The Diameter Storm in LTE : GET READY OR ELSE !!

As 4G networks expand and customer adoption increases, the wireless industry faces a new “signaling storm” – this one related to core network signaling using the Diameter protocol. With the migration to 3G, LTE- and IMS-based networks, the need to manage the growth in Diameter signaling has become critical to optimize the network and ease congestion in real time. Operators are addressing concerns about data capacity by migrating to LTE, offloading traffic to Wi-Fi, and deploying small cells. However, the impact of network signaling has gone largely unreported.

So what is Diameter ?? Diameter is an authentication, authorization, and accounting protocol for computer networks. It evolved from and replaces the much less capable RADIUS protocol that preceded it. Diameter and SIP are the protocols in LTE networks that replace SS7, which is used in 3G networks. SIP is the call control protocol used to establish voice, messaging, and multimedia communication sessions. Diameter is used to exchange subscriber profile information and for authentication, charging, QoS, and mobility between network elements.The Diameter protocol was originally envisioned to handle things like charging or simple policy control but was expanded to take on a much broader set of responsibilities such as :

# Registration, authorization, and authentication
# QoS/bandwidth-based admission control
# Charging
# Location

The DSR ( Diameter Signalling Router ) is at the core of the new Diameter network. Like the central nervous system, which relays messages from the brain to different parts of the body, the DSR integrates with Diameter-based control elements, relaying messages among them. It handles traffic management, routing, and load balancing across Diameter elements to ensure scalability and manage congestion. Each endpoint needs just one connection to a DSR to gain access to all other Diameter destinations, eliminating the point-to-point Diameter mesh. By moving intelligence from the network’s edge to its core, the DSR improves signaling performance and interoperability between endpoints, streamlines routing, and reduces network cost and complexity. Network expansion is simplified, because routing updates, maintenance, and interoperability tests are centralized at the DSR. From its vantage point in the network, the DSR provides an ideal point for networkwide policy binding and protocol mediation. As the network demarcation point, it creates a roaming gateway; linkages to cloud, OTT, and M2M providers; and a central point for security and topology hiding.

Why the storm in the LTE cauldron ? LTE networks are characterized by more boxes and increasing complexity. This means that even more signaling is required for these boxes to communicate with each other. Carriers often deal with signaling at the level of individual network elements rather that at the network level. That breeds inefficiency and far too many point-to-point connections. As the signaling load grows, the resulting “n-squared” increase in core signaling traffic can quickly overwhelm nodes in the network. In January 2012 NTT DoCoMo networks suffered a 4 hour network outage due to an abnormal spike in signalling traffic. One recent network outage prompted the operator to ask Google to reduce the amount of signalling from Android devices.

The signalling storm has two fronts: radio frequency (RF) signaling hitting the radio access network (RAN) and surging Diameter signaling traffic in the core network. Although the end result in both is the same—network congestion, service degradation, and dropped calls—the nature and causes of each are very different. It is important for operators to distinguish between the two. One increases network costs, whereas the other drives significant revenues that more than offset the minimal cost. This white paper illustrates the importance of network architecture in overall performance, as well as its role in the success or failure in the mobile data market.Increased RF signaling fuels RF interference in the RAN, which decreases the amount of spectrum that is available for useful, revenue-generating flows such as user data. Moreover, RF signaling drives growth in other forms of signaling traffic, including S1-MME signaling between the eNodeB and MME and Diameter signaling in the network core.

Diameter is also the protocol for policy and charging in 3G networks. In both cases, Diameter enables revenue-generating personalized mobile data services, including tiers, loyalty programs, application-specific QoS, and value add for over-the-top (OTT) and machine-to-machine (M2M). There is a direct correlation between Diameter traffic and data revenue. As service providers begin to monetize their IP networks, the volume of Diameter signaling increases.The Diameter signaling storm is being driven by the cumulative impact of the growth in connected devices and applications, personalized service plans, and an increasingly mobile subscriber base. The problem is compounded by the legacy Diameter architecture itself, which has no signaling core to efficiently manage the increasing load of signaling traffic passing back and forth between the Diameter-based nodes.

According to Acme Packet, by 2015, 44,000 Diameter transactions per second (TPS) will occur for every one million subscribers. For a moderately sized LTE deployment of five million subscribers, a mobile service provider will need to process between 220,000 and one million Diameter transactions per second. Online charging is the largest area of growth for Diameter signaling MPS as service providers migrate their charging networks to all IP-based architectures — forecast to increase from nearly 18,000 MPS to nearly 14 million MPS by 2016, for a CAGR of 280 percent. Subscriber authentication will generate 5.4 billion messages in 2016. Social networking activity is forecasted to spike from about 155 million Diameter messages in 2011 to 17 billion in 2016.

VoLTE and video streaming will sharply increase Diameter signaling with about 36 billion and 30 billion Diameter messages, respectively, in 2016 — generating high amounts of Diameter signaling due to Quality of Service (QoS) requirements. Policy has the largest impact on total Diameter signaling traffic with nearly 24 million MPS crossing LTE networks by 2016 in support of policy use cases —a CAGR of 269 percent over the 2011-2016 period — based on the growth of sophisticated data plans, personalized services, and over-the-top (OTT) and advertising models. The chattiest applications can generate as many as 2,400 network signaling events per hour.The increasing use of cloud-based software will add to the problem, because server-based data and applications must synchronize constantly with the device accessing them.

All of the resulting signaling will result in network outages because the servers involved in processing various AAA, QoS, or charging functions are not equipped to deal with spikes in volume. As proven during Hurricane Sandy and other natural disasters, congestion of the core signaling network is a key concern operators have to address when friends and families flood lines in search of loved ones. When the core fails, nothing works, therefore making the core becomes a critical component in the network. Geographic redundancy and traffic control is paramount to a robust signaling network that can survive any crisis.

It’s time for operators to adopt strategies that allow them to manage traffic growth and mitigate the impact of Apps and connected devices on network signalling. Regulation of applications that require frequent updates may serve to ease signaling traffic to some extent, but it could stifle the popularity of the Apps that have become so appealing to mobile subscribers. Unlike the ongoing 3G signaling storm which is being created by smartphone-based applications and social networking services, the Diameter signaling phenomenon can also have positive implications in the form of new revenue-generating opportunities.There is no slowdown in Diameter signaling growth in sight. Billions of connected devices taking advantage of new mobile broadband networks, new applications and new service plans are all conspiring to create an explosion in Diameter signaling traffic. The result? New stresses on operator policy servers, charging systems, subscriber databases, and gateways in IP networks.

In fact, the release of the Apple iPad 3 in September 2012 unleashed an unprecedented signaling tide on the network. More than 3 million iPads were sold in its first weekend on the market, and that has shown no letup in subsequent releases. Features such as a 5-megapixel camera, high-definition video, OTT services such as Facebook and Twitter, as well as a wide variety of data-heavy consumer and business applications are virtually guaranteed to spin off Diameter messages at a fast rate. Moreover, as sales increase, subscribers will begin using iPads outside of LTE coverage spots. Every time the device moves between LTE and 3G/4G access networks, it will have to register on the correct access network technology, which will generate yet another level of Diameter signaling.

Bottom Line : Only fatalists and fools don’t see a Tsunami bearing down upon them at full speed !!

Sadiq Malik ( Telco Strategist )


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