data transmission

• Network architectures define how devices within a network are connected and communicate
• Client-server

  Network architecture in which a system is divided between a server and a client
• Client= A device that requests acces to services, resources and data from a server
• Server= System that provides services, resources and data to clients
• Peer to peer

  Network architecture which allows 2 or more devices to connect and share resources without requiring a separate server
• Peers= Have equal status and can act as consumers and providers of resources.
• P2P may be faster than Client-Server, as P2P networks have algorithms that optimize direct exchange
• P2P may be less secure than client-server, as peers communicate directly, and it's hard to verify the authenticity of resources, and services like filtering, antivirus, etc, are delegated to each peer.
• Public IP:

  These are globally unique and they identify a device on the internet. They are assigned by Internet Service Providers (ISP) to individual users or organizations (THE ROUTER)
• Private IP:

  These are used within a private network (home or business network) and they cannot be used to communicate directly with devices outside the private network (internet). Devices within the same local network can communicate with each other using these private IP addresses. To communicate outside, they need to go through the router (public IP).
• PORTS:

  An access point for data entry or exit 

  • Can either be hardware or software 
  • Ports allow computers to decide which application should handle data received on a network. 
• FIREWALL: 

  Firewall is a program that restricts data allowed into and out of a network, based on a set of rules. It blocks certain data, not eliminate it.

  • One of the ways it does this is to close certain ports 
  • Often the firewall is a dedicated machine that does nothing else
• A port number determines which service or program on a server it wants to use
• Ports are always associated with an IP addresss
• A Node is any device connected to a network

  A Workstation is a computer connected to the network
• A Proxy server is like a normal server but it manages the data between the user's device and the Internet. A proxy server acts on behalf of the user. All requests to the Internet go to the proxy server first, which evaluates the request and forwards it to the Internet.
• An internet service provider (ISP) is a company that provides access to the internet. 

  • ISPs can provide this access through multiple means, including dial-up, DSL, cable, wireless and fiber-optic connections.
• A ISP offers a number of internet related services, such as: 

  • access to internet 
  • email
  • website hosting 
  • applications
• Data transmission is the process of sending information from one device to another over a network.

  • When talking about data transfer we mean the transfer of binary digits 1s and 0s, these are represented by electrical signals, pulses of light, radio waves.
• DATA TRANSMITION Directions: 

  • Simplex: One way (radio broadcast)
  • Half-duplex: Two-way, but not at the same time (walkie talkie)
  • Full-duplex: Two-way, at the same time (telephone) CONCURRENTLY. 
• DATA TRANSMITION Speed:

  The speed of data transmission across a network can vary. 

  • Speed is measured in bps(bits (zeroes and ones) per second), not Bps(Bytes per second)
  • The bandwidth of a network refers to the maximum amount of data that can be transmitted over the network in a given time period.
• ADSL (Asymmetric Digital Subscriber Line) is a way to access the internet using existing copper wire telephone lines

  • Asymmetric because you can download much faster than you can upload 
  • Carried over a normal telephone line but at high frequencies that it is separable from voice 
  • ADSL can be used at the same time as voice, unlike dial-ups. 

  Several ways: Dial up, fiber, ADSL…
• PACKET SWITCHING COMMUNICATION

  Its a way to transmit data that consists in breaking down the data in smaller chunks and then reassembling them at the destination into coherent data. 

  • A data packet is a formatted unit of data carried on a packet-switched network.
  • Data broken into small chunks called packets (64kb maximum for IP)
  • Packets might take totally different routes to their destination 
  • Example: Internet 
• SWITCHING

  Networks have more than one path to transmit data. Switching is the process of transferring data packets from one device to another in a network
• ADVANTAGES: PACKET SWITCHING

  • Full use of available bandwidth: The instant that a data has been sent, the bandwidth is free to be used by other parties. 
  • If one channel goes down, packets will just take a different route
  • Devices of different speeds can communicate easily: In circuit switched communication the devices have to agree to send data at a slower speed. 
  • Reduces lost data packets because packet switching allows resending of packets
• DISADVANTAGES: PACKET SWITCHING

  • Not ideal for applications that are in constant use, such as high volume voice calls
  • There is a lack of security protocols for data packets during transmission
• CIRCUIT SWITCHED COMMUNICATION 

  It's a way to transmit data that consists of a dedicated channel established between both parties. It sends data in one go, in order. 

  • Physical path.
  • If a channel is busy, no one else can connect. 
  • Example: Landline telephone connection 
• ADVANTAGES CIRCUIT SWITCHED

  • Packets are always delivered in the correct order
  • There is a dedicated channel to pass all data, this means there is a very low possibility of data loss
• DISADVANTAGES CIRCUIT SWITCHED

  • Inefficient as it reserves system resources but doesn’t use them completely. 
  • Establishing the connection from the source to the destination can take too long.
  • Circuit switching requires more bandwidth and is more expensive.
• Standards are agreements about hardware or software, designed to facilitate the interoperability and compatibility between devices.

  • Open standards are often international and can be modified, accessed and anyone can know all the details of it. Examples: USB (hardware) and PDF (software).
  • Closed standards are owned by an individual or company and can only be modified by people who hold a suitable license. Examples: DOC, MP3, HDMI (hardware)
• Protocols are an internationally agreed set of rules to ensure transfer of data between devices. A standard protocol is one that is recognized as the standard for a specific type of transfer

  • Data is a huge sequence of 1 and 0s, and protocols is an agreed way of deciding what it all means 
  • Always software
  • Examples: 

  1. HTTP (Hypertext transfer protocol): Web pages 
  2. IP
  3. SMTP (Simple Messagfe Transfer protocol): For sending email
  4. TCP (transmission control protocol): To make sure data packets get received properly. 
• ADVANTAGES OF PROTOCOLS: (ESSENTIAL FUNCTIONS)

  • Ensure data integrity 

  Data integrity, refers to the overall completeness, accuracy and consistency of data. Some protocols can detect packet loss and request that a lost packet be resend. They also have sequence numbers so that packets can be reordered if they arrive in the wrong order. 
• ADVANTAGES OF PROTOCOLS: (ESSENTIAL FUNCTIONS)

  • Manage flow control 

  One host on a network might be able to send data much faster than another one can receive it. Some protocols established a common data transmission speed between hosts to avoid this problem
• ADVANTAGES OF PROTOCOLS: (ESSENTIAL FUNCTIONS)

  • Prevent deadlock 

  Deadlock occurs when all hosts are waiting to receive data before they can continue sending. Some protocols haver timers that can detect and prevent deadlock situations
• ADVANTAGES OF PROTOCOLS: (ESSENTIAL FUNCTIONS)

  • Manage congestion 

  Congestion refers to when when a node carries so much data that results in delay or data packet loss. Some protocols can detect network congestion and reduce their data transmission rate to prevent the network from collapsing. 
• ADVANTAGES OF PROTOCOLS: (ESSENTIAL FUNCTIONS)

  • Perform error checking

  ​​Error checking refers to the techniques used to detect noise introduced into data while it is transmitted.

  Some protocols use some sort of checksum field to detect errors
• NODE VS HOST:

  A network node is any device connected to a network. A host is a node that participates in user applications, either as a server, client, or both.
• Media: 

  • Metal wires: Fluctuating (irregular) electrical voltages
  • Fiber optic cable: Visible light bouncing off the walls inside a cable 
  • Wireless: Electromagnetic spectrum, including radios…
• CONSIDERATION WHEN CHOOSING MEDIA: 

  Speed

  Reliability

  Cost

  Security
• Speed varies because:

  1. Bandwidth: The maximum theoretical data transmission speed that your network provider has given you.
  2. Transmission medium: Copper wire, wireless, satellite… all have different maximum speeds
  3. Length of line: All data travels at some finite speed. The distance the data has to travel affects the time it takes 
  4. Network traffic: The more network traffic, the slower the data transfer on a connection will be. 
  5. Interference: Physical factors like strength and placement of antennas/obstacles in the path can affect how wireless signals reach their target