Multiplex communications – Diagnostic testing
Reexamination Certificate
1998-12-30
2004-04-20
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Diagnostic testing
C370S252000
Reexamination Certificate
active
06724729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates generally to network analyzers, and more specifically to synchronizing distributed systems for monitoring and analysis.
2. Description of Related Art
Local Area Network (LAN) analysis instruments are used to measure, characterize and test data streams on LAN systems. A prior art analyzer can have a control port that allows a remote entity, typically a personal computer (PC) executing the appropriate analysis software, to control the analyzer. The connection between the PC and the analyzer is usually a physical communications link, such as an RS-232 (presently referred to as an EIA/TIA 232) serial port, or a 10/100 megabits per second Ethernet link.
Certain tests, using test systems including two or more LAN analyzers, require that a test be started and stopped on multiple system analyzers at the same time. This requirement ensures that the data gathered from multiple data streams can be correlated together. Moreover, the internal timers of the multiple analyzers need to be synchronized together to ensure that time references from multiple measurements can be correlated.
Prior art systems for synchronization of distributed network analyzers include special and distinct cabling to provide the appropriate electrical signals between analyzers in a collection of analyzers for a particular network. The prior art cabling is also designed for specific analyzer requirements. For example, the Wandel & Goltermann Technologies, Inc., (located in Research Triangle Park, N.C.) DA-30 network analyzer provides clock synchronization and counter coordination by placing two analyzers in the same cabinet with the controller computer. The controller computer's clock is used to run both analyzers.
The network analyzers described in U.S. Pat. Nos. 5,535,193 and 5,590,116 operate most effectively when a bus, completely separate from the network to be analyzed, interconnects the analyzers. The bus for these systems preferably comprises several multiconductor computer cables that extend between parallel ports on each analyzer and the compatible port of the control computer, forming a daisy-chain parallel connection.
One disadvantage of the prior art occurs for daisy-chained, or bussed analyzers because these configurations place a limit on the number of analyzers that can be physically connected. For example, certain bus structures such as Small Computer System Interface (SCSI) buses, or IEEE 488 instrumentation buses limit the number of analyzers based on current drive and voltage limitations. For example, SCSI buses typically accommodate no more than eight analyzers. Prior art systems also typically use separate cables for control and clock information.
SUMMARY OF THE INVENTION
One aspect of the invention provides a method for synchronizing a distributed system. The distributed system includes synchronized analyzers and data streams. The distributed system supports multicast communications. The method includes selected synchronized analyzers receiving multicast information and communication packets. Each selected synchronized analyzer has processing resources including a synchronization decoder circuit, and one or more packet capture, analysis and generation circuits. The multicast information includes destination data corresponding to addresses of the selected synchronized analyzers. The synchronization decoder circuit decodes the multicast information. Responsive to the multicast information, the synchronization decoder circuit generates local signals. The synchronization decoder circuit transfers the local signals to one or more selected packet capture, analysis and generation circuits (PCAGC's).
In some embodiments, the synchronization decoder circuit receives the multicast information. For some of these embodiments, the synchronized analyzer processing resources include a medium access controller having a first data link layer address, and a central processing unit receiving the communications packets through the medium access controller. The synchronization decoder circuit has a second data link layer address. The first data link layer address differs from the second data link layer address.
In some embodiments, the data streams comprise transmitted data packets and include monitored data streams selected for analysis at one or more monitored analysis locations. The method includes, responsive to the local signals and the communication packets, the selected PCAGC's beginning processing of monitored data packets from monitored data streams at a start time. For some of these embodiments, the processing is adapted to analyze and manage the distributed system.
For some of the embodiments where the selected PCAGC's begin processing, the method includes the selected PCAGC's: capturing received monitored data packets at a monitored data receipt time, and labeling portions of the received monitored data packets with time-stamps to form time-stamped portions. The time-stamps correspond to the monitored data receipt times. The processing of the monitored data packets includes the selected PCAGC's: analyzing the time-stamped portions, the analyzing including generating analysis data, and storing segments of the time-stamped portions and corresponding analysis data in a memory. For some of these embodiments, the distributed system includes a control unit adapted to transmit the multicast information, and the method includes the selected PCAGC's transmitting analysis information corresponding to the analysis data to the control unit.
In some embodiments, the multicast information includes synchronization packets and control packets, and the local signals include synchronization signals and control signals. In some embodiments, the distributed system has analysis locations disposed in the data streams, and each of the selected packet capture, analysis and generation circuits is connected to one or more monitored analysis locations.
In some embodiments, the synchronization decoder circuit of a first selected synchronized analyzer receives the multicast information at a first multicast receipt time. The selected synchronized analyzers are adapted to ensure that the first multicast receipt time differs from the multicast receipt time corresponding to any other selected synchronized analyzer by no more than a maximum synchronization time. The maximum synchronization time comprises a parameter related to a smallest useful packet size and a network speed. The maximum synchronization time is less than approximately one microsecond. For some of these embodiments, the method further includes, responsive to the multicast information and the communication packets, the selected PCAGC's completing a first process for a first set of monitored data packets, the completing for each selected synchronized analyzer occurring at an end time.
In some embodiments, the synchronized analyzer processing resources include a central processing unit. The method includes the central processing unit receiving the communication packets. Responsive to the communication packets, the central processing unit generates commands; and the central processing unit sends the commands to the PCAGC's.
In some embodiments, the distributed system includes a control unit and a first network link. The first network link connects the control unit to the synchronized analyzers and connects the synchronized analyzers to each other. The synchronized analyzer includes a medium access controller. The method includes the control unit transmitting the multicast information through the first network link to the selected synchronized analyzers, and the control unit transmitting the communications packets through the first network link and the medium access controller to the central processing units of the selected synchronized analyzers. In other words the first network link is reused for transferring the multicast information, thereby avoiding the use of extra cabling for synchronization and control packet communication. For some of these embodime
Finisar Corporation
Harper Kevin C.
Workman Nydegger
Yao Kwang Bin
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