Transport layer

• Layer 4
• 포트를 이용한 프로세스 간 커뮤니케이션(포트는 16bit number)
• tcp, udp

UDP

• connection-less protocol
• 헤더의 total length: length of the UDP packet = IP packet length – IP header length
• 다음과 같은 상황에서 사용

  • own flow control, error control이 있는 프로토콜에서 쓰임

    ex.TFTP

  • Multicast application (일대다 통신)

  • Protocols for management ex. SNMP

TCP

• connection-oriented protocol
• sender buffer, receive buffer
• TCP segment : a portion of the byte stream + TCP header
• bi-directional
• The first byte in the stream is assigned a random number between 0 and 2^32-1
• 기능
  • flow control
  • congestion control
  • error control

If PSH flag is set, the receiver sends the buffered data to the application – used for interactive applications such as remote terminals

When URG field is set, the urgent pointer points to the starting point of the normal data

TCP sliding window