connection
Click on the red underlined text to get to the source
...
TCP is a connection-oriented, end-to-end reliable protocol designed to
fit into a layered hierarchy of protocols which support multi-network ...
... TCP should be able to operate above a
wide spectrum of communication systems ranging from hard-wired
connections to packet-switched or circuit-switched networks.
...
... operating system provides to an
application process for manipulating files. For example, there are
calls to open and close connections and to send and receive data on
established connections. It is also expected that the TCP ...
... calls to open and close connections and to send and receive data on
established connections. It is also expected that the TCP can
asynchronously ...
... TCP is to provide reliable,
securable logical circuit or connection service between pairs of
processes. To provide this service ...
... a socket. A pair of sockets uniquely identifies each connection.
That is, a socket may be simultaneously used in multiple
...
... That is, a socket may be simultaneously used in multiple
connections.
...
...
Connections:
...
... sockets, sequence numbers, and window sizes, is called a connection.
Each connection is uniquely specified by a pair of sockets ...
... sequence numbers, and window sizes, is called a connection.
Each connection is uniquely specified by a pair of sockets
identifying its two sides.
...
... When two processes wish to communicate, their TCP's must first
establish a connection (initialize the status information on each
side). When their communication is complete, the connection is
...
... establish a connection (initialize the status information on each
side). When their communication is complete, the connection is
terminated or closed to free the resources for other uses.
...
...
Since connections must be established between unreliable hosts and
over the unreliable internet ...
... communication system that provides two-way data flow on logical
connections between process ports.
...
... by the user on the TCP
to OPEN or CLOSE a connection, to SEND or RECEIVE data, or to obtain
STATUS about a connection ...
... connection, to SEND or RECEIVE data, or to obtain
STATUS about a connection. These calls are like other calls from user
programs on the operating system, for example, the calls to open, read
...
...
A stream of data sent on a TCP connection is delivered reliably and in
order at the destination.
...
... Connection Establishment and Clearing ...
... sockets at the ends. A
local socket may participate in many connections to different foreign
sockets. A connection ...
... connections to different foreign
sockets. A connection can be used to carry data in both directions,
that is, it is "full duplex".
...
... the "appropriate" processes by some means. We envision that processes
may "own" ports, and that processes can initiate connections only on
the ports they own. (Means for implementing ownership is a local
...
... socket arguments. In return, the TCP supplies a (short) local
connection name by which the user refers to the connection in
subsequent calls. There are several things that must be remembered
...
... TCP supplies a (short) local
connection name by which the user refers to the connection in
subsequent calls. There are several things that must be remembered
about a connection ...
... connection in
subsequent calls. There are several things that must be remembered
about a connection. To store this information we imagine that there
is a data structure called a Transmission Control Block ...
... Transmission Control Block (TCB). One
implementation strategy would have the local connection name be a
pointer to the TCB for this connection ...
... connection name be a
pointer to the TCB for this connection. The OPEN call also specifies
whether the connection establishment is to be actively pursued, or to
...
... TCB for this connection. The OPEN call also specifies
whether the connection establishment is to be actively pursued, or to
be passively waited for.
...
...
A passive OPEN request means that the process wants to accept incoming
connection requests rather than attempting to initiate a connection.
Often the process requesting a passive ...
... A passive OPEN request means that the process wants to accept incoming
connection requests rather than attempting to initiate a connection.
Often the process requesting a passive OPEN will accept a connection
request ...
... connection.
Often the process requesting a passive OPEN will accept a connection
request from any caller. In this case a foreign socket of all zeros
...
... passive OPEN request with an unspecified
foreign socket. Then a connection could be made with any process that
requested a connection to this local socket ...
... socket. Then a connection could be made with any process that
requested a connection to this local socket. It would help if this
local socket ...
... active OPENs
from other processes and be informed by the TCP when connections have
been established. Two processes which issue active OPENs to each
...
...
The procedures to establish connections utilize the synchronize (SYN)
control flag and involves an exchange of three messages. This
...
... command. The matching of local and foreign sockets determines when a
connection has been initiated. The connection becomes "established"
when sequence numbers ...
... sockets determines when a
connection has been initiated. The connection becomes "established"
when sequence numbers have been synchronized in both directions.
...
...
The clearing of a connection also involves the exchange of segments,
in this case carrying the FIN control flag.
...
...
The data that flows on a connection may be thought of as a stream of
octets. The sending user indicates in each SEND ...
... security option to provide precedence and security on a per connection
basis to TCP users. Not all TCP ...
... them to specify the desired security level, compartment, and
precedence of connections.
...
... sender of the segment is expecting to
receive. Once a connection is established this is always sent.
Data Offset: 4 bits ...
... TCP which sends this segment.
This field must only be sent in the initial connection request
(i.e., in segments with the SYN ...
... Before we can discuss very much about the operation of the TCP we need
to introduce some detailed terminology. The maintenance of a TCP
connection requires the remembering of several variables. We conceive
of these variables being stored in a connection record called a
...
... to introduce some detailed terminology. The maintenance of a TCP
connection requires the remembering of several variables. We conceive
of these variables being stored in a connection record called a
Transmission Control Block or TCB ...
... socket numbers, the security and
precedence of the connection, pointers to the user's send and receive
buffers, pointers to the retransmit queue ...
...
A connection progresses through a series of states during its
lifetime. The states are: LISTEN, SYN ...
... state when there is no TCB, and therefore,
no connection. Briefly the meanings of the states are:
...
...
SYN-SENT - represents waiting for a matching connection request
after having sent a connection request.
...
... SYN-SENT - represents waiting for a matching connection request
after having sent a connection request.
SYN ...
...
SYN-RECEIVED - represents waiting for a confirming connection
request acknowledgment after having both received and sent a
connection request.
...
... SYN-RECEIVED - represents waiting for a confirming connection
request acknowledgment after having both received and sent a
connection request.
ESTABLISHED - represents an open connection ...
... connection request.
ESTABLISHED - represents an open connection, data received can be
delivered to the user. The normal state for the data transfer ...
... state for the data transfer phase
of the connection.
FIN-WAIT-1 - represents waiting for a connection ...
... connection.
FIN-WAIT-1 - represents waiting for a connection termination request
from the remote TCP, or an acknowledgment of the connection ...
... connection termination request
from the remote TCP, or an acknowledgment of the connection
termination request previously sent.
...
... termination request previously sent.
FIN-WAIT-2 - represents waiting for a connection termination request
from the remote TCP.
...
... TCP.
CLOSE-WAIT - represents waiting for a connection termination request
from the local user.
...
... from the local user.
CLOSING - represents waiting for a connection termination request
acknowledgment from the remote TCP.
...
... LAST-ACK - represents waiting for an acknowledgment of the
connection termination request previously sent to the remote TCP
(which includes an acknowledgment of its connection ...
... connection termination request previously sent to the remote TCP
(which includes an acknowledgment of its connection termination
request).
...
... TIME-WAIT - represents waiting for enough time to pass to be sure
the remote TCP received the acknowledgment of its connection
termination request.
...
... termination request.
CLOSED - represents no connection state at all.
...
...
A TCP connection progresses from one state to another in response to
events. The events are the user calls, OPEN, SEND ...
... +---------+ +---------+
TCP Connection State Diagram
Figure 6.
...
...
A fundamental notion in the design is that every octet of data sent
over a TCP connection has a sequence number. Since every octet is
sequenced, each of them can be acknowledged. The acknowledgment
...
... SYN and FIN
are the only controls requiring this protection, and these controls
are used only at connection opening and closing. For sequence number
purposes, the SYN ...
...
The protocol places no restriction on a particular connection being
used over and over again. A connection is defined by a pair of
...
... The protocol places no restriction on a particular connection being
used over and over again. A connection is defined by a pair of
sockets. New instances of a connection ...
... connection is defined by a pair of
sockets. New instances of a connection will be referred to as
incarnations of the connection. The problem that arises from this is
...
... sockets. New instances of a connection will be referred to as
incarnations of the connection. The problem that arises from this is
-- "how does the TCP identify duplicate segments ...
... TCP identify duplicate segments from previous
incarnations of the connection?" This problem becomes apparent if the
connection is being opened and closed in quick succession, or if the
...
... incarnations of the connection?" This problem becomes apparent if the
connection is being opened and closed in quick succession, or if the
connection breaks with loss of memory and is then reestablished.
...
... connection is being opened and closed in quick succession, or if the
connection breaks with loss of memory and is then reestablished.
...
... To avoid confusion we must prevent segments from one incarnation of a
connection from being used while the same sequence numbers may still
be present in the network ...
... TCP crashes and loses all knowledge of the
sequence numbers it has been using. When new connections are created,
an initial sequence number ...
...
For each connection there is a send sequence number and a receive
sequence number. The initial send sequence number ...
...
For a connection to be established or initialized, the two TCPs must
synchronize on each other's initial sequence numbers. This is done in
...
... synchronize on each other's initial sequence numbers. This is done in
an exchange of connection establishing segments carrying a control bit
...
... segment was an old delayed one or not,
unless it remembers the last sequence number used on the connection
(which is not always possible), and so it must ask the sender to
...
... sequence numbers transmitted on
each active (i.e., not closed) connection shall delay emitting any
TCP segments ...
... TCP does not have any memory of the
sequence numbers it last used on a given connection. For example, if
the TCP were to start ...
... the TCP were to start all connections with sequence number 0, then
upon crashing and restarting ...
... restarting, a TCP might re-form an earlier
connection (possibly after half-open connection resolution) and emit
packets with sequence numbers ...
... TCP might re-form an earlier
connection (possibly after half-open connection resolution) and emit
packets with sequence numbers identical to or overlapping with
...
... packets still in the network which were emitted on an earlier
incarnation of the same connection. In the absence of knowledge
about the sequence numbers used on a particular connection ...
... connection. In the absence of knowledge
about the sequence numbers used on a particular connection, the TCP
specification recommends that the source delay for MSL seconds
...
... specification recommends that the source delay for MSL seconds
before emitting segments on the connection, to allow time for
segments from the earlier connection ...
... connection, to allow time for
segments from the earlier connection incarnation to drain from the
system.
...
... initial sequence number values are not immune from this problem
(i.e., even if time of day is used to select an initial sequence
number for each new connection incarnation).
...
... starting with
sequence number S. Suppose that this connection is not used much
and that eventually the initial sequence number function (ISN(t))
...
... segment sent by this TCP on a particular connection. Now suppose,
at this instant, the host crashes, recovers, and establishes a new
...
... at this instant, the host crashes, recovers, and establishes a new
incarnation of the connection. The initial sequence number chosen is
S1 = ISN(t) -- last used sequence number ...
... S1 = ISN(t) -- last used sequence number on old incarnation of
connection! If the recovery occurs quickly enough, any old
duplicates in the net bearing sequence numbers in the neighborhood ...
... of S1 may arrive and be treated as new packets by the receiver of
the new incarnation of the connection.
...
... host may not know for how long it
crashed nor does it know whether there are still old duplicates in
the system from earlier connection incarnations.
...
... Implementors may provide TCP users with the ability to select on a
connection by connection basis whether to wait after a crash, or may
informally implement the "quite time" for all connections ...
... TCP users with the ability to select on a
connection by connection basis whether to wait after a crash, or may
informally implement the "quite time" for all connections.
...
... connection by connection basis whether to wait after a crash, or may
informally implement the "quite time" for all connections.
Obviously, even where a user selects to "wait," this is not
necessary after the host ...
... block of space-time is occupied by the octets of the last emitted
segment, if a new connection is started too soon and uses any of the
sequence numbers in the space-time footprint of the last segment ...
... sequence numbers in the space-time footprint of the last segment of
the previous connection incarnation, there is a potential sequence
number overlap area which could cause confusion at the receiver.
...
... Establishing a connection ...
... The "three-way handshake" is the procedure used to establish a
connection. This procedure normally is initiated by one TCP and
responded to by another TCP ...
... SYN" segment can potentially make it appear, to the
recipient, that a simultaneous connection initiation is in progress.
Proper use of "reset" segments can disambiguate these cases.
...
...
Several examples of connection initiation follow. Although these
examples do not show connection synchronization ...
... Several examples of connection initiation follow. Although these
examples do not show connection synchronization using data-carrying
segments ...
... valid (i.e., the data must be buffered at the receiver until the
connection reaches the ESTABLISHED state). The three-way handshake
...
... state). The three-way handshake
reduces the possibility of false connections. It is the
implementation of a trade-off between memory and messages to provide
information for this checking.
...
... The principle reason for the three-way handshake is to prevent old
duplicate connection initiations from causing confusion. To deal with
this, a special control message, reset, has been devised. If the
...
... FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT), it
aborts the connection and informs its user. We discuss this latter
case under "half-open" connections below.
...
... aborts the connection and informs its user. We discuss this latter
case under "half-open" connections below.
...
...
Half-Open Connections and Other Anomalies
...
...
An established connection is said to be "half-open" if one of the
TCPs has closed or aborted the connection at its end without the
...
... An established connection is said to be "half-open" if one of the
TCPs has closed or aborted the connection at its end without the
knowledge of the other, or if the two ends of the connection have
...
... TCPs has closed or aborted the connection at its end without the
knowledge of the other, or if the two ends of the connection have
become desynchronized owing to a crash that resulted in loss of
memory. Such connections ...
... connection have
become desynchronized owing to a crash that resulted in loss of
memory. Such connections will automatically become reset if an
attempt is made to send data in either direction. However, half-open
connections ...
... connections will automatically become reset if an
attempt is made to send data in either direction. However, half-open
connections are expected to be unusual, and the recovery procedure is
mildly involved.
...
...
If at site A the connection no longer exists, then an attempt by the
user at site B to send any data on it will result in the site B TCP
...
... site B TCP that something is wrong, and it is expected to abort the
connection.
...
... A is likely to start again from the beginning or from a recovery
point. As a result, A will probably try to OPEN the connection again
or try to SEND on the connection ...
... connection again
or try to SEND on the connection it believes open. In the latter
case, it receives the error message "connection ...
... connection it believes open. In the latter
case, it receives the error message "connection not open" from the
local (A's) TCP. In an attempt to establish the connection ...
... connection not open" from the
local (A's) TCP. In an attempt to establish the connection, A's TCP
will send a segment ...
... example shown in figure 10. After TCP A crashes, the user attempts to
re-open the connection. TCP B, in the meantime, thinks the connection
...
... SYN> -->
Half-Open Connection Discovery
Figure 10.
...
... sent and, being unsynchronized, sends a reset (RST) because it has
detected a half-open connection. TCP B aborts at line 5. TCP A will
...
... TCP B aborts at line 5. TCP A will
continue to try to establish the connection; the problem is now
reduced to the basic 3-way handshake of figure 7.
...
... TCP A crashes and TCP B
tries to send data on what it thinks is a synchronized connection.
This is illustrated in figure 11. In this case, the data arriving at
TCP ...
... TCP A from TCP B (line 2) is unacceptable because no such connection
exists, so TCP A sends a RST ...
...
Active Side Causes Half-Open Connection Discovery
Figure 11.
...
...
In figure 12, we find the two TCPs A and B with passive connections
waiting for SYN. An old duplicate arriving at TCP ...
... RST) must be sent whenever a segment arrives
which apparently is not intended for the current connection. A reset
must not be sent if it is not clear that this is the case.
...
...
1. If the connection does not exist (CLOSED) then a reset is sent
in response to any incoming segment except another reset. In
...
... in response to any incoming segment except another reset. In
particular, SYNs addressed to a non-existent connection are rejected
by this means.
...
... security level or compartment which
does not exactly match the level and compartment requested for the
connection, a reset is sent.
If our SYN ...
... cannot raise the precedence level to match ours this will be
detected in the next segment it sends, and the connection will be
terminated then). If our SYN has been acknowledged (perhaps in this
...
... state.
3. If the connection is in a synchronized state (ESTABLISHED,
FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK ...
... and an acknowledgment indicating the next sequence number expected
to be received, and the connection remains in the same state.
...
... security level, or compartment, or
precedence which does not exactly match the level, and compartment,
and precedence requested for the connection,a reset is sent and
connection goes to the CLOSED state ...
... and precedence requested for the connection,a reset is sent and
connection goes to the CLOSED state. The reset takes its sequence
number from the ACK ...
... state, otherwise the receiver
aborts the connection and goes to the CLOSED state. If the receiver
...
... receiver
was in any other state, it aborts the connection and advises the user
and goes to the CLOSED state.
...
... Closing a Connection ...
... CLOSE is an operation meaning "I have no more data to send." The
notion of closing a full-duplex connection is subject to ambiguous
interpretation, of course, since it may not be obvious how to treat
...
... interpretation, of course, since it may not be obvious how to treat
the receiving side of the connection. We have chosen to treat CLOSE
in a simplex fashion. The user who CLOSEs may continue to RECEIVE
until he is told that the other side has CLOSED also. Thus, a program
...
... TCP will reliably deliver all
buffers SENT before the connection was CLOSED so a user who expects no
data in return need only wait to hear the connection was CLOSED
...
... buffers SENT before the connection was CLOSED so a user who expects no
data in return need only wait to hear the connection was CLOSED
successfully to know that all his data was received at the destination
...
... destination
TCP. Users must keep reading connections they close for sending until
the TCP says no more data.
...
... receiving a FIN will ACK but not
send its own FIN until its user has CLOSED the connection also.
...
... TCP
can ACK it and tell the user that the connection is closing. The
user will respond with a CLOSE, upon which the TCP can send a FIN to
...
... until its own FIN is acknowledged whereupon it deletes the
connection. If an ACK is not forthcoming, after the user timeout
the connection ...
... connection. If an ACK is not forthcoming, after the user timeout
the connection is aborted and the user is told.
...
...
A simultaneous CLOSE by users at both ends of a connection causes
FIN segments to be exchanged. When all segments ...
...
The intent is that connection be allowed only between ports operating
with exactly the same security ...
...
A connection attempt with mismatched security/compartment values or a
lower precedence value must be rejected by sending a reset. Rejecting
...
... security/compartment values or a
lower precedence value must be rejected by sending a reset. Rejecting
a connection due to too low a precedence only occurs after an
acknowledgment of the SYN has been received.
...
... segments and possibly raise the precedence level they use on the
connection.
...
...
Once the connection is established data is communicated by the
exchange of segments. Because segments ...
... networks that compose an
internetwork system and the wide range of uses of TCP connections the
retransmission timeout must be dynamically determined. One procedure
...
... the currently available data buffer space available for this
connection.
...
... least X percent of the maximum allocation possible for the
connection (where X might be 20 to 40).
...
... may provide combinations or subsets of the basic functions in
single calls. In particular, some implementations may wish to
automatically OPEN a connection on the first SEND or RECEIVE
issued by the user ...
...
(a) general information about a connection (e.g., interrupts,
remote close, binding of unspecified foreign socket ...
... [, timeout] [, precedence] [, security/compartment] [, options])
-> local connection name
...
... processes it serves and will check the authority of the process
to use the connection specified. Depending upon the
implementation of the TCP, the local network ...
... passive flag is set to passive, then this is a
call to LISTEN for an incoming connection. A passive open may
have either a fully specified foreign socket ...
... have either a fully specified foreign socket to wait for a
particular connection or an unspecified foreign socket to wait
for any call. A fully specified passive ...
... active OPEN command, the TCP will begin the procedure to
synchronize (i.e., establish) the connection at once.
...
... destination within the timeout period, the TCP
will abort the connection. The present global default is five
minutes.
...
... operating system will verify
the users authority to open a connection with the specified
precedence or security/compartment. The absence of precedence
...
...
The precedence for the connection is the higher of the values
requested in the OPEN call and received from the incoming
request, and fixed at that value for the life of the
...
... requested in the OPEN call and received from the incoming
request, and fixed at that value for the life of the
connection.Implementers may want to give the user control of
this precedence negotiation ...
... connection name will be returned to the user by the TCP.
The local connection name can then be used as a short hand term
for the connection defined by the <local socket ...
... The local connection name can then be used as a short hand term
for the connection defined by the <local socket, foreign socket>
...
... This call causes the data contained in the indicated user buffer
to be sent on the indicated connection. If the connection has
not been opened, the SEND ...
... buffer
to be sent on the indicated connection. If the connection has
not been opened, the SEND is considered an error. Some
...
... SEND first; in which case, an
automatic OPEN would be done. If the calling process is not
authorized to use this connection, an error is returned.
...
... If no foreign socket was specified in the OPEN, but the
connection is established (e.g., because a LISTENing connection
has become specific due to a foreign segment ...
... socket was specified in the OPEN, but the
connection is established (e.g., because a LISTENing connection
has become specific due to a foreign segment arriving for the
...
... socket
becomes specified, an error will be returned. Users can use the
STATUS call to determine the status of the connection. In some
implementations the TCP may notify the user when an unspecified
...
...
If a timeout is specified, the current user timeout for this
connection is changed to the new one.
...
... is both subject to deadlocks (for example, both sides of the
connection might try to do SENDs before doing any RECEIVEs) and
offers poor performance, so it is not recommended. A more
...
... been acknowledged by the distant TCP. We could optimistically
assume eventual success. If we are wrong, the connection will
close anyway due to the timeout. In implementations of this
kind (synchronous ...
... synchronous), there will still be some asynchronous
signals, but these will deal with the connection itself, and not
with specific segments or buffers ...
... receiving buffer associated with the
specified connection. If no OPEN precedes this command or the
calling process is not authorized to use this connection, an
...
... specified connection. If no OPEN precedes this command or the
calling process is not authorized to use this connection, an
error is returned.
...
...
Format: CLOSE (local connection name)
...
...
This command causes the connection specified to be closed. If
the connection is not open or the calling process is not
...
... This command causes the connection specified to be closed. If
the connection is not open or the calling process is not
authorized to use this connection, an error is returned.
...
... the connection is not open or the calling process is not
authorized to use this connection, an error is returned.
Closing connections is intended to be a graceful operation in
...
... authorized to use this connection, an error is returned.
Closing connections is intended to be a graceful operation in
the sense that outstanding SENDs will be transmitted (and
retransmitted), as flow ...
... to the destination. It should also be clear that users should
continue to RECEIVE on CLOSING connections, since the other side
may be trying to transmit the last of its data. Thus, CLOSE
means "I have no more to send" but does not mean "I will not
...
...
The user may CLOSE the connection at any time on his own
initiative, or in response to various prompts from the TCP
...
... connection requires communication with the
foreign TCP, connections may remain in the closing state for a
short time. Attempts to reopen the connection ...
... connections may remain in the closing state for a
short time. Attempts to reopen the connection before the TCP
replies to the CLOSE command will result in error responses ...
...
Format: STATUS (local connection name) -> status data
...
... excluded without adverse effect. Information returned would
typically come from the TCB associated with the connection.
...
... foreign socket,
local connection name,
receive window,
send window,
...
...
Depending on the state of the connection, or on the
implementation itself, some of this information may not be
available or meaningful. If the calling process is not
...
... implementation itself, some of this information may not be
available or meaningful. If the calling process is not
authorized to use this connection, an error is returned. This
prevents unauthorized processes from gaining information about a
connection ...
... connection, an error is returned. This
prevents unauthorized processes from gaining information about a
connection.
...
...
Format: ABORT (local connection name)
...
... removed, and a special RESET message to
be sent to the TCP on the other side of the connection.
Depending on the implementation, users may receive abort
indications for each outstanding SEND ...
...
Local Connection Name Always
Response String Always
Buffer ...
... destination. It is
also important to preserve the return route to answer connection
requests.
...
... TCP does in response to each of the events. In many
cases the processing required depends on the state of the connection.
...
... Error responses are given as character strings. For example, user
commands referencing connections that do not exist receive "error:
connection not open".
...
... commands referencing connections that do not exist receive "error:
connection not open".
...
... Create a new transmission control block (TCB) to hold connection
state information. Fill in local socket ...
... caller does not have access to the local socket specified,
return "error: connection illegal for this process". If there is
no room to create a new connection ...
... connection illegal for this process". If there is
no room to create a new connection, return "error: insufficient
resources".
...
... active and the foreign socket is specified, then change the
connection from passive to active, select an ISS. Send a SYN ...
... STATE
Return "error: connection already exists".
...
... TCB does not exist)
If the user does not have access to such a connection, then return
"error: connection illegal for this process".
...
... If the user does not have access to such a connection, then return
"error: connection illegal for this process".
Otherwise, return "error: connection ...
... connection illegal for this process".
Otherwise, return "error: connection does not exist".
LISTEN STATE ...
... TCB does not exist)
If the user does not have access to such a connection, return
"error: connection illegal for this process".
...
... If the user does not have access to such a connection, return
"error: connection illegal for this process".
Otherwise return "error: connection ...
... connection illegal for this process".
Otherwise return "error: connection does not exist".
LISTEN STATE ...
... user. If no text is awaiting delivery, the RECEIVE will get a
"error: connection closing" response. Otherwise, any remaining
text can be used to satisfy the RECEIVE.
...
... STATE
Return "error: connection closing".
...
... TCB does not exist)
If the user does not have access to such a connection, return
"error: connection illegal for this process".
...
... If the user does not have access to such a connection, return
"error: connection illegal for this process".
Otherwise, return "error: connection ...
... connection illegal for this process".
Otherwise, return "error: connection does not exist".
LISTEN STATE ...
...
Strictly speaking, this is an error and should receive a "error:
connection closing" response. An "ok" response would be
acceptable, too, as long as a second FIN is not emitted (the first
FIN may be retransmitted though).
...
... STATE
Respond with "error: connection closing".
...
... TCB does not exist)
If the user should not have access to such a connection, return
"error: connection illegal for this process".
...
... If the user should not have access to such a connection, return
"error: connection illegal for this process".
Otherwise return "error: connection ...
... connection illegal for this process".
Otherwise return "error: connection does not exist".
LISTEN STATE ...
...
Any outstanding RECEIVEs should be returned with "error:
connection reset" responses. Delete TCB, enter CLOSED state ...
... RST>
All queued SENDs and RECEIVEs should be given "connection reset"
notification; all segments ...
... TCB does not exist)
If the user should not have access to such a connection, return
"error: connection illegal for this process".
...
... If the user should not have access to such a connection, return
"error: connection illegal for this process".
Otherwise return "error: connection ...
... connection illegal for this process".
Otherwise return "error: connection does not exist".
LISTEN STATE ...
... ACK
Any acknowledgment is bad if it arrives on a connection still in
the LISTEN state. An acceptable reset segment ...
... valid, since
it could not have been sent in response to anything sent by this
incarnation of the connection. So you are unlikely to get here,
but if you do, drop the segment, and return.
...
... If the ACK was acceptable then signal the user "error:
connection reset", drop the segment, enter CLOSED state,
...
...
If SND.UNA > ISS (our SYN has been ACKed), change the connection
state to ESTABLISHED, form an ACK ...
... bit is set
If this connection was initiated with a passive OPEN (i.e.,
came from the LISTEN state ...
... passive OPEN (i.e.,
came from the LISTEN state), then return this connection to
LISTEN state and return. The user need not be informed. If
...
... LISTEN state and return. The user need not be informed. If
this connection was initiated with an active OPEN (i.e., came
from SYN ...
... from SYN-SENT state) then the connection was refused, signal
the user "connection refused". In either case, all segments ...
... state) then the connection was refused, signal
the user "connection refused". In either case, all segments
on the retransmission ...
... queues should be
flushed. Users should also receive an unsolicited general
"connection reset" signal. Enter the CLOSED state, delete the
...
... queues should be
flushed. Users should also receive an unsolicited general
"connection reset" signal. Enter the CLOSED state, delete the
...
... Note this check is placed following the sequence check to prevent
a segment from an old connection between these ports with a
different security ...
... different security or precedence from causing an abort of the
current connection.
fourth, check the SYN ...
... segment queues should be flushed, the user should also
receive an unsolicited general "connection reset" signal, enter
the CLOSED state, delete ...
...
If the FIN bit is set, signal the user "connection closing" and
return any pending RECEIVEs with same message, advance RCV.NXT
...
... state if the user timeout expires, flush all queues, signal
the user "error: connection aborted due to user timeout" in general
and for any outstanding calls, delete the TCB ...
... connection ...
... Initial Sequence Number. The first sequence number used
on a connection, (either ISS or IRS). Selected on a clock
based procedure. ...
... that the receiver should delete the connection without further
interaction. The receiver can determine, based on the
...
... 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
...
... bit in the incoming segment, occupying one sequence
number, used at the initiation of a connection, to indicate
where the sequence numbering will start. ...
... The precedence of the connection. ...
... Dalal, Y. and C. Sunshine, "Connection Management in Transport Protocols", Computer Networks ...