RFC 2140 (rfc2140) - Page 2 of 11
TCP Control Block Interdependence
Alternative Format: Original Text Document
RFC 2140 TCP Control Block Interdependence April 1997
The TCP Control Block (TCB)
A TCB is associated with each connection, i.e., with each association
of a pair of applications across the network. The TCB can be
summarized as containing [9]:
Local process state
pointers to send and receive buffers
pointers to retransmission queue and current segment
pointers to Internet Protocol (IP) PCB
Per-connection shared state
macro-state
connection state
timers
flags
local and remote host numbers and ports
micro-state
send and receive window state (size*, current number)
round-trip time and variance
cong. window size*
cong. window size threshold*
max windows seen*
MSS#
round-trip time and variance#
The per-connection information is shown as split into macro-state and
micro-state, terminology borrowed from [5]. Macro-state describes the
finite state machine; we include the endpoint numbers and components
(timers, flags) used to help maintain that state. This includes the
protocol for establishing and maintaining shared state about the
connection. Micro-state describes the protocol after a connection has
been established, to maintain the reliability and congestion control
of the data transferred in the connection.
We further distinguish two other classes of shared micro-state that
are associated more with host-pairs than with application pairs. One
class is clearly host-pair dependent (#, e.g., MSS, RTT), and the
other is host-pair dependent in its aggregate (*, e.g., cong. window
info., curr. window sizes).
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