Control and Reliability of Optical Networks in Multiprocessors
Abstract
Optical communication links have great potential to improve the performance of interconnection networks within large parallel multiprocessors, but semiconductor laser drive control and reliability problems inhibit their wide use. This report describes a number of system-level solutions to these problems. The solutions are simple and inexpensive enough to be practical for implementation in the thousands of optical links that might be used in a multiprocessor. Semiconductor laser reliability problems are divided into two classes: transient errors and hard failures. It is found that for transient errors, the computer system might require a very low bit-error-rate (BER), such at 10(exp-23), without error control. Optical links cannot achieve such rates directly, but a much higher link-level BER (such as 10(exp-7) would be acceptable with simple error detection coding. A feedback system is proposed that will enable lasers to achieve these error levels even when laser threshold current varies. Instead of conventional techniques using laser output monitors, a software-based feedback system can use BER levels for laser drive control. Experiments demonstrate that this method is feasible anti has other benefits such as laser wearout tracking and optical loss compensation. For hard failures, one can provide redundant spare optical links to replace failed ones. Unfortunately, this involves the inclusion of many extra, otherwise unneeded optical links. A new approach, called 'bandwidth fallback,' is presented that allows continued use of partially failed channels while still accepting full- width data inputs, providing high reliability without any spare links. Redundancy, Optical communication, Laser drive control, Feedback, Interconnection, Semiconductor laser, Threshold current, Switch network, Bit error rate.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 22, 1993
- Accession Number
- ADA277385
Entities
People
- James J. Olsen
Organizations
- Massachusetts Institute of Technology