X-Git-Url: http://git.meshlink.io/?p=utcp;a=blobdiff_plain;f=README;fp=README;h=0f91f871c9eef353439f57f6dc21af9846ffe649;hp=1c9baf62e2917fa1466b9f53bff1706fe9180988;hb=e5db16f2c3e5debdc60b129f8f271faa1c482959;hpb=bfde83247774e40b3d178852d286b00e6be75132

diff --git a/README b/README
index 1c9baf6..0f91f87 100644
--- a/README
+++ b/README
@@ -21,6 +21,7 @@ TODO v1.0:
 * Implement send buffer
 * Window scaling
 * Handle retransmission
+  - Proper timeout handling
 
 TODO v2.0:
 
@@ -44,6 +45,15 @@ Fast transaction:
 
 Does this need special care or can we rely on higher level MACs?
 
+RFCs
+----
+
+793  Transmission Control Protocol (Functional Specification)
+2581 TCP Congestion Control
+2988 Computing TCP's Retransmission Timer
+
+
+
 INVARIANTS
 ----------
 
@@ -61,30 +71,87 @@ INVARIANTS
 
 - SYN and FIN each count as one byte for the sequence numbering, but no actual byte is transferred in the payload.
 
+CONNECTION TIMEOUT
+------------------
+
+This timer is intended to catch the case when we are waiting very long for a response but nothing happens.
+The timeout is in the order of minutes.
+
+- The conn timeout is set whenever there is unacknowledged data, or when we are in the TIME_WAIT status.
+- If snd.una is advanced while the timeout is set, we re-set the timeout.
+- If the conn timeout expires, close the connection immediately.
+
+RETRANSMIT TIMEOUT
+------------------
+
+(See RFC 2988, 3366)
+
+This timer is intended to catch the case where we didn't get an ACK from the peer.
+In principle, the timeout should be slightly longer than the maximum latency along the path.
+
+
+- The rtrx timeout is set whenever snd.nxt is advanced.
+- If the rtrx timeout expires, retransmit at least one packet, and re-set the timeout.
+
 STATES
 ------
 
-CLOSED: this connection is cloed, all packets received will result in RST.
+CLOSED: this connection is closed, all packets received will result in RST.
+  RX: RST
+  TX: return error
+  RT: clear timers
+  RST: ignore
 
 LISTEN: (= no connection yet): only allow SYN packets, it application does not accept, return RST|ACK, else SYN|ACK.
+  RX: on accept, send SYNACK, go to SYN_RECEIVED
+  TX: cannot happen
+  RT: cannot happen
+  RST: ignore
 
 SYN_SENT: we sent a SYN, now expecting SYN|ACK
+  RX: must be valid SYNACK, send ACK, go to ESTABLISHED
+  TX: put in send buffer (TODO: send SYN again with data?)
+  RT: send SYN again
 
 SYN_RECEIVED: we received a SYN, sent back a SYN|ACK, now expecting an ACK
+  RX: must be valid ACK, go to ESTABLISHED
+  TX: put in send buffer (TODO: send SYNACK again with data?)
+  RT: send SYNACK again
 
 ESTABLISHED: SYN is acked, we can now send/receive normal data.
+  RX: process data, return ACK. If FIN set, go to CLOSE_WAIT
+  TX: put in send buffer, segmentize and send
+  RT: send unACKed data again
 
 FIN_WAIT_1: we want to close the connection, and just sent a FIN, waiting for it to be ACKed.
+  RX: process data, return ACK. If our FIN is acked, go to FIN_WAIT_2, if a FIN was also received, go to CLOSING
+  TX: return error
+  RT: send unACKed data or else FIN again
 
-FIN_WAIT_2: FIXME
+FIN_WAIT_2: our FIN is ACKed, just waiting for more data or FIN from the peer.
+  RX: process data, return ACK. If a FIN was also received, go to CLOSING
+  TX: return error
+  RT: should not happen, clear timeouts
 
 CLOSE_WAIT: we received a FIN, we sent back an ACK
+  RX: only return an ACK.
+  TX: put in send buffer, segmentize and send
+  RT: send unACKed data again
 
 CLOSING: we had already sent a FIN, and we received a FIN back, now waiting for it to be ACKed.
+  RX: if it's ACKed, set conn timeout, go to TIME_WAIT
+  TX: return an error
+  RT: send unACKed data or else FIN again
 
 LAST_ACK: we are waiting for the last ACK before we can CLOSE
+  RX: if it's ACKed, go to CLOSED
+  TX: return an error
+  RT: send FIN again
 
 TIME_WAIT: connection is in princple closed, but our last ACK might not have been received, so just wait a while to see if a FIN gets retransmitted so we can resend the ACK.
+  RX: if we receive anything, reset conn timeout.
+  TX: return an error
+  RT: should not happen, clear rtrx timeout
 
 SEND PACKET
 -----------
@@ -113,6 +180,7 @@ RECEIVE PACKET
 
 - Drop invalid packets:
   - Invalid flags or state
+  - ACK always set
   - hdr.seq not within our receive window
   - hdr.ack ahead of snd.nxt
 - Handle RST packets