1. Feature Guide
  2. Introduction to Diameter Signaling Router
  3. Diameter Routing Challenges

1.1 Diameter Routing Challenges

For years operators have employed signaling system 7 (SS7) as the international, standardized protocol to communicate globally between operator networks. In LTE and IMS networks, many of the functions performed bySS7-based signaling in current networks are replaced by equivalent functions based on the Diameter protocol. Operators expect the same network behavior and robustness currently provided by SS7 networks.

Without a separate Diameter signaling infrastructure at the network core to facilitate signaling between network elements, endpoints such as Mobility Management Entities (MMEs) and Home Subscriber Servers (HSSs) must utilize direct signaling connections to each other, forming a mesh-like network architecture. Network endpoints must handle all session related tasks such as routing, traffic management, redundancy and service implementation. Implementing an IMS or LTE network without a signaling framework may be sufficient initially, butas traffic levels grow, the lack of a capable signaling infrastructure poses a number of challenges:
  • Scalability and load balancing: Each endpoint must maintain a separate SCTP association or TCP connection with each of its Diameter peers and keep track of the status of each association. This network arrangement increases the overheads on the endpoints as the number of nodes increases, and the endpoints have the additional responsibility of load balancing. This burden is made more complex with the responsibility of load balancing placed on each end point.
    • Congestion control: Diameter lacks well-defined congestion control mechanisms found in other protocols such as SS7. For example, if an HSS has multiple Diameter front ends, the lack of sufficient congestion control increases the risk of a cascading HSS failure.
    • Secure Network interconnect: A fully meshed network is completely unworkable when dealing with connections to other networks because there is no central interconnect point, which also exposes the operator’s network topology to other operators and can lead to security breaches.
    • Interoperability: Protocol inter working becomes unmanageable as the number of devices supplied by multiple vendors increases. With no separate signaling or session framework, interoperability testing (IOT) must be performed at every existing node when a new node or software load is placed in service. IOT activities consume a considerable amount of operator time and resources, with costs increasing in proportion to the number of tests that must be performed.
    • Support for legacy EIR: A need for MAP to Diameter inter working is required as transitions are made and LTEis quickly introduced into a network while still needing to support legacy HLRs.
    • Support for both SCTP and TCP implementations: SCTP elements cannot communicate with TCP elements. Without a central conversion element, operators will either have to upgrade TCP elements or require all elements in the network to support both stacks.
    • Subscriber to HSS mapping: When there are multiple HSS in the network, subscribers may be homed on different HSS. Therefore, there must be some function in the network that maps subscriber identities to HSSs. With no separate Diameter signaling infrastructure, that task must be handled by a standalone Subscription Locator Function (SLF), or by the HSS itself. Either approach wastes MME (or call session control function[CSCF]) processing and can add unnecessary delays. The HSS approach wastes HSS resources and may even result in the need for more HSSs than would otherwise be necessary.
    • Policy and charging rules function (PCRF) binding: When multiple PCRFs are required in the network, there must be a way to ensure that all messages associated with a user’s particular IP connectivity access network(IP-CAN) session are processed by the same PCRF. This requires an element in the network that maintains session binding dynamically.

In recognition of Diameter routing issues, 3GPP has defined the need for a Diameter signaling infrastructure and a Diameter border infrastructure as shown below which is taken from TR 29.909. In addition, the GSMA has specified the need for a Diameter Proxy Agent as shown below which is taken from PRD IR.88.

Figure 1-2 3GPP Inter/Intra-operator Diameter infrastructure


3GPP Inter/Intra-operator Diameter infrastructure

Figure 1-3 GSMA roaming implementation architecture


GSMA roaming implementation architecture