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Diameter Control for LTE Roaming


Kevin MitchellBy Kevin Mitchell

The pace of LTE growth continues to impress: 113 service providers have launched LTE and more than 200 more have committed to the next generation mobile technology, according to the Global Mobile Suppliers Association (GSA). Though these results are promising in terms of securing LTE coverage, the industry faces a number of issues when it comes to providing full-service parity and being able to shut down legacy 2G/3G networks. One is support of both voice and messaging natively on LTE, which the GSMA voice over LTE (VoLTE) initiative is pursuing, and a handful of operators have launched. The second issue is LTE roaming. Subscribers expect it and service providers can monetize it: Juniper Research estimates roaming revenues to reach $80 billion in 2017. To truly transition mobile communications into the LTE era, both of these issues need resolution.

Enabling customers to use voice and data sessions on the go is no simple task, as the underlying network has changed, not just the radio layer (which due to spectrum fragmentation presents another challenge to LTE roaming). Both aspects of roaming – attachment to the visited network and use of data or voice services – require the replacement of legacy architecture based on SS7 with a new approach with Diameter signaling. In addition to the architectural evolution, Diameter itself has some challenges as it is a signaling protocol running on an IP network, which lacks the security, congestion management, and quality controls of its predecessor SS7 in TDM networks.

The Diameter protocol serves two purposes when roaming: 1) providing authentication and authorization of a roaming subscriber on the visited network, and 2) carrying charging and quality of service (QoS) profiles between the visited and home networks. As this Diameter exchange of information takes place across network borders and likely involves other third-party transport networks, there are some distinct challenges to make it work smoothly:

  • Connection management – It is impossible to directly connect to every possible roaming partner and network due to the number of elements that would have to be provisioned and the volume of routes to be managed.
  • Network Downtime – In the world of IP, service providers are exposed to security threats as critical service elements interface with external networks; these threats may result in network downtime or the compromise of critical data.
  • Overload – Network outages may occur because the servers that process authentication, QoS and charging cannot typically handle unexpected spikes in traffic due to unplanned usage or misconfiguration of equipment.
  • Interoperability – Although Diameter is a standard protocol, there are numerous interpretations of the protocol, as well as network differences in transport or IP protocols that may cause network incompatibility and transaction failures between networks.
  • Lack of visibility – Service provider networks send and receive information across multiple nodes, elements and vendors. The information in these messages is critical for network planning, troubleshooting, and settlement between mobile operators as well as roaming hubs; however, given the distributed nature, it is difficult to collect, correlate, and analyze this information into usable data.

For roaming to work, these challenges must be overcome. With that in mind, the GSMA defined the Diameter Edge Agent (DEA), a new signaling control element at the roaming border that provides security, interworking, routing, traffic management and network intelligence. The key functions include:

  • Security – Signaling rate limiting and encryption protects the network, services and customers with signaling rate limiting and encryption.
  • Interworking Mediation and interworking of the differences in the IP, transport and Diameter protocols and vendor environments used between operators allow service providers to connect to more partners and accelerates time to market.
  • Routing – Examination of messages along with policy-driven route engines allow service providers to apply business rules including roaming steering and preferred network selection.
  • Traffic management – Optimizes network performance and prevents outages by load balancing, managing congestion, and routing around failures
  • KPI and traffic statistics – Aggregates key traffic data and provides key performance indicators (KPI) that aid in network planning, optimization, faster time to resolution, and settlement

As they have done for 3G, wholesale roaming hubs and IPX carriers will play a large role in making LTE roaming possible. They provide a single connection that support voice and data roaming and can reach operators around the world — which significantly simplifies the process. The simplification comes in streamlining global connectivity (one connection, hundreds of partners), settlement and reporting. They can also provide hosted DEA or Diameter management functions for mobile service providers, including signaling protocol, IP address incompatibilities and codecs, to enable rapid connectivity and reduce costs.

In the end, this investment in Diameter control is about delivering the quality of experience for subscribers. As roaming is essential to mobile, so the DEA is to Diameter signaling and making it all possible.

Kevin Mitchell leads service provider product and solution marketing at Acme Packet, focusing on IMS service delivery, next generation signaling core and interconnect and roaming. He directs marketing strategy and sales support for Acme Packet's solutions encompassing VoLTE, RCS, SIP trunking, fixed mobile convergence, VoIP services, SIP interconnect and LTE roaming.


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