OSI Models

  • OSI model is the most fundamental model used in networking.
  • Stands for open systems interconnection.
  • This model provides a framework in dictating how all network devices send, receive and interpret data.
  • The OSI model consists of 7 layers
    • Application
    • Presentation
    • Session
    • Transport
    • Network
    • Data link
    • Physical

At every individual layer that data travels through, specific processes take place, and pieces of information are added to this data, which is what we’ll come to discuss in the upcoming tasks within this room. However, for now, we only need to understand that this process is called encapsulation.

7. Application Layer

  • it is the most familiar layer.
  • every day-to-day application such as email clients, browsers… come under this.
  • Graphical User Interface is Part of Application Layer.
  • other protocols include DNS which is how the web address is translated into IP address.

6. Presentation Layer

  • layer in which standardization starts to take place.
  • This layer acts as a translator for data to and from the application layer.
  • Security features such as data encryption (like HTTPS when visiting a secure site) occur at this layer.

5. Session Layer

  • once the data is correctly translated from presentation layer session layer begin creating connection to the destination devices.
  • when connection is established, the session is created.
  • Session Layer synchronizes the two computers to ensure they are on the same page.
  • Once the checks are in place data is sent as in the form of packets
  • sessions are unique - data cannot travel over different sessions, but in fact, only across each session instead.

4. Transport Layer

  • plays a pivotal role in transmitting data.

  • it follows one of two different protocols on data transmission:

    • TCP

    • UDP

      TCP

  • Transmission control Protocol: Designed with reliability and guarantee in mind. Serves a constant connection between two devices for the amount of time it takes for the data to be send and received.

  • Incorporates error checking in the design.

  • it guarantees that the packets are received and reassembled in the proper order.

Advantages of TCP Disadvantages of TCP
Guarantees the accuracy of data. Requires a reliable connection between the two devices. If one small chunk of data is not received, then the entire chunk of data cannot be used.
Capable of synchronizing two devices to prevent each other from being flooded with data. A slow connection can bottleneck another device as the connection will be reserved on the receiving computer the whole time.
Performs a lot more processes for reliability. TCP is significantly slower than UDP because more work has to be done by the devices using this protocol.

  • used in situations like file sharing, internet browsing or sending an email.

    UDP

  • User Datagram Protocol

  • there is no synchronization between the two devices.

  • any data the sent via UDP is sent whether it gets there or not.

Advantages of UDP Disadvantages of UDP
UDP is much faster than TCP. UDP doesn’t care if the data is received.
UDP leaves the application layer (user software) to decide if there is any control over how quickly packets are sent. It is quite flexible to software developers in this sense.
UDP does not reserve a continuous connection on a device as TCP does. This means that unstable connections result in a terrible experience for the user.
  • UDP is useful in situations where there are small pieces of data being sent.
  • protocols used for discovering (ARP, DHCP) or larger files such as video streaming where the video will be pixelated when a packet of data is lost.

3. Network

  • layer where routing and re-assembly takes place.
  • routing determines the optimal path for the data chunks to be sent.
  • The protocol used to find the optimal path include OSPF (Open Shortest Path First) and RIP (Routing Information Protocol)
  • the path is determined the following factors:
    • which is the shortest?
    • which is more reliable?
    • which path hast the faster physical connection.
  • focuses on the physical addressing of the transmission.
  • it receives packets from the network layer and adds in the physical MAC address of the endpoint.
  • inside every device there is a NIC (network interface card) which comes with the MAC address to identify it.
  • They are set by the manufactures and burned into the card. they can’t be changed.
  • they can be spoofed. the physical address is used to identify where the information is sent.
  • it is the also the job of data link to present the data in a format suitable for transmission.

1. Physical

  • this layer references the physical components of the hardware used in networking.
  • it is the lowest layer.
  • devices use electrical signal to send data across devices using 1’s and 0’s.