Report on t h e 20th Fault-Tolerant Computing Symposium Dr. Stanislaw J. Piestrak Technical University of Wroclaw Institute of Cybernetics Engineering Technical University of Wroclaw 50-372 Wroclaw, POLAND e-mail: sjp%amargosa@dkuug, dk I would like thank the SIGDA for providing me with a travel grant which enabled me to participate the symposium and present my paper. The 20th Int. Annu. Symp. on Fault-Tolerant Computing (FTCS'20) was held from 26th to 29th June, 1990 at the Newcastle Crest Hotel, Newcastle upon Tyne, UK. It has been a long time tradition of the FTC Symposia to have an outstanding high quality technical program. And the FTCS'20 was not an exception. It featured a well balanced program with contributions from both industry and academia which presented recent advances in the theory and commercial applications of fault-tolerant techniques. The symposium was organized into 19 sessions with 61 presentations. As usual, the symposium program was formed on a highly competitive basis: the papers were selected from 224 submissions, each refereed on average by four reviewers. Attending the FTCS'20 presented me not only with an opportunity to deliver my talk on the testability of sorting networks and their new applications, but also to view the current state of the art in the field of FTC. It was also an exceptional opportunity to meet and exchange ideas with the many other researchers from around the world. Since my reserach interest involves fault-tolerant design and testability, I was p a r t i c u l a r l y interested in technical talks regarding these subjects. However, I found the opening session particularly interesting. It featured three invited talks on t h e architecture of large-scale fault-tolerant computer networks for critical applications. First, Mr. M. N. M e y e r s o f AT&T p r e s e n t e d t h e a n a l y s i s of the nation-wide o u t a g e o f t h e AT&T's US l o n g - d i s t a n c e telephone switching network which took p l a c e o n J a n . 15, 1990 f r o m 2 . 5 0 pm t h r o u g h l l . 5 0 pm. The incident started with a hardware failure i n one o f t h e fault-tolerant Electronic Switching S y s t e m s (E SSs ) p l a c e d i n t h e N Y C . The r e c o v e r y of the faulty ESS was f o l l o w e d by s o f t w a r e r e c o v e r y a c t i o n s w h i c h , due t o i n c o r r e c t operation of the critical areas of software, eventually cascaded through the whole long-distant network. The incident, which involved a highly-reliable computer system using sophisticated fault-tolerant design techniques, pointed out the importance of proper verification of operation of a network of computers under critical conditions. The s e c o n d presentation, delivered b y Mr. Mr. E. Thomas, J. R e e v e s , a n d C. B i r k s , d e a l t with the Association f o r P a y m e n t C l e a r i n g S e r v i c e s (CHAPS) s y s t e m w h i c h p r o v i d e s the electronic credit transfer s e r v i c e f o r o v e r 300 b a n k s in the UK. F i n a l l y , dr. F. Cristian f r o m IBM d e s c r i b e d t h e f a u l t - t o l e r a n t techniques adopted in the SIGDA Newsletter, vol 21, number I

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