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HTTP/1.0, 1.1 and Beyond, An Evolutionary Perspective on HTTP. Henrik Frystyk Nielsen. Purpose of this Talk. Why did HTTP end up the way it did? What caused new features to be introduced? Nobody could have predicted the path it took! Kiss (Keep it simple, stupid!) principle is essential

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Presentation Transcript
purpose of this talk
Purpose of this Talk
  • Why did HTTP end up the way it did?
    • What caused new features to be introduced?
    • Nobody could have predicted the path it took!
    • Kiss (Keep it simple, stupid!) principle is essential
  • What is HTTP, really?
    • The Basic HTTP Building Blocks
  • Bare Bone HTTP
    • In every big protocol there is a small waiting to get out
  • Common Comments and Questions about HTTP
    • On performance, state, complexity, extensibility

HTTP - an Evolutionary Perspective

once upon a time
Once Upon a Time...
  • HTTP started out as a simple hypertext protocol
  • Send GET request - get back a document
    • Hypertext was what you asked for and what you got
  • There was no information about the documents you retrieved - was embedded in the document
  • This were the early days of HTTP/0.9

HTTP - an Evolutionary Perspective

then came the img hack
Then came the <IMG …> hack
  • No more only text based documents
  • Needed type information to distinguish images from text
  • MIME provided a mechanism for describing protocol messages
    • Was adopted for describing HTTP messages
    • A major cross road on the evolutionary path
  • HTTP/1.0 was on its way

HTTP - an Evolutionary Perspective

then came proxies and gateways
Then came Proxies and Gateways
  • First to get access to other systems like Gopher and WAIS
    • Bootstrap mechanism for accessing information
  • Then to traverse firewalls
    • Turned out to be better than mechanisms like SOCKS
  • And soon caching became popular based on last modified dates and heuristics
  • Proxies crucial piece of Web architecture
    • Allows for new levels of indirection

HTTP - an Evolutionary Perspective

in the mean time
In the Mean Time...
  • People wanted faster renditions of their pages containing text, images and audio
  • Solution: Use multiple, parallel TCP connections
    • This actually makes a lot of sense
    • TCP sockets are easy to program
    • You get a lot of resources from the OS and the Net
    • It seems to be a lot faster!
  • One problem - impact on Net a disaster
    • Web applications were wasting huge amounts of resources. Servers did not do any real work

HTTP - an Evolutionary Perspective

the more the merrier
The More the Merrier
  • People wanted all their information in their browser
  • Use of POST to represent “strange ideas”
  • POST is not AUTOMATABLE!
    • Difference from Automated!
    • It is not a question of handling strange ideas!
    • It is a question of letting your computer handle strange ideas!
  • HTTP become a byte transport
  • Lack of interoperability

HTTP - an Evolutionary Perspective

the web was commercialized
The Web was Commercialized
  • Vanity host names become popular
    • Everybody wants their own domain name (www.henrik.com)
  • Due to a misoptimization, this could only be done using multiple IP addresses
    • Result is that many machines have multiple IP addresses
    • Examples of 100 or more IP addresses pr machine

HTTP - an Evolutionary Perspective

and fueled by advertisement
…and Fueled by Advertisement
  • Main accounting mechanism was hit counts in the form of TCP connections
  • No trust in heuristic caching - bust it!
    • We loose revenue every time a cache serves a cached document

HTTP - an Evolutionary Perspective

result the internet was on its knees
Result: The Internet was on its Knees
  • Several reports of busy links collapsing - no data got through
  • IP addresses were consumed at very high rate
  • But… I don’t think that HTTP would have the position it has today as the most used protocol if started with HTTP/1.1

HTTP - an Evolutionary Perspective

http 1 1 the big fire fighter
HTTP/1.1 - The Big Fire Fighter
  • Main purpose was to fix three problems
    • Provide a semantically well-defined caching model
    • Support vanity hostnames
    • Limiting waste of TCP connections
  • Criteria for solutions was that the end user would see a clear win
    • People need personal incentives to change
    • Implementors need clear market benefit to implement

HTTP - an Evolutionary Perspective

hmm looks promising
Hmm, Looks Promising!
  • Success criteria was met
  • In our performance work, we could show that
    • HTTP/1.1 cuts down Round Trip Times by a lot
    • Cut down TCP overhead by a factor of three
    • Cut down time to transfer data by a factor of 2
  • We can blast out PPP, LANs and WANs
    • Have not made explicit testing on wireless
    • Would urge people to help doing this

HTTP - an Evolutionary Perspective

but how can we extend it
But How can We Extend it?
  • HTTP is not a centrally controlled protocol
    • Has maybe never been
    • It’s extended by everybody for any possible purpose
  • Clearly suffering from “HTTP is the hammer - everything is a nail” syndrome
  • No structured way of extending HTTP
  • Lack of type information
    • Using POST as a tunnel mechanism
    • Reducing HTTP to a byte transport
  • We need a more powerful framework!

HTTP - an Evolutionary Perspective

http the next generation
HTTP - the Next Generation
  • HTTP-NG is generic application level protocol
    • A simple, extensible framework
  • Explicit Layering and modularization
    • Break up the big “lump” style HTTP message
  • Extensibility at the core
    • Lessons from our HTTP/PEP/Mandatory work
  • Can the Web be implemented using Distributed Object technology?

HTTP - an Evolutionary Perspective

so what is http anyway
So What is HTTP anyway?
  • Let’s have a quick look at the model
  • It looks like MIME but isn’t quite
    • HTTP is a layered Protocol
    • Has Scope, Proxying and Caching
    • Has inherent fuzziness built in
      • Content negotiation and redirections
  • It looks like RPC but isn’t quite
    • Proxies are explicit in the interfaces
    • Has the notion of end-to-end and hop-by-hop scope
    • Interfaces are both vertical and horizontal
    • Headers separated from methods

HTTP - an Evolutionary Perspective

methods headers and status codes
Methods, Headers, and Status Codes
  • No explicit relationship between methods, header fields and status codes in an HTTP message. Relationship must be defined implicitly
  • Methods to be performed on the resource
    • A priori agreement of semantics. Can’t be extended dynamically
  • Headers carry information about the parties involved, the transaction, the message body or the resource
    • Unknown header fields must be ignored without affecting the outcome of the transaction
  • Status Codes are the results returned by the server
    • Status codes are somewhat easier to extend, as unknown status codes must be treated as the x00 code of that class.

HTTP - an Evolutionary Perspective

common questions about http
Common Questions about HTTP
  • People often discard HTTP using inaccurate assumptions
  • Not a question of “HTTP all over” but a path for evolvability
  • Working our way towards a generic application level protocol framework
    • An important goal of HTTP-NG!

HTTP - an Evolutionary Perspective

why is http 1 1 so big
Why is HTTP/1.1 so big?
  • I have often heard: We only need a small subset, not the whole thing
  • What does it really take to be an HTTP application? Not a lot!
  • Most features defined by header fields have a request part and a response part.
  • The SHOULD and MUST requirements in which header field to support often comes in pairs: if you support a certain feature then you have to support all header fields associated with that feature.

HTTP - an Evolutionary Perspective

http is for http urls right
HTTP is for HTTP URLs, right?
  • HTTP can handle arbitrary URIs - not only “http://…”
  • This is a consequence of Proxies and Gateways in the HTTP model
  • I don’t believe in Gateways
    • I want one information space with a consistent set of services
  • URI space is getting more complex
    • New URI schemes on a daily basis
    • A serious problem for interoperability

HTTP - an Evolutionary Perspective

i can t use http i need state
I can’t use HTTP - I need state!
  • HTTP is inherently a stateless protocol
    • Request-response pairs are independent but not necessarily idempotent.
    • POST, as well as sequences of PUT and DELETE, changes state
  • State can be built on top of HTTP
    • Often sufficient to add a simple header field or a parameter on an existing one
  • Cookies is state at a higher level
    • Involves the end-user and hence concerns about privacy etc.

HTTP - an Evolutionary Perspective

http is for tcp only
HTTP is for TCP Only!
  • There is (almost) nothing that binds HTTP to TCP
    • HTTP is known to run on top of non-TCP networks
  • Often said that UDP is faster than TCP
    • Pipelining changes this dramatically: requests and responses take fragments of TCP packets
  • UDP Support should be done by layering
    • Many examples of MIME based protocols supporting UDP at the application level
    • Doesn’t make sense!

HTTP - an Evolutionary Perspective

http can t handle streamed data
HTTP can’t handle Streamed Data
  • There is a difference between Controlling and Transmitting
  • HTTP is not a real time protocol
  • But can be used to control audio/video streams
    • Essentially as a remote control protocol

HTTP - an Evolutionary Perspective

http is too slow
HTTP is too Slow!
  • Well, performance is relative
  • HTTP is not a fast protocol - but there are not very many fast protocols around
    • POP is really bad with respect to round trips (RTT).
    • CORBA is really bad with respect to bytes and RTTs
  • On wireless, RTT is the factor that kills you
    • HTTP/1.1 is fairly good at avoiding RTT delays

HTTP - an Evolutionary Perspective

more information on the web
More Information on the Web
  • HTTP-NG Project
  • HTTP-NG Activity
  • HTTP-NG Working Groups (W3C Members only)
  • HTTP/1.x Overview
  • W3C Member Site
  • W3C

HTTP - an Evolutionary Perspective

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