By Jory Cohen Made for CISC856, Spring 2010 Thanks to Dr. Amer, Mike Belshe(Google), Jon Leighton

 Experimental protocol being researched by Google and the UD PEL  Application-layer protocol for transporting content over the web, designed specifically for minimal latency

 HTTP is inefficient ◦ Single request per connection  Browsers now open 6 connections per domain for concurrency ◦ Only clients can initiate requests ◦ Header size – 200 bytes to over 2 KB ◦ Redundant headers ◦ Optional data compression

 Multiplexed requests ◦ No limit to number of requests over SPDY connection  Prioritized requests  Compressed headers and data  Server push and server hint  Only changes way data is written to network ◦ SPDY keeps cookies, encoding negotiations, etc. same as HTTP

 Streams can be bi-directional  SPDY allows for unlimited concurrent streams over a single TCP connection  Fewer network connections need to be made, and fewer, but more densely packed, packets are issued

 The client can request as many items as the client wants from the server, and assign a priority to each request  SPDY compresses request and response HTTP headers, resulting in fewer TCP PDUs and fewer bytes transmitted

 Server pushes to the client before something is requested ◦ Valuable for visiting a webpage, server knows everything that should be requested ◦ Reduces the client’s processing time before being able to send out subsequent requests ◦ Server must open multiple streams

ClientServer HTTP Get request Response for HTTP Get Server push Server Push Example Stream 1 Stream 8 Stream 6 Stream 4 Stream 2

 Server tells client that it will probably ask for certain resources ◦ Client can request resources due to server hint much faster than without ◦ Client can also make decision to ignore hint given by the server ◦ Has similar benefit to server push, reduces processing time necessary at client before new requests are sent to the server

ClientServer HTTP Get request Response for HTTP Get Server hints to client Client request based on hint Server responses Server Hint Example Stream 1 Stream 2 Stream 3 Stream 5 Stream 7 Stream 9 Streams 3,5,7,9

 Connections started by the client must be odd  Connections started by the server must be even  Stream number 99 can be initiated before stream number 2  No steam ID of 0  Stream must be set to be unidirectional in SYN_STREAM, default would be bi-directional

 Client sends SYN_STREAM to open connection  Client can begin sending data or requests for data without waiting for response  After client is done sending, client sets the FLAG_FIN flag and connection is half closed

ClientServer SYN_STREAM Data or Requests Stream ID = 1 SYN_STREAM Data or Requests Stream ID = 3 SYN_STREAM Stream ID = 2 Data or Requests SYN_REPLY SYN_REPLY Stream 3 & Data Stream 1 Stream ID = 1

 Normal termination ◦ Both sides have sent FLAG_FIN  Abrupt termination ◦ One side sends RST_STREAM  TCP connection teardown ◦ Both sides must realize that the connection was abnormally terminated

ClientServer Data + FLAG_FINStream 3 Data reply for Stream 3 Data reply for Stream 3 + FLAG_FIN

4244 bytes on wire, 9978 total bytes uncompressed. 42% of bytes without compression. 861 bytes on the wire, 2299 total bytes uncompressed. 37% of bytes without compression.

 NOOP ◦ Receiver does nothing, ignores PDU  PING ◦ Used to test RTT, takes priority over data  GOAWAY ◦ Used for graceful termination ◦ Contains a last good stream number  HEADERS ◦ Used to send additional headers that would not fit in a previous PDU  WINDOW_UPDATE ◦ Used for per stream flow control in SPDY

 SETTINGS ◦ Used to communicate ID/value pairs  Upload bandwidth  Download bandwidth  Round trip time  Maximum concurrent streams  Current CWND  Persistence of previous settings

Download of 25 websites with 1% constant packet loss. Download was run 10 times for each site and average page load time is reported. [1]

Download of 25 websites with 1% constant packet loss. Download was run 10 times for each site and average page load time is reported.[1]

Download of 25 websites with 1% constant packet loss. Download was run 10 times for each site and average page load time is reported.[1]

 SPDY enabled Chrome browser with Flip-in- mem server  SPDY “plug-in” for wireshark  Use SCTP with SPDY

 SPDY protocol specification protocol/spdy-protocol-draft2  SPDY white paper whitepaper [1]  SPDY homepage with other resources