Session controllers to the rescue

Session controllers, a new breed of intelligent networking technology, work synergistically with softswitches to help carriers and other service providers deliver voice and other real-time services over IP

Technology innovation and an evolution in deployment strategies–driven by the exacting demands of the service providers that withstood the last two years of market sluggishness–have spawned a new architecture to deliver real-time services such as voice and video.  Session controllers, a new breed of intelligent networking devices, provide the underpinnings for this architecture. These devices address the unique challenges that arise when carriers and service providers use Internet Protocol (IP) to deliver real-time services to their carrier partners and their enterprise customers. 

The original blueprint for IP voice communication, anchored by softswitch technology, was driven by competitive local exchange carriers (CLECs) and the vendors that sold to them. The softswitch was a critical element in carriers’ network plans because they required low-dollar investments, helped minimize cost of ownership for existing services and provided some of the tools necessary to roll out next-generation services. The drive to deploy softswitch technology diminished with the demise of the CLEC.

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Now the carrier landscape consists of traditional service providers such as the local exchange carriers (LECs) and  interexchange carriers (IXCs), and new, regionally focused carriers and service providers that cater to the needs of the larger carriers or the specialized needs of the enterprise. 

IP-based carriers delivering wholesale voice-over-IP (VoIP) services have quickly adopted session controller technology for flexible and cost-effective connectivity with their carrier customers.  Today, these carriers look to both softswitches and session controllers to synergistically enable voice and other real-time services over IP. Session controllers provide Layer 5 routing and control to manage real-time traffic flows between IP networks. 

A Key Role

Session controllers afford carriers the advanced management functionality to overcome network security, signaling interworking and multi-vendor interoperability issues that traditionally have prevented seamless interconnection of session initiation protocol- (SIP-) and H.323-based networks via IP. Carriers can simplify their networks and develop a larger breadth of network services with session controllers operating in the core of the network and at network peering points.

Typically, functionality is distributed among session controllers deployed at different points within a carrier network and at the enterprise. Edge session controllers, handling a carrier’s connections to its enterprise customers and service provider partners, provide network security, call admission control, signaling interoperability, service quality control and facilities for law enforcement.

CLECs believed that softswitches would inexpensively replicate the PSTN. In today’s networks, however, softswitches provide carriers with a mechanism to IP-enable their TDM-based networks.

Core session controllers, meanwhile, perform session routing and service-level call admission control (for example, enforcing policies that might limit the total number of calls originating from a carrier partner via multiple ingress points). In essence, the core session controller leverages policies to route traffic among the many peering points a carrier may have with its enterprise customers and other service providers.

Voice-centric softswitches provide different, but complementary, functionality.

Softswitch technology focuses on the control of voice-based media gateways and the routing of voice calls between the public switched telephone network (PSTN) and the IP network. In this environment, softswitch vendors face many challenges, including how to support the many variants of SS7 signaling protocol that are deployed around the world. Session controllers, on the other hand, tackle a much broader variety of real-time services delivered via packet networks and use the SIP and H.323 signaling protocols. Softswitch and session controller technologies must co-exist to bridge the PSTN and emerging IP-based networks. 

CLECs believed that softswitches would inexpensively replicate the PSTN. In today’s networks, however, softswitches provide carriers with a mechanism to IP-enable their TDM-based (time division multiplexing) networks. Softswitches have been shifted to the network edge, and session controllers treat softswitches and their associated media gateways as IP endpoints that can service voice calls from the PSTN.

Enabling the IP PBX

Enterprises are also interested in simplifying and securing their private networks by deploying small-scale session controllers  that support the deployment of IP PBXs.

One key value proposition of the IP PBX is the ability to integrate voice and data on the same access medium, which  eliminates the access charges associated with a network connection dedicated for voice. However, traditional data firewalls do not have the Layer 5 intelligence to secure the signaling and media streams associated with VoIP and other real-time media. An enterprise session controller provides this capability and also solves issues of protocol interoperability that exist among the enterprise IP PBX and carrier-based applications and services.

Supporting multiple business strategies

The lure of both top- and bottom-line benefits is pushing large carriers such as the IXCs to move aggressively to all-IP operations. There will be new revenues realized by hosting video and multimedia applications–market opportunities taking shape now that will ultimately prove country-specific.

Regional carriers and service providers, meanwhile, are gaining ground against their larger competitors by providing traditional services at lower costs while also offering specialized services to meet the needs of their regional customers.

Session controllers support all of these business strategies by reducing the carrier investment needed to provide traditional voice services while also enabling increased returns on deployed infrastructure. More importantly, this technology provides carriers with the underpinnings to deploy additional, interactive IP communications that deliver competitive differentiation.

Many VoIP service providers use TDM to connect with other partner carriers. This requires a pair of media gateways linked in a back-to-back configuration to convert voice traffic from VoIP to TDM and back to VoIP. Session controllers enable carriers to use IP to connect their networks and avoid the use of TDM. Because digital signal processor (DSP) resources are no longer needed, the session controller is able to reduce the cost of peering by 50% to 80%, depending on the capacity of the network interconnection. Carriers can also enjoy a greater return on investment in their existing TDM equipment, as TDM switch ports now used for VoIP-to-VoIP traffic can be harvested and redeployed for TDM traffic.

Operationally, carriers can be leaner organizations, with personnel trained on simpler IP technologies alone. The use of VoIP peering simplifies peering and reduces turn-up time and cost. One large carrier estimates that VoIP peering costs one-sixth of what traditional TDM approaches cost.

The new architecture for delivering real-time services is poised to radically transform business voice communications. Relying on a synergistic array of session controllers and softswitches, carriers will experience heightened return on investment for existing services and be able to simply and profitably introduce VoIP and other real-time services.

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Dan Dearing is Vice President of Marketing for NexTone Communications, Inc., Germantown, MD.

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