Network Working Group
INTERNET-DRAFT Mick O'Doherty
draft-odoherty-http-display-and-connect-info-00.txt Nortel Networks
Oct 2000
HTTP Display and network connection characteristics
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026 [1].
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1. Abstract
This document defines an extension to the HTTP [2] protocol to allow a
client/user agent describe its display and network connection
characteristics to a server when making a request. As HTTP may be used by a
client/user agent which does not have a display or does not want to make
this information available, providing this information is optional.
2. Introduction
2.1 Overview
This document defines an extension to the HTTP [2] protocol to allow a
client/user agent describe its display and network connection
characteristics to a server when making a request. As HTTP may be used by a
client/user agent that does not have a display or does not want to make this
information available, providing this information is optional.
More and more devices are being developed to support WWW browser
functionality, and many of these devices have display's which are smaller
(typically) or larger than the usual computer monitor size and which may
have different resolution, color etc characteristics.
In parallel there are more and more ways to connect to the Internet and the
bit rates of the various connection types vary greatly.
Internet Draft HTTP Display and Connection Characteristics
A content provider may want to tailor their content for particular display
types and for connections with particular connection rates.
A HTTP request can indicate the exact device that sent the request (see [2]
section 14.43), but this is probably too much information for most content
providers and would mean updating the server every time a new device was
added.
In addition the content provider may use Java script to query the screen
size and resolution information from the browser and to estimate the
connection rate. This is a viable alternative to what is being suggested
here - the advantage providing this info in the HTTP request has is that the
information is available as soon as the request is received, and, also, some
browsers may not support Java script.
This extension allows a device to indicate its exact display and network
connection characteristics and the server then to decide whether they fit
into a particular grouping for the content it provides - for instance it may
have one set of content for displays which are around mobile phone screen
size, another for screens around palmtop computing device size (or perhaps
two formats here to allow for the 'portrait' or 'landscape' format of
devices typically available) and another for PC monitor size screens.
Similarly, a content provider may wish to have content targeted specially
for large display sizes.
Looking at the connection, the content provider may want to avoid graphics
and formats that are heavy users of bandwidth for user agents connected via
low bandwidth connections. For instance it might have one display format for
Palm top users connected via low speed 2G wireless links connection and
another for those connected via higher speed 3G wireless or connected via a
LAN.
It is assumed that the reader is familiar with the HTTP protocol [2],
although the intent of the document should be clear with just an outline
understanding of the protocol.
3. Encoding the display information
Looking at [2] we can see that the format of a HTTP response is defined by
the following (extracted directly from the RFC [2] and all section numbers
refer to [2]):
HTTP-message = Request | Response ; HTTP/1.1 messages
Request = Request-Line ; Section 5.1
*(( general-header ; Section 4.5
| request-header ; Section 5.3
| entity-header ) CRLF) ; Section 7.1
CRLF
Internet Draft HTTP Display and Connection Characteristics
[ message-body ] ; Section 4.3
and that a request header in turn is defined by:
request-header = Accept ; Section 14.1
| Accept-Charset ; Section 14.2
| Accept-Encoding ; Section 14.3
| Accept-Language ; Section 14.4
| Authorization ; Section 14.8
| Expect ; Section 14.20
| From ; Section 14.22
| Host ; Section 14.23
| If-Match ; Section 14.24
| If-Modified-Since ; Section 14.25
| If-None-Match ; Section 14.26
| If-Range ; Section 14.27
| If-Unmodified-Since ; Section 14.28
| Max-Forwards ; Section 14.31
| Proxy-Authorization ; Section 14.34
| Range ; Section 14.35
| Referer ; Section 14.36
| TE ; Section 14.39
| User-Agent ; Section 14.43
To add the display and network connection characteristics information
proposed here to this definition the following new request headers are
added:
Display-Characteristics : *NEW
Network-Connection ; *NEW
These are then defined as:
Display-Characteristics = 1*( Display-Characteristic-Field)
Display-Characteristic-Field = Display-Type
| Display-Diagonal-Size
| Display-Height
| Display-Width
| Display_colors
| Display-Resolution
Display-type = "TEXT-ONLY" | "LINE PRINTER" | "BRAIL" | "VDU" | 1*ALPHA
Display-diagonal-size = "Display-Diagonal-Size" ":" 1*DIGIT
Display-height = "Display-Height" ":" 1*DIGIT
Display-width = "Display-Width" ":" 1*DIGIT
Internet Draft HTTP Display and Connection Characteristics
Display-Colours = "Display-Colours" ":" 1*DIGIT
Display-resolution = "Display-Resolution" ":" 1*DIGIT
Network-Connection = "Network-Connection" ":" 1*DIGIT
The value Display-Diagonal-size will be the diagonal measurement of the
display in millimetres. Display-Height and Display-Width will be the number
of pixels high and wide that the display is. Display resolution will be the
number of pixels per inch and Display-Colours will be the number of Colours
in the Colour Pallet.
The value for network connection will be the bandwidth of the connection to
the network in kilo bits per second (k bps). Sometimes the bottleneck in a
system may not be in the direct connection but in some other point of the
network (for instance a PC may be connected directly to a Gigabit LAN but
it's external connection to the Internet may be via a 28k bps link) so the
user agent may choose to give the figure for the bottleneck as this is the
more useful information.
An example of how this might be used is:
Display-Type : VDU
Display-Diagonal-Size : 320
Display-Height : 768
Display-Width : 1024
Display-Colours : 256
Display-Resolution : 96
Network-Connection : 58
4 Defaults
No default values will be specified - a server/content provider can decide
for themselves what to imply by the lack of one or more of the fields (or a
lack of all the fields). For instance one fairly logical assumption, for the
time being at least, would be to assume a PC type display as the default for
the display information.
5. Security
As with other similar optional information presented by a user agent/client
to a server using HTTP, the client can choose not to make this information
available if they do not wish to divulge these details.
6. Examples
Sports Information web site
---------------------------
As an example lets imagine a Sports Information website, www.Z2ZSports.com.
Internet Draft HTTP Display and Connection Characteristics
They would like users to simply have to type in their URL on their browsers
no matter what device they are using and for their content to be optimised
for the users display.
This means that a user accessing it from an internet enabled mobile phone
with the typical small screens available today, will probably get just text
and very simply text like graphics.
A user accessing from a Palm type computing platform will get something that
looks much more like a Mini web site, with the layout optimised for that
screen size and shape.
And users using a browser on a PC will get the usual PC Browser web display,
which may also be the default if no information is supplied in the HTTP
request.
In addition they may have a service to sports bars that have very large
displays and they may want to offer a specialised format for these customers
that takes advantage of the big screen and the different audience type.
News Service web site
--------------------
Another example might be a News service, say www.z2zNews.com. This might
provide simple text based news to users who have a low bandwidth connection
(regardless of screen size) and graphics and video and sound clips to users
who have a higher bandwidth connection.
7. Acknowledgements
The author would like to thank all the people in Nortel Networks who
provided input and feedback.
8. References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC
2026, October 1996.
2 R. Fielding, et al., "RFC 2616 Hypertext Transfer Protocol -- HTTP/1.1"
Author's Address
Mick O'Doherty
Nortel Networks
Concorde Road
Maidenhead
Berkshire
SL6 4AG
England
mdoherty@nortelnetworks.com
Internet Draft HTTP Display and Connection Characteristics