CMPE 150 Winter 2009 Lecture 15 Februaryy 26 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 Problem Assignment 6 On class web page this afternoon Due Tuesday March 3 Today s Agenda IIntro to T Transport LLayer Connections Berkeley Sockets QOS Addressing TSAP of TPDU Flow Control Buffering Protocols UDP RTP TCP Congestion management Timers RTT estimates Exponential backoff Text Readings Today Chapter 6 6 Sections 6 6 1 1 1 1 6 6 1 3 1 3 6 2 1 6 2 1 6 6 6 3 6 36 5 TCP Tuesday Chapter 6 6 Section 6 6 6 6 TCP Performance 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 Types of Transport Services Connection less versus connectionoriented Connection less C ti l service i no llogical i l connections no flow or error control Connection oriented Based on logical connections connection setup data t transfer f connection ti teardown t d Flow and error control Quality of Service User may specify QoS parameters at the transport layer At connection setup time time user may define preferred acceptable and minimum values for various service parameters Transport layer determines whether it s possible to provide required p q service based on available network service s Transport Layer QoS Parameters 1 Connection establishment delay y time to establish connection Connection establishment failure probability probability connection is not established within maximum establishment time Throughput bytes transferred per second measured over a time interval interval Transport Layer QoS Parameters 2 Transit delay time between sending a message and receiving it on the other side measured by the transport entities Residual error ratio ratio of messages in error to total messages sent Priority way for user to indicate that some connections are more important Resilience probability connection is terminated due to congestion etc Transport Layer QoS Only few transport protocols provide QoS parameters Most just try to minimize residual error rate rate QoS parameters specified by transport user when connection is setup Desired and minimum acceptable values can be specified p Service negotiation Transport Service Primitives Allow transport users e e g g application programs to access transport service service Example connection oriented transport service primitives PRIMITIVE TPDU Sent Meaning LISTEN CONNECT SEND none listen for connection Connection Req try to establish connection DATA send data RECEIVE none waits it for f data d t DISCONNECT Disc Req try to release connection TPDU Transport protocol data unit Messages sent between transport entities TPDUs are contained in network network layer layer packets which in turn are contained in DLL frames Frame header Packet header TPDU header TPDU payload Transport Service Primitives 3 A state diagram for a simple connection management scheme Transitions labeled in italics are caused byy ppacket arrivals The solid lines show the client s state sequence The dashed lines show the server s state sequence Berkeley Sockets 1 Set of transport level primitives made available by Berkeley UNIX UNIX Server side SOCKET create new communication end point BIND attach local address to socket once server binds address clients can connect to it LISTEN listen for connection non blocking ACCEPT accept new connection SEND RECEIVE send and receive data CLOSE release connection Berkeley Sockets 2 Client side SOCKET create socket CONNECT try to establish connection SEND RECEIVE send and receive data y release CLOSE release connection symmetric Transport Layer Addressing Transport Layer Address Port TSAP Network Layer Address IP address NSAP Addressing TSAPs NSAPs and transport connections Transport Protocol Issues Addressing Address of the transport level transport level entity entity TSAP transport service access point analogous l tto NSAP NSAP Internet TSAP IP address local port Internet NSAP IP address There may be multiple TSAPs on one host Typically only one NSAP Transport Service Access Point Network Service Access Point Example 1 Finding g the time of day y from a time of dayy server Time Time of day of day server process on host 2 attaches itself to TSAP 122 and waits for requests e g through LISTEN Application process TSAP 6 on host 1 wants to find out the time of day issues CONNECT specifying TSAP 6 as source and TSAP 122 as destination Example 2 Transport p entity y on host 1 tries to establish transport p connection between its TSAP 6 and the TSAP 122 on host 2 Transport entity on host 2 contacts process on TSAP 122 if it agrees transport connection established t bli h d Finding Services 1 Well Well known known TSAP TSAP Time of day server has been using TSAP 122 forever so every users know itit Initial connection protocol special process server that th t proxies i for f less l well known services Process server listens to set of ports at the same time Users CONNECT to a TSAP TSAP and if there are no servers process server is likely to be listening It them spawns requested server Finding Services 2 Name or directory service service Name server listens to well known TSAP User sends service name and name server responds with service s TSAP New N services i need d tto register i t with ith name server Finding Fi di th the server s network t k address dd Hierarchical addresses solve this problem i e the NSAP is part of the TSAP Connection Establishment CONNECTION REQUEST and CONNECTION ACCEPTED TPDUs Problem delayed duplicates duplicates Duplicates can re appear and be taken as the real messages messages Solution messages age and are di discarded d d after ft some ti time need d tto discard ack s Maximum hop count Timestamp Avoiding Duplicates 1 Solution by Tomlinson 1975 Sunshine and dD Dalal l l 1978 1978 2 identically numbered TPDUs are never outstanding at the same time Bounded packet lifetime Each host has its clock Clock as a counter that increments itself itself bits counter bits
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