2. Problems with HTTP 1.0 in Wireless Environment Bandwidth and Delay Caching POSTing
3. Bandwidth & Delay HTTP not designed with following in mind: Low-bandwidth & High delay connections HTTP header: Quite large Redundant fields Readable for humans & Transferred in plain ASCII HTTP is stateless: Repeated transfer of information fields with each request.
4. Bandwidth & Delay Server transfers uncompressed contents. A TCP connection is used for each item on a web page. Hence the overhead includes exchange of 7 PDUs for: Three-way Handshake, Data Transmission & Reliable disconnection. TCP slow-start: This mechanism is built-into TCP, causes additional problem. Causes unnecessary high delays.
5. Bandwidth & Delay DNS Lookup: Necessary for many items on the web page Reduces bandwidth and increases delay even further. DNS Server: Each time browser reads a hyperlink reference to a new server, it has to: Resolve the logical name into an IP Address This has to be done before fetching the item from the server Requires additional request to DNS server over the wireless link This adds round-trip time to the delay.
6. Caching Present-day pages contain Dynamic Objects, cannot be cached: Access Counter, Time, Date or Other customized items: Customized pages are created on-demand (CGI, Servlets, ASP) Names of the links are generated dynamically Caching algorithms cannot detect access to the same content if link differs Home page of some sites are created dynamically, depending on: Type of browser, Client hardware, Client location, etc… Hence, even if cache could store some static content, its often impossible to merge with dynamic remainder of the page.
7. Caching Mobility quite often inhibits caching: Way of accessing the web server changes over time due to change in access point. 3. Many security mechanisms inhibit caching, authentication is often needed.
8. POSTing Sending content from client to server has additional problems if: Client gets disconnected. POST request cannot be fulfilled in disconnected state. Server could be simulated by accepting the posting via, additional process. This causes additional problems Eg: If real server does not accept posting or if server cannot accept deferred posting
9. Approaches for HTTP & HTML to adapt to Wireless Environment Image scaling True color, higher resolution scaled to few colors, lower resolution Content transformation Eg: Converting PDF to Text Content extraction & Semantic compression Abstract generation Extracted from the document (or) Use HTML headlines Special language & protocols Replace HTML & HTTP with HDML & HDTP Push Technology
10. Improvements in HTTP 1.1 Connection Reuse: Persistent connection Caching Enhancement Bandwidth Optimization Supports: Compression Negotiation of compression parameters & Different compression styles: Hop-by-hop End-to-end Security
11. Caching Enhancements Stores cacheable response; reducing response time and saving bandwidth. Caching tries to achieve Semantic Transparency: Cache should not affect client or server besides increasing the performance. Correctness of cache entries needs to enhanced: To fetch the most up-to-date copy of an item: Revalidate item with the original server Provide warnings if the freshness has been violated. Web pages contain information about cacheability & semantic transparency: A special tag allows for identification of the content and helps to determine if two different URIs map to same content. More tags can indicate if content is cacheable, cacheable in private caches only, etc… HTTP 1.1 defines a large set of cache control directives.
