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COMPUTER NETWORKS UNIT 5
- 1. UNIT:5 APPLICATION LAYERS- ARCHITECTURE,DYNAMIC DOCUMENTS,HTTP,WEB DOCUMENTS, CLIENT SITE DOGUMENTS
- 2. ARCHITECTURE The WWW today is a distributed client/server service, in which a client using a browser can access a service using a server. However, the service provided is distributed over many locations called sites. Client (Browser) Server Uniform Resource Locator Cookies Topics discussed in this section:
- 4. Browser
- 5. WEB DOCUMENTS: The documents in the WWW can be grouped into three broad categories: static, dynamic, and active. The category is based on the time at which the contents of the document are determined. Static Documents Dynamic Documents Active Documents Topics discussed in this section:
- 8. Effect of boldface tags
- 9. Dynamic document using CGI
- 10. Beginning and ending tags
- 11. Dynamic document using server-site script
- 12. Dynamic documents are sometimes referred to as server-site dynamic documents. SERVER-SITE DYNAMIC:
- 13. Active document using Java applet
- 14. Active document using client-site script
- 15. Active documents are sometimes referred to as client-site dynamic documents. CLIENT-SITE DYNAMIC:
- 16. HTTP: The Hypertext Transfer Protocol (HTTP) is a protocol used mainly to access data on the World Wide Web. HTTP functions as a combination of FTP and SMTP. HTTP Transaction Persistent Versus Nonpersistent Connection Topics discussed in this section:
- 17. HTTP uses the services of TCP on well- known port 80.
- 18. HTTP transaction
- 19. Request and response messages
- 20. Request and status lines
- 21. Methods
- 22. Status codes
- 24. Header format
- 25. General headers
- 26. Request headers
- 27. Response headers
- 28. Entity headers
- 29. example
- 30. Example
- 32. DOMAIN NAME SPACE To have a hierarchical name space, a domain name space was designed. In this design the names are defined in an inverted-tree structure with the root at the top. The tree can have only 128 levels: level 0 (root) to level 127. Label Domain Name Domain Topics discussed in this section:
- 33. Example of using the DNS service
- 35. Domain names and labels
- 36. FQDN and PQDN
- 37. Domains
- 38. DISTRIBUTION OF NAME SPACE The information contained in the domain name space must be stored. However, it is very inefficient and also unreliable to have just one computer store such a huge amount of information. In this section, we discuss the distribution of the domain name space. Hierarchy of Name Servers Zone Root Server Primary and Secondary Servers Topics discussed in this section:
- 39. Hierarchy of name servers
- 41. A primary server loads all information from the disk file; the secondary server loads all information from the primary server. When the secondary downloads information from the primary, it is called zone transfer.
- 42. DNS IN THE INTERNET DNS is a protocol that can be used in different platforms. In the Internet, the domain name space (tree) is divided into three different sections: generic domains, country domains, and the inverse domain. Generic Domains Country Domains Inverse Domain Topics discussed in this section:
- 43. DNS IN THE INTERNET
- 44. Generic domains
- 46. Country domains
- 47. Inverse domain
- 48. RESOLUTION Mapping a name to an address or an address to a name is called name-address resolution. Resolver Mapping Names to Addresses Mapping Addresses to Names Recursive Resolution Caching Topics discussed in this section:
- 51. DNS MESSAGES DNS has two types of messages: query and response. Both types have the same format. The query message consists of a header and question records; the response message consists of a header, question records, answer records, authoritative records, and additional records. Header Topics discussed in this section:
- 52. Query and response messages
- 53. Header format