WJEC GCSE Computer Science Unit 1 Internet Communication Protocols

Objectives Explain how Domain Name System (DNS) Servers and Internet Protocol (IP) addresses work The role of cookies in a web browser

MAC Addresses A MAC address (media access control address), also known as a physical address or a hardware address, is a unique hexadecimal number given to any communication device, such as a network interface card. Routing tables store the MAC address of communication devices in computer systems on its network, as the address is permanent and does not change like an IP address. MAC addresses are made up of 6 x 2 digit hexadecimal numbers: 1A-FE-0C-23-DD-B4 is an example of a MAC address MAC addresses allow network engineers to see which devices are connected to the network.

IP Addresses An IP address is an address which is allocated to a computer system on a network. It is used by the TCP/IP protocol to uniquely identify computer systems on a network, thus allowing communication between them. In routing tables the corresponding IP address of a unique MAC address is stored and updated as necessary. IP Addresses are made up of 4 numbers between 0-255: 31.234.45.182 is an example of an IP address! IP addresses allow network engineers to see where a device is on a network.

Domain Name System (DNS) A Domain Name System (DNS) is a distributed database that matches IP addresses to computer system resources. One example of this is to match an IP address to a human friendly domain name. For example, if you wanted to visit the Google search engine, the computer system on which the website is stored has an IP address assigned to it; 173.194.34.191. Your computer system sends a request to its DNS server for the IP address that is mapped to the domain name www.google.co.uk. The DNS server returns the IP address 173.194.34.191, which allows your computer system to communicate with the computer system where the Google search engine is stored. If the DNS server cant find the IP address for the domain name that you have searched for it sends the request to another DNS server higher in the hierarchy. If no DNS servers can find the IP address for the domain name then a DNS error is returned.

Workbook Complete section 5 Q4

Cookies Cookies are small text files stored on a computer system. They allow websites to store a small amount of uniquely identifying data on your computer system while you are visiting their website. It may be useful as the website can then identify you without requesting that you identify yourself each time, e.g. by entering a username and password. Another use of a cookie would be when you wish to add items to a shopping basket over a period of time. The cookie allows you to store this information between separate browsing sessions.

Search Engines A search engine is an application that can be accessed over the Internet which can be used to search for websites on a particular topic. An index of topics will be built up by programs known as bots or crawlers. These programs visit websites and record information about their content. Users wanting information about a topic will access a search engine and search for their chosen topic by entering keywords that may be associated with the topic. A search engine will then look through its index and return a list of websites that are associated with the keywords.

Workbook Complete section 5 Q5-6