Diff: tcp/tcp.txt

Revision:

75:603b10404183

Parent:

72:19457bba58d0

Child:

79:f50e02fb5c94

--- a/tcp/tcp.txt	Mon Oct 29 09:33:44 2018 +0000
+++ b/tcp/tcp.txt	Tue Oct 30 22:11:22 2018 +0000
@@ -6,52 +6,21 @@
 TCB     == Transmission Control Block
 RTO     == Retransmission Time Out
 
-Protocol
-========
-Goes:
-0       SYN
-1       Data (length == MSS)
-1+  MSS Data (length == MSS)
-1+2xMSS Data (length <  MSS) + FIN
+Only received packets with a sequence of 1 (position == 0) is handled; any others are ignored. This works because we only handle the first line.
+
+From RFC793
+Reset Processing
 
-TcpHandleReceivedPacket
-=======================
-Called from the network stack
-Reads the header to get: the src and dst ports; the ACK and SEQ numbers; SYN, ACK, PSH, RST and FIN flags 
-Only handles dst port 80 (HTTP)
-Retrieves the TCB for the src port
-Handles RST or SYN requests
-Subtract the initial sequence numbers to get the position in the query from the SEQ num and the position in the reply from the ACK num.
-If the position in the query is not the same as the TCB recd bytes then adjust the TCB recd bytes
-If the position in the reply is not the same as the TCB sent bytes then adjust the TCB sent bytes
-Increment the TCB recd bytes by the received datalength and by 1 for a SYN or FIN
-Handle the packet according to the TCB state, for established connections pass the position in the query and the position in the reply
-Set the ACK number to the TCB recd bytes plus the ISN
-Set the SEQ number to the TCB sent bytes plus the ISN
-Increment the TCB sent bytes by the sent datalength and by 1 for a SYN or FIN
-Swap the ports
-Return to the network stack for unicast transmission
+  In all states except SYN-SENT, all reset (RST) segments are validated
+  by checking their SEQ-fields.  A reset is valid if its sequence number
+  is in the window.  In the SYN-SENT state (a RST received in response
+  to an initial SYN), the RST is acceptable if the ACK field
+  acknowledges the SYN.
 
-Todo
-====
-Separate the work into TcpHandleReceivedPacket and TcpPollForPacketToSend: this would allow RTO to be implemented.
-Need to add the IP to the TCB
-Change TCB_ACK_WAIT and TCB_FIN_WAIT to TCB_CLOSE_ACK_WAIT and TCB_CLOSE_FIN_WAIT
-Add state TCB_SEND_ACK_WAIT
-Add ackdBytes to TCB so that can tell if sentBytes has been acked or not; if so then send the next; if not and within timeout then wait; if not and RTO then send again
-
-State
-=====
-State               Received        Do              New state
-TCB_EMPTY           SYN             record ISN      TCB_SYN_RECEIVED
-TCB_SYN_RECEIVED    ACK                             TCB_ESTABLISHED
-TCB_ESTABLISHED     
-TCB_ACK_WAIT
-TCB_FIN_WAIT
-
-State
-TCB_EMPTY           do nothing
-TCB_SYN_RECEIVED    if (TCB.sent == 0) or (TCB.sent == 1 and TCB.ackd == 0 and RTO) then send SYN ACK and ISN.
-TCB_ESTABLISHED     if (!TCB.finished) then send from TCB.sent. if RTO and TCB.ackd < TCB.sent then resend TCB.ackd
-TCB_ACK_WAIT
-TCB_FIN_WAIT
+  The receiver of a RST first validates it, then changes state.  If the
+  receiver was in the LISTEN state, it ignores it.  If the receiver was
+  in SYN-RECEIVED state and had previously been in the LISTEN state,
+  then the receiver returns to the LISTEN state, otherwise the receiver
+  aborts the connection and goes to the CLOSED state.  If the receiver
+  was in any other state, it aborts the connection and advises the user
+  and goes to the CLOSED state.
\ No newline at end of file