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Open Shelf Architectures Provide Foundation For Next-Generation Softswitches

By Stuart Jamieson, Artesyn Communication Products


As telecom OEMs (TEMs) retool and replace their traditional Class 4 and Class 5 switches with packet-based platforms, they must grapple with the age-old question of what to build in house, and what to outsource. What many TEMs are finding is that they can no longer remain competitive from a cost or time-to-market perspective developing custom systems from scratch in house. And even if they could, they lack the manpower. It takes a large staff to design, develop, manufacture, maintain, test, and support proprietary architectures in house, and TEMs are reducing their workforces, not expanding them.

To facilitate outsourcing, many softswitch OEMs are adopting open architectures with standard interfaces such as PICMG 2.16 and AdvancedTCA. These platforms reduce design, test, and manufacturing costs by enabling TEMs to utilize standard, pre-tested, off-the-shelf components, which enjoy larger economies of scale. They reduce stocking costs by enabling TEMs to standardize on a smaller number of blades and modules that can be reused across multiple product lines. They enhance functionality by giving TEMs easy access to best-of-breed third-party products. And they enhance product differentiation by enabling TEMs to focus on value-added application software and services.

Open Platforms Evolve
PICMG 2.16 and ATCA are the first open platforms that can provide the telecom-specific features that TEMs need to build scaleable, field upgradeable, high-availability infrastructure systems. Theyre also the first open platforms to provide the flexibility and headroom that TEMs need to keep ahead of the fast-changing softswitch landscape.

Both PICMG 2.16 and ATCA provide the bandwidth needed to support large number of blades working together at the shelf level to perform compute- and data-intensive control and media processing functions. They also provide the packet- and TDM-based transport mechanisms that are needed to implement softswitch functions such as signaling and media gateways, which facilitate interoperability with the PSTN.

PICMG 2.16 supports packet-based Ethernet transfers over the backplane at speeds of up to 1 Mbit/sec per channel. It also provides a dedicated H.110 telephony bus for acquiring and processing TDM data. ATCA provides a redundant (up to full mesh) switched fabric that scales up to 10 Mbit/sec per channel and supports multiple packet based protocols (Ethernet, PCI Express, RapidIO, etc). Both PICMG 2.16 and ATCA blades are hot swappable, enabling the blades to be upgraded and replaced in the field without disrupting overall service, a key requirement for maximizing availability.

To enhance flexibility and make outsourcing even easier, both PICMG 2.16 and ATCA are available with mezzanine expansion options. By combining a generic PICMG 2.16 or ATCA blade with application specific modules for media processing, signaling, packet processing, network management and control, TEMs can outsource a broad range of functions at the blade or module level. This modular approach not only speeds time to market and provides access to low-cost mass market products, it reduces the number of unique blades that TEMs and service providers have to design, manufacture, and stock. For field replaceable mezzanine solutions like AdvancedMC, it enables service providers to service, provision, and spare their systems with a finer degree of granularity, thus reducing cost.

Most PICMG 2.16 systems use PMC (PCI Mezzanine Card) for mezzanine expansion. PMC is also available in telecom-friendly configurations such as ProcessorPMC (PrPMC) and PTMC (PCI Telephony Mezzanine Card). These mezzanine formats can support TDM data transfers (in addition to PCI) and enable processors residing on the module to act as the master processor for the PICMG 2.16 blade.

ATCA systems can also utilize PMC mezzanine expansion. However, PICMG has developed a module specification specifically for ATCA known as AdvancedMC, which is optimized for ATCAs switched fabric, physical size, hot swap, and system management facilities.

Both PICMG 2.16 and ATCA platforms support Integrated Peripheral Management Interfaces (IPMI), a system management interface that enables network management systems to directly provision, control, and program all softswitch subsystems. Through IPMI, shelf management and network management systems can monitor and control individual blades, negotiate power allocation, detect faults, and coordinate failover. As befitting the next generation of mezzanine modules, AdvancedMC modules also support IPMI, giving shelf managers even greater visibility into and control over blade and module operation.

Softswitch Architecture Evolves
Todays most advanced softswitches offer packet-based wireline and wireless call control, switching, and application services. Distributed throughout the packet network, softswitches work together to establish connections and facilitate the transport of user data between end points. They also control, and in some cases contain, the signaling and media gateways that bridge packet networks with the PSTN and maintain compatibility with traditional PSTN terminals, while supporting the latest IP-based (SIP and H.323) end points.

The term softswitch is often used interchangeably with MGC (Media Gateway Controller). Increasingly, however, the term softswitch refers to a more highly integrated platform that combines the MGC with the media gateway, signaling gateway, shelf management, network management system, and interfaces for billing and provisioning. Collectively, these systems replace and interoperate with the Class 5 switches that are used throughout the PSTN to provide trunking, SS7 networking, translations, routing and network services.

To see how softswitch components interact with each other and the PSTN, it is helpful to trace the call control process for two cases, one in which both endpoints are IP based, and the other in which one of the endpoints is PSTN and the other is IP. When both endpoints are IP based, the source end point (such as a VoIP phone) initiates the call by sending a request to the MGC, which locates the destination endpoint and responds to the source endpoint (either number not found or trying). The MGC then sends a request to the destination endpoint, which, if available, starts ringing. The MGC also sends a message to the source endpoint to start ringing. Once the call is answered at the destination endpoint, and the MGC receives a pick-up message, it sets up a bi-directional voice channel through the media gateway, which performs (if necessary) the VoIP voice data processing (e.g., echo cancellation, codec conversion).

The call process is more complex when one or both of the end points are PSTN (phone, modem, fax, and so on). Consider the case, for example, where the originating end point is a PSTN phone, and destination is a VoIP phone. After the PSTN phone picks up and starts dialing, the PSTN switch sends an ISUP message to the MGC (via the SIGTRAN signaling gateway), which sends a request to the VoIP phone. If the VoIP phone is available, the MGC tells it to starts ringing. The MGC also sends a ringing sound (via the media gateway) to the PSTN switch, which relays it to the PSTN phone. When the VoIP phone picks up, the MGC informs the PSTN switch, which works with the MGC to set up a bidirectional voice channel through the media gateway.

Open platforms like PICMG 2.16 and AdvancedTCA provide an excellent platform for building scaleable, high-availability softswitches, from dedicated MGCs, to complete softswitch systems with integrated gateways, network management, application and accounting functionality. These platforms reduce time to market and cost by enabling TEMs to outsource substantial portions of their softswitch design. They also reduce capital and operational expenditures by providing a modular, flexible, field upgradeable framework that can be serviced and provisioned with a fine degree of granularity, and readily adapted to support next-generation softswitch services and architectures. IT

Stuart Jamieson is the Business Development Director with Artesyn Technologies, Communications Products Division. For more information, please visit the company online at

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