cs244a-Introduction to Computer Networking-Unit2

Unit2

学习目标：

1. how TCP set up a connection
2. what TCP segment looks like
3. how can TCP be in high performance
4. detect errors
5. Finite State Machine, a basic tools and approach to network protocol design

2.1 The TCP service model

1. Transmission Control Protocol(TCP)
   • connection:
     • two-way communication channel
     1. A -> B
     2. B -> A
   • at both ends of the connection, TCP keeps a state machine to keep track of how the connection is doing
2. Connection setup: 3-way hadnshake
   1. SYN:
      • 方向：A向B
      • A request conn with B
   2. SYN + ACK:
      • 方向：B向A
      • SYN：B request conn with A
      • ACK: B agree to conn with A
   3. ACK:
      • 方向：A向B
      • A agree to conn with B
3. Data trasmission
   • stream of bytes service
   • using TCP segments
     • SSH一次segment只有1个byte
4. Connection teardown
   • closing the connection and both ends can clean up the state associated with the state machine
   1. FIN:
      • 方向：A向B
   2. （Data+） ACK：
      • 方向：B向A
   3. FIN:
      • 方向：B向A
   4. ACK:
      • 方向：A向B

5. The TCP service model

   Property	Behavior
   Stream of bytes	Reliable delivery service
   Reliable delivery: 4 mechanism for reliability	1. Acknowledgments indicate correct delivery 2. Checksums detect corrupted data 3. Sequence numbers detect missing data 4. Flow-control prevents overrunning receiver
   In-sequence	Data delivered to application in sequence transmitted.
   Congestion Control	Controls network congestions

6. The TCP Segment Format
   
7. The Unique ID of the TCP connection
   • 104-bit globally unique ID(Internet wide)
     • IP:
       1. IP Dest Addr
       2. IP Src Addr
       3. Protocol ID
     • TCP:
       1. Dest Port
       2. Src Port
   • Host A increments source port for every new connection: unique source port number(16bits)
   • TCP picks random ISN(Initial Sequence Number) to avoid overlap with previous connection with same ID
8. Sequence Numbers
   • ISN(initial sequence number): 表明发送的第一个字节的序列号
   • Ack sequence number：
     1. 表明下一个期待的字节的序列号
     2. 表明已经接受到的字节数
9. Summary
   • TCP provides in-order, reliable delivery of a stream of bytes between application processes.

cs244a-Introduction to Computer Networking-Unit2

原文：https://www.cnblogs.com/Willendless/p/11884355.html