计算机网络原理(英文版)课_Chapter3.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * TCP Connection Management (cont.) Closing a connection: client closes socket: clientSocket.close(); Step 1: client sends TCP FIN control segment to server Step 2: server receives FIN, replies with ACK. Closes connection, sends FIN. client FIN server ACK ACK FIN close close closed timed wait FIN——FINish TCP Connection Management (cont.) Step 3: client receives FIN, replies with ACK. Enters “timed wait” - will respond with ACK to received FINs Step 4: server, receives ACK. Connection closed. client FIN server ACK ACK FIN closing closing closed timed wait closed TCP Connection Management (cont) TCP client lifecycle TCP Connection Management (cont) TCP server lifecycle Chapter 3 outline 3.5 Connection-oriented transport: TCP segment structure reliable data transfer flow control connection management 3.6 Principles of congestion control 3.7 TCP congestion control 3.1 Transport-layer services 3.2 Multiplexing and demultiplexing 3.3 Connectionless transport: UDP 3.4 Principles of reliable data transfer rdt Model GBN（Go Back N） SR（Selective Repeat ） Principles of Congestion Control Congestion: informally: “too many sources sending too much data too fast for network to handle” 有限的出站速率、有限的包缓冲区、过快的包注入、不合适的超时时间 接收方 包溢出 发送方超时重传 网络负载进一步加重 Approaches towards congestion control End-end congestion control: no explicit feedback from network congestion inferred from end-system observed loss, delay approach taken by TCP Network-assisted congestion control: routers provide feedback to end systems single bit indicating congestion (SNA, DECbit, TCP/IP ECN, ATM) explicit rate sender should send at(明确发送方可发速率） Two broad approaches towards congestion control: ECN (Explicit Congestion Notification) Chapter 3 outline 3.5 Connection-oriented transport: TCP segment structure reliable data transfer flow control connection management 3.6 Principles of congestion control 3.7 TCP congestion control 3.1 Transpo