Which properties of HTTP waste bandwidth? What is the additional problem using HTTP/1.0 together with TCP? How does HTTP/1.1 improve the situation?

Authors Avatar

Assignment 2

  1. Which properties of HTTP waste bandwidth? What is the additional problem using HTTP/1.0 together with TCP? How does HTTP/1.1 improve the situation?

The Hypertext Transfer Protocol (HTTP) is a stateless application protocol. An HTTP transaction consists of an HTTP request issued by a client and an HTTP response from a server. Stateless means that all HTTP transactions are independent of each other. HTTP does not remember and transaction, request, or response.

HTTP causes many problems in wireless networks:

  • Bandwidth and delay: HTTP has not been designed with low bandwidth and high delay connections in mind. HTTP protocol headers are quite large and redundant. Many information fields are transferred repeatedly with each request because HTTP is stateless. Servers transfer content uncompressed. As TCP connections are typically used for each item on the web page, a huge overhead comes with each item in HTTP/1.0. Another problem is caused by the DNS look-up, necessary for many items on a web page, reducing bandwidth and increasing the delay even further.
  • Caching: Caching in quite often disabled by content providers. Many companies want to place advertisements on web pages and need feedback, e.g. through the number of clicks. Many present-day page contain dynamic objects that cannot be cached, e.g., access counters.
  • POSTing: Sending content form a client to a server can cause additional problems if the client is currently disconnected. The POST request cannot be fulfilled in a disconnected state.

HTTP/1.1 offers several improvements:

  • Connection re-use: Clients and servers can use the same TCP connection for several requests and responses. A client may send multiple requests at the beginning of a session, and the server can send all responses in the same order.
  • Caching enhancements: A cache may now also store cacheable responses. The correctness of cached entries has been enhanced. A special tag allows for the identification of content and helps to determine if two different URIs map to the same content. Several more tag determines if content is cacheable.
  • Bandwidth optimisation:  HTTP/1.1 supports not only compression, but also the negotiation of compression parameters and different compression styles. It allows for partial transmission of objects.
  • Security: HTTP/1.1 comprises further mechanisms to check message integrity and to authenticate clients, proxies, and servers.
  1. Why HTTP/HTML is not suitable for mobile applications and devices? Describe some approaches that might help wireless access and some system supports for mobile www.

HTML is broadly used to describe the content of web pages in the World Wide Web. HTML was designed for standard desktop computers with relatively high performance, a colour high-resolution display, mouse, sound system, and large hard disks. Web pages using the current HTML often ignore these differences in end-systems. Pages are designed primarily for a nice presentation of content, not for efficient transfer of this content. HTML itself offers almost no way of optimising pages for different clients or different transmission technologies. Web pages typically ignore the heterogeneity of end-systems altogether.

Some approaches that might help wireless access:

  • Image scaling: pictures can be scaled down to fewer colors, lower resolution or to just image title. The user can then decide to download the picture separately.
  • Content transformation: Because handled devices have limited browsers, special converters could translate the documents into plain text.
  • Content extraction/ semantic compression: Headlines or keywords could be extracted from a document and presented to a user. The user could then decide to download more information. An abstract from some given text could be automatically generated.
  • Special languages and protocols: Some approaches try to replace HTML and HTTP with other languages and protocols better adapted to a wireless environment, such as Handheld Device Transport Protocol (HDTP) and the Handheld Device Markup Language (HDML).
  • Push technologies: Instead of polling the content from a server, the server could alsoo push content to the client. This avoids the overhead of setting up new connection for each item (this is a limited function for content like news, road condition, etc.).
  • Application gateway: Used to provide www content to users with mobile phones, and comprise entities for compression, filtering, content extraction and automatic adaptation to network characteristics.
  • Caching/ pre-fetching: It is the only way of supporting partially disconnected web browsers. The user can go offline and still browse through the cached content.
Join now!

 

  1. What is WAP? Simply describe the functions of each layer in WAP protocol stack. What are major differences between WAP 2.0 and WAP 1.x? What influenced the WAP 2.0 development?

The basic objectives of WAP are to bring diverse Internet content and other data services to digital cellular phones and other wireless, mobile terminals. WAP is a protocol suit that enables global wireless communications across different wireless network technologies. It creates a framework for the development of content and applications that scales across a very wide range of wireless bearer networks and wireless devices types. WAP is independent ...

This is a preview of the whole essay