By Richard A. Quinnell, Contributing Editor
ATCA vs. MicroTCA— WHAT'S THE DIFFERENCE?
The Advanced Telecommunications Architecture (ATCA) serves as a framework for creating core telecommunications systems using standards-based components. Over time, such components help increase system performance and reduce system cost by promoting competition and allowing designers to assemble systems from interoperable, best-inclass elements. The MicroTCA architecture, currently under development, seeks to achieve the same goals for lowercost,-network edge, and enterprise applications. Low cost is one of the primary targets for the MicroTCA design. The current goal is to create a bare-bones, low-end MicroTCA system—including chassis, backplane, and virtual carrier card—for less than $500. The supporters of MicroTCA anticipate that the potential for high production volumes of advanced mezzanine cards, used in both ATCA and MicroTCA, will keep the card costs down, as well.
Let's take a look at the MicroTCA ARCHITECTURE
The MicroTCA architecture parallels that of ATCA, which simplifies the porting of applications and system management software to the MicroTCA platform. The two primary active components of a MicroTCA system are:
- Advanced Mezzanine Cards (AMC).
- Virtual Carrier Managers (VCM)
The AMCs are the system's workhorses, providing the processing power and system I/O. The VCM is the system's heart, managing data flow, fault management, and system control. As many as two VCM cards and 12 AMCs can operate together as a subsystem. All of the cards are hotswappable, allowing field replacement without needing to shut down system power.
The VCM utilizes the Intelligent Platform Management Interface (IPMI) to control system operation. It also provides the fabric switch for the AMC interconnections. The VCM functions as a replacement for the carrier module used in ATCA systems so that the AMCs can function without change in either ATCA or MicroTCA systems.
AMCs provide all of the MicroTCA system's functionality. They exchange data with one another over 60 high-speed serial bus lanes through the switch fabric that the VCM manages. The serial buses are physical-layer agnostic. MicroTCA systems can use 1- or 10-Gigabit Ethernet, PCI Express, Serial RapidIO, and other serial formats. All that is required of the serial bus is that it be capable of Internet Protocol (IP) transport. The backplane electrical specifications allow serial operations as fast as 12.5 Gbits/second.
In addition to the active system elements, the system definition includes power and cooling modules. As many as four power sources and two cooling system elements can be included in a MicroTCA system. The power sources may be able to support a 48V nominal dc source, as in ATCA systems, or an ac mains power source. The multiple power sources and cooling system elements allow a MicroTCA system to offer redundancy for fault tolerance.
The physical configurations available for MicroTCA design include both rackmount and stand-alone versions. Within a given chassis, the system can provide one, two, or four independent subsystems, each with its own VCM, to provide redundancy on a subsystem level as well as the redundancy available with individual elements. As with the ATCA systems they mimic, MicroTCA systems aim at providing 99.999% availability for telecommunications applications.
More info about MicroTCA Enclosures
The system enclosure for MicroTCA systems allow for several different configurations along with an ability to mix and match AMC sizes within an enclosure. The two basic formats are
- Cube enclosures (left)
- 19-inch rack-mount enclosures (right)
Within those basic formats are options for incorporating the power supply and fans in the sub-rack or make these elements independently rack-mountable.
Within the basic formats, there are many ways to divide up the space into isolated subsystems. Each subsystem must have a virtual carrier controller (VCC) to manage the card collection. Within a single enclosure, however, there may be one, two, or four independent subsystems, depending on how the backplane is configured. Further, the subsystems can contain a mixture of single-or double-wide cards of full or half height if the backplane allows.
The Advanced Mezzanine Card TAKES FLIGHT
The Advanced Mezzanine Card (AMC), defined by the PCI Industrial Computer Manufacturers Group (PICMG), was created to foster flexibility in the construction of ATCA blades. The blades were effectively carriers for the AMC modules, providing many opportunities for system developers to mix and match I/O and processor functions. The ATCA rack also provided card management for fault recovery and hot-swapping operations.
The AMCs, however, are capable in their own right. They offer many of the features needed in a telecommunications system, including system management interfaces, high-speed serial interconnections, and hot-swap capability. In addition, unlike many mezzanine-card formats, AMCs are front loadable and offer front-panel connector space. In effect, they can function as microblades providing processor power and system I/O when plugged into an appropriate backplane— without a carrier card.
AMC form factors allow four configurations but are all 180.6-mm deep, allowing them to fit within the envelope of traditional 300-mm deep European rack-mounted telecommunications equipment as well as the deeper US equipment racks. Cards can be single width and full height (73.5 mm x 13.88 mm) or half height (8.18 mm) as well as double width and full or half height. This gives developers enough flexibility to create cards as small as possible for their functionality.
Power dissipation of AMCs is currently limited to 60W for double wide cards. There is discussion within PICMG, however, to determine if 80W is attainable without compromising system reliability. The single-wide, full-height cards should require no more than 40W and the half-height cards no more than 20W to avoid heat problems in a system design.
Specifications for the AMCs are available from PICMG at www.picmg.org. An abbreviated version is available to the general public. Full specifications are free to PICMG members and available for purchase by non-members.
Where does MicroTCA GO FROM HERE?
The final specification details for MicroTCA are still being determined by the PICMG committees. Among the topics still to be resolved are the location and distribution of clocking within the sub-racks and the location of JTAG test control within the system. In addition, the connector definitions need refinement. As of today, MicroTCA systems cannot be created, although several proof-of-concept prototypes have been demonstrated at shows such as SuperComm 2005.
Nonetheless, the expected timeline of MicroTCA introductions indicates that developers should begin planning for them now. Members of the MicroTCA committee expect to put the proposal to ballot in April, 2006, which would allow system development to begin in earnest in the latter third of the year. This implies an initial rollout of MicroTCA systems in early 2007 with volume production occurring in the latter part of the year.
Developers do not need to wait, however. Even though the details of MicroTCA are still in limbo, the core elements are not. The AMC cards are fully specified as part of the ATCA system definition from PICMG. This means that developers can work on their functional system definitions and AMC card development now. By the time the MicroTCA specification is ratified, developers will be ready to begin assembling their AMC boards into a full MicroTCA system.
Who are the Advanced MEZZANINE CARD SUPPLIERS?
CREATIVE ELECTRONIC SYSTEMS
YAMAICHI ELECTRONICS USA INC.,
San Jose, CA.
Product URL: Click here for more information