MicroTCA is the latest generation of open-architecture platforms developed for telecom equipment design. The first telecom platform, AdvancedTCA, combined a hot-swappable, multi-protocol switched fabric backplane with large form-factor cards and a high power capability to allow the creation of high-density, high-performance telecom systems.

In 2005, the definition of AdvancedMC mezzanine modules enhanced the modularity of AdvancedTCA systems by allowing developers to create blades that combined individually hot-swappable interface modules, mixing and matching functions as needed.

Taking this modularity to the next level, MicroTCA leverages AdvancedMC modules to meet the needs of compact, low-cost systems by connecting AdvancedMC cards directly to a backplane, without the need for a carrier card.

Eliminating the ATCA carrier allows MicroTCA to offer a wide variety of form factors for designers to choose from, including custom “pico” assemblies for applications that need only a few modules for the entire system.

MicroTCA, like ATCA, is based on AdvancedMC

AdvancedMC modules employ a field-replaceable serial packet interface that can have as many as 20 I/O channels running as fast as 12.5 Gbits/sec per channel. The channels are protocol-agnostic, enabling them to support a variety of packet-oriented communications protocols, including Ethernet, PCIExpress, and Serial RapidIO.

Physically, the modules offer several footprints (Figure 1) as well as power capacity as great as 80W. AdvancedMC modules are hot-swappable, enabling them to be individually field-replaced without taking the system off-line. In addition, they support IPMI (Integrated Peripheral Management Interface) system management, which enhances availability and serviceability by allowing shelf management to identify faults and take corrective action at the module level. IPMI utilizes an I2C-based physical interface that allows monitoring of system health characteristics such as voltages, temperatures, and fan speeds. IPMI also supports automatic event notification, remote shutdown and restart, and dynamic power allocation to individual AdvancedMC modules.

Figure 1: AdvancedMC modules come in a variety of standard sizes to support design flexibility.

In MicroTCA, AdvancedMC modules plug directly into the backplane without requiring any modification. To replace the control functions of the ATCA carrier, MicroTCA utilizes a MicroTCA Carrier Hub (MCH). This module provides the switched fabric, shelf management and optional clock distribution, for a chassis, acting as a fabric-star hub offering one or more high-speed serial lanes to each module along with a central switch for the lanes. One MCH module can support as many as 12 AdvancedMC modules in a system.

The backplane of a MicroTCA system can be designed to support star, dual-star, and mesh topologies. For high-availability telecom system designs, the backplane can provide redundant IPMI interfaces, allowing two MCH modules to be employed in a single chassis. In addition, the backplanes support the connectivity for redundant power sources, the intelligence being provided by the power modules themselves.

In addition to the backplane and modules, a MicroTCA system (Figure 2). consists of at least one AdvancedMC, at least one MCH, and all the interconnect, power, cooling, and mechanical resources needed to support them. These resources include the sub rack, power modules, backplane, and cooling units. Together the cards and their support resources form a shelf that can operate as a stand-alone system or be combined with other shelves to create a larger system.

Figure 2: The MicroTCA specifications cover the full system design, including controllers, power sources, and cooling systems in addition to the modules and backplane.

Various systems sizes and footprints provide flexibility for design options

One significant advantage of MicroTCA is that it allows the functionality of ATCA to be scaled to very small configurations. The AdvancedMC module’s physical definitions have proven generous enough to allow the implementation of complex telecom functions in a single module, while small enough to allow cost-efficient design partitioning. By using those modules directly, without a carrier card, MicroTCA gives designers considerable flexibility in design reuse.

An ATCA server blade, for instance, might use a processor AMC connected via serial ATA (SATA) or serial attached SCSI (SAS) to a hard-disk AMC and via serial RapidIO to an E1/T1 interface AMC. The carrier board provides the module interconnections and the whole assembly forms a server blade that would connect with other blades over gigabit Ethernet to form a large network server system for a central office installation.

Using MicroTCA, the same design can be scaled down to the equivalent of a single blade to meet the needs of a local area network without implementing a full ATCA system. The processor AMC, E1/T1 AMC and disk drive AMC plug directly into the MicroTCA backplane and the MCH automatically establishes the GbE Interface between all the modules and the rest of the network. The MCH can also provide sRIO connectivity between the E1/T1 AMC and the processor AMC, to allow mini-server to have connectivity to the telecom network. Finally the SATA/SAS connection between the processor AMC and the disk drive AMC is provided by point-to-point links on the backplane. In some cases however, disk arrays may be managed by a dedicated AMC controller.

These designs could take advantage of MicroTCA’s “pico” shelf size, which allows for a minimum configuration of one or two AdvancedMC modules in a fully functional shelf. The pico size is well suited to systems with modest performance needs and a minimum of available space. Other small-footprint configurations, including custom designs, are also possible within the MicroTCA specification.

MicroTCA can also target traditional rack-mount enclosure installations, offering several standard options (Figure 3). Rack-mounted shelves can accept compact, mid or full, single-or double modules in mixed configurations. A special configuration, the cube, provides additional flexibility. Cubes can be designed to fit together to occupy a rack width while remaining independent functions, providing a finer degree of modularity than a full rack-wide shelf.

Figure 3: Compact designs with a variety of form factors are possible within the MicroTCA specification.

These different system footprints allow designers to trade off size and system capability to create the optimum mix for their applications. The range of performance levels achievable using MicroTCA, as defined by backplane bandwidth, covers a host of applications, including digital loop carriers, optical ADMs, wireless base stations, and Fiber-to-the-Curb optical network units (Figure 4).

Figure 4: Systems built to the MicroTCA specification are compact, but offer enough performance to handle a wide range of telecom applications.

In designing their systems, however, developers will need to pay careful attention to air flow and heat. The board density that MicroTCA achieves along with the power ratings the AMC boards support means that MicroTCA systems can easily develop hot spots.

Design efforts should include a full thermal profile for the system, including evaluating board placement as it affects air flow. In addition, designers creating custom AMC modules should follow the power limits suggested in the AMC specification and not try to run their boards “hot” to squeeze out additional performance. Variations from the specifications make it harder to obtain MicroTCA’s full benefits.

Reducing costs through reuse of components

MicroTCA’s full benefits include providing vendors with increased market opportunities for their AdvancedMC modules, which can reduce costs for system developers. Because the carrier and shelf management functions of a MicroTCA system replicate the management of the ATCA architecture, MicroTCA development efforts can apply AdvancedMC modules and their support software without modification. By thus extending the applicability of AdvancedMC modules to smaller, lower-cost systems, MicroTCA enables vendors to enjoy greater production volumes and realize economies of scale that allow them to lower prices. Similarly, developers of custom AMC modules for their own ATCA systems can enjoy the cost reduction benefits of reusing their module designs to create a product family with a range of performance levels.

Many aspects of the MicroTCA and AdvancedMC standards serve to enhance this reuse. For example, the standards allow three different fitting types for AdvancedMC connectors: compression, surface-mount, and press fit. For each of these three types of connectors a common footprint has been was proposed, aiming to provide multiple sources for backplane connectors. This will allow competition in that market space, and permit replacement of one connector manufacturer for another.

AdvancedMC modules offer physical compatibility despite individual differences in the module’s manufacturing process. By thus providing a common interface requirement, a TEM can allow vendors to provide similar functions. This then allows multiple sourcing, which in turn, lowers developer risk when applying the modules and as a byproduct encourages the adoption of AdvancedMC. This common interface ability is especially important in markets where developers do not want to depend on a single vendor.

The reuse of ATCA elements along with the size and performance scalability of MicroTCA now extends the range of the Advanced Telecommunications Computing Architecture (ATCA) to cover nearly all telecommunications applications. The original ATCA specification covers the larger end of system needs, while MicroTCA provides a more compact architecture that offers considerable design flexibility for smaller installations. At the same time, by leveraging the modular software and hardware developed for ATCA, MicroTCA keeps development costs down while maintaining the performance and reliability that telecommunications applications require.

Stuart Jamieson is an Architect with Emerson Network Power.