rfc908.txt
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STATUS Request
Returns the status of a connection. The parameters include
the connection identifier and the address of the status
buffer.
Page 19
RFC-908 July 1984
3.7 Event Processing
This section describes one possible sequence for processing
events. It is not intended to suggest a particular
implementation, but any actual implementation should vary from
this description only in detail and not significantly in
substance. The following are the kinds of events that may occur:
USER REQUESTS
Open
Send
Receive
Close
Status
ARRIVING SEGMENT
Segment Arrives
TIMEOUTS
Retransmission Timeout
Close-Wait Timeout
User request processing always terminates with a return to
the caller, with a possible error indication. Error responses
are given as a character string. A delayed response is also
possible in some situations and is returned to the user by
whatever event or pseudo interrupt mechanism is available. The
term "signal" is used to refer to delayed responses.
Processing of arriving segments usually follows this general
sequence: the sequence number is checked for validity and, if
valid, the segment is queued and processed in sequence-number
order. For all events, unless a state change is specified, RDP
remains in the same state.
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RDP Specification Protocol Operation
3.7.1 User Request Events
The following scenarios demonstrate the processing of events
caused by the issuance of user requests:
Open Request
CLOSED STATE
Create a connection record
If none available
Return "Error - insufficient resources"
Endif
If passive Open
If local port not specified
Return "Error - local port not specified"
Endif
Generate SND.ISS
Set SND.NXT = SND.ISS + 1
SND.UNA = SND.ISS
Fill in SND.MAX, RMAX.BUF from Open parameters
Set State = LISTEN
Return
Endif
If active Open
If remote port not specified
Return "Error - remote port not specified"
Endif
Generate SND.ISS
Set SND.NXT = SND.ISS + 1
SND.UNA = SND.ISS
Fill in SND.MAX, RMAX.BUF from Open parameters
If local port not specified
Allocate a local port
Endif
Send <SEQ=SND.ISS><MAX=SND.MAX><MAXBUF=RMAX.BUF><SYN>
Set State = SYN-SENT
Return (local port, connection identifier)
Endif
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RFC-908 July 1984
LISTEN STATE
SYN-SENT STATE
SYN-RCVD STATE
OPEN STATE
CLOSE-WAIT STATE
Return "Error - connection already open"
Close Request
OPEN STATE
Send <SEQ=SND.NXT><RST>
Set State = CLOSE-WAIT
Start TIMWAIT Timer
Return
LISTEN STATE
Set State = CLOSED
Deallocate connection record
Return
SYN-RCVD STATE
SYN-SENT STATE
Send <SEQ=SND.NXT><RST>
Set State = CLOSED
Return
CLOSE-WAIT STATE
Return "Error - connection closing"
CLOSE STATE
Return "Error - connection not open"
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RDP Specification Protocol Operation
Receive Request
OPEN STATE
If Data is pending
Return with data
else
Return with "no data" indication
Endif
LISTEN STATE
SYN-RCVD STATE
SYN-SENT STATE
Return with "no data" indication
CLOSE STATE
CLOSE-WAIT STATE
Return "Error - connection not open"
Send Request
OPEN STATE
If SND.NXT < SND.UNA + SND.MAX
Send <SEQ=SND.NXT><ACK=RCV.CUR><ACK><Data>
Set SND.NXT = SND.NXT + 1
Return
else
Return "Error - insufficient resources to send data"
Endif
LISTEN STATE
SYN-RCVD STATE
SYN-SENT STATE
CLOSE STATE
CLOSE-WAIT STATE
Return "Error - connection not open"
Status Request
Return with:
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RFC-908 July 1984
State of connection (OPEN, LISTEN, etc.)
Number of segments unacknowledged
Number of segments received not given to user
Maximum segment size for the send side of the connection
Maximum segment size for the receive side of the connection
3.7.2 Segment Arrival Events
The following scenarios describe the processing of the event
caused by the arrival of a RDP segment from a remote host. The
assumption is made that the segment was addressed to the local
port associated with the connection record.
If State = CLOSED
If RST set
Discard segment
Return
Endif
If ACK or NUL set
Send <SEQ=SEG.ACK + 1><RST>
Discard segment
Return
else
Send <SEQ=0><RST><ACK=RCV.CUR><ACK>
Discard segment
Return
Endif
Endif
If State = CLOSE-WAIT
If RST set
Set State = CLOSED
Discard segment
Cancel TIMWAIT timer
Deallocate connection record
else
Discard segment
Endif
Return
Endif
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RDP Specification Protocol Operation
If State = LISTEN
If RST set
Discard the segment
Return
Endif
If ACK or NUL set
Send <SEQ=SEG.ACK + 1><RST>
Return
Endif
If SYN set
Set RCV.CUR = SEG.SEQ
RCV.IRS = SEG.SEQ
SND.MAX = SEG.MAX
SBUF.MAX = SEG.BMAX
Send <SEQ=SND.ISS><ACK=RCV.CUR><MAX=RCV.MAX><BUFMAX=RBUF.MAX>
<ACK><SYN>
Set State = SYN-RCVD
Return
Endif
If anything else (should never get here)
Discard segment
Return
Endif
Endif
If State = SYN-SENT
If ACK set
If RST clear and SEG.ACK != SND.ISS
Send <SEQ=SEG.ACK + 1><RST>
Endif
Discard segment; Return
Endif
If RST set
If ACK set
Signal "Connection Refused"
Set State = CLOSED
Deallocate connection record
Endif
Discard segment
Return
Endif
Page 25
RFC-908 July 1984
If SYN set
Set RCV.CUR = SEG.SEQ
RCV.IRS = SEG.SEQ
SND.MAX = SEG.MAX
RBUF.MAX = SEG.BMAX
If ACK set
Set SND.UNA = SEG.ACK
State = OPEN
Send <SEQ=SND.NXT><ACK=RCV.CUR><ACK>
else
Set State = SYN-RCVD
Send <SEQ=SND.ISS><ACK=RCV.CUR><MAX=RCV.MAX><BUFMAX=RBUF.MAX>
<SYN><ACK>
Endif
Return
Endif
If anything else
Discard segment
Return
Endif
Endif
If State = SYN-RCVD
If RCV.IRS < SEG.SEQ =< RCV.CUR + (RCV.MAX * 2)
Segment sequence number acceptable
else
Send <SEQ=SND.NXT><ACK=RCV.CUR><ACK>
Discard segment
Return
Endif
If RST set
If passive Open
Set State = LISTEN
else
Set State = CLOSED
Signal "Connection Refused"
Discard segment
Deallocate connection record
Endif
Return
Endif
Page 26
RDP Specification Protocol Operation
If SYN set
Send <SEQ=SEG.ACK + 1><RST>
Set State = CLOSED
Signal "Connection Reset"
Discard segment
Deallocate connection record
Return
Endif
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