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+ Network Working Group
+
+
+ Request for Comment 147
+
+ NIC 6750
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+ The Definition of a Socket
+
+ Joel M. Winett
+
+ Lincoln Laboratory
+
+ 360/67
+
+ 7 May 1971
+
+
+Category: C1, C3, D1, H
+RFC obsoleted: None
+RFC updated: None
+Related RFCs: RFC-129 (NIC-5845)
+
+
+
+
+
+ This material has not been reviewed for public release and is intended
+ only for use with the ARPA network. It should not be quoted or cited
+ in any publication not related to the ARPA network.
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+ [Page 1]
+
+ MASSACHUSETTS INSTITUTE OF TECHNOLOGY
+ LINCOLN LABORATORY
+
+TO: Network Socket Committee and Network Community 7 May 1971
+
+FROM: J. M. Winett (LL)
+
+SUBJECT: The Definition of a Socket
+
+A socket is defined to be the unique identification to or from which
+information is transmitted in the network. The socket is specified as a 32
+bit number with even sockets identifying receiving sockets and odd sockets
+identifying sending sockets. A socket is also identified by the host in
+which the sending or receiving processer is located.
+
+Previous network papers postulated that a process running under control of
+the host's operating system would have access to a number of ports. A port
+might be a physical input or output device, or a logical I/O device
+supported by system calls to the host's operating system. The latter
+category includes a) I/O directed to a physical device which is being
+spooled by the operating system, b) a physical device whose basic
+characteristics have not been altered but whose access has been limited and
+possibly transformed by a mapping algorithm (e.g. device address mapping or
+cylinder relocation as in virtual mini disks), c) access to a file system
+through a directory and access method maintained by the operating system,
+d) a procedure for process to process communications, e) a procedure for
+machine to machine communication (such as defined by the network protocol.)
+
+A socket has been defined to be the identification of a port for machine to
+machine communication through the ARPA network. Sockets allocated to each
+host must be uniquely associated with a known process or be undefined. The
+name of some sockets must be universally known and associated with a known
+process operating with a specified protocol. (e.g., a logger socket, RJE
+socket, a file transfer socket). The name of other sockets might not be
+universally known, but given in a transmission over a universally known
+socket, (c. g. the socket pair specified by the transmission over the
+logger socket under the Initial Connection Protocol (ICP). In any case,
+communication over the network is from one socket to another socket, each
+socket being identified with a process running at a known host.
+
+The question arises as to whether socket names must be known to users of
+network programs or whether the specification of sockets can be made
+transparent to the user. Also, should the socket used at one time by a
+process be the same socket used at a later time by the same process for the
+same purpose? If sockets are not transparent to the user, then the sockets
+used must not be dependent on the order in which network connections are
+made.
+
+
+
+
+ [Page 2]
+
+Network Socket Committee and Network Community 7 May 1971
+
+The definition of a socket is also related to the accounting procedures
+followed for network usage. Network Control Programs (NCPs) should log
+each connection made and record the time the connection was made, the time
+the connection was closed, the number of messages and number of bits
+transmitted over the connection, the sending and receiving hosts, and the
+sockets at the sending host and receiving host which participated in the
+connection. In order for these sockets to be meaningful, they should be
+identifiable with the user, account, or process name with which each socket
+is associated.
+
+It has previously been suggested that the sockets used by a network user be
+identified with that user no matter which host he used for network
+communications. Users would be registered at some host and be identified as
+a user from that host even if he used the system as a second host to
+communicate with the system at a third host.
+
+To satisfy the above requirements within the name space of a 32 bit socket,
+the following procedure is suggested. This procedure has been implemented
+with the NCP on the Lincoln Laboratory 360/67 system and is used by all
+processes making use of network facilities. ) A 32 bit socket is divided
+into an 8 bit "home" field, a 16 bit "user" field and an 8 bit "tag" field.
+The tag consists of a 7 bit "plug" and a one bit "polarity" where a "0"
+polarity indicates a receive socket and a "1" polarity indicates a send
+socket. Thus a user on one host system may run processes with up to 128
+send sockets and 128 receive sockets. This procedure allows for 256 hosts
+and 65,536 users per host. The only difficulty is in mapping user or
+process identifiers at a host into a 16 bit user number. This may be done
+through a table lookup, possibly using a hash coding technique. Though
+many systems have a unique run time index associated with each process, if
+this index were used as the user number, the user number would not be the
+same each time the process were used for network activity. What is
+required, is a unique mapping from a process identifier (usually a
+character string) into a 16 bit binary number.
+
+The sockets used for facilities following a common network protocol, such
+as the ICP, should also follow this socket definition. Thus the logger
+socket at the Lincoln Laboratory 360/67 would be, and is, x'0A0000 01, ',
+i.e. home 10, user 0, and tag 1.
+
+This procedure for defining sockets enables an accounting procedure for
+identifying users of network facilities and for measuring network usage.
+
+ [ This RFC was put into machine readable form for entry ]
+ [ into the online RFC archives by BBN Corp. under the ]
+ [ direction of Alex McKenzie. 12/96 ]
+
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+
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+ [Page 3]
+