Transcript PowerPoint format

The Bandwidth
Management Advisory
Service - BMAS
http://www.bmas.ja.net
Ingrid Evans & George Neisser
Manchester Computing
University of Manchester
[email protected]
[email protected]
Background to BMAS
Recent years have witnessed growth in:
Dynamic Web content.
Multimedia and real-time applications.
Expansion of JANET user base to include FE
colleges.
Advisory Requirement
Identified
In recognition of the changing types of web
traffic, UKERNA carried out a survey in 2002
amongst academic institutions.
The following conclusions were drawn:
There is a general need for web caching.
There is a need for generic advice.
An Invitation to tender was issued Summer
2002.
Manchester & Loughborough awarded contract.
BMAS
BMAS Remit: to deliver leading-edge
state-of-the-art advice to UK academic
institutions on how to maximise the efficiency
of their bandwidth resource utilisation
Staffed by the former JWCS team.
Plenty of experience.
Will expand to include new and on coming
bandwidth management techniques and
technologies.
What is Bandwidth
Management?
In general terms, Bandwidth Management is the
control and monitoring of your network
bandwidth allocation to get best use out of said
link.
Bandwidth Management can encompass
various techniques and policies
Your requirements will depend on numbers of
users, work profiles, teaching and research
programmes, connection capacity etc, etc.
How does bandwidth
management affect me?
As a Web Manager you may want wonder how
bandwidth management affects you.
Consider the following :
“Dear Web manager, we would like streaming
media incorporated onto our web pages……”
How else does bandwidth
management affect me?
Did you know that making your site cacheable
will make it load more quickly for your visitors
and reduce load on your server?
If a site loads quickly people will revisit.
Any other points about
bandwidth management?
What about data compression? Compression
techniques could also help to enhance your site
visitors experience by making your site load
quickly.
Time to sit and think a
while…..
 We’d now like you to divide into groups and spend about
5 -10 minutes discussing how you have implemented
bandwidth management techniques on your website.
 If you do not think think that you have implemented any
techniques, then consider how bandwidth management
might affect your website.
Think about :
Streaming media, and it’s implications for your site.
Also, discuss the known advantages of caching.
Consider image file formats too and how they might
impact on bandwidth.
Ways to enhance your website using
bandwidth management techniques
Why, and how to, make your site cacheable.
Bandwidth isn’t a problem on campus.
Maybe, but what about external visitors and
distance learning etc? Most people at home
still use dial-up.
A cached website will be returned to the user from a
much nearer location than the site of origin thus
making it load quicker.
How to make your site
cacheable
Add HTTP headers
HTTP headers give control over how browser
and proxy caches handle your web objects.
Not seen in HTML as they are sent by the
server before the HTML.
What do HTTP headers do?
Cache control headers can be quite
specific and control freshness, bypass of
the cache etc with the settings such as:
Max-age =(seconds)
Public
No-cache
Must-revalidate
What else can you do to make
your site cacheable?
 Refer to objects consistently using the same URL
Use a common library of images
Make caches store images and pages that don’t change
often by specifying a far off Expires header
If a resource changes (in particular a downloadable file),
change it’s name
Don’t change files unnecessarily to avoid falsely young
‘Last modified” dates. Only copy files to the server which
have actually changed as opposed to copying the entire site.
Use cookies only where necessary as they are difficult to
cache.
Minimise use of SSL
Writing cache-aware scripts hints and tips.
 When using scripting, don’t POST if possible. POST
method is almost impossible to cache. GET is preferred
Don’t embed user specific information in the URL
Don’t assume that all requests from a user are from
the same host as caches can work together in a variety
of infrastructure
Generate Content-Length response headers. This
allows for the response of the script to be used in a
persistent connection and allows the client to request
multiple objects on one TCP/IP connection thus making
the site seem much faster.
Keeping your visitors happy!
How about reverse caching?
Reverse caching and http-acceleration can
directly benefit web managers
Reverse caches can offload the delivery of
static content from your web server.
Requests to web sites are intercepted by reverseproxy caches with held objects being returned to the
requestor as if from the original web site.
Using http-acceleration can make a proxy server
act as an output buffer for dynamic web content.
Reverse proxy caching
advantages
Simpler and faster than web servers
Can be preloaded with content
Can be set to automatically retrieve updated
content.
Possible to have multiple reverse proxies as they
can communicate via ICP (Internet cache protocol)
Can act as defence against hackers as they are
another ‘layer' between the outside world and your
data.
Reverse proxy caching
advantages
Can improve server performance whilst adding
web site traffic surge protection.
Some high-end reverse proxy cache devices
have features which can distribute, as opposed to
store, multimedia formats such as Apple
QuickTime, Windows Media or Real Network's G2
format.
This distribution of multimedia from the network
edge as opposed to the web server, can drastically
reduce server and network bandwidth load
Reverse proxy caching - not
to be confused with……
Prefetching or web acceleration
There is some debate as to whether the practice
of prefetching or web acceleration actually ends
up generating more web traffic in the end!
More details about reverse
proxy and http-acceleration
See :
http://www.nwfusion.com/reviews/2000/0410revtrend.html
For more details about implementing caches and
advanced cache features re multimedia.
Brian Davidson's excellent caching site at
http://www.web-caching.com/mnot_tutorial/how.html
Also : Chapter 13 of ‘Strategies for Web Hosting
and Managed Services” by Doug Kaye - Wiley
Computer Publishing 2002
What about dynamic content
such as streaming media?
Streaming media is becoming much more
widely used as a teaching aide and for distance
learning.
Why should that affect you?
What about dynamic content
such as streaming media?
You may have been asked to incorporate
streaming media into your website.
New advancements in HTML-like languages
mean that complex integrated media can be
generated. Video can be used in conjunction with
text and Powerpoint to provide interactive media
using
the
SMIL
language
(Synchronised
Multimedia Integration Language)
What about bandwidth and
streaming media?
Being aware of some of the issues with these
components means that you should be able to
maintain a fast, efficient website, even if you are
using dynamic media.
Streaming media points for
consideration
There are various software solutions available
which will generate streaming content. The big 3
are:
Real Networks Server
Apple QuickTime
Windows Media Server
Each software package has it’s advantages and
disadvantages.
Remember from the outset to consider the
number of users who will be viewing your media,
and at what bit rate
The importance of bit rate
When encoding media files, they should be
optimised for the speed of the recipients
connection .
This is especially important if you think that a lot
of your content will be viewed out of campus
(i.e. via dial up). Files which are not optimised in
this way may result in poor quality for your
visitors and more load on your webserver
generated by visitors trying to view the files on
your server.
The importance of bit rate
Another consideration with bit rate is the fact
that some file formats, such as Apple’s
QuickTime, work better with a higher bit rate of
1000Kbps.
Web server v streaming server
If you only have a few streaming media files, then
loading streaming server software onto your
website should suffice.
If however, you wish to include:
A lot of streaming content
Files which stream at different speeds (for
visitors in different locations)
Complex integrated media
You should possibly consider a dedicated
streaming server. This will also relieve load from
your web server .
A word about complex
integrated media….
Files generated in this way such as those
created using the SMIL language, have their
media divided into components which are then
streamed separately, but viewed as one file by
the visitor.
This process obviously has bandwidth
implications
Streaming media
recommendations
Consider your audience from the outset and what
THEIR bit rate will be
Choose appropriate streaming software taking into
consideration performance over various bit rates
Think about how much streaming media will be
included on your website. If there is a lot, you may be
better off with a dedicated streaming server
Will integrated media be used? If so, think about
bandwidth usage for these types of files
If you run streaming media from your web server,
perhaps you should consider a “viewing policy”
limited by user groups, location or time
Bandwidth Management
techniques - data compression
As a web master you will probably be
responsible for developing a web policy and
overseeing the upload of pages from many
different sources.
Bandwidth Management
techniques - data compression
Encouraging your contributors to be aware of
data compression can reduce bandwidth
consumption and make your WebPages load
more quickly.
Bandwidth Management
techniques - data compression
It’s a simple solution but when used on a large
site, data compression can prevent slow
downloads and thus reduce visitors waiting time.
What do we mean by data
compression?
In a web management context we’re primarily
referring to image compression using a variety
of formats such as JPEG, GIF, PNG etc.
File format features:
JPEG - A lossy compressor which produces
very small file sizes
GIF - A lossless compressor. Can incorporate
transparency into an image.
PNG - Lossless compressor can be used as
patent free replacement for GIF. Can also
incorporate transparency
So where do I come in?
Encourage your contributors to use one of the
aforementioned image file formats
Persuade them not to use large file formats such
as Bitmap (.bmp)
Images should not be anymore than a couple of
centimetres squared in size. If larger, or more
detailed images are required or where there are a
few images, encourage the use of thumbnails. The
Tucows site at http://tucows.mirror.ac.uk/index.html
has a lot of thumbnail software listed.
So where do I come in?
Resolution is an important factor. Do not use
images for the web that have been specifically
created for print. Such images will have an
unnecessarily high resolution which will increase
file size dramatically whilst monitors only have a
resolution of 72 ppi.
A lot to take in!
If you take some bandwidth management
techniques into consideration, your website will
load quickly, and your visitors will see a high
quality website
A lot to take in!
Remember the following points:
Make your website cacheable by:
Use of HTTP headers
Reverse caching
http-acceleration
Don’t forget
Think about the implications of using streaming
media:
Consider which streaming server software is best
for you
Decide how much streaming media will be used
now and in the near future
Assess what your streaming media users’ bit rate
will be.
And another thing!
There’s also data compression
Use compressed image file formats
such as JPEG, GIF and PNG
Encourage
appropriate.
use
of
thumbnails
where
Encourage use of smaller, more widely
spaced images.
You don’t get away that easily..
We’d like you to search on the web and see
what you can find on the subject of “Bandwidth
Management” that is applicable to you.
Try http://www.zdnet.com
http://www.bravenet.com
http://www.w3c.org - info re image compression
http://www.web-caching.com/ - info re reverse
caching etc
Finally….
Do visit our website at: http://www.bmas.ja.net
Or email us at: [email protected]
You can call us on (0161) 2756008
Keep revisiting our website as our content will
continue to increase.
It’s good bye from me…
And it’s goodbye from him…