the CSP. They do this by performing the signaling, media and call control interworking between the applications and different network domains. Implicit in the successful deployment of service brokers is the capability of delivering the required interworking without necessitating changes to either the applications or the networks. The risk of “breaking something” in the migration of the applications is removed by not touching or modifying existing code. Let’s take a look at how a service broker might fit within two of the most popular network proposals, IMS and VoLGA. LTE Voice over IMS Service brokers provide the capability of extending current voice services by providing seamless call/session interworking between the packet switched LTE access network, and circuit-switched 3G applications without requiring changes to either. For those CSPs that have fixed line networks as well, they are also able to reutilize voice services that may have been only offered in that network domain to new wireless LTE subscribers. LTE clients are able to access all applications they previously used, such as prepaid, CRBT, voice VPN, find me/follow me, etc., and therefore are not required to change their subscribed services. From a network perspective, the service broker enables the IMS network to see the existing applications as new SIP-based applications, by providing the interworking required. As far as the IMS network is concerned, the service broker is the SIP server, while to the existing SCPs the service broker is an existing 3G MSC (News - Alert).
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