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GLOSSARY Connected: An Internet Encyclopedia
GLOSSARY

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GLOSSARY

GLOSSARY


1822
          BBN Report 1822, "The Specification of the Interconnection of
          a Host and an IMP".  The specification of interface between a
          host and the ARPANET.

ACK
          A control bit (acknowledge) occupying no sequence space, which
          indicates that the acknowledgment field of this segment
          specifies the next sequence number the sender of this segment
          is expecting to receive, hence acknowledging receipt of all
          previous sequence numbers.

ARPANET message
          The unit of transmission between a host and an IMP in the
          ARPANET.  The maximum size is about 1012 octets (8096 bits).

ARPANET packet
          A unit of transmission used internally in the ARPANET between
          IMPs.  The maximum size is about 126 octets (1008 bits).

connection
          A logical communication path identified by a pair of sockets.

datagram
          A message sent in a packet switched computer communications
          network.

Destination Address
          The destination address, usually the network and host
          identifiers.

FIN
          A control bit (finis) occupying one sequence number, which
          indicates that the sender will send no more data or control
          occupying sequence space.

fragment
          A portion of a logical unit of data, in particular an internet
          fragment is a portion of an internet datagram.

FTP
          A file transfer protocol.

header
          Control information at the beginning of a message, segment,
          fragment, packet or block of data.

host
          A computer.  In particular a source or destination of messages
          from the point of view of the communication network.

Identification
          An Internet Protocol field.  This identifying value assigned
          by the sender aids in assembling the fragments of a datagram.

IMP
          The Interface Message Processor, the packet switch of the
          ARPANET.

internet address
          A source or destination address specific to the host level.

internet datagram
          The unit of data exchanged between an internet module and the
          higher level protocol together with the internet header.

internet fragment
          A portion of the data of an internet datagram with an internet
          header.

IP
          Internet Protocol.

IRS
          The Initial Receive Sequence number.  The first sequence
          number used by the sender on a connection.

ISN
          The Initial Sequence Number.  The first sequence number used
          on a connection, (either ISS or IRS).  Selected on a clock
          based procedure.

ISS
          The Initial Send Sequence number.  The first sequence number
          used by the sender on a connection.

leader
          Control information at the beginning of a message or block of
          data.  In particular, in the ARPANET, the control information
          on an ARPANET message at the host-IMP interface.

left sequence
          This is the next sequence number to be acknowledged by the
          data receiving TCP (or the lowest currently unacknowledged
          sequence number) and is sometimes referred to as the left edge
          of the send window.

local packet
          The unit of transmission within a local network.

module
          An implementation, usually in software, of a protocol or other
          procedure.

MSL
          Maximum Segment Lifetime, the time a TCP segment can exist in
          the internetwork system.  Arbitrarily defined to be 2 minutes.

octet
          An eight bit byte.

Options
          An Option field may contain several options, and each option
          may be several octets in length.  The options are used
          primarily in testing situations; for example, to carry
          timestamps.  Both the Internet Protocol and TCP provide for
          options fields.

packet
          A package of data with a header which may or may not be
          logically complete.  More often a physical packaging than a
          logical packaging of data.

port
          The portion of a socket that specifies which logical input or
          output channel of a process is associated with the data.

process
          A program in execution.  A source or destination of data from
          the point of view of the TCP or other host-to-host protocol.

PUSH
          A control bit occupying no sequence space, indicating that
          this segment contains data that must be pushed through to the
          receiving user.

RCV.NXT
          receive next sequence number

RCV.UP
          receive urgent pointer

RCV.WND
          receive window

receive next sequence number
          This is the next sequence number the local TCP is expecting to
          receive.

receive window
          This represents the sequence numbers the local (receiving) TCP
          is willing to receive.  Thus, the local TCP considers that
          segments overlapping the range RCV.NXT to
          RCV.NXT + RCV.WND - 1 carry acceptable data or control.
          Segments containing sequence numbers entirely outside of this
          range are considered duplicates and discarded.

RST
          A control bit (reset), occupying no sequence space, indicating
          that the receiver should delete the connection without further
          interaction.  The receiver can determine, based on the
          sequence number and acknowledgment fields of the incoming
          segment, whether it should honor the reset command or ignore
          it.  In no case does receipt of a segment containing RST give
          rise to a RST in response.

RTP
          Real Time Protocol:  A host-to-host protocol for communication
          of time critical information.

SEG.ACK
          segment acknowledgment

SEG.LEN
          segment length

SEG.PRC
          segment precedence value

SEG.SEQ
          segment sequence

SEG.UP
          segment urgent pointer field

SEG.WND
          segment window field

segment
          A logical unit of data, in particular a TCP segment is the
          unit of data transfered between a pair of TCP modules.

segment acknowledgment
          The sequence number in the acknowledgment field of the
          arriving segment.

segment length
          The amount of sequence number space occupied by a segment,
          including any controls which occupy sequence space.

segment sequence
          The number in the sequence field of the arriving segment.

send sequence
          This is the next sequence number the local (sending) TCP will
          use on the connection.  It is initially selected from an
          initial sequence number curve (ISN) and is incremented for
          each octet of data or sequenced control transmitted.

send window
          This represents the sequence numbers which the remote
          (receiving) TCP is willing to receive.  It is the value of the
          window field specified in segments from the remote (data
          receiving) TCP.  The range of new sequence numbers which may
          be emitted by a TCP lies between SND.NXT and
          SND.UNA + SND.WND - 1. (Retransmissions of sequence numbers
          between SND.UNA and SND.NXT are expected, of course.)

SND.NXT
          send sequence

SND.UNA
          left sequence

SND.UP
          send urgent pointer

SND.WL1
          segment sequence number at last window update

SND.WL2
          segment acknowledgment number at last window update

SND.WND
          send window

socket
          An address which specifically includes a port identifier, that
          is, the concatenation of an Internet Address with a TCP port.

Source Address
          The source address, usually the network and host identifiers.

SYN
          A control bit in the incoming segment, occupying one sequence
          number, used at the initiation of a connection, to indicate
          where the sequence numbering will start.

TCB
          Transmission control block, the data structure that records
          the state of a connection.

TCB.PRC
          The precedence of the connection.

TCP
          Transmission Control Protocol:  A host-to-host protocol for
          reliable communication in internetwork environments.

TOS
          Type of Service, an Internet Protocol field.

Type of Service
          An Internet Protocol field which indicates the type of service
          for this internet fragment.

URG
          A control bit (urgent), occupying no sequence space, used to
          indicate that the receiving user should be notified to do
          urgent processing as long as there is data to be consumed with
          sequence numbers less than the value indicated in the urgent
          pointer.

urgent pointer
          A control field meaningful only when the URG bit is on.  This
          field communicates the value of the urgent pointer which
          indicates the data octet associated with the sending user's
          urgent call.


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Connected: An Internet Encyclopedia
GLOSSARY

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