Cisco projects a 75% compound annual growth rate for the number of 4G devices between 2012 and 2017, from 60 million to 992 million. 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.
We have written about how Open Channel Signaling Optimization dramatically reduces unnecessary radio access network (RAN) (mobile) signaling. It can also help carriers to address the challenges of Diameter signaling. To understand how, let’s examine the nature of Diameter signaling.
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.
In 3G networks, the signaling bottleneck is located at the radio network controller (RNC). The bottleneck in LTE networks moves into the core network, at the mobility management entity (MME). However, many core network signaling events have their origin in radio access network signaling, so excessive and unnecessary RAN signaling will exacerbate the coming Diameter signaling challenge.
Diameter Signaling in Depth
The Diameter protocol exchanges information in transactions, which consist of requests from a Diameter client and responses from a Diameter server. The elements participating in the Diameter transaction include:
- Clients who generate Diameter messages requesting information
- Servers that respond to the request for information from the clients
- Agents that route, process, or redirect Diameter messages between the client and the server
The Diameter protocol was originally envisioned to handle things like charging or simple policy control. However, today Diameter has taken on a much broader set of responsibilities. In today’s networks, the functions of the Diameter protocol can be broadly grouped into the following categories:
- Registration, authorization, and authentication
- QoS/bandwidth-based admission control
It is beneficial that Diameter has been adopted for all these uses and that it has been able to accommodate them. The downside is that there hasn’t been a focus on the network-level robustness of the protocol. Congestion management, peer congestion control, and redirecting on failure were not considered part of the protocol. Nor were they designed into each network element. This has significant potential to create problems in light of the following:
- Increasing traffic volume: 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.
- Proliferating network elements: 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.
- No network-level means of managing signaling: 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.
All of the resulting signaling has resulted in network outages because the servers involved in processing various AAA, QoS, or charging functions are not equipped to deal with spikes in volume.
Controlling Diameter Signaling
To meet such challenges, a number of vendors are offering products that they call Diameter routing solutions. These products sit at the center of the LTE core network, and are designed to centrally and intelligently help distribute and scale network signals. These new devices focus solely on managing and routing signals, and they have very powerful processing capability.
Diameter routing solutions are one way of managing the Diameter signaling storm. But it’s important to remember that a significant portion of Diameter signaling originates as RAN signaling when devices connect to the network. That is to say, RAN signaling is upstream from core network signaling.
Not every Diameter signaling event originates in the RAN, but many of them do. A complementary approach for reducing Diameter signaling is therefore to reduce the number of times that devices connect to the radio network, and hence reduce the associated signaling messages.
Chatty apps constantly poll for updates, which causes devices to generate mounds of RAN signaling that in turn drives Diameter signaling in LTE networks. Often this mobile signaling is unnecessary in the sense that no updates are available – meaning that the signaling activity yields no benefit to the end user.
It makes sense to optimize signaling at the client before it ever generates a signaling event, and this can be done without adversely impacting end-user experience. That’s where our Open Channel Signaling Optimization comes in.
By dramatically reducing unnecessary mobile signaling, Signaling Optimization lightens the load on the MME in LTE networks. (It also lightens the load on the RNC in 3G networks). Carriers concerned about the Diameter signaling storm should consider Signaling Optimization to address this important root cause of signaling overload in the LTE core network.