tren(7)                             CLIX                             tren(7)



  NAME

    tren - DoD trailer decapsulation STREAMS module

  DESCRIPTION

    The tren module is the Department of Defense (DoD) trailer decapsulation
    STREAMS module created to improve the performance of the Transmission
    Control Protocol/Internet Protocol (TCP/IP) on some machines.  A frame
    format that placed the transport layer data immediately after the Ethernet
    header, with the transport headers following the data was created.  Early
    versions of this trailer mechanism did not provide a way to turn trailer
    encapsulation on and off.  To communicate with a system with trailer
    encapsulation on, it is necessary on a CLIX machine to push the tren
    module between the ip device and the et Logical Link Interface (LLI)
    device to decapsulate these frames.  Doing so puts the transport layer
    headers immediately after the Ethernet header followed by the transport
    layer data.

    To set up a stream to be linked below ip and that will decapsulate
    incoming trailer encapsulated frames, the LLI device must be opened for
    the desired physical network (/dev/et0) and the device must be bound to
    the trailer Service Access Point (SAP) TRLR_SAP (0x1001).  Then the tren
    streams module must be pushed onto the stream.  Finally, the device
    /dev/ip must be opened and the tren module linked below the ip stream.

    The trailer module may be pushed only onto a stream terminated by an LLI
    device that is bound to the trailer SAP.

    Once the tren module has been pushed onto a stream, all messages received
    on the module's write side will be transparently passed on to the module's
    downstream neighbor.  All messages received on the module's read side will
    be transparently passed on to the module's upstream neighbor as well, with
    the exception of M_PROTO messages carrying DL_UNITDATA_IND primitives.
    These messages contain trailer encapsulated frames that will be
    decapsulated to look like ordinary ip frames and passed upstream.

  FILES

    /usr/include/sys/lihdr.h   LLI header file.

  NOTES

    The incd command is used at boot time to configure the STREAMS drivers and
    modules that implement network protocols, including tren.  Manual
    configuration is not usually necessary.

  RELATED INFORMATION

    Commands:  incd(8)




  2/94 - Intergraph Corporation                                              1

  tren(7)                             CLIX                             tren(7)



    Functions:  ioctl(2)

    Files:  et(7), ip(7), streamio(7)



















































  2                                              Intergraph Corporation - 2/94