Network Working Group R. Trace
Internet-Draft A. Foresti
Expires: September 2, 2012 S. Singhal
O. Mazahir
H. Nielsen
G. Montenegro
Microsoft
Mar 2012
HTTP Speed+Mobility
draft-montenegro-httpbis-speed-mobility-00
Abstract
The design of HTTP--how every application and service on the web
communicates today--can positively impact user experience,
operational and environmental costs, and even the battery life of the
devices you carry around.
Improving HTTP starts with speed. Apps--not just browsers--should
get faster too. More and more, apps are how people access web
services, in addition to their browser. Improving HTTP should also
make mobile better, particularly to ensure great battery life and low
network cost on constrained devices. People and their apps should
stay in control of network access. Finally, to achieve rapid
adoption, HTTP 2.0 needs to retain as much compatibility as possible
with the existing Web infrastructure. Done right, HTTP 2.0 can help
people connect their devices and applications to the Internet fast,
reliably, and securely over a number of diverse networks, with great
battery life and low cost.
This document describes "HTTP Speed+Mobility," a proposal for HTTP
2.0 that emphasizes performance improvements and security while at
the same time accounting for the important needs of mobile devices
and applications. The proposal starts from both the Google SPDY
protocol and the work the IETF has done around WebSockets. The
proposal is not a final product but rather is intended to form a
baseline for working group discussion.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 2, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.1. Layered Architecture . . . . . . . . . . . . . . . . . 6
1.1.2. Existing standards . . . . . . . . . . . . . . . . . . 6
1.1.3. Network Cost and Power . . . . . . . . . . . . . . . . 7
1.1.4. Flexibility in deployment . . . . . . . . . . . . . . 8
1.1.5. Client is in control of content . . . . . . . . . . . 8
2. Technical Details . . . . . . . . . . . . . . . . . . . . . . 9
3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
4. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Over the course of its almost two decades of existence, the HTTP
protocol has enabled the web to experience phenomenal growth and
change the world in more ways than its creators might have imagined.
HTTP's designers got many design principles right, including
simplicity and robustness. These charateristics allow billions of
devices to support and use HTTP in a multitude of communication
scenarios.
Improving HTTP starts with speed. Web sites have become complex. A
single site could comprise of hundreds of different elements (from
images to videos to ads to news feeds and so on) that need to get
retrieved by the client before the page can be fully displayed.
Users expect all of this to happen securely and instantly across all
their devices and applications. In many scenarios, HTTP fails to
meet these expectations. Speed improvements need to apply not only
for browsers but also for apps. More and more, apps are how people
access web services, in addition to their browser.
The core of the speed problem is that HTTP only allows for a
unidirectional request / response model, and it relies on multiple
TCP connections for concurrency (pipelining is formally supported by
the protocol but is seldom implemented in practice). This leads to a
variety of issues, such as additional round trips for connection
setup, slow-start delays, and potentially connection rationing: the
client may not be able to dedicate too many connections to any single
server, and the server needs to protect itself from denial-of-service
attacks. As a result, users are often disappointed in the perceived
performance of websites.
Improving HTTP should also make mobile better. For example, people
want their mobile devices to have better battery life. HTTP 2.0 can
help decrease the power consumption of network access. Mobile
devices also give people a choice of networks with different costs
and bandwidth limits. Embedded sensors and clients face similar
issues. Mobile considerations require that HTTP be network efficient
while simultaneously being sensitive to the limited power,
computation, and connectivity capabilities of the client device.
1.1. Overview
This proposal describes a multiplexing solution to enable efficient
delivery of content across a broad variety of scenarios, including
mobile apps and devices. It is intended to serve as a baseline for
discussion within the HTTPbis working group.
This HTTP proposal adheres to the following principles:
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Maintain the existing HTTP semantics. In particular, the meaning
of messages traversing a hybrid (1.1/2.0) request chain must be
preserved. Any deviation from this principle would represent an
extension to HTTP and should be treated as such.
Be as broadly applicable and flexible as the current protocol. As
part of that, it must enable servers and clients to select
security and compression depending on their own communication
needs.
Work with the current Web infrastructure including switches,
routers, proxies, load balancers, security systems, DNS servers
and NATs.
Account for the needs of modern mobile clients, including power
efficiency and connectivity through costed networks.
The proposal's intended outcome is a protocol that can be quickly and
widely adopted in the industry, and start delivering real value to
end users without imposing undue burden on hardware and software
vendors, as well as administrators of legacy equipment. Implementors
should also find it easy to understand due to the familiarity of some
of its key concepts, which are aligned with innovations that were
adopted in recent HTML5 specifications like WebSockets.
To achieve these goals, this proposal recommends to optimize HTTP
without changing its semantics by implementing a session layer
between TCP and HTTP that will support multiplexing of multiple HTTP
requests/responses. The session layer would have the following
properties:
It would maintain the integrity of the layered architecture.
It would use an upgrade mechanism similar to that of WebSockets.
This would enable compatibility with existing proxies and
connection models, without creating a mandatory dependency on TLS.
[Same as SPDY] The protocol would define two types of frames: data
and control.
[Same as SPDY] The session layer would enable negotiation of
multiple simultaneous streams for HTTP requests with minimal
overhead.
[Same as SPDY] The session layer would allow for prioritizing
delivery of content to ensure highest value traffic is delivered
first.
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The session layer would enable future extensions to HTTP 2.0 for
new scenarios like server push (those extensions would be
documented separately).
These properties are described in more detail below.
1.1.1. Layered Architecture
HTTP relies on an in-order, reliable transport to ensure delivery of
application data. TCP has almost exclusively provided the reliable,
ordered delivery of HTTP messages from one computer to another since
its inception. TCP accounts for adverse network conditions such as
congestion, or other unpredictable network behavior. Any HTTP 2.0
proposal should leverage the reliable transport and not attempt to
replicate functions generally accepted as addressed by other layers.
Conversely, any proposals for enhancing functionality typically
provided by other layers of the networking stack (e.g. congestion
control provided by the transport layer) should be brought to the
attention of, and discussed in, proper IETF forums (e.g. TCPM WG).
During the charter proposal discussion, the security and applications
area directors suggested an additional paragraph on security work and
authentication. If new work is undertaken in this regard, it should
be done by existing IETF security groups in this area.
1.1.2. Existing standards
HTTP at its core is a simple request-response protocol. The working
group has clearly stated that it is a goal to preserve the semantics
of HTTP. Thus, we believe that the request-response nature of the
HTTP protocol must be preserved. The core HTTP 2.0 protocol should
focus on optimizing these HTTP semantics, while improving the
transport via a new session layer. Additional capabilities that
introduce new communication models like unrequested responses must be
treated as an extension to the core protocol, and explored separately
from the core protocol.
Additionally, HTTP 2.0 should prefer models that are compatible with
the existing Internet and, where possible, reuse existing protocol
mechanisms. One primary example is in protocol negotiation where the
WG should avoid a proliferation of methods, and instead consider
using the HTTP 1.1 Upgrade header as it is used in the WebSocket
protocol. This will help HTTP 2.0 to be readily deployed on the
existing internet, and maintain compatibility with existing web sites
and client environments (such as some educational networks).
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1.1.3. Network Cost and Power
Any new protocol for transporting HTTP data on the Internet must also
take into account the types of systems and devices that use HTTP and
how they are connected to the Internet. The growth of the Internet
of the next decade (and longer) will be fueled by mobile apps and
mobile devices, as well as by the cheap, limited-capability devices
envisioned by the "Internet of Things." For all these devices, speed
is only one design tenet: considerations about battery life,
bandwidth limitations, processor and memory constraints, and various
policy mandates will also challenge designers and users. For
instance, the user of a device connected over mobile broadband may
need to minimize the amount of data sent in order to conserve
bandwidth, minimize power usage and monetary cost of communication.
Furthermore, transmitting the same amount of data may have radically
different power implications depending on how the transfer is
structured: for example, when operating over a mobile broadband
interface it is more efficient to use a single larger transfer than
to space out the transmission in multiple smaller transfers.
Multiple transfers may cause multiple radio transitions between low
and high powered states, causing additional battery drain.
In short, the choice among speed, cost, and power is not a simple
one. At times, speed may be the most important consideration. Other
times, bandwidth cost or battery life may be the deciding factor.
HTTP 2.0 must allow developers to optimize for the specific
constraints of their problem space (which might change over time)
rather than imposing a "one size fits all" solution to a generic
problem. For example, a server push extension could be a good
optimization for many scenarios where content updates to web pages
revisited over time are infrequent, and where the client has plenty
of bandwidth as well as the needed processing power to either handle
the updates instantly, or cache them for later processing. On the
other hand, it is not likely to be appropriate in situations where
content is being transmitted over a costed link. Neither it will be
when the client is running several applications that use network
bandwidth concurrently, and bursty, server-initiated content
transmissions would interfere with their smooth operation. Rather
than forcing developers to choose between using all the features of
HTTP 2.0 or sticking with HTTP 1.1, it would be better to provide
mechanisms for developers to fine tune the capabilities of HTTP 2.0
to a specific set of requirements.
In summary, the goals of higher speed, lower cost, lower power may
often be aligned. For instance, having less data sent on the wire
will allow pages to load faster, allow the radio to power down sooner
and consume less bandwidth. But given the variety of the scenarios
where HTTP 2.0 will be used, this will not always be the case. For
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example, a device whose battery is about to run out, or whose cache
is near capacity can provide a better user experience by disabling
all (or most) server push updates while retaining the other
optimizations available in HTTP 2.0. Accordingly, the working group
should consider power and cost as well as speed in designing
extensions to HTTP 2.0.
1.1.4. Flexibility in deployment
HTTP is used in a vast array of scenarios and a variety of network
architectures. There is no "one size fits all" deployment of HTTP.
For example, at times it may not be optimal to use compression in
certain environments. For constrained sensors from the "Internet of
things" scenario, CPU resources may be at a premium. Having a high
performance but flexible HTTP 2.0 solution will enable
interoperability for a wider variety of scenarios. There also may be
aspects of security that are not appropriate for all implementations.
Encryption must be optional to allow HTTP 2.0 to meet certain
scenarios and regulations. HTTP 2.0 is a universal replacement for
HTTP 1.X, and there are some instances in which imposing TLS is not
required (or allowed). For example, a "random thought of the day"
web service has very little need for it, nor does a sensor spewing
out a temperature reading every few seconds.
1.1.5. Client is in control of content
Because of the variety of clients on the Internet and the number of
connection scenarios, clients must be able to define what content is
downloaded. The app or browser is in the best position to assess
what the user is currently doing and what data is already locally
available. For example, most of the browsers in use today have
powerful caches that should be leveraged to store web elements that
change infrequently. Clients need the ability to inform the server
about cached elements that do not need to be downloaded. In
addition, a particular client may have security and compatibility
needs with regard to the data being sent. HTTP 2.0 proposals should
not force the client to download content that has not been requested
and may already be cached. Furthermore, the client must have the
option to decline unwanted or uneeded content. Ideally this feedback
from the client to the server would allow for incremental approval of
content to enable an efficient "push" extension to deliver the right
content.
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2. Technical Details
To be added within the next few days in version 01.
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3. Acknowledgements
Thanks to the following individuals who have also contributed with
discussions and text: Brian Raymor, Ravi Rao, Dave Thaler, Ivan
Pashov, Jitu Padhye, Jean Paoli, Michael Champion, NK Srinivas,
Sharad Agarwal and Rob Mauceri.
This document incorporates materials from
http://tools.ietf.org/html/draft-mbelshe-httpbis-spdy-00.
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4. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
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Authors' Addresses
Rob Trace
Microsoft
Email: Rob.Trace@microsoft.com
Adalberto Foresti
Microsoft
Email: aforesti@microsoft.com
Sandeep Singhal
Microsoft
Email: Sandeep.Singhal@microsoft.com
Osama Mazahir
Microsoft
Email: OsamaM@microsoft.com
Henrik Frystyk Nielsen
Microsoft
Email: HenrikN@microsoft.com
Gabriel Montenegro
Microsoft
Email: Gabriel.Montenegro@microsoft.com
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