The signaling gateway bridges next-generation IP and traditional packet-switched telephony networks (PSTNs) that handle, for example, the signals for establishing, controlling, and billing calls. Gateway design calls for the blending of IP-based protocols, conventional switched-circuit protocols, operating systems, management, and high-reliability hardware system design. MicroTCA, AdvancedMC hardware, and offthe- shelf software can provide building blocks to develop standalone signaling gateway designs that can scale with the growing demand for IP-based telephony.
Telephony needs two types of gateways: the media gateway for handling voice, video, and data, and the signaling gateway to handle call control. Some European telephony systems use the same physical link for both functions. Therefore, the media and signal gateways can be the same device. However, others—including the networks in North America—have signals and media travel on different physical links. Consequently, developers can separate the media and signaling gateways into independent units.
One way to address both types of installations is to create a standalone signaling gateway in module form that can serve as a component or building block in either system type. The module form allows it to plug into an available AMC site to create a combined gateway design as one system element. Or, it can serve as the basis of a pure signaling gateway that scales to handle growing call volume simply by adding more gateway modules.
The gateway module hardware design has to provide PSTN ports, typically handling E1/T1/J1 PSTN signals at a 64-kbit/s data rate for each SS7 link, with grouping for high-speed links (both clear and ATM-based). Gateways also have processors that can run both PSTN and IP networking stacks and at least two IP ports, such as Gigabit Ethernet connections, so they have redundant links to the IP network. While this seems simple, the design of a standalone gateway module can become a major challenge.
To meet telecom needs, the gateway must be designed to be available at least 99.999% (five nines) of the time. This requires an ability to cope with software and hardware failures while maintaining uninterrupted service. The ability to upgrade and/or replace hardware and software is another critical part of supporting five nines, requiring software redundancy with load-sharing and fail-over capability. In addition, the hardware supporting that software, including the module, rack, power modules, fans, and interconnect, must detect and respond to system failures (utilizing redundant hardware), provide the means to hot-swap equipment, and support a mechanism for software/firmware upgrade.
System management support is also needed because the gateway typically operates in the network as a “black box,” functioning without operator intervention. Thus, it needs to provide self-management of its hardware and protocol stack operations, including failure detection and response. Furthermore, the design needs support for setup and control of the gateway’s operation when it’s first installed in the network.
XTCA MEETS GATEWAY NEEDS
One way to reduce the magnitude of this challenge is to use a base framework that handles these required functions for the modules/blades, freeing the designer to focus on the gateway functions. The Advanced Telecommunications Computing Architecture (ATCA) and MicroTCA (combined, they’re considered xTCA) are open specifications that can address these system needs. Numerous vendors have created system building blocks based on these specifications.
A signaling gateway design based on ATCA or MicroTCA specifications, then, starts out with a significant amount of the work already completed and available as off-the-shelf hardware and software from a variety of suppliers. The specifications’ controlling organization, PICMG (PCI Industrial Computer Manufacturers Group), runs an interoperability program to promote interoperability, freeing designers to mix and match components as desired.
Both ATCA and MicroTCA use a modular design approach that builds system management and hot-swap capability into its components. As part of this, the Advanced Mezzanine Card (AMC) was initially developed as an extension to the flexibility of ATCA (by providing a hot-swappable mezzanine card for such purposes as I/O) and has since expanded its role to become the basic foundation of MicroTCA.
In ATCA, the AMC, as its name implies, is a mezzanine card that resides on a larger system card or blade, which then plugs into the system backplane. In MicroTCA, the same AMC card plugs directly into a backplane. With this approach, a common AMC design can serve without modification in systems providing a large level of scalability.
The ATCA and MicroTCA architectures offer built-in support for the design of high-availability systems. Each AMC module incorporates a module management controller (MMC) that provides a mechanism for remote control of the module’s power, operation, and backplane connection.
For MicroTCA, a MicroTCA carrier hub (MCH) within the chassis provides system management and interacts with each module’s MMC (Fig. 1). (In ATCA systems, these functions reside in combinations with the shelf management controller and the IPMC on the ATCA card capable of supporting AMCs). The interaction between MCH and MMC allows the MCH to turn AMCs on or off, interrogate them, and disable their backplane access. This gives the MCH an ability to deliver services such as electronic keying, fault detection, and fault isolation at the module level.
Options within the MicroTCA architecture support the use of redundant power supplies, cooling fans, and MCH control modules. As a result, a system can readily be designed with full hardware redundancy running high-availability system software, much of it available off-the-shelf.
Emerson’s Centellis 1000 MicroTCA chassis, for example, provides a single MCH module, with redundant power supplies. It can hold as many as 10 additional full-size AMCs, allowing it to support a variety of applications. The Centellis 500 MicroTCA chassis is a low-cost-of-entry solution using one standard MicroTCA MCH and power module to support four mid-size AMCs. The two solutions offer designers flexibility in gateway size and architecture for their particular application.
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