Overview on Web Caching

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Overview on Web Caching

• COSC 513 Class Presentation
• Instructor Prof. M. Anvari
• Student name Wei Wei
• ID 103765

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Web Caching A Key Technique for Internet

• 1.What is Web Cache and what is Web Caching?
• Web Cache sits between server(s) and
  client(s)
• Web Caching technique to use cache concept on
  the web.
• 2.Why use Web Cache?
• Reduce latency
• Reduce traffic.

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• 3.Kinds of Web Caches
• Browser Caches
• 1) use disk and memory (size 550MB)
• 2) local to machine private cache.
• Proxy Cache
• 1) an application-layer network service
• 2) operated on dedicated hardware (550 GB hard
  disk, 64512MB RAM)
• 3) shared by many users.

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• 4.Any difference between proxy and cache?
• Proxy refers to an important aspect of design
• Strictly speaking, proxy does not always cache
  the replies pass through it
• Use term proxy cache to mean Web Cache which is
  implemented as a HTTP proxy.
• 5.Advantages of Web Caching
• objects delivered to clients with higher
  throughput and lower latency
• cache hits reduce WAN traffic

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• load on original servers reduced
• isolate end-users from network failure.
• 6.Disadvantages of Web Caching
• lose precious access counts when cache hits are
  served
• manual configuration often required
• cannot be implemented totally transparently
• received stale information
• require additional resources
• single point of failure.

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• 7.Other features of caching
• Depending on specific perspective ,the following
  features might be considered either good or bad
• servers cannot see client IP
• log file data can be used in different way
• related to above issues, cache can be used to
  block certain requests.
• 8.Web Caching effectiveness measures
• hit ratio (how about 304 Not Modified)
• byte hit ratio (reply but not request)

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• service time (underestimate at least 2 network
  RTTs).
• 9.How Web Cache work?
• Have to determine when to serve an object from
  the cache, if its available
• rules are set in protocols (HTTP 1.0 1.1)
• rules set by administrators of cache (either
  browser user or proxy administrator).
• Common rule
• 1) If objects headers tell cache not to keep the
  object, it wont. Also , if no validator is

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• present, most cache will mark the object
  uncacheable.
• 2) If the object is authenticated or secure, it
  wont be cached.
• 3) A cached object is considered fresh (that is,
  able to be sent to a client without checking with
  the origin server) If
• it has an expire time or other age-controlling
  set, and is still within the fresh period.
• If a browser cache has already seen the object ,
  and has been set to check once a session.

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• If a proxy cache has seen the object recently,
  and it was modified relatively long ago.
• Fresh documents are served from cache directly
  without checking with origin servers.
• 4) If an object is stale, the origin server will
  be asked to validate the object , or tell the
  cache whether the copy that it has is still good.

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• Together, freshness and validation are the most
  important ways that caches work with content.
• Fresh object available instantly from cache
• Validated object will avoid resending if not
  changed.

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Conclusion
As Web service becomes more popular, users are
suffering network congestion and server
overloading. Web caching is viewed to be one of
the efficient techniques to alleviate server
bottleneck and network traffic, thereby minimize
the user access latency. Note This presentation
only covers a small part of the final report.