The 7 OSI Model Layers govern the complete process of sending data from the source to the destination. The source refers to the sender while the destination refers to the receiver of the send information.

Let’s assume you are sending an email to your friend. The email has to leave your email account and travel through the internet to your friend’s Gmail account.

In so doing, the email message you send has to pass through the seven-layer to successfully get delivered to your friend’s account.

List of the 7 Layers of OSI Model

Below are the seven layers of the OSI model. Note that the layer number is specific. Also, the layer should follow one another as in the below order.

  • Layer 1: Physical Layer
  • Layer 2: Data Link Layer
  • Layer 3: Network Layer
  • Layer 4: Transport Layer
  • Layer 5: Session Layer
  • Layer 6: Application Layer
  • Layer 7: Presentation Layer

The 7 OSI Model Layers Functions, Processes Protocols, Data, Format, and Devices/Tools

As mentioned earlier, the 7 layers assist in transmitting information between the sender and the receiver. Each of the 7 layers has a specific role during transmission.

To perform the above roles, each layer uses technology or protocols that handle the transmitted information.  Different layers use different devices or tools and data in these layers is in a specific format.

Below is a summary of the function, information format, technology or protocols, and devices or tools used in each of the 7 layers.

Layer 1: Physical Layer

Function: Layer 1 performs data encoding and transmission. This involves converting your email text into an electrical signal.

Process: Encoded Data is transmitted either through broadband or baseband techniques.

Data format: Transmitted data in this layer are referred to as Bits. Transmitted data may be in bits or volts. Bits (0s or 1s) are using in case of digital transmission. Whereas information is in voltage in the case of analogue data transmission.

Technologies: Layer 1 technologies include STM, SDH and RJ45.

Devices: Layer 1 devices include hubs, repeaters, fibre optic cable (FOC), and ethernet cables.

Layer 2: Data Link Layer

Function: Layer responsible for physical addressing of layer 1 devices.

Processes: Physical addressing is achieved through Mac access control, frame acknowledgement, frame sequencing, and frame error checking processes.

Data format: Frames. Data in this layer is referred to as frames.

Protocols:  Layer 2 protocols include Token Ring, HDLC, ATM, Ethernet, PPP, Frame Relay, and MAC/LLC.

Devices: Layer 2 devices include are switches, bridges, network cards, and modems.

Layer 3: Network Layer

Function: Layer that performs logical addressing and path determination.

Processes: Above is achieved through routing, frame fragmentation, subnet-traffic control, and logical address mapping processes.

Data format: Information n layer 3 are referred to as packets.

Protocols:  Layer 3 protocols include IP, ICMP, IPsec, IGMP, ICMP, and ARP.

Device: Layer 3 devices include Routers, Layer-3 Switches, and Brouters

Layer 4: Transport Layer

Function: This layer manages the end-to-end connection and reliability.

Processes: Above roles are achieved through data segmentation, data traffic control, and data acknowledgement processes.

Data format: Segments. Data at this stage is broken into small pieces referred to as segments.

Protocols:  in this layer include UDP, TCP, SSL, SCTP, and TLS.

Devices: Layer 4 devices are firewalls and Gateways.

Layer 5: Session Layer

Function: Layer that manages the host-to-host session. A session is a logical connection between the sender and the receiver devices.

Processes: Host-to-host session is ensured through session establishment, session maintenance, and session termination processes.

Data format:  Information in this layer is known as data. 

Protocols: Layer 5 protocols include RTP, SIP, and TCP.

Devices: Session layer use logical ports to establish a connection.

Layer 6: Presentation Layer

Function: Layer that performs data compression and data encryption/decryption. 

Processes: data encryption is achieved through code conversion and character translation processes.

Format: Information in this layer is known as data. 

Protocols: Layer 6 protocols include HTML, MP3, DOC, Sockets, MP4, and JPEG.

Layer 7: Application Layer

Function: This end user layer that allows the user to access sent information or create the information to be sent. An example is this layer allows you to read your friend’s email or create the email you want to send to your friend.

Processes: some of the processes in this layer include Resource sharing and remote file access.

Data format: Information in this layer is known as data. Note that this data is now in the version a human can understand. The data could be a text message, image, audio clip, and video among others.

Protocols: Layer 7 protocols include SMTP, POP3, DNS, FTP, SSH, Telnet, and HTTP.

Tools: Data is presented to the user through the User Application program. The programs present what was sent or create what is to be sent. A good example of the program is a browser that delivers a website search.