Web Proxy Caching

1. Web Proxy Caching By Miquel Company

2. Contents • Basics of Proxy Caching • Cache Consistency • Proxy Cache Cooperation. • Benefits of using Proxies. • Dangers of using Proxies. • Commercialized sofware. T110.456 Next Generation Cellular Networks

3. Basics of Web Proxy Caching. • Definition: A Web cache sits between one or more Web servers (also known as origin servers) and a client or many clients, and watches requests come by, saving copies of the responses for itself. Then, if there is another request for the same URL, it can use the response that it has, instead of asking the origin server for it again. T110.456 Next Generation Cellular Networks

4. Basics of Web Proxy Caching. • Why use them? • To reduce latency: Because the request is satisfied from the client instead of the origin server, it takes less time for the client to get the object. • To reduce traffic: Because each object is only gotten once from the server, it reduces the amount of bandwith used by a client. T110.456 Next Generation Cellular Networks

5. Basics of Web Proxy Caching. • How does it work: • Without Proxy: T110.456 Next Generation Cellular Networks

6. Basics of Web Proxy Caching. • How it works? T110.456 Next Generation Cellular Networks

7. Basics of Web Proxy Caching. • How it works?: • When a client asks for an object, the proxy server looks for the object in the cache. If it is inside the cache we’ve got a Hit. And then de proxy returns the cached object to the client. • If the object is in the cache but it is not valid, the proxy server asks for the object to the origin server, and checks if the cached object is the same on the origin server. If it is the proxy sends the object to the client. If it is not, the proxy downloads the object from the server. • If the object asked by the client is not cached then we’ve got a Miss, and the proxy cache has to look for it on the outside internet. T110.456 Next Generation Cellular Networks

8. Cache Consistency • What is consistency?: If the original object changes after the cache had save a copy then the copies immediately become out of date.The consistency tries to have all the stored copies up to date. T110.456 Next Generation Cellular Networks

9. Cache Consistency • Inconsistence problems: • Waste of HDD space: It’s better to use the HDD space for Up-date copies than to Out-dated copies. • Out-dated objects: The client gets wrong information and may get angry. • Waste of trafic: If we don´t keep the copies the proxy has to look for them everytime the client demands it. • Having an Inconsistent cache is useless. T110.456 Next Generation Cellular Networks

10. Cache consistency • Different ways of having a consistent cache: (soft consistency) • Checking the staleness of an object at regular time intervals. • Defining document’s TTL: The TTL depends on the time the object changes. • More changing objects => More the cache refreshes the object. • Less changing objects => The cache refreshes the object less times. T110.456 Next Generation Cellular Networks

11. Cache Consistency • Different ways of having a consistent cache: (hard consistency). • The proxy checks the staleness of the object each time the object is requested. • It doesn´t save to much bandwith. • All the objects requested in hard consistency are ,for sure, up-to-dated objects. T110.456 Next Generation Cellular Networks

12. Proxy Cache Cooperation • Several servers can form a server hierarchy: • Parent servers: They’re on top of the hierarchy, they receive petitions of local servers (children). And if they don’t have the requested object ask their parents, or to the original server. • Siblings: If the original cache don’t have a copy of the requested object it sends a request to their siblings (brothers) and if they don’t have the requested object then the proxy ask to his parents. T110.456 Next Generation Cellular Networks

13. Proxy cache cooperation T110.456 Next Generation Cellular Networks

14. Proxy cache cooperation • Problems: • Cache hierarchies can yield successive reductions in network traffic, but there is a cost in replication of disk storage. When a request is passwd up a branch the returning response is likely to be saved by each cache it passes though. • Worst latency: You have to check in several servers if they have the object saved. Less time than looking for the original object. T110.456 Next Generation Cellular Networks

15. Benefits of using Proxies: • Reduces traffic bandwith: More clients using the same bandwith, than without using proxy. • Reduces latency: The client gets the requested object sooner than going to look for it outside the LAN. • Improves network security: All the requests passes through the same point. T110.456 Next Generation Cellular Networks

16. Dangers of using proxies. • Ok, proxies save traffic bandwith, reduces latency, and increases Network security, but: • You can get out-to-date content • More difficult to code web-sites. More difficult to configure web-servers. • Lost of privacy for the client: You can keep a logfile in the proxy server telling which objects have you looked for. T110.456 Next Generation Cellular Networks

17. Actual Proxy Servers: • Squid: The most widely used. The better working and the free one.http://www.squid-cache.org/ • Microsoft ISA Server 2004 : Microsoft developed ISA to replace Microsoft proxy server. It’s fully functional with Active Directoryhttp://www.microsoft.com/isaserver/ • Apache: Apache web server has a module to do reverse caching (experimental).http://httpd.apache.org/docs-2.0/mod/mod_cache.html • Cisco Cache Engine: sits next to (mostly) Cisco routers and receives transparently redirected HTTP requests http://www.cisco.com/warp/public/cc/pd/cxsr/500/index.shtml • CERN/W3C HTTPd: It was the original proxy server.http://www.w3.org/hypertext/WWW/Daemon/Status.html T110.456 Next Generation Cellular Networks

18. Real Life Example: • Cesca: Supercomputing center of Catalonia. The have the parent proxy cache that gives support to all catalonian universities. • Cesca Proxy server is the parent server of several campus, like UPC’s Campus Nord, or UB’s Zona Universitaria. T110.456 Next Generation Cellular Networks

19. Real Life Example: T110.456 Next Generation Cellular Networks

20. Real Life Example: T110.456 Next Generation Cellular Networks

21. Real Life Example: T110.456 Next Generation Cellular Networks

22. Real Life Example: T110.456 Next Generation Cellular Networks