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Keywords: FTP, DTP, data, manager
Network Working Group V. Cerf
Request for Comments #163 19 May 71
NIC #6775 UCLA - NMC
Categories: D.7 Computer Science
Updates: None
Obsoletes: None
DATA TRANSFER PROTOCOLS
This is an informal statement of material discussed at the SJCC. There
are two peoblems.
1. Movement of data from one site to another.
2. Interpretation of the data at receiving site.
The first task (1) requires a simple protocol which accomplishes the
following
1) Standard connection procedure for connecting
transmitting and receiving processes
2) Standard packaging which allows network to
collect the transmitted data stream in the
right order and know when the end of the
file has been reached.
Standard Connection Procedure
Suppose every HOST has a process charged with the responsibility of
sending and receiving files between -HOSTS-(processes?)[The Data
Manager]. If the Data Manager offers to listen on a given socket for
file xmt requests, then ICP is sufficient to establish a connection
between a serving Data Manager and a using process.
We have completely avoided the discussion of data interpretation, and
also the problem of control. For instance, we have not said how a
process can ask the Data Manager to send a file of a par- ticular name,
nor how to end the transmission of a file. This is deferred for later.
Another desirable ability is to have processes transmit files to each
other independent of the HOST Data Manager. ICP should suffice, for the
creation of a full duplex connection. File naming, and format
interpretation are left to the individual process to solve.
It is of interest to note that files need not have names. If two
processes are connected, then the file name is in a sense implicit in
the sending and receiving socket pair. One imagines, however, that
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connections with Data Managers for the purpose of file transmission are
too transient to serve as permanent file names, so information about
file name will be needed by the Data Manager. This information could be
supplied either embedded in the file transmission data stream, or
supplied over a separate control connection established at ICP time.
It seems reasonable that a Data Manager have a network-wide, fixed
socket number on which it is listening to service data transmission
requests.* In this sense, it acts much like the Network Logger. For
inter-process file transmission, less rigidity seems called for, and we
can leave such decisions to the individual peocesses communicating with
each other. Public processes at serving HOSTS could have known (nia
NIC?) sockets over which file transmission is acceptable.
Standard Packaging
We naively imagine that very little in the way of formatting is needed
to move data across the connection. A few bits (8?) at the beginning of
transmission could specify the formatting protocol (e.g. arbitrary bit
string until connection closed, count field + data, break chars, etc.)
Depending on the selected format mode, the appropriate control bits will
or will not appear interspersed betweeen the data bits. Message
boundaries are totally transparent.
A way of ending the file, possibly without closing the connection, is
useful, although closing the connection after the RFNM from final
"record" sent is received by the sending process might be adequate
(sufficient, but not palatable?)
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