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What is a Diameter Signaling Controller (DSC)

What is a Diameter Signaling Controller (DSC)

Diameter Signaling Controller or DSC is a term coined by the industry that collects several functions of the signaling or control plane in Long Term Evolution (LTE) networks.  These include the Diameter Routing Agent (DRA) defined by the 3GPP, the Diameter Edge Agent (DEA) defined by the GSMA and the Diameter Interworking Function (IWF) defined by 3GPP and GSMA. Like SS7 signaling which was used in 3G and earlier networks, Diameter is the signaling protocol used in LTE networks to handle messages for subscription, policy and charging management. The diagram below shows how the various elements of the 4G Evolved Packet Core (EPC) are connected by Diameter signaling.

Why DSC?

With the rapid growth in the number of LTE devices, particularly smart phone and tablets, and the prevalence of connection hungry applications, the volume of Diameter messages in the EPC has exploded. Early LTE adopters found that the amount of signaling traffic across multiple instances of network elements had caused congestion problems.  Some network outages had been attributed to this “signaling storm.”  The answer was the Diameter Routing Agent (DRA) which provides traffic management, load balancing and session binding while reducing the “mesh” of signaling connections across multiple network elements.  For SS7 networks the Signaling Transfer Point (STP) was used to facilitate a carrier-grade infrastructure. For Diameter, the Diameter Signaling Controller (DSC) is used for providing the same carrier-grade infrastructure in the EPC.

When a network operator migrates to LTE from older technologies, there is an incompatibility between signaling systems. The Diameter Interworking Function (IWF) was developed to allow 4G networks to interoperate with 3G network elements. The DEA provides an interworking capability for Diameter and SS7 as well as vendor variants of both.

Now that LTE operators are beginning to roam, there is a need for an edge device that provides security and topology hiding between the network operator and its IP Exchange (IPX) and roaming partners, much like the Session Border Controller (SBC) in IP networks. The DEA acts as the entry point to the home LTE network and supports all Diameter interfaces from the visitor LTE network. Security is provided across non-trusted domains and the visitor network does not need to be aware of the topology of the home network.

DSC Trends

The first operators to migrate to LTE were typically large Tier 1 operators with multiple instances of network elements like the HSS, PCRF, PCEF and OCS. They quickly realized the need for the DRA function and created this market niche. At the same time, there was a need for compatibility with legacy network elements.  As a result a level of interworking functionality was combined with the routing function. Some network element vendors built this functionality directly into their network elements as opposed to a standalone routing element. While both methods have had some success, operators seem to prefer the stand alone DRA. However smaller operators may not have multiple HSS, OCS, etc. and don’t have the resulting congestion problem. The DRA is typically a Tier 1 market.

The Diameter Edge Agent (DEA) is a different story. Almost all LTE network operators will want an edge device for LTE roaming, whether it is located in their own network or at their IPX.  The volume of signaling traffic associated with roaming is clearly smaller than what occurs in the core network, allowing for a less expensive, scaled down solution. This function can be combined with the DRA in the core for the Tier 1 operators.  However, the rest of the operators will prefer the standalone DEA.

As a pure software solution, the functions of the DSC lend themselves well to the Software Defined Network (SDN), and Network Functions Virtualization (NFV).  Many major network operators have started evaluating SDN for better CAPEX ROI, lowering OPEX and for providing better ways to monetize infrastructure by having their  control plane managed in the cloud.

“Article contributed by Diametriq – www.diametriq.com.” 

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