Protocol

Reference: [Book] Network Introduction for IT Engineers

The term protocol is used when referring to rules/conventions
In networking, the term protocol is also used to refer to communication rules

Physical aspect
- Data transmission media, signal conventions, line specifications, etc.
- Ethernet is widely used
Logical aspect
- Protocol specifications for devices to communicate with each other
- TCP/IP is widely used

Protocols were mostly developed based on binary bits to use small amounts of data efficiently
- Strict agreements were made to transmit content with the minimum number of bits, and communication was only possible when these agreements were strictly followed

Application level protocols widely use character-based protocols rather than bit-based ones
- HTTP and SMTP are representative protocols
- Instead of transmitting messages in bits, they use characters to represent and transmit headers, header values, and data
- While less efficient than bit-based protocols, they are defined in characters, allowing free header definition and extensibility

Generally, TCP/IP is called a protocol stack rather than a protocol
- TCP and IP are protocols that operate on separate layers, but since they are used together, such a bundle of protocols is called a protocol stack
- The TCP/IP protocol stack includes not only TCP and IP but also a wide variety of application layer protocols such as UTP, ICMP, ARP, HTTP, SMTP, and FTP
The TCP/IP protocol stack is divided into the following 4 parts
- Physical layer
  - Ethernet
- Network layer
  - Helps data find its way to the destination
- Transport layer
  - Helps properly assemble split packets into data form
- Application layer

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