SPDY is a protocol that uses a single TCP connection to request and receive web page resources in parallel through multiplexed streams, allowing for header compression and prioritization of resources to reduce page load times. It works by establishing a single TCP connection between a client and server based on IP addresses, then streaming HTTP requests and responses concurrently over that connection through prioritized streams.

1. What is SPDY?
 Framing layer implementing streams above TCP or TLS
 Optimized for HTTP
How does it work?
 Single client-server TCP connection - based on IP
addresses, not hostnames
 HTTP Requests and Responses are streamed in parallel
over the TCP session
Optimizations
 Compressed HTTP Headers in SYN_REPLY and
SYN_RESPONSE requests
 Chunked responses to prevent head-of-line blocking

2.  To target a 50% reduction in page load time
 To minimize deployment complexity
 To avoid the need for any changes to the content by
website authors
 To allow many concurrent HTTP requests to run across a
single TCP session.
 To reduce the bandwidth currently used by HTTP by
compressing headers and eliminating unnecessary headers.
 To make SSL the underlying transport protocol, for better
security and compatibility with existing network
infrastructure
Goals for SPDY

3. What is a web page?
 86 resources
 13 hosts
 800+KB
 only 66% compressed (top sites are ~90% compressed)

4. Who is using SPDY?
Google Chrome
All Google Web Properties
Mozilla Firefox
Twitter
Amazon Silk
Others: Contendo, Strangeloop, iPhone client,
Apache mod-spdy, nginx beta, jetty, netty,
libraries in python, node.js, erlang, ruby, go, and
C

5. New Features
 Multiplexing
 Prioritization
 Compression
 Server Push
 Transparent to HTTP application servers
deployable today

6. Improvements
 One Connection per Domain to Exchange All Data
 Multiplexed requests on the same connection
 Permanent Connection to the server
 Compression of Headers
 Prioritized Requests
 Server Push
 Security by Design
 HTTP Compatibility
 Per-request flow control (Supported in SPDY v3)

7. Bottlenecks of HTTP Connections
 HTTP relies on multiple connections for concurrency
 Several problems caused by this
 Additional round trips for connection setup
 Slow-start delays
 Connection rationing by the client, where it tries
to avoid opening too many connections to the single
server
 The goal of SPDY is to reduce web page load time.

8. SPDY Layers
 SPDY is split into 2 layers:
 Framing Layer - which multiplexes a TCP
connection into independent, length-prefixed
frames. The framing layer is tailored to the
needs of the HTTP Protocol and Server push
 HTTP Layer - which specifies the overlaying of
HTTP Request/Response pairs on top of the
framing layer
 SPDY Framing layer runs on top of the reliable transport protocol like
TCP
 SPDY Connections are persistent connections
 SPDY is commonly used with TLS

9. SPDY Frame Types
Two types of Frames:
 Control Frame contains
• a version number
• a frame type
• length
 Data Frame contains
• a stream ID
• flags
• length for the payload carried after the common header.
 There is always a common header which is 8 bytes in length.
 The first bit indicates that whether the frame is a control frame
or a data frame.

10. SPDY Streams
 Streams are independent sequences of bi-directional data
cut into frames
 Streams are bidirectional – regular HTTP Requests for
Clients and unidirectional (server push) for servers
 Streams may be created by either client or server
 Streams optionally carry a set of name/value header pairs
 Streams may be cancelled

11. SPDY Stream Frames
 Types of SPDY Stream Frames:
SYN_STREAM - Open a new stream
SYN_REPLY - Remote Acknowledgement of newly
opened stream
RST_STREAM - Close a stream

12. HTTP Request / Response

13. SPDY Session Setup

14. SPDY Sample Transaction

15. SPDY Response Delivery