# TCP/IP

## 1. IP/IP Packet

### IP (Internet Protocol)

Transmits data in communication units called packets to specified IP addresses

### IP Limitations

* Connectionless: Even if there's no recipient for packets or service is unavailable, client still sends packets as-is
* Unreliable: If there's a failure in servers during data transmission and packets are lost, client cannot detect it, and packets may not arrive in order

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## 2. TCP

### TCP Segment

Includes source PORT, destination PORT, transmission control, sequence, verification information, etc. that can supplement source IP and destination IP information of IP packets

### TCP (Transmission Control Protocol) Characteristics

* Connection-oriented: TCP 3-way handshake (virtual connection)
* Data transmission guarantee: Because it returns responses
* Order guarantee: If packets don't arrive in order, can request packet retransmission based on information in TCP segment
* Reliable protocol

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## 3. UDP

### UDP (User Datagram Protocol) Characteristics

* Simple protocol with only PORT and checksum (duplicate check) field information added to IP
* Has almost no functionality but can be customized
* Connectionless: No TCP 3-way handshake
* No data transmission guarantee
* No order guarantee
* Data transmission and order are not guaranteed but simple and fast
* Frequently used for services where continuity is more important than reliability (ex. real-time streaming)
