1. HTTP/1.0, 1.1 and Beyond, An Evolutionary Perspective on HTTP
Henrik Frystyk Nielsen

2. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

3. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

4. 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
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HTTP - an Evolutionary Perspective

5. 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
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HTTP - an Evolutionary Perspective

6. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

7. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

8. The Web was Commercialized
Vanity host names become popular
Everybody wants their own domain name (
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
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HTTP - an Evolutionary Perspective

9. …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
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HTTP - an Evolutionary Perspective

10. 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
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HTTP - an Evolutionary Perspective

11. 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
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HTTP - an Evolutionary Perspective

12. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

13. HTTP - an Evolutionary Perspective
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!
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HTTP - an Evolutionary Perspective

14. 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?
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HTTP - an Evolutionary Perspective

15. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

16. 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.
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HTTP - an Evolutionary Perspective

17. 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!
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HTTP - an Evolutionary Perspective

18. HTTP - an Evolutionary Perspective
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.
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HTTP - an Evolutionary Perspective

19. HTTP is for HTTP URLs, right?
HTTP can handle arbitrary URIs - not only “
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
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HTTP - an Evolutionary Perspective

20. 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.
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HTTP - an Evolutionary Perspective

21. HTTP - an Evolutionary Perspective
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!
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HTTP - an Evolutionary Perspective

22. 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
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HTTP - an Evolutionary Perspective

23. HTTP - an Evolutionary Perspective
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
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HTTP - an Evolutionary Perspective

24. 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
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HTTP - an Evolutionary Perspective