quic 2 ietf-transport-draft-ietf-quic-transport-09

quic的优点

•  Low-latency connection establishment
•  Multiplexing without head-of-line blocking
•  Authenticated and encrypted header and payload
• Rich signaling for congestion control and loss recovery
• Stream and connection flow control 
• Connection  migration and resilience to NAT rebindin
• Version negotiation

 QUIC packet type：Long Header Format  or short header
 Long Header Format：

0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
|1| Type (7) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+                                     Connection ID (64) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                    Packet Number (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                         Version (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                         Payload (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                        

　　 Long headers are used for packets that are sent prior to the completion of version negotiation and establishment of 1-RTT keys.
Once both conditions are met, a sender switches to sending packets  using the short header

• Header Form: The most significant bit (0x80) of octet 0 (the firstoctet) is set to 1 for long headers.
• Long Packet Type: The remaining seven bits of octet 0 contain the packet type. This field can indicate one of 128 packet types
  • packet types are defined:
  • 
• Version: Octets 9 to 12 contain the selected protocol version. This field indicates which version of QUIC is in use and determines how
  the rest of the protocol fields are interpreted

Short Header Format：

 The short header can be used after the version and 1-RTT keys are negotiated.

• Packet Numbers:

The packet number is an integer in the range 0 to 2^62-1. The value is used in determining the cryptographic nonce for packet encryption.
Each endpoint maintains a separate packet number for sending and receiving. The packet number for sending MUST increase by at least
one after sending any packet, unless otherwise specified (see Section 5.7.1). A QUIC endpoint MUST NOT reuse a packet number within the same
connection (that is, under the same cryptographic keys). If the packet number for sending reaches 2^62 - 1, the sender MUST close the
connection without sending a CONNECTION_CLOSE frame or any further packets; a server MAY send a Stateless Reset (Section 7.9.4) in
response to further packets that it receives.