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2004.4.29. UDP TCP 1 My computer Bridge Router Data Your computer Data Application Application Transport Transport Network Network Network Link Link Link Link Physical Physical Physical Physical 2 My computer Bridge Router Data Data Data Your computer Application layer PDU Data Data Data Data Data Data Data Data Data Data Data Data Data Data 3 Rise of the Stupid Network Voice network Intelligence inside the network • encoding/decoding • echo cancellling • conference bridges • etc. Internet: idiot savant’s network Just deliver the bits 4 Is IP going to take over the world? Not yet Only a small portion of the comm market • Compared to TV/cable/radio/movie market Link utilization low • less than 50% compared to 80+% of telephone Robust • troubling problems of routing protocols Simple Real-time application support 5 Multiplexing/Demultiplexing To extend IP’s delivery service Between Web Email 2 end systems to 2 processes SoriBada Web Email SoriBada Application Application Transport Transport Network Network Link Link Physical Physical 6 UDP Message Queues Lineage VoD Player MP3 player UDP 7 Connectionless Transport: UDP User Datagram Protocol Provides only mux/demux and light error control No initial connection setup overhead No connection state Small packet header overhead Finer application-level control source port # length destination port # UDP header = Total 8 bytes checksum 8 UDP Checksum For error detection No recovery, only detection What happens if an error is detected? Why does UDP have a checksum? Checksum calculation Over UDP header and UDP data (+ some of IP header) 16-bit-long 1’s complement of the sum odd-numbered UDP data -> padded with 0 9 Connection-oriented: TCP Transmission Control Protocol For reliable data transfer 3-way handshaking for connection setup Error checking Flow control Congestion control Error-free, in-order delivery of data to application layer 10 TCP Header 15 0 Source Port Number 16 31 Destination Port Number Sequence Number Acknowledgement Number Header Reserved Length TCP Flags TCP Checksum Window Size Urgent Pointer 11 TCP Connection Tear-Down: 2-Army Problem Attack! OK! ?? OK! ?? 12 Closing a TCP Connection Client Server FIN ACK FIN Time-wait ACK Closed 13 TCP Congestion Control Window size function of • receiver buffer size • delay x bandwidth Several flavors Reno/Tahoe/Vegas 14 Rethinking the design of the Internet: The end to end arguments vs. the brave new world 15