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RFC 0133 

NETWORK WORKING GROUP                                   R. L. Sunberg
Request for Comments #133                               Harvard University
 IC 6710                                                 27 April 1971


    [Categories C.4, C.5, C.6, D.4, D.7, D.7]

1A  Handshaking

1A1 I think that Mr Bhushan(RFC #114, NIC 5823) is not strict enough in

    his concept of a transaction sequence.  Every transaction should

    prompt a response from its recipient )recall Kalin's crates --

    RFC #60, NIC 4762).  Control should pass back and forth until the

    server terminates.  The server  always gets the last word (more on

    error recovery later).

1A2 Some sample interchanges are given.

    User                Server          Comments
    <...>       ==>                     Establish a connection
                <==     <...>
    <...>    ==>                     Identify self
                <==     <+>             Ok, ready

    <...>    ==>                     Retrieval request
                <==                 I've got your file
            ==>                     Send it
                <==     <,><...>        Here's the first part
            ==>                     Got it
                <==     <+>             All done

    <...>    ==>                     Store request
                <==                 Ok, go ahead
    <#><...>    ==>                     Here's some protection stuff
                <==                 Ok
    <*><...>    ==>                     Here's the file
                <==     <+>             Got it.  All done.

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NWG/RFC #133

    See section 2B, below, for examples of error recovery.

1B  Extensions to the file transfer protocol

1B1 The file transfer protocol needs a mechanism for accessing

    individual records of a file.  This will be particularly useful

    when very large data bases appear on the network.  The following

    definitions should be added to the protocol:

    The store(s) and retrieve(R) requests have the data field format

    , where  has the syntax:


      The  syntax is changed to:


    If a retrieve(R) request is given with a data field with 

    syntax rather than  syntax, then the returned data will

    consist of the record following the matching .  If a store(s)

    request is given with a data field of  syntax, then the

    supplied data will replace the record following the matching

    .  If the keyname does not exist, the record will be

    appended to the named file.  The individual installation must

    provide the linkage between the  and the record it


    In addition, the lookup(L) request will provide a list of keynames

    into a file (or the name of a file which contains the keynames).

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NWG/RFC #133

1B2 Transaction code F (request File directory) requests a listing of

    available files.  The data field of the F transaction is of the

    form:  GSGS...  All files in the server system

    which match one or move of the given  specifiers are

    listed in a return file.  The format of the data fiels of this

    file is:  GSGS...  If a  field in

    the request transaction does not include a  field, the

    default is all files on the given device.  Some examples are given:


    This example requests a list of all files on the disk specified by

    [62,50] plus all files named JOE.  The response could contain in

    the data field:


    This message states that in the [62,50] area of the disk there are

    files ALPHA, BETA, and JOE, and that JOE is also a file in the

    [10,50] area of the disk.


2A  Error recovery procedures have been noticeably lacking to date.

    The usual approach has been to close the connection and start from

    scratch.  Mr Bhushan proposes a third level abort but doesn't

    really detail the implementation.  I propose a multilevel error

    recovery procedure as follows.

2B  If an error occurs which does not cause a loss of third level

                                                                [Page 3]
NWG/RFC #133

    transaction boundaries and only affects one side of a duplex

    connection, a third level recovery is possible via a transaction

    sequence abort.  An example is given:

    User                Server          Comments
    <...>    ==>                     Send me this file
                <==                 Ok, I've got it
            ==>                     Ready
                <==     <*><...error>   Here it is (with an error)
    <->      ==>                     No.  (data) error
                <==     <->          Sorry, forget it
    <...>    ==>                     Send the file (again)
                |<==                Ready (doesn't get there)
                ...                     (waiting)
    <-><0>      ==>                     Error, timeout
                <==     <-><0>          Sorry, forget it
    <...>    ==>                     Send the file (third time)
                <==                 Got it
            ==>                     Ready
                <==     <*><...>        There it is
            ==>                     Got it
                <==     <+>             Done (finally>

    Note that the server always gets the last word in error situations

    as well as normal transmission.

2C  Although the above examples are given in terms of Bhushan's

    transaction codes, this form of error recovery is implementable in

    any protocol which uses flagged blocking and duplex connections.

2D  If errors cannot be recovered as above, then some meanst must be

    available to clear the link completely and resynchronize.  I

    suggest that an 8-bit argument be appended to the interrupt-on-link

    NCP message (INR, INS).  The receiver would send  to

    indicate that the block boundaries were lost and all incoming data

    is being discarded.  The sender, upon receiving the INR, would

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NWG/RFC #133

    flush all queued output and wait for the link to clear.  The NCP

    would then send a  message and, when it was received

    (RFNM returned), a negative termination would be sent on the link.

    The receiver begins accepting data again when the INS is received.

    This assumed that any process can flush untransmitted data and

    detect a clear link.  Note that this method is useable on any

    simplex connection.

2E  If all else fails, one can resort to closing the faulty socket.


3A  I suggest that the NCP be given a version number and the next

    version include two new message types:

         ('Who aRe yoU?')  requests a version number from the

    receiving host and   ('I AM')     supplies that


3B  The messages would probably be initially used in a 'can I talk to

    you?' sense or not at all.  Eventually, it would take on a 'what

    can you do?' meaning.  Accordingly, the  field should be

    large (32 bits?) for expansion.

       [ This RFC was put into machine readable form for entry ]
          [ into the online RFC archives by Jose Tamayo 4/97 ]

                                                                [Page 5]

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