Phone: (469) 634-4200


McKinney, TX (Nov 18, 2013) – A dsTest® Case History: Surviving EPC Node Failure.

Verify your DRA/DSC will protect the HSS and PCRF from signaling storms caused by an outage within the core network.

Scaling up an LTE core network is a major challenge for operators, particularly the Diameter signaling load generated by user management, dynamic policy, and charging.  Service providers, Operators and Original Equipment Manufacturers (OEM) are scaling their networks and networks elements for the extremely high volume of Diameter signaling traffic that is expected in the next few years.

Network elements such as the Mobility Management Entity (MME), Policy and Charging Enforcement Function (PCEF), Policy and Charging Rules Function (PCRF), and Home Subscriber Server (HSS) along with the Diameter Routing Agent/Diameter Signaling Controller (DRA/DSC), must be prepared for this traffic volume.  These nodes have the difficult task of maintaining the state of the subscribers, one of the most valuable resources for a network operator.  Other nodes, such as Online Charging Systems (OCS) will also begin to see high traffic volume as more LTE elements come online.  Part of the preparation is devising reasonable high availability and recovery for the networks and the nodes that make up the networks.

When a node fails within the network, a signaling storm is created.  The DRA/DSC, a critical component of the LTE core network, will need to sort out this signaling storm, routing traffic to the remaining network nodes until the faulty node is restored to service.  Among its many responsibilities is that of balancing Diameter signaling traffic in the Evolved Packet Core (EPC) between clients and the available destination servers.

In this specific Case, dsTest was used to verify that the DRA/DSC is engineered for, and capable of, handling this failure event from the time the node fails until it is back in service.

Case Setup

A network diagram of the Case is shown in Figure 1:

In order to test the network setup to verify the objective, we established a test situation with the following parameters:

  • Two regions consisting of MMEs, PDN Gateways (PGW) and Serving Gateways (SGW);
  • Simulation of Diameter traffic when a PGW/PCEF in a region goes down and subscribers are moved to a new PGW.

In order to test this simulation, we established the following criteria:

  • Two million subscribers spread equally between two EPC network regions;
  • PGW in region 1 shuts down;
  • Subscribers must return using a different packet core node (MME, SGW, PGW) but with the same eNodeB.

The message flow for the signaling of a subscriber that must be rerouted by the DRA is shown in Figure 2.

The subscriber attaches and establishes a policy session with the PCRF.  At this point, Region 1 PGW fails.

Case Results

dsTest maintained the state of the subscribers returning to the network after their session is lost.  When sessions are lost for the 1 million subscribers in Region 1, dsTest throttled the subscribers at a rate that has been established as a safe rate based upon the known capabilities of the DRA/DSC and remaining in-service network nodes.  Since the rate at which subscribers reconnect depends upon how fast subscribers can get through the new MME, we chose 30K TPS, based on customer input/requirements.  This equates to 15K subscribers trying to authenticate per second.  In addition to the 30K TPS the MME will generate, downstream traffic for the Gx sessions plus the related cancel messages from the HSS will add more TPS to the network under test.

For more information regarding this Case, or to find out how Developing Solutions‘ core network emulation and test solutions can be used to solve your network testing requirements, contact Developing Solutions, Inc. at or (877) 233-8350.

Read more about dsTest.

dsTest References Guides

About dsTest

dsTest originates, receives, and processes signaling traffic into and from the core network.  Multiple emulated nodes can be coordinated to simulate the UE traffic for complex signaling interactions such as VoLTE.  Unlike some test tools, dsTest provides stateful, standards-based applications that react appropriately to both expected and unexpected events without the need for scripting.

dsTest surpasses all other tools with its capacity, its performance, and the ease with which you can customize the scenarios and messages to achieve your testing goals.

About Developing Solutions, Inc.

Developing Solutions focuses on providing test solutions for core network interfaces in Policy & Charging Control (PCC), Subscriber Management, Authentication Accounting & Authorization (AAA), and Diameter Routing Agents (DRA).  Developing Solutions was founded in 2002, and has extensive experience in the Telecom and Datacom industries, including both NEM and test equipment manufacturers.  The company is located in the DFW Metroplex.