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Transport Layer

  • use
    • main responsibility, transfer the data completely
    • receives the data from the upper layer and converts them into smaller units known as segments.
    • termed as an end-to-end layer,provides a point-to-point connection between source and destination to deliver data reliably.
    • ensures that messages are transmitted in the order in which they are sent and there is no duplication of data.
    • end to end delivery of the data
    • udp and tcp protocols are used
    • flow control - don't send more data
    • congestion control - too many packets in the network
    • segmentation - dividing into packets
    • error correction
  • protocols
    • TCP
    • UDP
  • pdu
    • segment

Ports

  • both udp and tcp have - (1-65535) number of ports, \(2^{16} - 1 = 65535\)
  • because port no is a 18 bit number (2 byte)

  • well known ports - 1 to 23
  • registered ports - 1024 - 49151, assigned by IANA, internet assigned number authority
  • dynamic ports, generated by pc, bound by the port you create on pc, rest of remaining ports
  • use netstat on windows

Some common ports

tcp

  • ftp - 21, file transfer protocol
  • ssh - 22
  • telnet - 23
  • smtp - 25
  • http - 80
  • https - 443
  • pop - 110
  • dns - 53

udp

  • tftp - 69, trivial ftp
  • dhcp - 67/68
  • smtp
  • dns - 53