Networks

Networks allow a computer to connect to other computers as well as other external resources in order to do the following:

  • Share resources - such as printers, software or application servers

  • Communicate and exchange data - examples: email, voice, video conferencing

  • Multi user games and entertainment

  • Allow businesses to provide e-commerce apps such as online shopping and online payments

Hosts and data transmission:

  • Each host or machine on the network has a unique network address

  • Data is sent through data packets

Data packets:

  • It is split into two, the header and the data

  • Header contains the following: Packet number, address of the sender, destination address, length of data, error correcting info

  • The data part contains the actual data such as a small message

Networking themes:

  • Topology such as: bus, ring, or star

  • Network scope such as: LAN, WAN, metropolitan area

  • Network access control such as: intranet, internet

Topology’s:

  • Bus - each machine is connected to a single back bone cable. Advantages: simple, cheap, good for small networks. Disadvantages: Frequent collisions, if the back bone cable fails it all stops working, limited cable length.

  • Ring - each machine is connected to a ring of cable. Advantages: fewer collisions, ordered transmission using tokens, tokens constantly circulate through the ring. Disadvantages: Cable failure brings the whole network down, tokens have to be passed through each node, difficult to extend with kore machines

  • Star - Each machine is connected to a central hub. Advantages: problems are isolated to a single branch, does not bring the whole network down. Disadvantages: if the central hub is a single point then the whole network goes down, limitations on amounts of cable. (Most popular type of network in homes)

  • Wireless networks tend to use a star topology, the central node is called the access point, machines will use the access point to communicate to each other

Network scopes:

  • Local area network (LAN) - local and small area such as inside someones house

  • Metropolitan area networks (MANs) - limited geographical area (not sure anything about)

  • Wide area network (WAN) - multinational global areas, with is made by connecting many LANs connected together

Connecting networks together:

  • A router has the same function of a switch however a router allows you to connect to the wider network and adds some routing intelligence

  • The router knows the destination of data packets, address gateway to the next network

  • Data packets are passed between routers until it reaches its desired destination

Internet-working software layers:

  • Application layer - constructs message, includes destination address information

  • Transport layer - chops message into data packets

  • Network layer - organises routing of packets through the internet

  • Link layer - handles actual transmission of packets

Real time routing:

  • Dynamic nodes?

  • Routing finds the optimum path from one node to another

  • Network routers are constantly searching for viable communication pathways, sorting the current set of viable pathways to find the best path

  • Uses algorithms such as dijsktras shortest path algorithm

Network protocols:

  • The rules networks have when communicating to each other

  • Protocols provide control, fairness and accuracy when communicating

  • Control - makes sure packets are sent in an orderly fashion

  • Fairness - makes sure each computer has an equal share of the network

  • Accuracy - makes sure data is not corrupted

The OSI model:

  • Abstract model of networking

  • Helps hardware and software vendors position themselves in the market place

TCP/IP:

  • Data packets are routed around using two protocols: Transmission control protocol (TCP), internet protocol (IP).

  • Provide multi level abstraction from the physical hardware topology of the network

  • Each machine can do several things at once which all involve communicating with packets but it does not get mixed up due to using multiple ports

TCP Ports:

  • Each port is associated with an application and a protocol for sending data

IP addresses:

  • Every device on a network has an IP address

  • It is split into two parts: network portion, host portion

  • Network portion - identifies a particular network?

  • Host portion - identifies a host device on the network

Domain name system:

  • Provides a name to the ip address to a website so that users of the web dont need to remember the ip address of the website

IP look-up process:

  • When accessing a webpage the users server will contact the master root servers to get the address for the next server

  • When the machine has gotten the full IP address the machine can start to send its data packets