Information Technology Reference
In-Depth Information
Table 24.2
TCB parameters
Send sequence variables
Receive sequence variables
Current packet variable
RCV.NXT Receive next
SEG.SEQ Segment sequence
number
SEG.ACK Segment
acknowledgement number
SEG.LEN Segment length
SND.UNA
SND.NXT Send next
SND.WND Send window
SND.UP Send urgent pointer
RCV.WND Receive window
RCV.UP Receive urgent pointer
IRS Initial receive sequence number
SND.WL1 Segment sequence
number used for last window
update
SND.WL2 Segment acknowl-
edgement number used for last
window update
ISS Initial send sequence num-
ber
SEG.WND Segment window
SEG.UP Segment urgent
pointer
SEG.PRC Segment precedence
value
•
LISTEN - this is the state in which TCP is waiting for a remote connection on a given
port.
•
SYN-SENT- this is the state where TCP is waiting for a matching connection request
after it has sent a connection request.
•
SYN-RECEIVED - is the state where TCP is waiting for a confirming connection re-
quest acknowledgement after having both received and sent a connection request.
•
ESTABLISHED - this is the state that represents an open connection. Any data received
can be delivered to the application program. This is the normal state for data to be trans-
mitted.
•
FIN-WAIT-1- this is the state in which TCP is waiting for a connection termination re-
quest, or an acknowledgement of a connection termination, from the remote TCP.
•
FIN-WAIT-2 - this is the state in which TCP is waiting for a connection termination re-
quest from the remote TCP.
•
CLOSE-WAIT - this is the state where TCP is waiting for a connection termination re-
quest from the local application.
•
CLOSING - this is the state where TCP is waiting for a connection termination request
acknowledgement from the remote TCP.
•
LAST-ACK - this is the state where TCP is waiting for an acknowledgement of the con-
nection termination request previously sent to the remote TCP.
•
TIME-WAIT - this is the state in which TCP is waiting for enough time to pass to be
sure the remote TCP received the acknowledgement of its connection termination re-
quest.
•
CLOSED - this is the notational state, which occurs after the connection has been closed.
