December 1999
NI222 : NETWORKS AND THE INTERNET

QUESTION 2

Total Marks: 15 Marks

• Question 1
• Question 3
• Question 4
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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Explain the difference between Intranets and Extranets.

Intranets are collections of networks that are administered by a single entity or organisation (1).Extranets are the services provided to users outside the organisation through its own network (1).

Explain the role of HTML,HTTP and URL in the process of Web interaction between a Web browser Client and a host computer.

Information of Web is organised as Hyper Text Mark-up Language files (1).Web browsers retrieve these HTML files from the Web servers using a specialised protocol, the Hyper Text Transport Protocol (1).Web browsers identify the HTML files by using Uniform Resource Locators (URLs)address (1).

Explain why data flows down a protocol stack synchronously,but flows up a protocol stack asynchronously.

The data flow downward synchronously through a protocol stack is usually via system calls (1),so the module is aware of the data coming from the module above it (1). Typically,an interrupt-handling scheme is used to pass data upwards (1).Hence a module cannot predict or not aware when the module below it will pass data coming off the network (1).
Give full credit for alternative valid explanations.

Discuss any three issues that distinguish network applications from traditional applications.

Any three of the following:

Data representation (1):makes use of different standards for representing data across heterogeneous machines.E.g.ASCII,EBCDIC,GIF and MIME (1).
Interaction (1):interaction between the network applications can be either symmetric or asymmetric (1).
Security (1):Privacy and authentication of data across the network are provided by encryption and digital signature techniques (1).
Compression (1):to minimise the number of bits sent and to reduce the cost associated, the data is compressed before sending it (1).
Give full credit for alternative valid explanations.