1.4 strucutre of the internet

• The internet is a network of inter-connected Networks
• Directing traffic is similar to a road network, data traffic is directed to any location if the destination address is known.
• The main part of the internet is known as the backbone
• There a set of dedicated connections that connect several large network at various points in the world, these points are then connected by regional network-usually controlled by internet service providers (ISPs)
• An ISP provides access to individual end-users.
• IP Version 4 (IPv4) addresses are made up of four octet values (numerical values described by 8 bits each separated by a full stop)
• IPv4 only provides 4.3 billion addresses for 6 billion people therefore to counteract that we use IPv6 which provides more than trillions of addresses.
• URLS are used to specify the means of accessing a resource across a network and its location
• Domain Name system (DNS) servers are dedicated computers with an index of domain names and their corresponding IP addresses.
• When a computer queries a DNS server for a domain name, the server returns an IP address that the computer can sue to send a message to it.
• Resolving an Ip address

  (Find bbc.co.uk-the domain name is resolved from right to left)

  1. Local client request a local ip from a local dns server
  2. If local dns server doesn't know it refers it to the root server
  3. root server tells server to go to the .uk server.
  4. It refers it back to the .co server.
  5. Once it finds it, it will return the IP address in the clients server.
• Domain names must be unique otherwise DNS requests could be confused
• Five global internet registries are responsible for allocating IP addresses to specific domain names. These registries work together to maintain a database of address assignments that ensure an IP is used once and domain names are distinct.
• pruchasable domain names:

  .com

  .uk

  .net
• One computer-that is not connected to any other computing device is called a standalone
• When you connect two or more computers together they form a network
• There are two types of network:

  Local Area Network (LAN)

  Wide Area Network (WAN)
• A Local area network (Lan) is where two or more computers are connected together within a small geographical area, for example confined to one building or site
• Network topologies is the arrangement of the various computing devices, which make up a computer network:

  Bus topology: an arrangement where nodes are connected in a daisy chain by a single central communications channel

  Start topology: an arrangement where a central node or hub provides a common connection point for all other nodes
• Advantages of Lan:

  Shared storage

  Fast communications

  Multiple access points
• Operation of a bus network

  1. All nodes are connected to a single backbone cable
  2. Each end of the backbone is connected to either a terminator or a computer which stops signals 'bouncing back'
  3. Each node is passive
  4. Data is sent in one direction at a time only
  5. Only one computer can transmit successfully at any one time
• Bus network Advantages

  1. Inexpensive to set up
  2. Devices can easily be added
  3. Good for small networks
• Bus network Disadvantage

  1. Main cable is a point of failure
  2. Limited cable length
  3. Performance degrades with heavy use, owing to data "collisions"
  4. Poor security
• When using a star network, computers are connected to a central node. This is often a switch. A switch sends each communication to the specific computer it is intended for.
• Star network advantages

  1. Easy to isolate problems
  2. Good performance
  3. More secure if a switch is used as data is sent only to the recipient.
• Star network Disadvantages

  1. Can be expensive to set up because of the length of cable required
  2. Central device is point of failure
• physical topology of a network defines how the devices are physically connected

  logical topology defines how the devices communicate across the physical topologies.
• Wifi is a wireless networking technology providing high speed internet and network connections
• Wireless components

  1. Wireless Network interface Card (NIC)
  2. Station consists of a computer and an NIC
  3. Station share a radio frequency channel
  4. Wireless Access Point (WAP) requires a connection to a router, and the router requires a connection to a modem