Protocol analyzers

General block diagram of the protocol analyser is demonstrated on the following figure:

    
    o     +------------+   +---------+         +------+   +-----------+
  t b --->|            |   | event   |         Capture|   | event     |
  e j --->| measuring  |-->|   and   |-------+>|filter|-->|  and      |
  s e <---| interface  |   | message |       | |      |   | message   |
  t c <---|            |<+ |retriever|<---+  | |      |<+ | buffer    |
    t     +-----+------+ | +---------+    |  | +------+ | |Capture RAM|
                |        |                |  |          | +-----+-----+
                ^        |                ^  |          ^       |
                |        | +-----------+  | +v-------+  | +-----v-----+
                |        +<| message   |  | |state   |  | |  Report   |
                |          | generator |<---|machine |  | | generator |
                |          +-----------+  | +--------+  | | and filter|
                |                ^        |     ^       | +-----+-----+
                |                |        |     |       |       |
          +-----+----------------+--------+-----+-------+-------v-----+
          |             Control computer                              |
          |           configuration and                               |
          |   display, storage, recording of results                  |
          +-----------------------------------------------------------+

• Measuring interface module(s)
  fit the standard access points of the media network to the inner circuits of the tool. Almost the whole range of standard interfaces is used here: V/X interfaces, ISDN BRI PRI interfaces, LAN (Ethernet, token-ring, FDDI) interfaces, SDH, ATM etc. It is also in use to build several (types of) interfaces into the analysers.
• Event and message gainer module
  These modules of the analyser disassemble the frames of the tested interface and pick out of them the transmitted data and the information related to the status of the interface (e.g. control signals).
• (Capture) filter module
  Users often interested in only a part of the data forwarded through the interface. Data filtering is possible with the help of the filtering bank in the analyser, and this way the amount of the information to be stored can be reduced. Applied filters can be built in, or specified by the user. Several filters can operate side by side. Filtering criteria: equal, not equal, greater than, lower than, indeterminate; applicable for bit, byte, string.
• Event and message archiver (Capture RAM)
  There is a large trace archiver of more Mbytes in the protocol analyser for recording data retrieved from the network. Moreover, there is also a possibility for recording the retrived data at the hard disk of the control computer.
• Report generator and filtering module
  Report generator decodes message stored in the Capture RAM according to the standards, making them readable for the user this way. We can filter decoded messages with the help of the report filter for displaying. Filtering criteria are protocol-dependent.
• Message generator module
  Protocol analyser is applicable not only for examining signals going through the interface, but also it is able to giving signals to the interface in a framed form ("measuring signals").
• State machine
  We can program into the state machine, what kind of response messages has the analyser give to the received message, namely what kind of protocol it has to realize.
• Control computer
  Control computer - which is usually a built-in one - have several tasks:
  • control of functional units of the protocol analyser
  • running of applications in connection with process of measuring result, or measuring signal generation (monitor, report generator, emulator, statistics, performance test)
  • handling of recording, and (remote control) interfaces providing a connection with the outside world.