OSI Model

Summary: The Physical Layer of the OSI model sets standards for sending and receiving electrical signals between devices.

Functions: 

• Conversion of digital data (bits) to electric pulses, radio waves, or pulses of light.

• Specifications for cables and connectors.

• Dictates physical topology.

• Coordinate rules for sending and receiving electrical signals.

Information Format Associated: Bits

Devices Associated:  NICs, repeaters, hubs, WAPs, and modems

TCP/IP: Network

Summary: The Data Link Layer defines the roles for hosts as they access the Physical layer

Functions: 

• How physical network devices are identified on the network by defining a unique hardware address (MAC address)

  • Physical network device identification

• Defines how and when devices have access to the LAN and can transmit on the network medium .

  • Media access control and logical topology.

• Verify that the data received from the Physical layer is error free .

  • Parity and cyclic redundancy check (CRC).

• Controls the rate of data transmission between hosts .

  • Flow Control.

Data Link layer is divided into two Layers: Media Access Control (MAC) and Logical Link Control (LLC):

The LLC is the upper sublayer. It:

• Is an interface between the MAC sublayer and the Network layer.

• Provides flow control and transmission for analog and/or digital streams of over a shared link for the logical link.

The MAC layer is the lower sublayer. It:

• Controls the hardware.

• Provides flow control and transmission for analog and/or digital streams of over a shared link.

Information Format Associated: Frames

Devices Associated:  Switches, bridges and NICs, and WAPs

TCP/IP: Network

Summary: The Network Layer describes how data is routed across networks.

Functions: 

• Identifies hosts and networks by using logical addresses.

• Maintains a routing table.

• Uses routing protocols to route data.

  • Determines the next network point where data should be sent.

Information Format Associated: Packet

Devices Associated:  Routers, Layer 3 Switches

TCP/IP: Internetwork

Summary: The Transport Layer makes sure data gets from point A to point B safely and reliably 

Functions: 

• Reliable message delivery

• End-to-end flow control

• Data segmentation and reassembly

• Port and socket number assignment.

Information Format Associated: Data Segment

Networking Function Associated: Port Number

TCP/IP: Transport

Summary: The Session Layer manages the sessions in which data are transferred. A session refers to each client connection.

Functions:

• Connection establishment

• Management of multiple sessions.

  •  A server can concurrently maintain thousands of sessions.

• Assigning session ID numbers to each session to keep data streams separate.

• Setting up, Maintaining, and Closing Sessions

Information Format Associated: N/A

Networking Function Associated: Session ID Number

TCP/IP: Application

Summary: The Presentation Layer formats presents data in a form compatible for receipt by the Application layer or the destination system.

Functions: 

• Data format specifications

• Data encryption and compression

• Negotiates data transfer syntax between systems. It converts character sets to the correct format.

• Restores data through decryption and decompression.

Information Format Associated: N/A

Networking Function Associated: Encapsulation

TCP/IP: Application

Summary: The Application Layer integrates network functionality into the host operating system and enables communication between network clients and services.

Functions: 

• Enabling of communication between network clients and services.

• Integration of network functionality into the host operating system.

• Services typically associated with the Application layer include:

  • Hypertext Transfer Protocol (HTTP)

  • Telnet

  • File Transfer Protocol (FTP)

  • Trivial File Transfer Protocol (TFTP)

  • Simple Network Management Protocol (SNMP)

Information Format Associated: N/A

Networking Function Associated: HTTP

TCP/IP: Application