Optoelectronics and Telecom Conference Proceedings


Author: Shawn Arnold
Company: iSuppli Corporation
Date Published: 11/14/2001   Conference: Optoelectronics and Telecom

Abstract: As the Telecommunications industry continues to search for greater transmission speeds, there has been continued migration towards optics as a basis for interconnects. This transition increasingly will move design away from the more common copper wire solutions currently available. As the “need for speed” continues to escalate, one of the gating items in existing backplane type system design is the ability to transfer the optical signals from one plug-in card or daughter card to another, or from one shelf to another, or from one system to another. The typical solution in existing designs and implementation is to individually plug optical fiber cables into the rear, or output, of cPCI or equivalent mechanical chassis, then separately, return the optical fiber cables as inputs to other cards even on the same shelf or alternately to a secondary shelf within the same chassis or rack. This solution creates a “rats-nest” or “spaghetti factory” chaotic management effect on the rear of the racks. Since many of these racks contain 1000, or greater, optical interconnects, and since these are most typically established in a redundant configuration, a standard redundant Optical Switch may have 2048, or greater, optical fiber cable interconnects, establishing a daunting management problem.

When these high density optical interconnect systems are assembled in the factory, there are many hours of manual labor involved in the assembly. Each manual hour represents the opportunity for potential build error, as would be inherently implied by the need to connect these 2048 optical cables. Even under the relatively controlled environment of a factory floor, crossed, or mis-wired optical cables are experienced as a common problem. The dual problems of labor inefficiency and opportunity for error are exacerbated when the systems products are installed in the field where service personnel are required to troubleshoot and/or fix one, among many, of these optical cables buried, perhaps, amongst the 2048 possible choices.

The International Product Design Inc., IPD, DigitalOptical backplane solution provides a hybrid of two current backplane technologies, utilizing a rigid FR-4, or other PCB laminate material base substrate and an optical backplane. By combining the optical backplane and the rigid backplane and providing a method to optically interconnect this DigitalOptical backplane to the plug-in or daughter cards, it becomes possible to remove all of the optical cables that exit the chassis as outputs only then to return as input cables, allow inter or intra chassis optical interconnection, and board-backplane-board optical interconnections. Current electromechanical standards include PICMG 2.16 Packet Switching Backplane, cPCB and VME64x. For the purposes of this article I will reference the cPCI specification, although the VME64x J0/P0 connector is identical to the cPCI P3 connector in location and function and all references to cPCI P3 infer VME64x J0/P0 compatibility. The bus is stated to be IEEE 802.3ab compliant and when implemented in the proposed manner establishes an Embedded System Area Network, ESAN. The bus, by use of the industry standard Ethernet, carries the advantage of allowing the ESAN to be “Hot Swap” capable with currently available software. This product will offer a very large advantage to Original Equipment Manufacturers, OEMs, attempting to release optical Fabric and Node Card products to market. This bus may also be used to remove overhead, (non-PCI based functions), from the PCI bus if the bus is implemented. The PICMG 2.16 cPSB committee has assured that this architecture will be robust by adding redundancy to the Node cards by provisions for dual Fabric cards, or the ability of each Node card to receive, or send, data to, or from, each of the Fabric cards. In the event of a failure of one of the Fabric cards, flexibility is provided for the second Fabric card to manage all of the data to, or from, the Node cards. In the event of a Node card failure, the Node card can be removed as a resource by the Fabric cards with an alert issued to the system operator of the failure of the Node card in order that it can be replaced without bringing down the entire system, establishing the Hot Swap capability.

Conceptual Overview- Currently, in the majority of applications, copper backplanes are used to deliver discrete signals, analog and digital, in either a daisy-chain, point-to-point or a bussed fashion, across a monolythic substrate to individual plug-in card slot positions. Typically, backplanes are also used to deliver power(s) and GND(s) to the individual plug-in or daughter card slots. Optical backplanes, which are currently in their infancy, are typically used solely to distribute optical cables from point to point in a serial manner. Recognizing that some optical backplane manufacturers have used splicing technologies to create multiple fiber cables from a single fiber, which could also be used for our application, this technology is very expensive and inaccurate at this time.

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