This article originally appeared in Telecom Engine.
While their predictions may vary, virtually every industry analyst foresees staggering growth in mobile data in the next five to ten years. ABI Research expects a 39% compound annual growth rate from 2011 to 2016 in mobile data traffic. Looking out to the year 2020, Jeffries forecasts a 100x ramp in mobile data, and, the firm admits, that’s likely a conservative estimate. Faced with this looming data deluge, operators are turning to all-IP networks like IMS and LTE, which rely heavily on Diameter protocol, to move and monetize their data traffic.
Diameter’s Network Role
Diameter handles critical functions within the control and service planes of 3G and 4G IP networks. It provides the AAA framework to give subscribers permission to access services and enable operators to bill customers based on filters like usage and time of day. It’s essential for mobility management, enabling subscribers to roam freely in partner networks. And, it’s the language network elements like PCRFs, GGSNs, charging systems, subscriber databases, and application servers use to communicate with each other.
But, there’s a hitch many operators haven’t considered as they deploy their all-IP IMS and LTE networks. As the data traffic swells, so will Diameter signaling activity. With most current networks solutions, each Diameter-based element communicates with every other component through direct signaling links, creating a spider web of connections. Each Diameter node must handle all session-related tasks such as routing, traffic management, redundancy, and service implementation. In the near term, deploying an IMS or LTE network without a signaling core may be adequate. However, as traffic levels swell, the lack of a capable signaling infrastructure creates problems related to scalability, congestion control, network interconnect, subscriber to HSS mapping, and PCRF binding. The situation is very similar to what operators encountered with early SS7 deployments and ultimately resolved by creating centralized, hierarchical routing network.
Creating a Signaling Layer in IP Networks
The Diameter protocol defines a new network node – the Diameter agent – which operators can leverage to create a Diameter signaling layer in IP networks. The DA performs essential network tasks like relay, proxy, redirect, and translation. Centralizing these functions in the network core eliminates the Diameter mesh, a consequence of having point-to-point signaling connections. Endpoints like MMEs, HSSs and CSCFs are relieved of routing, traffic management and load balancing tasks, which improves signaling performance and network scalability. From its vantage point in the network core, the DA provides a centralized location for Diameter mediation as well as a gateway to other networks to support roaming, security and topology hiding. And, the benefits don’t stop there. The DA can be employed to address a variety of use cases specific to IMS and LTE networks.
As the demands on LTE networks grow, operators often deploy additional MMEs and HSS front ends to support increasing loads. But, if there’s no separate Diameter signaling core, adding new elements creates its own challenge. Since Diameter uses SCTP or TCP for transport, each network resource in the EPC must have a direct SCTP or TCP connection to every element with which it communicates. The end result is a logical mesh network. As a result, the addition of a new node requires network, configuration and routing updates at each and every network element, a costly and time consuming process.
Acting as a Diameter relay, the DA reduces the number of SCTP or TCP associations in the network. When new elements are added, they are connected to a mated pair of DAs – not to every other resource in the network. The task of maintaining routing tables and status updates is simplified, since changes are required only at the DA rather than at every endpoint. The centralized DA proxies information for decentralized elements like MMEs and HSSs. Then end result: a less complex, more scalable network with lower OPEX.
When multiple PCRFs are deployed in a network, there has to be a mechanism to balance the assignment of user sessions across them and make sure that all messages associated with a particular user’s session are handled by the same PCRF. That’s no simple task since messages can arrive on different interfaces like the Gx and Rx and may be identified by different elements such as an IMSI or IP address.
A Diameter agent deployed at the network core can provide static binding or dynamic load sharing across PCRFs when a user’s session is first established. The DA ensures that subsequent messages for that subscriber over the Gx, S9, Gxx, or Rx reference points are sent to the same PCRF. That functionality can be extended across multiple DAs in the network, which communicate with each other to act like a single, logical DRA.
HSS Address Resolution
With multiple HSSs in an LTE network, subscribers can be homed on different platforms. Operators, therefore, need a way to maintain the association of subscribers to HSSs. The DA centralizes routing data and provides the mapping between a subscriber identity such as an IMS public ID or IMSI and an HSS. With that flexibility, operators can map individual subscriber numbers to a particular HSS, easily move subscribers from one HSS to another, or even split subscriber number ranges across different HSSs. Since routing data is centralized, HSS provisioning is much easier, and updates can be performed dynamically as new HSSs are placed in service
Operators are turning to all-IP networks like IMS and LTE to provide the bandwidth to support swelling data loads. However, if those networks are deployed without a separate Diameter signaling core, a host of challenges related to scalability, security, mobility management, and routing will arise as traffic loads escalate. Providers can overcome these challenges by leveraging the Diameter agent’s proxy, redirect, relay, and translation capabilities. Consolidating these functions at a DA in the network core creates a Diameter signaling layer that relieves endpoints of routing, traffic management and load balancing responsibilities. The resulting architecture provides the flexibility and scalability to support even the most data-intensive devices and applications.