IWMW 2003: C7 Bandwidth Management Techniques: Technical And Policy Issues
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The Bandwidth Management Advisory Service (BMAS) aims to provide UK academic institutions with advanced advice on optimizing bandwidth resource utilization in response to increased dynamic web content and multimedia applications. It emphasizes techniques like caching, data compression, and reverse proxy caching to improve website performance and manage bandwidth for both on-campus and external users. The document highlights methods for making websites cacheable and offers thoughtful considerations for incorporating streaming media effectively.
IWMW 2003: C7 Bandwidth Management Techniques: Technical And Policy Issues
- 1. http://www.bmas.ja.net Ingrid Evans & George Neisser Manchester Computing University of Manchester ingrid.evans@man.ac.uk George.Neisser@mcc.ac.uk The Bandwidth Management Advisory Service - BMAS
- 2. 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.
- 3. 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.
- 4. 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.
- 5. 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.
- 6. 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……”
- 7. 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.
- 8. 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.
- 9. 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.
- 10. 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.
- 11. 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.
- 12. 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
- 13. 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
- 14. 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.
- 15. 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 reverse- proxy 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.
- 16. 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.
- 17. 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
- 18. 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!
- 19. 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
- 20. 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?
- 21. 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)
- 22. 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.
- 23. 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
- 24. 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.
- 25. 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.
- 26. 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 .
- 27. 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
- 28. 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
- 29. 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.
- 30. 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.
- 31. 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.
- 32. 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
- 33. 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.
- 34. 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.
- 35. 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
- 36. A lot to take in! Remember the following points: Make your website cacheable by: Use of HTTP headers Reverse caching http-acceleration
- 37. 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.
- 38. And another thing! There’s also data compression Use compressed image file formats such as JPEG, GIF and PNG Encourage use of thumbnails where appropriate. Encourage use of smaller, more widely spaced images.
- 39. 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
- 40. Finally…. Do visit our website at: http://www.bmas.ja.net Or email us at: support@bmas.ja.net 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…
Editor's Notes
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- #4: <number> The UK HE and FE community were asked if they thought there was a need for the centralised JANET Web Cache Service to continue and the overall conclusion was whilst there was no need for the centralised cache structure, an advisory service who could offer information about caching and generic advice, would be useful.
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