OSI Model Layers and Protocols

OSI Layers and Protocols

• The OSI model has several protocols that operate within each layer, which will be discussed.
• Advantages of the OSI reference model include:
  • Clear distinction between services, interfaces, and protocols
  • Protocols are well-hidden and can be replaced as technology changes
  • Supports both connection-oriented and connectionless services
• Drawbacks of the OSI reference model include:
  • The model was devised before protocol invention
  • Fitting protocols is a tedious task
  • It is only used as a reference model

Encapsulation and Decapsulation

• Encapsulation is a process that hides or protects data from outside interference, making it simpler to use.
• It involves a lower-layer protocol receiving data from a higher-layer protocol and converting it into a recognizable format.
• Access to internal systems is arranged through a set of interfaces.
• Encapsulation can be compared to sending a letter with an envelope, address, and postage, which represents data encapsulation.

Encapsulation Process

Application Layer (Layer 7)

• Responsible for exchanging information between computer and network
• Defines user requests
• Interface layer between network applications used by users

Presentation Layer (Layer 6)

• Determines whether encryption or data translational is needed
• Adds header to data

Session Layer (Layer 5)

• Checks application requests and verifies services on the server
• Adds header to data (optional)

Transport Layer (Layer 4)

• Ensures proper connection with the server
• Converts information into segments
• Performs error checking and merging data
• Guarantees data wholeness
• Forms L4PDU

Network Layer (Layer 3)

• Adds network addresses for request and server
• Converts segments into packets
• Adds network header and forms L3PDU

Data Link Layer (Layer 2)

• Arranges packets into individual frames
• Adds MAC addresses (destination and source)
• Adds trailer to frame
• Ensures packet delivery via routers
• Transmits to media
• Data must fit within 46-1500 bytes of Ethernet frame