Chapter VIII network programming socket (2): Explanation transport layer (TCP / UDP)

8.2 Explanation transport layer TCP / UDP

As a software program ape, we can only decide what the application layer protocol. Other layers are fixed

TCP

• Stream protocol known as TCP protocol (streaming protocol): pass like water, like, we need a two-way pipeline
  • Establish a connection (dig the pipeline) :( 3-way handshake)
    • 1 Handshake: A client sent a request to the server (SYN = 1, Seq = x): I'm going to connect you, okay? →
    • Two handshakes: the server replies to the client request (ACK = 1, Seq = x): can. At the same time, the server to the client sends a request (SYN = 1, Seq = y): I have to connect you, okay?

    • 3-way handshake: a client server's reply to the request (ACK = 1, Seq = y): can.

      This establishes a two-way connection

  • Disconnect: As the server does not necessarily pass through after the client's data, it requires four steps (four break)
    • 1: The client sends a request to the server end (FIN = 1)

    • 2: the server's reply to the requesting client (ACK = 1)

      Here the server will transmit the data to the client transmits a disconnection request End Chuancai

    • 3: the server sends a request to the client (FIN = 1)

    • 4: The client requests the server to reply (ACK = 1)

SYN = 1 indicates that this is a request
ACK = 1 indicates that this is an acknowledgment
seq = x indicates the serial number is x, the service side is used to confirm the end of the service responses sent just I

TCP is a reliable protocol, what is reliable agreement? Reliable is specified: When the sender sends the data to the receiving end when the other end will reply with a message telling the sender that I received. If the sender did not receive a reply, it is re-issued.

• TCP Features:
  • Transmission efficiency is low

  • Reliable data transmission

    TCP protocol, also known as streaming protocol (STREAM), because the data flow is sent, so stick pack phenomenon occurs

  • Streaming protocols:
    • Stick pack phenomenon occurs
    • Not send dummy data
    • Send and receive can be many to many

UDP

• UDP does not require digging pipe (no connection exists), as long as know the target, direct contracting will not be confirmed if it was received.
  • UDP transmission speed quickly: without establishing a connection, do not need to confirm if it was received

  • Unreliable protocol (if the network and other problems, most likely packet loss)

    UDP protocol, also known as Datagram Protocol (DataGRAM), will not stick pack phenomenon

  • Datagram Protocol:
    • Stick pack phenomenon does not occur
    • Null data can be sent (comes header, so the data is not actually empty)
    • sendto and recvfrom is one relationship