Acceptance of telecom industry standards for rack-mounted server equipment — in the form of the PCI Industrial Computer Manufacturer’s Group (PICMG) standards — is gaining momentum throughout global market channels. The objectives of those standards are certainly attractive in terms of streamlining economy and efficiency for both carriers and telecom equipment manufacturers across a number of areas. Their aim is to reduce development time and costs, as well as to help reduce the total cost of ownership. They are also intended to offer high levels of modularity and configurability while delivering high levels of service availability (99.999% and greater) and supporting appropriate scalability of system performance and capacity.
The PICMG standards address all aspects of server-based operation — everything from hardware and software compatibility to interconnection standards and physical configurations. Even the fastening and mounting hardware requirements of each unique specification play an important role in trouble-free hot-swapping of modular components in an open architecture rack-mounted installation (Figure A.).
Within the overall PICMG standards for modular telecom applications, there are three levels of specifications:
- AdvancedTCA® (also known as Advanced Telecom Computing Architecture or ATCA) is the common name for the PICMG 3.0 core standard that dictates board, backplane and shelf mechanical assembly, power distribution, and connectivity required for system management. This application is devoted to larger rack-mounted installations at central offices forming the core of a system.
- AdvancedMC™ (also known as Advanced Mezzanine Card) addresses the AMC.0 stand ard for a series of individual-function mezzanine card modules assembled onto a single carrier board that then mounts into an AdvancedTCA rack system. With multiple modules per carrier and multiple module height options, this application provides greater flexibility for adding discrete functions at the periphery of the system.
- MicroTCA™ (also known as Micro Telecom Computing Architecture or μTCA) is complementary to the AdvancedTCA standard and defines the use of AMC.0 mezzanine cards plugged directly into a backplane. This permits the configuration of multi-function applications with a lower entry cost or smaller physical size.
In addition to providing specifications for connector and signal interfaces, each level also has its own specifications for front-panel fastener and access hardware. These specifications provide for the convenience of safe hot-swappable component replacement, flexible configuration options, common physical dimensions, and multi-vendor compatibility.
Essential Factors of the AdvancedTCA Standard
The mounting hardware specifications of the Advanced - TCA standard (PICMG 3.0) revolve around several key points — protection of electronic circuitry during hot-swapping, reliable engagement of the faceplate/circuit board during operation, and allowances for electrostatic discharge (ESD) or electromagnetic compatibility (EMC). A variety of hardware solutions developed according to these specifications offer advantages for telecom carriers, equipment OEMs, and contract manufacturers who adopt the standard and match the appropriate hardware solutions to their specific equipment designs.
A complete AdvancedTCA fastening hardware solution includes a series of components each designed to meet the dimensions and functionality of the standard (Figure B):
- Handles. AdvancedTCA handles serve multiple functions. Most important, they rotate to lock the board in place (ensuring that their board-edge connectors interface properly with the backplane of the shelf). They also provide a feature to activate and deactivate a microswitch to signal a hot-swap event. Designed to allow for maximum faceplate I/O space, they also provide an easy means of gripping the board for removal.
- Captive retention screws. These screws provide a physical means of anchoring board faceplates to the rack system. Their captive design assures that they stay with the board/faceplate assembly when it is removed, preventing loss of the fasteners and potential damage that could be caused by screws falling into other electronically active components.
- Alignment safety ground pins. These provide a physical alignment device for precise positioning, as well as a safe path for grounding the circuit board during insertion and removal.
- Keying blocks and Rear Transition Module (RTM) alignment pins. These components are designed to ensure proper positioning and contact between compatible circuit boards and their backplane connections. Different pin configurations are available to ensure that only appropriately designated boards can make an electronic connection.
Essential Factors of the AdvancedMC Standard
Modular flexibility for configuration, reconfiguration, and module replacement are essential concepts in the AdvancedMC standard. The AMC.0 standard allows for multiple mezzanine card modules of three different heights (compact, mid-size, or full-size) and two different widths (single or double) to be configured on a single carrier board that then fits into a standard AdvancedTCA chassis backplane. Two to four full-size or mid-size AdvancedMC modules, or four pairs of compact AdvancedMC modules, fit across the face of a single carrier board. Each module typically performs one discrete function. This design permits up to eight discrete functions to fit on a single AdvancedMC carrier board occupying the same form factor as an AdvancedTCA front board. In the event of a component failure, all other functions on the carrier board can continue uninterrupted while only the single faulty module is hot-swapped out for replacement. There are three types of hardware components in the AMC.0 standard (Figure C).
- AdvancedMC Module Handle. Like the AdvancedTCA handles, AdvancedMC Module Handles provide the capability to activate and deactivate a micro - switch to signal a hot-swap event of a single module from an AdvancedMC Carrier Board. Each handle is required to have three distinct positions of operation: module latched, with microswitch engaged; module latched, with microswitch disengaged; and module unlatched with card able to be extracted.
- Light Pipe Bracket. The AMC.0 standard calls for color-coded status LEDs operated by signals from the module and its mating microswitch as a means of identifying the operating status of the module. It permits using either an LED on the front edge of the module circuit board or using a light pipe to connect to an LED farther back on the board. An AdvancedMC light pipe bracket consists of both a light pipe housing and a light pipe lens to transmit the signal from an LED located farther back on the board.
- AdvancedMC Carrier Board Handles. The cutaway carrier boards used to hold AdvancedMC modules have the same form factor as an AdvancedTCA front board, but with most of the faceplate cut away to accommodate full-sized or paired compact AdvancedMC modules. That requires special handles that do not interfere with the insertion or extraction of the mezzanine card modules from the carrier — an upper latching handle, and a lower latching handle with a switch arm for microswitch actuation.
Essential Factors of the MicroTCA Standard
The MicroTCA standard is complementary to the original AdvancedTCA standard, in terms of using discrete function boards or modules that plug directly into a backplane. But it allows for much smaller physical configurations, such as a 4U high 19-inch shelf or an 8-inch cube. This makes it very useful for a variety of smaller, more affordable configuration applications such as WiMAX access points, DSLAMs, and VoIP access gateways to high-end telecom applications.
Because the MicroTCA standard takes advantage of the same module formats that are used in the AdvancedMC standard, the module handles and light pipes are physically the same as those used for AdvancedMC installations.
- MicroTCA Module Handles. Using the same handles as those used for mezzanine card modules in the AdvancedMC installations provides for consistent form, fit, and function throughout an installation or an organization.
- MicroTCA Light Pipes. The light pipes provide an indication of the operating status of the module, allowing for quick and easy identification and hot-swapping of modules during system use, without risk of shorting or equipment damage.
Status of PICMG Applications in Today’s Telecom Industry.
Although awareness and acceptance of the PICMG standards have grown steadily, implementation of each standard has followed the needs of the marketplace. While the AdvancedTCA concept was the first to be introduced, the AdvancedMC applications might soon outnumber AdvancedTCA applications in terms of number of units implemented and the amount of hardware sold. This is due, in part, to the nature of each application.
AdvancedTCA installations are geared toward the core of the network, so the majority of use is being seen in new (i.e. wireless) applications as opposed to extensive retrofitting of legacy applications. On the other hand, AdvancedMC applications, which provide greater flexibility for applications at the edge of the network, offer opportunities for faster growth in the near future.
However, while recognition and acceptance of the standards continue to grow, there are still some practical considerations to take into account in terms of physical implementation. One of those is that even within the standards, there can be dimensional variations that affect the relationship between a specific handle and a specific microswitch mounting style. For this reason, it pays to evaluate all facets of fit and functionality carefully in the early stages of system design. An experienced hardware provider can help you match appropriate handles and microswitches to ensure smooth operation. A guide to understanding the standards and front-panel hardware requirements is available from www.southco.com/ATCAguide .
This article was written by Rick Schlack, Senior Principal Engineer, Southco (Concordville, PA). For more information, contact Mr. Schlack at