Data Communications and Networking Chapter 2 Protocol Architecture TCP IP model and OSI Model[数据通信与网络第2章协议体系结构TCP IP模型和OSI模型](PPT-52).pptVIP

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Data Communications and Networking Chapter 2 Protocol Architecture TCP IP model and OSI Model[数据通信与网络第2章协议体系结构TCP IP模型和OSI模型](PPT-52).ppt

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Data Communications and Networking Chapter 2 Protocol Architecture TCP IP model and OSI Model[数据通信与网络第2章协议体系结构TCP IP模型和OSI模型](PPT-52)

* UDP Ports: multiplexing and demultiplexing Today’s operating systems support multi-processing, i.e., a number of applications can run simultaneously. Multiplexing: Each application program using UDP to send out data must first negotiate with the operating system to obtain a UDP port. Any datagram the application program sends through the port will have that port number in its UDP packet. Demultiplexing: UDP accepts incoming datagrams from the IP module, and demultiplexes based on the UDP destination port. * UDP Applications UDP’s advantages Finer application-level control over what data is sent, and when No connection establishment: saves time! No connection state Small packet header overhead: only 8 bytes Can support multicast Disadvantage: UDP is unreliable Applications using UDP: Streaming multimedia Internet Telephony Network management Routing protocols DNS * TCP RFC 793 /rfc/rfc793.txt TCP provides reliable communication between pairs of processes (by using positive acknowledgement with retransmission). No data loss, no error, no out-of-order (from the application’s point of view). TCP uses the idea of retransmission to recover packet loss. TCP is connection-oriented stream service. From the hosts’ point of view, two applications need to “setup” a TCP connection (like virtual circuit) before they use TCP to exchange data. But from the network’s point of view, they are still processing normal IP packets. Routers don’t distinguish between UDP packets and TCP packets. TCP connection is full-duplex. A TCP connection is recognized by (IPs, IPD, Ports, PortD, “TCP” ) TCP only supports point-to-point communication between TWO hosts. It cannot support multicast or broadcast which can be supported by UDP. Data is regarded as byte stream. The TCP must deliver exactly the same sequence of bytes to the receiver application, though the IP packets may arrive out of order. The stream is unstructured. There is no record boundaries. * TCP/IP Concepts * TCP segment A TCP app