CMPE 150 Winter 2009 Lecture 16 March 3 2009 P E Mantey CMPE 150 Introduction to Computer Networks Instructor Patrick Mantey mantey soe ucsc edu htt http www soe ucsc edu mantey d t Office Engr 2 Room 595J Office hours Tues 3 5 PM Mon 5 6 PM TA Anselm Kia akia soe ucsc edu Web site http www soe ucsc edu classes cmpe150 Winter09 Text Tannenbaum Computer p Networks 4th edition available in bookstore etc Syllabus Text Readings Today Chapter 6 6 Sections Sections 6 6 2 3 2 3 6 6 6 4 6 4 UDP UDP 6 5 TCP 6 6 TCP Performance Tuesday March 10 Chapter 7 1 7 1 DNS DNS 7 7 2 3 23 Chapter 7 4 Multimedia Internet Layering Level 5 Level 4 Level 3 Level 2 Level 1 Application Layer rlogin ftp SMTP POP3 IMAP HTTP Transport Layer a k a Layer a k a Host Host to Host to Host TCP UDP Network Layer y a k a Internet IP ICMP ARP Data Link Layer MAC sub layer a k a k Network N t k IInterface t f or Network Access Layer Physical Layer Transport Layer Connection Oi Oriented dS Service i Addressing Access Points Connection Request Establishment Delayed D l d Duplicate D li t P Packet k tP Problem bl Timer management Connection C points Connection Release Connection Release Asymmetric y release telephone p system y When one party hangs up connection breaks May cause data loss loss Symmetric release Treats T connection i as 2 separate unidirectional idi i l connections Requires R i each h tto b be released l d separately t l Symmetric Release How to determine when all data has been sent and connection could be released 2 2 army army problem Blue armyy 1 Blue army 2 White army larger th either than ith blue bl armies i White army Blue army together is larger If each blue army attacks it ll be defeated They win if attack together 2 Army 2 Army Problem 1 To synchronize attack attack they must use messengers that need to cross valley ll unreliable li bl Is there a protocol that allows blue army to win No Blue army 1 sends message to blue army 2 2 Blue army 2 sends ACK back Blue army 2 is not sure whether ACK was received 2 Army 2 Army Problem 2 Use 2 wayy handshake Blue army 1 ACKs back but it ll never know if the ACK was received Applying to connection release Neither side is prepared to disconnect until convinced other side is prepared to disconnect In practice practice hosts are willing to take risks risks Connection Release Protocol Send DR start timer DR DR Release connection Send ACK DR disconnection request Send DR start timer ACK Release connection Connection Release Scenarios 1 Send DR start timer DR DR Release connection Send ACK DR disconnection request Send DR start timer ACK Timeout Release connection Connection Release Scenarios 2 Send DR start timer DR disconnection request DR DR Timeout send DR start timer Send DR start timer DR Send DR start timer DR ACK Release connection Transport Layer Assumes Network is unreliable Sender buffers all TPDUs until acknowledged Receiver may also buffer Difficult to decide buffer size as TPDUs Dynamic buffer allocation may be best strategy Buffer size negotiated by exchange of control packets Deadlock can occur if control packets get lost Solution is periodic sending of control TPDUs containing acknowledgements and buffer status Flow Control and Buffering Premise Network is unreliable Consequence q Sender must buffer all TPDUs sent May need to retransmit Receiver needs to buffer Out of order TPDUs Flow control to application s maximize tranmission speed Sender TP layer also buffers to even flow from its application s smooth out bursts to match network Buffering negotiated between sender and receiver Hosts clients and servers may have each have many connections in contrast to link layer point to point point to point Buffer pool Flow Control and Buffering a Chained fixed size buffers b Chained variable sized buffers One c O llarge circular i l buffer b ff per connection ti Multiplexing Upward Multiplexing One IP address shared by multiple Transport Layer processes ports Downward D dM Multiplexing lti l i Use multiple p virtual circuits to g get more bandwidth e g join multiple ISND lines to get a higher g bandwidth Multiplexing a Upward multiplexing multiplexing multiplexing b Downward Crash Recovery Transport p layer y can handle crashes of network layer Transport expects errors in network Machine crash causes transport p layer y crash Recovery more challenging Related to database commit Cannot be managed at Transport Layer Crash Recovery Client States S0 no TPDUs outstanding S1 one TPDU outstanding End to end End to end Ack Perfect end to end acknowledgement means 1 if you gett it th 1 the ack k the th ttaskk was completed 2 if you do not get the ack the task was not completed Can t do both at the same time and guarantee either both or neither were done Example database update transaction commit commit Probably impossible Saltzer 1984 Recovery Principal Principal Layer y above with enough g status information can recover from crash of the layer below below Recovery from crash at layer N needs to be done att llayer N 1 who h mustt have h necessary status t t info The Internet Transport Protocols UDP U User D Datagram t P Protocol t l Introduction to UDP Connectionless C IP IP with a short header Carries source and destination ports Sends segments with ith 8 b byte te header Introduction to UDP The UDP header header The Internet Transport Protocols UDP U User D Datagram t P Protocol t l Introduction to UDP Connectionless Connectionless IP with a short header carries ports Sends segments with 8 byte header No No flow control No error control No N retransmission t i i ffor b bad d segments t The Internet Transport Protocols UDP U User D Datagram t P Protocol t l Introduction to UDP Connectionless C IP IP with a short header carries ports Used with client server and realtime multimedia The Internet Transport Protocols UDP U User D Datagram t P Protocol t l Introduction to UDP Connectionless C IP IP with a short header carries ports Used with client server and realtime multimedia Remote Procedure Call The Real Time Transport Protocol Remote Procedure Call Steps in making a remote procedure call call The stubs are shaded Client makes a local procedure call an alternative to sockets Real time Real time Transport Protocol RTP Basic function support multiplexing of real time data streams into a single stream of UDP packets Header field specifies encoding May include timestamps give relative time for each packet for synchronization of audio and video and to help reduce
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