The Diameter Signaling Controller Old Wine in a New Bottle?

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1 The Diameter Signaling Controller Old Wine in a New Bottle? A Whitepaper June 2012 Anjan Ghosal President and CEO Abstract: Of late there has been quite a bit of talk of the new world order and the emergence of the Diameter Signaling Controller (DSC). Is that really the case? For the veterans of the telecommunications industry that saw the progression of control signaling over the past twenty years, this is more like history repeating itself. Some of the challenges facing the signaling industry today were faced in legacy networks over thirty years ago as the industry moved from in-band to common channel signaling. This led to the rapid development of the concept of the control signaling network and its related network elements. This paper deals with some of the similarities and differences between network architectures and control signaling protocols of yesterday and today. It will show why it is essential to have a well grounded knowledge of the past to be able to effectively solve the problems of the future! 1/7

2 Advent of the Signaling Channel Since the advent of switches in telecommunication networks, there has been the need for a way to signal the switch to appropriately route the call. In the early days this was done in-band along with the voice path. However, that was very slow and resource intensive, so in the 1970 s the researchers at Bell Laboratories came up with the brilliant idea to separate the voice and the signaling network. This led to the growth of the signaling network, a low-capacity, low-latency and high-speed network exclusively for sending signaling traffic. Network elements had two types of interfaces: a high-speed low-bandwidth interface for signaling control (often over V.35 of RS449 interfaces) and a low-speed and high-bandwidth interfaces for voice or bearer path (often over T1 or E1 interfaces). All call set up messages (originating number, terminating number) were sent between the originating and destination locations via the signaling interface while the actual voice data moved on the bearer channel. Fast forward to 2012 and the idea of separating the control channel and the bearer channel has remained intact. What has changed though is that instead of two separate interfaces, this information flows through a common high speed packet network using IP as the underlying protocol 1. 1 Purists would probably call this the merging back of the control and bearer channels as now they flow through the same network once again. Big difference being that this is a high speed packet network where each packet may take a different path to get to the same destination. 2/7

3 From Call Setup Signaling to Everything Signaling While the signaling channel was originally designed for sending call set up messages, network and application designers quickly found the potential of this high speed separate channel signaling too tempting to pass up. As creative marketing wizards dreamt up new services like free phone and virtual private networks, the role of SS7 signaling became even more prominent. This led to the SS7 protocol being enhanced to include a transaction oriented layer called the Transaction Capabilities Application Part (TCAP) together with application layers like the Advanced Intelligent Network (AIN) and INAP. The advent of wireless networks led to the addition of many new networks elements to deal with the mobility aspects of the new network. There were elements like the Home Location Register (HLR), Visitor Location Register (VLR), Equipment Identification Register (EIR) and the AUC (Authentication Center). All these elements needed to communicate with each other via a signaling protocol. Once again the TCAP layer was enhanced by new application parts like the Mobile Application Part (MAP) and CAMEL. So what started as a mechanism to enable faster call set up, quickly expanded to become that all encompassing protocol to control the entire wireless network. This quickly led to rapid growth in signaling traffic, a problem that network operators needed to correct. Managing Signaling Traffic in Legacy Networks The exponential growth of SS7 traffic created some of the same problems that we are likely to encounter in LTE signaling network. Routing: Traffic management and routing became very critical in the evolution of the network. New elements focused on managing this traffic were introduced in the network. 3/7

4 Virtual addressing: As the networks grew, it became critical to provide some level of virtual addressing to aid in network administration. This was done via the Global Title, a virtual addressing scheme neatly built into the SS7 protocol layer. Reliability: Centralization of all signaling also made it a critical point for the network. The network failures at AT&T and Bell Atlantic in the early 90s which brought the entire phone system to a halt were a stark reminder of the risk of centralization. (It was bad enough to trigger a congressional hearing, though it was rather amusing to see congressmen trying to understand the intricacies of SS7!) This led to a lot of work around reliability, congestion management and failover and also to modifications in the overall network architecture. Some of this was built into the protocol layer while others had to be implemented in the application layer. Protocol Conversion: Another necessary evil that had to be addressed early in the cycle was to mediate between the various flavors of SS7 among multiple vendors. This gave rise to a myriad of signaling gateways. Security: By its closed nature legacy SS7 is implicitly secure. Plus, using the GTT concept, the STP provides a kind of topology hiding. Managing the deluge of signaling traffic gave to the rise of a new network element called the Signal Transfer Point (STP). 4/7

5 Diameter the New SS7 In many respects Diameter is the new SS7, but with some key differences as explained later. Diameter messaging has become the language of choice for new network elements to communicate and is fast becoming the heart of the LTE network. So it is very likely that some of the problems that showed up in SS7 will show up again here. However, there are some very key differences and characteristics in today s network architecture which amplify the problem. Flat architecture: The telecom industry has moved from a hierarchical network (remember the Class 4, Class 5 and the elk!) to a flat architecture. This has increased the efficiency of the network by allowing most elements to talk to each other without traversing up and down a network hierarchy. However, this has also made the network extremely mesh-like (or should we say messy!). This has exacerbated the problem of traffic management. New network elements: As we have migrated from the fixed 56Kbps (Who can even recollect what that was?) to a variable unlimited bandwidth network, new network elements have come into being. New acronyms like PCRF and PCEF have popped up (like we did not have enough already!). New calling plans have been put in place. All this has led to a plethora of new signaling requirements. Virtual address support: While there was inherent support for virtual addressing in the SS7 protocol which simplified network isolation, this is unfortunately not available in Diameter. So virtual routing addressing has to be achieved at the Application Level (rather than the network level) leading to more complexity in developing routing logic. 5/7

6 The Diameter Signaling Controller Diametriq s predecessor, IntelliNet Technologies, was one of the early pioneers of this market. As early as 2006, IntelliNet sponsored the Diameter Interoperability Event when there were only a handful of players in this market and Diameter was viewed primarily as an enhancement to the RADIUS protocol. However, as Diameter network elements multiplied, there was a need to address some of the issues outlined earlier. So in 2011 the industry finally identified a new network element called the Diameter Signaling Controller (DSC) comprised of signaling functions defined by the 3GPP, IETF and GSMA. The DSC functions as a multipurpose centralized node for all Diameter signaling similar to a Signaling Transfer Point (STP) in an SS7 network. However it also contains the necessary differences to deal with the new network architecture. The core function of this node is to enable smart routing of Diameter messages between the various network elements. In addition, this is a convenient location for implementing network interoperability. Both these functions are standard in the STP. However, where there is a key difference is the need for flexibility. While the SS7 network provided limited functionality, the LTE network provides a plethora of bandwidth and application options that will require the DSC to evolve rapidly over the next few years. The co-existence of applications on this platform will be the norm rather than the exception. The Diameter Routing Engine (DRE) provides this flexibility to either develop applications or to run third party applications on a traditional DSC. 6/7

7 About Diametriq Built on the assets of IntelliNet Technologies, a wireless solutions company founded in 1992, Diametriq offers high performance Diameter signaling solutions to meet the needs of LTE wireless operators. The company s standards compliant Diameter Routing Engine (DRE) includes a Diameter Routing Agent (DRA), Diameter Edge Agent (DEA), a Subscription Locator Function (SLF) and a Diameter Interworking Function (IWF). For more information, please visit 7/7