In general, it is sufficient to collapse 5,6,and 7 layers into a single layer and consider application protocols like HTTP.
[7] Application Layer
data unit : message
protocol : HTTP, SMTP, FTP, SIP, etc.
As the final destination, application layer is commonly used for the multiple applications to communicate with each other.
[6] Presentation Layer
data unit : message
protocol : ASCII, MPEG, etc.
Presentation Layer handles the encoding or decoding the data exchanged at the application layer. (e.g., converting ASCII to UTF-8)
[5] Session Layer
data unit : message
protocol : NetBIOS, TLS, etc.
Session Layer manages the opening, closing and managing of sessions between end-user application processes.
[4] Transport Layer
data unit : message
protocol : TCP, UDP, SCTP, etc.
Transport Layer carries message from the upper layers to the lower layers.
It manages errors and, if a message is too large, it segments it before passing it to Network Layer.
TCP, which is connection-oriented, and UDP, which is connectionless, are commonly used protocols.
[3] Network Layer
data unit : datagram, packet, etc.
protocol : IP, ICMP, ARP, RIP, BGP, etc.
Network Layer routes packets from host to host. often through multiple routers.
It creates packets using destination address from Transport Layer and delivers them to the destination’s Transport Layer.
In the context of the Internet, the IP protocol is the primary example.
[2] Data Link Layer
data unit : frame
protocol : PPP, Ethernet, Token ring, IEE 802.11(Wifi), etc.
This layer is responsible for transferring data between nodes on a network segment across the physical layer.
It provides the means to transfer data between network entities and may also detect and correct errors from the physical layer.
Ethernet protocol is representitive protocol, transferring frames between nodes using MAC address. i.e. Bridge, Switch HUB
[1] Physical Layer
data unit : bit
protocol : DSL, ISDN, etc.
Pyhisical Layer transmit electrical signals between devices, moving each bit of the data frame between nodes.
Ethernet includes serveral Physical Layer protocol. i.e. Repeater
