OSI Model

• L7 - Application Layer
• L6 - Presentation Layer
• L5 – Session Layer
• L4 – Transport Layer – Segment/Datagram
• L3 – Network Layer - Packet
• L2 – Data Link Layer - Frame
• L1 – Physical Layer – Bit/Symbol

Application Layer: is the 7th layer of the OSI model which is used by network applications. HTTP, HTTPS, FTP, SNMP, DHCP, POP3, IMAP, Telnet, SMTP are examples of L7 protocols.

Presentation Layer: the data received from L7 is in the form of characters and symbols. The presentation layer converts this data to machine-understandable binary format. Translation, compression and encryption is done at the presentation layer. SSL, NTP and DHCP are examples of L6 protocols.

Session Layer: helps in setting up and managing connections. It enables sending and receiving of data followed by the termination of the session/connection. Authentication and authorization are performed at the session layer. NetBIOS is an example of an L5 protocol.

Transport Layer: controls the reliability of communication through segmentation, flow control and error control. Data received from L5 is converted to segments. Each data unit has source and destination port numbers and sequence numbers. TCP (connection-oriented transmission) and UDP (connectionless transmission) are examples of L4 protocols.

Network Layer: works for transmission of data from one computer to another located in different networks. Logical addressing, routing and path determination is done at the network layer. IP, ARP, ICMP and IGMP are examples of L3 protocols.

Data Link Layer: receives the packet from L3 layer. Physical addressing is done at the data link layer using MAC address. Data link layer is embedded as software in NIC. This layer controls how data is placed and received from the media. MAC and ethernet are examples of the data link layer.

Physical Layer: converts the binary sequence into signal and transmits over local media. Light signal- optical fiber, Radio signal- wireless, electrical signal- copper cable.