International Business Machines Corporation

Ernst H Rothauser

Ronald Pete Luijten

Rolf Clauberg

Andreas Guenther Herkersdorf

Werner K Bux

Erwin A Zurfluh

Philippe A Janson

Johann R Mueller

Marco Heddes

Antonius J Engbersen

Daniel Wild

Hugo K Seitz

Heinz J Keller

Hans R Muller

Armin U Blancha

Roy C Dixon

The dynamic functional behavior of geographically distributed fast packet switching systems, including those which accommodate high-priority circuit switched traffic and low-priority packet switched traffic, are tested in real-time by sending test packets from one or more source nodes through the system to specific destinations that comprise a test packet analyzer. The test packets have the same structure as the data packets, but in their payload portion carry the entire information required to perform the testing. The nature of that test information depends on the characteristics of a set of predefined system errors the verification system is supposed to identify. For detecting errors, the test information would include an input address indicating the source of the test packet, a sequence number defining the order in which the packet should arrive at the destination, time bits relating to the packet length and/or to the expected packet transmission delay, and a cyclic redundancy code which covers the entire contents of the test packet, including its control portion. Each analyzer at a receiving station operates autonomously from the senders and processes all received traffic in real-time; this enables it to recognize all defined system errors, even those occurring with very low probability, at the packet level.

Method and apparatus for testing and evaluation of distributed networks

This chip-to-test (1) has a passivation layer and an overlayer at test points (4). The system comprises a vacuum chamber (8), means (2) for mounting and connecting the chip-to-test (1), a pulsed light source means (9) operable to scan the chip-to-test (1) for inducing photoelectron (15) emission therefrom, means (14) for exercising the circuits of the chip-to-test (1), means (18) for detecting the photoelectrons (15), having a detection threshold and delivering a sequence of signals representative of voltages at the currently scanned test point (4') or points as a function of the scanned point or scanning time, means (23) for flooding the chip-to-test (1) with electrons of energy lower than the detection threshold, means (21) for analyzing said sequence of signlas and means (22) for deriving therefrom a capacitive voltage contrast. The material of the overlayer has a work function lower than the photon energy and can be BeO, MgO, CaO, TiO2, more preferably SrO, Cs2O, BaO or a mixture thereof. This system facilitates testing of a chip-to-test whose passivation layer has a work function above the photon energy, and prevents charging-up of the passivation layer.

Method and system for contactless testing of electronic activity in an

In a communication system providing multiple access to transmission facilities for a plurality of stations (17, 21), two separate networks (11, 13) are provided: One is a token ring (11) on which access tokens and data are transmitted, the other is a high-speed optical fiber transmission ring (13) on which only large-volume data blocks are transmitted between particular stations (21) which are attached to both rings, but no access information. A token manager (27) in the token ring (11) provides at regular intervals particular tokens that are only used by the particular stations (21) for obtaining access to the high-speed ring (13), but also provides other tokens for regulating access to the token ring (11) for other stations (17). Special access nodes (23) are provided which allow to connect the particular stations (21) to the high-speed ring (13) without extending its length.

Communication system comprising overlayed multiple-access transmission

In a network of communication rings (R1 . . . R7, BB) interconnected by bridges (B1 . . . B4), access to each ring is regulated by a circulating token which is normally issued at irregular intervals depending on occurrence and length of messages. To enable communication of messages which have to be transmitted synchronously, i.e., at regular intervals, each ring has a synchronous bandwidth manager SBM which periodically issues a token for only synchronous information. Each SBM is located in a bridge node (13, 15) but only one of them which is located in a particular bridge node (15) is the master SBM from which all other SBM's are synchronized, using a synchronous token and/or special synchronization circuitry in each bridge. This allows a common period in the whole network for handling synchronous information, even if all rings have different bit rates.

Synchronization in a communication network of interconnected rings

In a communication network comprising block switching nodes interconnected by transmission links, a flow control mechanism is provided in each switching node for regulating the flow of addressed data blocks or messages. A hardware look-ahead mechanism effective within each node tests for each data block received from a link and buffered at an input port, whether it can be accepted at the appropriate output port of the same node for further transmission. A token mechanism effective over links permits maintenance at each output port of a node of an indication whether any data block can be accepted in the input port at the other end of the respective link. By the combined operation of look-ahead mechanisms and token mechanisms the flow of addressed messages in a direction where the transmission path is already filled up is prevented. This has a positive smoothing effect on overall traffic flow where short-time or local overloads occur.

Flow control mechanism for block switching nodes

A method is disclosed by which several data stations which use a single communication channel, and which are simultaneously ready to transmit a data packet, can send a request for channel allocation, and will be granted the channel each for one data packet transmission, all within one time frame without central control, polling, or collisions. Addresses of all data stations desiring channel allocation are interleaved and superimposed in a specific manner for transmitting the requests, and by observing the resulting common signal, each data station determines when it can send its data packet. An arrangement for a data station is also disclosed which comprises the means necessary for transmitting address characters in an interactive procedure simultaneously with other stations, and for determining the allocated packet time slot.

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Reichenburg, Switzerland

Ernst H Rothauser