[풀스택] UDP - User Datagram Protocol

 

 

 

UDP User Datagram Protocol

• The User Datagram Protocol (UDP) is called a connectionless, unreliable transport protocol.
• It does not add anything to the services of IP except to provide process-to-process communication instead of host-to- host communication.
• If UDP is so powerless, why would a process want to use it? Very simple protocol using a minimum of overhead
• if a process wants to send a small message and does not care much about reliability, it can use UDP
• if it sends a small message, taking much less interaction between the sender and receiver than it does using TCP

 

 

 

https://ko.wikipedia.org/wiki/TCP/UDP의_포트_목록 - 잘 알려진 포트 넘버들이 있다.

 

 

 

헤더가 구현된 방식 -> 보내는 포트의 번호 + 받는 포트의 번호 https://static.javatpoint.com/tutorial/computer-network/images/udp-protocol.png

 

 

 

 

IP 주소(3)와 포트 넘버(4)를 합하면, 특정 컴퓨터(서버)의 프로세스를 식별 가능하다 ! https://www.myreadingroom.co.in/images/stories/docs/dcn/user%20datagram_Header.JPG

 

 

 

UDP Operation

• Connectionless Services : 
  UDP provides a connectionless services that each datagram sent by UDP is an independent datagram.
• Flow and Error Control : 
  There is no flow control and hence no window mechanism.
  There is no error control mechanism in UDP except for the checksum.
• Encapsulation and Decapsulation :
  The UDP protocol encapsulates and decapsulates messages in an IP datagram.

 

 

 

Queuing at client site

• When a process starts, it requests a port No. from the operating system.
  The client process sends messages to the outgoing queue by using the source port No. specified in the request.
• UDP removes the messages one by one and, after adding the UDP header, delivers them to IP.
• An outgoing queue can overflow.
  If this happens, the OS can ask the client process to wait before sending any more messages.
• When a message arrives for a client, UDP checks to see if an incoming queue has been created for the port No. specified in the destination port No. field of the user datagram.
  If there is a queue, UDP sends the received user datagram to the end of the queue.

 

• 클라이언트 - 정보를 보내면 됨
  운영체제로부터 포트 번호를 부여받는다.
• 통신을 위한 포트번호를 운영체제에게 요구
  운영체제는 프로세스에게 통신 포트 번호를 준다
• UDP는 정보를 가지고 있어야함 - 메모리 공간 필요
  layer3 에게 받은 정보 - UDP 갖고 있다가, 4에게 줌
  * 상위 계층이 하위 계층에게 주면, 하위 계층은 읽어간다. 
• 본인이 밑으로 내릴 때 아래 계층의 큐에다 쓰고, 아래 계층은 그걸 다시 읽어 간다. 

 

 

 

Queuing at server site

• When it starts running, a server asks for incoming and outgoing queues, using its well-known port.
• When a message arrives for a server, UDP checks to see if an incoming queue has been created for the port number specified in the destination port number field of the user datagram.
• If there is a queue, UDP sends the received user datagram to the end of the queue.
  연결 설정 과정이 없다
• When a server wants to respond to a client, it sends messages to the outgoing queue, using the source port No. specified in the request.
• UDP removes the messages one by one and, after adding the UDP header, delivers them to IP.

 

 

 

Applications of UDP

• UDP is suitable for a process that requires simple request-response communication with little concern for flow and error control.
• 파일 사이즈가 작을 때, 서버와 가까이 있어 안정적일 때 -> UDP로 파일을 주고 받을 수 있다. 
• Not used for sending bulk data, such as FTP
• TFTP including internal flow and error control
• Suitable transport protocol for multicasting
• Used for some route updating protocols such as Routing Information Protocol (RIP)
  라우터끼리 간단한 정보 주고받을 때 
  
• Used for management processes such as SNMP.
  SNMP(Simple Network Management Protocol)란?
  UDP/IP(사용자 데이터그램 프로토콜/인터넷 프로토콜)를 사용하여 이더넷 연결을 통해 네트워크 관리 작업을 수행하는 응용 계층 프로토콜
  

 

• 구글 완전히 UDP 기반
  유튜브 - UDP 기반
  TCP를 걷어낸 새로운 통신 프로토콜 - 퀵으로 구현
  네이버 - 퀵 베이스, 4계층 통신 프로토콜로 넘어감
• 새로운 통신 프로토콜이 UDP 위에 설계되고 있다. 
  거의 모든 운영체제에 UDP는 있다.