Introduction

Historically, circuit switches were large, monolithic systems built upon proprietary hardware and closed architectures. These systems were expensive and each offered their own methodology to increase capacity and provide high availability. Communications with other switches in the network, via network signaling protocols, was often performed by tightly integrated purpose-built hardware and software.

 

Softswitches, on the other hand, leverage open computing technology to replicate circuit switch functionality. Softswitch architectures are composed of multiple open computing platforms where switching functions are disaggregated and divided amongst the computing platforms to provide scaling and high availability. Softswitch architectures are often based on a model where functions are allocated into three fundamental components; the Media Gateway (MG) where TDM circuits are converted to IP, the Media Gateway Controller (MGC) which manages the call, and the Signaling Gateway (SG) which provides the signaling interconnection, typically via SS7, to the network. Standard IP protocols based on recommendations from the Internet Engineering Task Force (IETF) are used to interconnect these components. The focus of this brief is the Signaling Gateway (SG) and its relationship with the network and the MGC components of the Softswitch.

 

Challenges

The Softswitch disaggregation of the circuit switch into Media Gateway (MG), Media Gateway Controller (MGC), and the Signaling Gateway (SG) has provided a flexible architectural model. However, with flexibility, new challenges arise. With the ability to add capacity to the SG and the MGC by adding platforms, unique challenges arise.

• One challenge is the need to route signaling traffic to the specific MCG platform responsible for the "circuit" identified in the signaling message. The MGC function is responsible for the management of the call and the related "circuits" that carry the call. Adding computing platforms to the MGC to increase capacity or to provide high availability implies that individual MGC components are each assigned responsibility for a portion of the circuits
• Another challenge is the need to provide a single network appearance to the network in spite of the number of computer platforms that share the responsibility of the SG. The SG function is responsible for providing the signaling interface to the network. As additional computing platforms are added to the SG to increase signaling capacity or to provide high availability, there is a need to maintain a single SS7 point code towards the network.

 

Various approaches have been taken to overcome some of these challenges. If a small softswitch is deployed, the SG and MGC could be integrated as a single unit. While this does not provide for scaling or high availability, the solution does overcome the problem of distributing signaling to multiple MGCs, which may be acceptable for smaller deployments.

 

Other approaches maintain a one-to-one pairing of SG to MGC, which also avoids the signaling distribution problem, but requires additional SG components as the systems scales and does not inherently provide a highly available signaling solution. Further, since each SG is a stand-alone unit, each additional SG could potentially require a separate SS7 point code, causing the softswitch to present multiple network appearances. Alternatively, the problem of signaling distribution can be transferred to the MGC, which would be required to re-route signaling to the appropriate MGC.

 

Solution

Ideally, many of these signaling-related issues could be undertaken by the SG, freeing the MGC to focus on the call and circuit-related tasks. Some of the characteristics of an SG that could take on the signaling responsibilities include:

• Providing a distributed and highly vailable architecture that can present a single point code and a single network appearance to the network, minimizing down time of the softswitch and creating carrier class reliability for the service provider and end customers.
• Allowing MGCs to receive only those signaling messages of interest by providing MGCs with the ability to register for segments of the signaling traffic based on circuit identification code (CIC). This will enable softswitches to grow incrementally by adding MGC computer platforms, following the IT industry's cost-effective method of adding capacity.

 

Ulticom nSignia eSTP

Ulticom's nSignia^® eSTP has been optimized to support the demanding requirements of the softswitch. Specific features that benefit the softswitch are as follows:

• Highly available architecture composed of multiple computing platforms maintaining a single point code and network appearance independent of the number of signaling links deployed
• Extending the IETF M3UA specification by allowing MGCs to register for routing keys based on CIC codes. This will enable nSignia eSTP to distribute signaling traffic to the correct MGC and, upon failure of primary MGC, nSignia eSTP can route traffic to a designated backup MGC, further offloading many of the signaling- related responsibilities from the MGC
• Providing the ability to expand and contract the number of circuits supported by a specific MGC, as well as the number of MGCs while the system is in operation, eliminating downtime for circuit maintenance and capacity changes
• On behalf of the MGC, nSignia eSTP distributes messages related to groups of circuits to all concerned MGCs, and then provides the network response to these "group messages" by aggregating the information from the MGCs, further minimizing the burden on the MGCs

 

Key Business Benefits

• Provides a highly available signaling solution in order to minimize downtime and increase service provider and user satisfaction
• Offloads signaling issues from the MGC, allowing the MGC to concentrate on its primary mission without getting involved in the intricacies of network signaling
• Enables rack and stack architectures based on IT technology, in order to allow equipment to be replaced and capacity incremented without network or customer impacts
• Turn-key delivery of Ulticom's nSignia eSTP together with world class support, enables the softswitch vendors to concentrate their attention on their core competencies