a piece of information that forms part of message sent through a computer network


Domain Name System: DNS

7 layers in OSI model

Layers in OSI model

Has 7 layers

layer 1 to 7: Please Do Not Throw Sausage Pizza Away

Layer 1: Physical layer

Layer 2: Data link layer

Layer 3: Network Layer

Layer 4: Transport Layer

Layer 5: Session Layer

Layer 6: Presentation Layer

Layer 7: Application Layer

Layer 1: Physical Layer


conversion between Data -> signal include:

  1. Pinout: pinout in our cable, pinout on pin that we plugged into computer

  2. voltages

  3. cable specification:

  4. NIC: network interface card: physical port & physical card inside our computer

Layer 2: Datalink Layer


Transfer from point to point

MAC address: unique

Package bits/data into frame

Layer 3: Network Layer

IP address is logical address, they;re not address hard-coded into interface network card. All computer with network interface card has MAC address and IP address.

Computer A needs to send data packets. Data packets are broken down into physical mean: electrical impulse. Electrical impulse are going to be sent out in our network interface card over a cable

Computer A (with MAC address ) need to send information to computer B. Computer B is in different network, different subnet to computer A. Because we need to connect to a different network, we need to have a "layer 3" devices. So their need to be 2 router for each computer A and B, and a cable between them to connect.

Layer 4: Transport Layer

Management/control the data

split our commucation into packet




Layer 5: Session Layer

where we establish our connection, handshake with other computers

Traffic control

control connection between computer

Layer 6: Presentation Layer

Format data:


layer 6 format the data for sending, and decrypted when received

Layer 7: Application Layer

Enable apps to access network