Diff: tcp/tcp.txt

Revision:

71:736a5747ade1

Child:

72:19457bba58d0

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tcp/tcp.txt	Sat Oct 20 18:56:13 2018 +0000
@@ -0,0 +1,49 @@
+Names
+=====
+ISN     == Initial Sequence Number
+SEQ num == Sequence Number is the sequence of the first byte of the sent data packet - unless a SYN in which case it is the ISN
+ACK num == Acknowledge Number is the next sequence number that the sender of the ACK is expecting
+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
+
+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
+
+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
+=====
+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_FIN_WAIT
+TCB_ACK_WAIT