ymodem.doc

XMODEM传输协议。 通信用代码。 C语言实现

    8.3  Data Flow Examples with CRC Option

    Here is a data flow example for the case where the receiver requests
    transmission in the CRC mode but the sender does not support the CRC
    option. This example also includes various transmission errors.  <xx>
    represents the checksum byte.

          Figure 12.  Data Flow: Receiver has CRC Option, Sender Doesn't

    SENDER                                        RECEIVER
                            <---                <C>
                                    times out after 3 seconds,
                            <---                <C>
                                    times out after 3 seconds,
                            <---                <C>
                                    times out after 3 seconds,
                            <---                <C>
                                    times out after 3 seconds,
                            <---                <nak>
    <soh> 01 FE -data- <xx> --->
                            <---                <ack>
    <soh> 02 FD -data- <xx> --->        (data gets line hit)
                            <---                <nak>
    <soh> 02 FD -data- <xx> --->
                            <---                <ack>
    <soh> 03 FC -data- <xx> --->
       (ack gets garbaged)  <---                <ack>
                                    times out after 10 seconds,
                            <---                <nak>
    <soh> 03 FC -data- <xx> --->
                            <---                <ack>
    <eot>                   --->
                            <---                <ack>

    Here is a data flow example for the case where the receiver requests
    transmission in the CRC mode and the sender supports the CRC option.  This
    example also includes various transmission errors.  <xxxx> represents the
    2 CRC bytes.
















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               Figure 13.  Receiver and Sender Both have CRC Option

    SENDER                                       RECEIVER
                              <---                 <C>
    <soh> 01 FE -data- <xxxx> --->
                              <---                 <ack>
    <soh> 02 FD -data- <xxxx> --->         (data gets line hit)
                              <---                 <nak>
    <soh> 02 FD -data- <xxxx> --->
                              <---                 <ack>
    <soh> 03 FC -data- <xxxx> --->
    (ack gets garbaged)       <---                 <ack>
                                         times out after 10 seconds,
                              <---                 <nak>
    <soh> 03 FC -data- <xxxx> --->
                              <---                 <ack>
    <eot>                     --->
                              <---                 <ack>




































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    X/YMODEM Protocol Reference      08-03-87                               27



    9.  MORE INFORMATION

    Please contact Omen Technology for troff source files and typeset copies
    of this document.


    9.1  TeleGodzilla Bulletin Board

    More information may be obtained by calling TeleGodzilla at 503-621-3746.
    Speed detection is automatic for 300, 1200, and 2400 bps.  TrailBlazer
    modem users may issue the TeleGodzilla trailblazer command to swith to
    19200 bps once they have logged in.

    Interesting files include RZSZ.ZOO, YZMODEM.ZOO, ZCOMMEXE.ARC,
    ZCOMMDOC.ARC, and ZCOMMHLP.ARC.


    9.2  Unix UUCP Access

    UUCP sites can obtain the current version of this file with
                     uucp omen!/u/caf/public/ymodem.doc /tmp
    A continually updated list of available files is stored in
    /usr/spool/uucppublic/FILES.  When retrieving these files with uucp,
    remember that the destination directory on your system must be writeable
    by anyone, or the UUCP transfer will fail.

    The following L.sys line calls TeleGodzilla (Pro-YAM in host operation).
    TeleGodzilla determines the incoming speed automatically.

    In response to "Name Please:" uucico gives the Pro-YAM "link" command as a
    user name.  The password (Giznoid) controls access to the Xenix system
    connected to the IBM PC's other serial port.  Communications between
    Pro-YAM and Xenix use 9600 bps; YAM converts this to the caller's speed.

    Finally, the calling uucico logs in as uucp.

    omen Any ACU 2400 1-503-621-3746 se:--se: link ord: Giznoid in:--in: uucp



    10.  REVISIONS

    8-03-87 Revised for clarity.
    5-31-1987 emphasizes minimum requirements for YMODEM, and updates
    information on accessing files.
    9-11-1986 clarifies nomenclature and some minor points.
    The April 15 1986 edition clarifies some points concerning CRC
    calculations and spaces in the header.






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    11.  YMODEM Programs

    ZCOMM, A shareware little brother to Professional-YAM, is available as
    ZCOMMEXE.ARC on TeleGodzilla and other bulletin board systems.  ZCOMM may
    be used to test YMODEM amd ZMODEM implementations.

    Unix programs supporting YMODEM are available on TeleGodzilla in RZSZ.ZOO.
    This ZOO archive includes a ZCOMM/Pro-YAM/PowerCom script ZUPL.T to upload
    a bootstrap program MINIRB.C, compile it, and then upload the rest of the
    files using the compiled MINIRB.  Most Unix like systems are supported,
    including V7, Xenix, Sys III, 4.2 BSD, SYS V, Idris, Coherent, and
    Regulus.

    A version for VAX-VMS is available in VRBSB.SHQ.

    Irv Hoff has added 1k blocks and basic YMODEM batch transfers to the KMD
    and IMP series programs, which replace the XMODEM and MODEM7/MDM7xx series
    respectively.  Overlays are available for a wide variety of CP/M systems.

    Questions about Professional-YAM communications software may be directed
    to:
         Chuck Forsberg
         Omen Technology Inc
         17505-V Sauvie Island Road
         Portland Oregon 97231
         VOICE: 503-621-3406 :VOICE
         Modem: 503-621-3746 Speed: 2400,1200,300
         Usenet: ...!tektronix!reed!omen!caf
         CompuServe: 70007,2304
         GEnie: CAF

    Unlike ZMODEM and Kermit, XMODEM and YMODEM place obstacles in the path of
    a reliable high performance implementation, evidenced by poor reliability
    under stress of the industry leaders' XMODEM and YMODEM programs.  Omen
    Technology provides consulting and other services to those wishing to
    implement XMODEM, YMODEM, and ZMODEM with state of the art features and
    reliability.

















    Chapter 11                                        Xmodem Protocol Overview











                                     CONTENTS


     1.  TOWER OF BABEL...................................................   2
         1.1  Definitions.................................................   2

     2.  YMODEM MINIMUM REQUIREMENTS......................................   4

     3.  WHY YMODEM?......................................................   5
         3.1  Some Messages from the Pioneer..............................   6

     4.  XMODEM PROTOCOL ENHANCEMENTS.....................................   9
         4.1  Graceful Abort..............................................   9
         4.2  CRC-16 Option...............................................   9
         4.3  XMODEM-1k 1024 Byte Block...................................  10

     5.  YMODEM Batch File Transmission...................................  12
         5.1  KMD/IMP Exceptions to YMODEM................................  16

     6.  YMODEM-g File Transmission.......................................  17

     7.  XMODEM PROTOCOL OVERVIEW.........................................  18
         7.1  Definitions.................................................  18
         7.2  Transmission Medium Level Protocol..........................  18
         7.3  File Level Protocol.........................................  19
         7.4  Programming Tips............................................  20

     8.  XMODEM/CRC Overview..............................................  22
         8.1  CRC Calculation.............................................  22
         8.2  CRC File Level Protocol Changes.............................  23
         8.3  Data Flow Examples with CRC Option..........................  25

     9.  MORE INFORMATION.................................................  27
         9.1  TeleGodzilla Bulletin Board.................................  27
         9.2  Unix UUCP Access............................................  27

    10.  REVISIONS........................................................  27

    11.  YMODEM Programs..................................................  28















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                                 LIST OF FIGURES


     Figure 1.  XMODEM-1k Blocks..........................................  11

     Figure 2.  Mixed 1024 and 128 byte Blocks............................  11

     Figure 3.  YMODEM Batch Transmission Session.........................  15

     Figure 4.  YMODEM Batch Transmission Session-1k Blocks...............  15

     Figure 5.  YMODEM Filename block transmitted by sz...................  16

     Figure 6.  YMODEM Header Information and Features....................  16

     Figure 7.  YMODEM-g Transmission Session.............................  17

     Figure 8.  XMODEM Message Block Level Protocol.......................  19

     Figure 9.  Data flow including Error Recovery........................  20

    Figure 10.  Message Block Level Protocol, CRC mode....................  22

    Figure 11.  Example of CRC Calculation written in C...................  23

    Figure 12.  Data Flow: Receiver has CRC Option, Sender Doesn't........  25

    Figure 13.  Receiver and Sender Both have CRC Option..................  26























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