The Internet (zigzag course notes) Flashcards
How is data sent across a network
Broken down into packets
What is the typical payload of a packet?
800 bits
What does the packet header do and what does it consist of?
Enables the packets to reach the destination and to be assembled in the correct order. Consists of:
- destination address
- source address
- checksum for error detection
- packet sequence number
What are the two main functions of packet switching?
Enable more than one device to share a data line
Find the most direct route for information travel
Packet switching was developed to replace circuit switching, and to make the broadcast of data more autonomous.
- eg a telephone system originally used dedicated connections between people calling each other.
- this is clearly suboptimal, a more efficient system sends packets of data across the network as they are required, resulting in potentially increased bandwidth across a given circuit
What does a router do
Forwards packets from one network to another. Each network will have a router which works out where to send packets which are not destined for the network they are actually within (when a packet is sent across the Internet, it will “hop” through many different routers before it reaches its destination)
Why are routers used
Every network hardware has a MAC address. Routers can therefore change the destination MAC address of a packet (to hop it to another router) without changing the destination IP address. This means that routers can forward packets from one to another, changing destination MAC as they go, while maintaining a record of the ultimate destination
How does the router transfer data
- The user prepares the message and sends it to the router.
- The router obtains the fastest route by checking its routing table
- When route is found, the message is transferred to another router
- If this router has the destination node in its network, it sends the message to that node, otherwise the process is repeated
What are gateways
Gateways are the entrance and exit of a network and can be considered as protocol converter
Main use of gateway?
To connect multiple different networks of different architectures, called an internetworking system
How does a gateway work?
- Takes in a packet from an external node and strips it down, removing all info apart from raw data
- This raw data is then repacked and sent over to another network using the protocol which that network supports, so the data can be transmitted without error
What is an internetwork?
A collection of independent networks that are connected to each other
- Each network functions on its own and does not depend on other networks
- An example of this is the Internet
-= The networks in an internetwork are joined together with routers which handle the URL requests to find certain volumes of information
What are the two types of Uniform Resource Identifier? What do they do?
Uniform Resource Identifier or Uniform Resource Name
A URI provides a unique reference for an Internet resource while not necessarily providing an exact location for the resource as it could a query in a database or to call some application.
This is why the term URL alone is not sufficient. A URL is an identifying location for a resource providing a means of getting the resource
Example of a URL and URN
the URL http://www.google.com is the URI that exclusively identifies an Internet resource, namely the google homepage. It describes the type of representation that is used, ie HTML. A URN however provides a way of exclusively identifying something, for instance an ISBN number for a book, which can identify a specific book but not provide any means of actually getting hold of that book
A URL is equivalent to a person’s phone number of postal address, while a URN is equivalent to a person’s name
What are domain names?
Domain names provide the text that is entered in the search bar of a web browser, and can be used by a domain name service to return the specific IP address of that domain name
- Eg the address ‘www.google.com’, then ‘www.google.com’ is the domain name with a hierarchy where ‘.com’ identifies the top-level part of the domain and is often related the the type of organisation that owns the name.
- The ‘google’ part, known as the second level domain, is a unique word identifier for a particular IP address.
- The ‘www’ provides the name of the hose server at the address which deals with internet requests
- It may also therefore be possible to find addresses such as ‘ftp.google.com’ which points to the server that deals with FTP requests
- subdomains can exist which fall in the hierarchy between the secondary and server part of the address eg ‘www.images.google.com’
Purpose of internet registries
- Only a finite number of IP addresses, so a system to facilitate the distribution of domain names and IP addresses
- This is the role of internet registries and registrars
- International organisation called the Internet Assigned Numbers Authority that decides which IP address are used in which regions and, the local Internet Registries and their registrars then distribute the addresses assigned to them according to local legislation
