Internet Surfer 2.0/Internet Surfer 2.0 (Wayzata Technology) (1996).iso/pc/text/mac/faqs.115

Text File | 1996-02-12 | 28KB | 672 lines

Frequently Asked Questions (FAQS);faqs.115


            completed, the slave will send mail to NOTIFY, which must
            be a legal mailing address on the slave.  If a SIZE field
            will appear but the n option does not appear, NOTIFY will
            always be present, typically as the string "dummy" or
            simply a pair of double quotes.
        SIZE
            This field is only present when doing size negotiation,
            with Taylor UUCP, SVR4 UUCP, QFT or FSUUCP.  It is the
            size of the file in bytes.  SVR4 UUCP, QFT and FSUUCP send
            the size in base 16 as 0x.... while Taylor UUCP sends the
            size as a decimal integer (a later version of Taylor UUCP
            will probably change to the SVR4 behaviour).

    The slave then responds with an S command response.
        SY START
            The slave is willing to accept the file, and file transfer
            begins.  The START field will only be present when using
            file restart.  It specifies the byte offset into the file
            at which to start sending.  If this is a new file, START
            will be 0x0.
        SN2
            The slave denies permission to transfer the file.  This
            can mean that the destination directory may not be
            accessed, or that no requests are permitted.  It implies
            that the file transfer will never succeed.
        SN4
            The slave is unable to create the necessary temporary
            file.  This implies that the file transfer might succeed
            later.
        SN6
            This is only used by Taylor UUCP and FSUUCP size
            negotiation.  It means that the slave considers the file
            too large to transfer at the moment, but it may be
            possible to transfer it at some other time.
        SN7
            This is only used by Taylor UUCP and FSUUCP size
            negotiation.  It means that the slave considers the file
            too large to ever transfer.
        SN8
            This is only used by Taylor UUCP.  It means that the file
            was already received in a previous conversation.  This can
            happen if the receive acknowledgement was lost after it
            was sent by the receiver but before it was received by the
            sender.

    If the slave responds with SY, a file transfer begins.  When the
    file transfer is complete, the slave sends a C command response.
        CY
            The file transfer was successful.
        CYM
            The file transfer was successful, and the slave wishes to
            become the master; the master should send an H command,
            described below.
        CN5
            The temporary file could not be moved into the final
            location.  This implies that the file transfer will never
            succeed.

    After the C command response has been received (in the SY case) or
    immediately (in an SN case) the master will send another command.

master: R FROM TO USER -OPTIONS SIZE
    The R and the - are literal characters.  This is a request by the
    master to receive a file from the slave.  I do not know how SVR4
    UUCP or QFT implement file transfer restart in this case.
        FROM
            This is the name of the file on the slave which the master
            wishes to receive.  It must not be in the spool directory,
            and it may not contain any wildcards.
        TO
            This is the name of the file to create on the master.  I
            do not believe that it can be a directory.  It may only be
            in the spool directory if this file is being requested to
            support an execution either on the master or on some
            system other than the slave.
        USER
            The name of the user who requested the transfer.
        OPTIONS
            A list of options to control the transfer.  The following
            options are defined (all options are single characters):
                d
                    The master should create directories as necessary
                    (this is the default).
                f
                    The master should not create directories if
                    necessary, but should fail the transfer instead.
                m
                    The master should send mail to USER when the
                    transfer is complete.
        SIZE
            This only appears if Taylor UUCP or FSUUCP size
            negotiation is being used.  It specifies the largest file
            which the master is prepared to accept (when using SVR4
            UUCP or QFT, this was specified in the -U option during
            the initial handshake).

    The slave then responds with an R command response.  FSUUCP does
    not support R requests, and always responds with RN2.
        RY MODE
            The slave is willing to send the file, and file transfer
            begins.  MODE is the octal mode of the file on the slave.
            The master treats this just as the slave does the MODE
            argument in the send command, q.v.
        RN2
            The slave is not willing to send the file, either because
            it is not permitted or because the file does not exist.
            This implies that the file request will never succeed.
        RN6
            This is only used by Taylor UUCP size negotiation.  It
            means that the file is too large to send, either because
            of the size limit specifies by the master or because the
            slave considers it too large.  The file transfer might
            succeed later, or it might not (this will be cleared up in
            a later release of Taylor UUCP).

    If the slave responds with RY, a file transfer begins.  When the
    file transfer is complete, the master sends a C command.  The
    slave pretty much ignores this, although it may log it.
        CY
            The file transfer was successful.
        CN5
            The temporary file could not be moved into the final
            location.

    After the C command response has been sent (in the RY case) or
    immediately (in an RN case) the master will send another command.

master: X FROM TO USER -OPTIONS
    The X and the - are literal characters.  This is a request by the
    master to, in essence, execute uucp on the slave.  The slave
    should execute "uucp FROM TO".
        FROM
            This is the name of the file or files on the slave which
            the master wishes to transfer.  Any wildcards are expanded
            on the slave.  If the master is requesting that the files
            be transferred to itself, the request would normally
            contain wildcard characters, since otherwise an `R'
            command would suffice.  The master can also use this
            command to request that the slave transfer files to a
            third system.
        TO
            This is the name of the file or directory to which the
            files should be transferred.  This will normally use a
            UUCP name.  For example, if the master wishes to receive
            the files itself, it would use "master!path".
        USER
            The name of the user who requested the transfer.
        OPTIONS
            A list of options to control the transfer.  It is not
            clear which, if any, options are supported by most UUCP
            packages.

    The slave then responds with an X command response.  FSUUCP does
    not support X requests, and always responds with XN.
        XY
            The request was accepted, and the appropriate file
            transfer commands have been queued up for later
            processing.
        XN
            The request was denied.  No particular reason is given.

    In either case, the master will then send another command.

master: H
    This is used by the master to hang up the connection.  The slave
    will respond with an H command response.
        HY
            The slave agrees to hang up the connection.  In this case
            the master sends another HY command.  In some UUCP
            packages the slave will then send a third HY command.  At
            this point the protocol is shut down, and the final
            handshake is begun.
        HN
            The slave does not agree to hang up.  In this case the
            master and the slave exchange roles.  The next command
            will be sent by the former slave, which is the new master.
            The roles may be reversed several times during a single
            connection.

After the protocol has been shut down, the final handshake is
performed.  This handshake has no real purpose, and some UUCP packages
simply drop the connection rather than do it (in fact, some will drop
the connection immediately after both sides agree to hangup, without
even closing down the protocol).

caller: \020OOOOOO\000
called: \020OOOOOOO\000

That is, the calling UUCP sends six O's and the called UUCP replies
with seven O's.  Some UUCP packages always send six O's.

------------------------------

From: UUCP-g
Subject: What is the 'g' protocol?

The 'g' protocol is a packet based flow controlled error correcting
protocol that requires an eight bit clear connection.  It is the
original UUCP protocol, and is supported by all UUCP implementations.
Many implementations of it are only able to support small window and
packet sizes, specifically a window size of 3 and a packet size of 64
bytes, but the protocol itself can support up to a window size of 7
and a packet size of 4096 bytes.  Complaints about the inefficiency of
the 'g' protocol generally refer to specific implementations, rather
than to the correctly implemented protocol.

The 'g' protocol was originally designed for general packet drivers,
and thus contains some features that are not used by UUCP, including
an alternate data channel and the ability to renegotiate packet and
window sizes during the communication session.

The 'g' protocol is spoofed by many Telebit modems.  When spoofing is
in effect, each Telebit modem uses the 'g' protocol to communicate
with the attached computer, but the data between the modems is sent
using a Telebit proprietary error correcting protocol.  This allows
for very high throughput over the Telebit connection, which, because
it is half-duplex, would not normally be able to handle the 'g'
protocol very well at all.

This discussion of the 'g' protocol explains how it works, but does
not discuss useful error handling techniques.  Some discussion of this
can be found in Jamie E. Hanrahan's paper, cited above.

All 'g' protocol communication is done with packets.  Each packet
begins with a six byte header.  Control packets consist only of the
header.  Data packets contain additional data.

The header is as follows:

    \020
        Every packet begins with a ^P.
    k (1 <= k <= 9)
        The k value is always 9 for a control packet.  For a data
        packet, the k value indicates how must data follows the six
        byte header.  The amount of data is 2 ** (k + 4), where **
        indicates exponentiation.  Thus a k value of 1 means 32 data
        bytes and a k value of 8 means 4096 data bytes.  The k value
        for a data packet must be between 1 and 8 inclusive.
    checksum low byte
    checksum high byte
        The checksum value is described below.
    control byte
        The control packet indicates the type of packet, and is
        described below.
    xor byte
        This byte is the xor of k, the checksum low byte, the checksum
        high byte and the control byte (i.e., the second, third,
        fourth and fifth header bytes).  It is used to ensure that the
        header data is valid.

The control byte in the header is composed of three bit fields,
referred to here as TT (two bits), XXX (three bits) and YYY (three
bits).  The control is TTXXXYYY, or (TT << 6) + (XXX << 3) + YYY.

The TT field takes on the following values:
    0
        This is a control packet.  In this case the k byte in the
        header must be 9.  The XXX field indicates the type of control
        packet; these types are described below.
    1
        This is an alternate data channel packet.  This is not used by
        UUCP.
    2
        This is a data packet, and the entire contents of the attached
        data field (whose length is given by the k byte in the header)
        are valid.  The XXX and YYY fields are described below.
    3
        This is a short data packet.  Let the length of the data field
        (as given by the k byte in the header) be L.  Let the first
        byte in the data field be B1.  If B1 is less than 128 (if the
        most significant bit of B1 is 0), then there are L - B1 valid
        bytes of data in the data field, beginning with the second
        byte.  If B1 >= 128, let B2 be the second byte in the data
        field.  Then there are L - ((B1 & 0x7f) + (B2 << 7)) valid
        bytes of data in the data field, beginning with the third
        byte.  In all cases L bytes of data are sent (and all data
        bytes participate in the checksum calculation) but some of the
        trailing bytes may be dropped by the receiver.   The XXX and
        YYY fields are described below.

In a data packet (short or not) the XXX field gives the sequence
number of the packet.  Thus sequence numbers can range from 0 to 7,
inclusive.  The YYY field gives the sequence number of the last
correctly received packet.

Each communication direction uses a window which indicates how many
unacknowledged packets may be transmitted before waiting for an
acknowledgement.  The window may range from 1 to 7, and may be
different in each direction. For example, if the window is 3 and the
last packet acknowledged was packet number 6, packet numbers 7, 0 and
1 may be sent but the sender must wait for an acknowledgement before
sending packet number 2.  This acknowledgement could come as the YYY
field of a data packet or as the YYY field of a RJ or RR control
packet (described below).

Each packet must be transmitted in order (the sender may not skip
sequence numbers).  Each packet must be acknowledged, and each packet
must be acknowledged in order.

In a control packet, the XXX field takes on the following values:
    1 CLOSE
        The connection should be closed immediately.  This is
        typically sent when one side has seen too many errors and
        wants to give up.  It is also sent when shutting down the
        protocol.  If an unexpected CLOSE packet is received, a CLOSE
        packet should be sent in reply and the 'g' protocol should
        halt, causing UUCP to enter the final handshake.
    2 RJ or NAK
        The last packet was not received correctly.  The YYY field
        contains the sequence number of the last correctly received
        packet.
    3 SRJ
        Selective reject.  The YYY field contains the sequence number
        of a packet that was not received correctly, and should be
        retransmitted.  This is not used by UUCP, and most
        implementations will not recognize it.
    4 RR or ACK
        Packet acknowledgement.  The YYY field contains the sequence
        number of the last correctly received packet.
    5 INITC
        Third initialization packet.  The YYY field contains the
        maximum window size to use.
    6 INITB
        Second initialization packet.  The YYY field contains the
        packet size to use.  It requests a size of 2 ** (YYY + 5).
        Note that this is not the same coding used for the k byte in
        the packet header (it is 1 less).  Most UUCP implementations
        that request a packet size larger than 64 bytes can handle any
        packet size up to that specified.
    7 INITA
        First initialization packet.  The YYY field contains the
        maximum window size to use.

The checksum of a control packet is simply 0xaaaa - the control byte.

The checksum of a data packet is 0xaaaa - (CHECK ^ the control byte),
where ^ denotes exclusive or, and CHECK is the result of the following
routine as run on the contents of the data field (every byte in the
data field participates in the checksum, even for a short data
packet).  Below is the routine used by Taylor UUCP; it is a slightly
modified version of a routine which John Gilmore patched from G.L.
Chesson's original paper.  The z argument points to the data and the c
argument indicates how much data there is.

int
igchecksum (z, c)
     register const char *z;
     register int c;
{
  register unsigned int ichk1, ichk2;

  ichk1 = 0xffff;
  ichk2 = 0;

  do
    {
      register unsigned int b;

      /* Rotate ichk1 left.  */
      if ((ichk1 & 0x8000) == 0)
        ichk1 <<= 1;
      else
        {
          ichk1 <<= 1;
          ++ichk1;
        }

      /* Add the next character to ichk1.  */
      b = *z++ & 0xff;
      ichk1 += b;

      /* Add ichk1 xor the character position in the buffer counting from
         the back to ichk2.  */
      ichk2 += ichk1 ^ c;

      /* If the character was zero, or adding it to ichk1 caused an
         overflow, xor ichk2 to ichk1.  */
      if (b == 0 || (ichk1 & 0xffff) < b)
        ichk1 ^= ichk2;
    }
  while (--c > 0);

  return ichk1 & 0xffff;
}

When the 'g' protocol is started, the calling UUCP sends an INITA
control packet with the window size it wishes the called UUCP to use.
The called UUCP responds with an INITA packet with the window size it
wishes the calling UUCP to use.  Pairs of INITB and INITC packets are
then similarly exchanged.  When these exchanges are completed, the
protocol is considered to have been started.

When a UUCP package transmits a command, it sends one or more data
packets.  All the data packets will normally be complete, although
some UUCP packages may send the last one as a short packet.  The
command string is sent with a trailing null byte, to let the receiving
package know when the command is finished.  Some UUCP packages require
the last byte of the last packet sent to be null, even if the command
ends earlier in the packet.  Some packages may require all the
trailing bytes in the last packet to be null, but I have not confirmed
this.

When a UUCP package sends a file, it will send a sequence of data
packets.  The end of the file is signalled by a short data packet
containing zero valid bytes (it will normally be preceeded by a short
data packet containing the last few bytes in the file).

Note that the sequence numbers cover the entire communication session,
including both command and file data.

When the protocol is shut down, each UUCP package sends a CLOSE
control packet.

------------------------------

From: UUCP-f
Subject: What is the 'f' protocol?

The 'f' protocol is a seven bit protocol which checksums an entire
file at a time.  It only uses the characters between \040 and \176
(ASCII space and ~) inclusive as well as the carriage return
character.  It can be very efficient for transferring text only data,
but it is very inefficient at transferring eight bit data (such as
compressed news).  It is not flow controlled, and the checksum is
fairly insecure over large files, so using it over a serial connection
requires handshaking (XON/XOFF can be used) and error correcting
modems.  Some people think it should not be used even under those
circumstances.

I believe the 'f' protocol originated in BSD versions of UUCP.  It was
originally intended for transmission over X.25 PAD links.

The 'f' protocol has no startup or finish protocol.  However, both
sides typically sleep for a couple of seconds before starting up,
because they switch the terminal into XON/XOFF mode and want to allow
the changes to settle before beginning transmission.

When a UUCP package transmits a command, it simply sends a string
terminated by a carriage return.

When a UUCP package transmits a file, each byte b of the file is
translated according to the following table:

       0 <= b <=  037: 0172, b + 0100 (0100 to 0137)
     040 <= b <= 0171:       b        ( 040 to 0171)
    0172 <= b <= 0177: 0173, b - 0100 ( 072 to  077)
    0200 <= b <= 0237: 0174, b - 0100 (0100 to 0137)
    0240 <= b <= 0371: 0175, b - 0200 ( 040 to 0171)
    0372 <= b <= 0377: 0176, b - 0300 ( 072 to  077)

That is, a byte between \040 and \171 inclusive is transmitted as is,
and all other bytes are prefixed and modified as shown.

When all the file data is sent, a seven byte sequence is sent: two
bytes of \176 followed by four ASCII bytes of the checksum as printed
in base 16 followed by a carriage return.  For example, if the
checksum was 0x1234, this would be sent: "\176\1761234\r".

The checksum is initialized to 0xffff.  For each byte that is sent it
is modified as follows (where b is the byte before it has been
transformed as described above):

      /* Rotate the checksum left.  */
      if ((ichk & 0x8000) == 0)
        ichk <<= 1;
      else
        {
          ichk <<= 1;
          ++ichk;
        }

      /* Add the next byte into the checksum.  */
      ichk += b;

When the receiving UUCP sees the checksum, it compares it against its
own calculated checksum and replies with a single character followed
by a carriage return.
    G
        The file was received correctly.
    R
        The checksum did not match, and the file should be resent from
        the beginning.
    Q
        The checksum did not match, but too many retries have occurred
        and the communication session should be abandoned.

The sending UUCP checks the returned character and acts accordingly.

------------------------------

From: UUCP-t
Subject: What is the 't' protocol?

The 't' protocol is intended for use on links which provide reliable
end-to-end connections, such as TCP.  It does no error checking or
flow control, and requires an eight bit clear channel.

I believe the 't' protocol originated in BSD versions of UUCP.

When a UUCP package transmits a command, it first gets the length of
the command string, C.  It then sends ((C / 512) + 1) * 512 bytes (the
smallest multiple of 512 which can hold C bytes plus a null byte)
consisting of the command string itself followed by trailing null
bytes.

When a UUCP package sends a file, it sends it in blocks.  Each block
contains at most 1024 bytes of data.  Each block consists of four
bytes containing the amount of data in binary (most significant byte
first, the same format as used by the Unix function htonl) followed by
that amount of data.  The end of the file is signalled by a block
containing zero bytes of data.

------------------------------

From: UUCP-e
Subject: What is the 'e' protocol?

The 'e' protocol is similar to the 't' protocol.  It does no flow
control or error checking and is intended for use over networks
providing reliable end-to-end connections, such as TCP.

The 'e' protocol originated in versions of HDB UUCP.

When a UUCP package transmits a command, it simply sends the command
as an ASCII string terminated by a null byte.

When a UUCP package transmits a file, it sends the complete size of
the file as an ASCII decimal number.  The ASCII string is padded out
to 20 bytes with null bytes (i.e. if the file is 1000 bytes long, it
sends "1000\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0").  It then sends the
entire file.

------------------------------

From: UUCP-G
Subject: What is the 'G' protocol?

The 'G' protocol is used by SVR4 UUCP.  It is identical to the 'g'
protocol, except that it is possible to modify the window and packet
sizes.  The SVR4 implementation of the 'g' protocol reportedly is
fixed at a packet size of 64 and a window size of 7.  Supposedly SVR4
chose to implement a new protocol using a new letter to avoid any
potential incompatibilities when using different packet or window
sizes.

Most implementations of the 'g' protocol that accept packets larger
than 64 bytes will also accept packets smaller than whatever they
requested in the INITB packet.  The SVR4 'G' implementation is an
exception; it will only accept packets of precisely the size it
requests in the INITB packet.

------------------------------

From: UUCP-x
Subject: What is the 'x' protocol?

The 'x' protocol is used in Europe (and probably elsewhere) with
machines that contain an builtin X.25 card and can send eight bit data
transparently across X.25 circuits, without interference from the X.28
or X.29 layers.  The protocol sends packets of 512 bytes, and relies
on a write of zero bytes being read as zero bytes without stopping
communication.  It originally appeared in some version of HDB UUCP.

------------------------------

From: UUCP-d
Subject: What is the 'd' protocol?

This is apparently used for DataKit muxhost (not RS-232) connections.
No file size is sent.  When a file has been completely transferred, a
write of zero bytes is done; this must be read as zero bytes on the
other end.

------------------------------

From: UUCP-h
Subject: What is the 'h' protocol?

This is apparently used in some places with HST modems.  It does no
error checking, and is not that different from the 't' protocol.  I
don't know the details.

------------------------------

From: Thanks
Subject: Thanks

Besides the papers and information acknowledged at the top of this
article, the following people have contributed help, advice,
suggestions and information:
    Earle Ake 513-429-6500 <[e-mail]>
    [e-mail] (Christopher J. Ambler)
    [e-mail] (Jonathan Clark)
    celit![e-mail] (Bill Davidson)
    [e-mail]
    Matthew Farwell <[e-mail]>
    "Jonathan I. Kamens" <[e-mail]>
    "David J. MacKenzie" <[e-mail]>
    [e-mail] (Jens-Uwe Mager)
    david nugent <[e-mail]>
    [e-mail]
    [e-mail] (Joey Pruett)
    James Revell <[e-mail]>
    Larry Rosenman <[e-mail]>
    Rich Salz <[e-mail]>
    [e-mail] (Karl Swartz)
    Dima Volodin <[e-mail]>
    [e-mail] (Jon Zeeff)

------------------------------

End of UUCP Internals Frequently Asked Questions
******************************
--
Ian Taylor | [e-mail] | First to identify quote wins free e-mail message:
``Things are either isolated units, or they form one inseparable whole.  If
  that whole be God, then all is well; but if aimless chance, at least you
  need not be aimless also.''
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From: [e-mail] (Brian Marcotte)
Newsgroups: rec.food.veg,news.answers
Subject: rec.food.veg FREQUENTLY ASKED QUESTIONS LIST (FAQ)
Summary: The following contains general information on all aspects
     of vegetarianism, and answers to common questions.
Keywords: FAQ
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Last-Modified: 1 Dec 1992


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This list is posted at the beginning of each month. The expiration
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The keeper of the FAQ wishes to thank everyone who contributed to this
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Suggestions, comments, additions and constructive criticisms can be
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