Merge pull request #870 from quicwg/draining-applicability

 Tweaks for the draining period

draft-ietf-quic-transport.md

@@ -1625,20 +1625,30 @@ from its peer.  These packets might have been sent prior to receiving any close
 signal, or they might be retransmissions of packets for which acknowledgments
 were lost.
 
-The draining period persists for three times the current Retransmission Timeout
-(RTO) interval as defined in {{QUIC-RECOVERY}}.  During this period, new packets
-can be acknowledged, but no new application data can be sent on the connection.
+The draining period exists to ensure that delayed or reordered packets are
+properly discarded.  This state SHOULD persist for three times the current
+Retransmission Timeout (RTO) interval as defined in {{QUIC-RECOVERY}}.  During
+this period no new application data can be sent on the connection.
 
 Different treatment is given to packets that are received while a connection is
-in the draining period depending on how the connection was closed.
-
-An endpoint that is in a draining period MUST NOT send packets unless they
-contain a CONNECTION_CLOSE or APPLICATION_CLOSE frame.
+in the draining period depending on how the connection was closed.  An endpoint
+that is in a draining period MUST NOT send packets unless they contain a
+CONNECTION_CLOSE or APPLICATION_CLOSE frame.
 
 Once the draining period has ended, an endpoint SHOULD discard per-connection
 state.  This results in new packets on the connection being discarded.  An
 endpoint MAY send a stateless reset in response to any further incoming packets.
 
+An endpoint MAY exit the draining period earlier if it can guarantee that its
+peer is also draining.  Receiving a CONNECTION_CLOSE or APPLICATION_CLOSE frame
+is sufficient confirmation, as is receiving a stateless reset.  However,
+disposing of connection state could result in delayed or reordered packets to be
+handled poorly.  For endpoints that have some alternative means to ensure that
+late-arriving packets on the connection do not create QUIC state, such as by
+closing the UDP socket, an abbreviated draining period can allow for faster
+resource recovery.  Servers that retain an open port for accepting new
+connections SHOULD NOT exit the draining period early.
+
 The draining period does not apply when a stateless reset ({{stateless-reset}})
 is sent.