March 3, 2015

Diameter: Solving LTE Session Control

Mobile operators LTE (Long Term Evolution) deployments have been underway since 2009, and many carriers across the globe have plans to retire their 3G networks in favor of LTE.  LTE / 4G LTE has already overtaken 3G as the predominant data platform in some mobile operators' networks and, there's good reason to believe that 4G traffic will be more than half of the total mobile traffic by 2017. Voice over LTE (VoLTE) is also being deployed and while still in early days, a recent Webtorials study on the VoLTE status will show that over 60% of carriers have started to deploy VoLTE, including those who offer commercial service and those who are in field trials.  

LTE has enabled much faster data speeds than 2G and 3G network platforms, and it also provides spectrum efficiencies not available in older platforms.  However, with LTE's faster mobile broadband speeds, coupled with the explosion of smart phones and mobile apps, the number of concurrent data sessions running across LTE presents a significant network management challenge.  The challenge is especially challenging in mobile data networks because sessions need to be passed between cell sites and mobile operators without dropping the data sessions.  

Fortunately, numerous tools are available to manage the network and back office elements needed for these mobile data sessions - including platforms that support traditional IP session control elements such as authentication, authorization and accounting (AAA) alongside newer architectures such as IP Multimedia Subsystem (IMS.) 

Diameter protocols and diameter signaling platforms (DSPs) are gaining widespread support as critical elements to manage the integrity of data and voice sessions and signaling across LTE networks.   Diameter signaling platforms work alongside session border controllers (SBCs) in an IMS architecture.  SBCs help maintain and secure session initiation protocol (SIP) sessions that control Voice over IP (VoIP) calls while diameter signaling controllers (DSCs) help manage data sessions.  

Both SBCs and DSCs help secure network traffic using encryption and by warding off denial of service attacks; they manage session / signaling control; and they help balance traffic loads across a multi-node network.  In some network topologies, DSC and SBC features can run on the same platform, and virtualization of SBC and DSC features and functionality has become increasingly commonplace.  

Diameter and DSCs play an especially important role in the deployment of VoLTE.  DSCs can provide roaming between different service provider networks with VoLTE, using a function known as Diameter Edge Agent (DEA). The DEA acts as a single point of contact between different mobile operators' networks, efficiently passing the users' AAA information so the users' session can be authorized for roaming.  

DSCs also enable roaming between a network provider's VoLTE and legacy 2G / 3G network.  This feature is especially important because it could take years before mobile operators to fully complete VoLTE deployment within their own network, and they will continue to use 2G / 3G voice platforms until they can retire the legacy voice architecture.  For networks that have not yet deployed fully deployed SIP for voice session control, the DSC can also provide Signaling System 7 (SS7) Interworking; SS7 remains commonplace in most legacy voice to set up and tear down voice calls.  

Another DSC element that works in tandem with the DSC is the Diameter Routing Agent (DRA).  The DRA routes signals to the Policy and Charging Rules Function (PCRF), providing important information to the network such as the user's QoS so that minimum QoS parameters can be maintained.  The DRA also determines the charging (billing) policy for packets in the LTE network.  

In conclusion, the need for Diameter features is apparent given the services that a DSC, DEA, and DRA perform.  No surprise, then that the DSC market grew 81% in 2014 "on the wings of LTE" according to the latest Infonetics report on the topic.   Given the growing deployments of LTE and the subsequent VoLTE rollouts, the need for DSCs and their companions will doubtless continue to grow in the coming year. 

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