CMPE 150 Introduction to Computer Networks Dr Chane L Fullmer chane cse ucsc edu Spring 2003 UCSC CMPE150 1 Class Information Class web site www soe ucsc edu classes cmpe150 Spring03 Class Newsgroup ucsc class cmpe150 TA Section First session Monday 5 00PM Spring 2003 Baskin White Boards area UCSC CMPE150 2 Optional Class Project Network programming project In lieu of taking final examination Goal Build an FTP client server from scratch Using C language Details on web page now Due by June 4th Spring 2003 UCSC CMPE150 3 Homework Assignments Homework assignment 1 Problems from text at end of chapter See web page for problem numbers Due by April 8 next Tuesday Spring 2003 UCSC CMPE150 4 CMPE 150 Introduction to Computer Networks LECTURE 2 Introduction and Background Cont Spring 2003 UCSC CMPE150 5 Principles of Computer Communication Protocol specification The description of the protocol is complete and accurate Safety A protocol does what it is supposed to do all the time Liveness A protocol does not leave any deadlocks Efficiency A protocol makes efficient use of available resources Fairness Fair or contractual use of resources Simplicity is desirable but not necessary Spring 2003 UCSC CMPE150 6 Internet Elements R R R R R R R R R Hosts The computers running user applications clients servers proxies Routers bridges switches Devices used to interconnect hosts and to forward data from source to destination host Networks Aggregations of hosts and routers Links between devices Spring 2003 UCSC CMPE150 7 What Is The Internet protocols Internet network of networks router server workstation mobile local ISP loosely hierarchical public Internet versus private intranet regional ISP Internet standards RFC Request for comments IETF Internet Engineering Task Force Spring 2003 UCSC company network CMPE150 8 Internet Example What does it take to get a page from the web Your client computer and attached router have to be configured Host and router communicate with each other typically through a LAN Host obtains the IP address of remote server from a name resolver Host starts an end to end reliable connection with remote server TCP is the protocol used end to end Data is broken into packets which are routed from host to server and from server to back over a large number of links computers dedicated to routing and networks Today you typically wait for a long time some times the server comes back and tells you that the page has not been found Spring 2003 UCSC CMPE150 9 Layering Model Purpose is to divide and conquer complex software and hardware needed to implement services Partition services and functions needed in system into layers Each layer of service is provided by peer protocol entities Communication can be point to point or multipoint Layer N packets NODE A Layer N Protocol Entity virtual communication interface NODE B protocol Layer N 1 Protocol Entity Spring 2003 Layer N Protocol Entity Layer N 1 Protocol Entity UCSC CMPE150 10 The OSI Architecture Proposed by the International Standards Organization Specifies the functions at each layer not the protocols that implement them APPLICATION PRESENTATION SESSION TRANSPORT NETWORK LINK PHYSICAL Spring 2003 End user services e g mail file transfer Web access Formatting encryption compression of data Setup and management of end to end dialogue End to end delivery of messages to processes TCP End to end transmissions of packets in net IP Transmissions of packets over a link PPP CSMA CD Transmission of bit over physical media SONET UCSC CMPE150 11 Protocol Description Specify the service to be provided by the protocol Specify assumptions about environment Specify vocabulary messages needed in the protocol Specify the algorithms used to process and exchange information in the protocol Specify format of messages in vocabulary Spring 2003 UCSC CMPE150 12 Protocol Correctness A protocol must be safe and live Safety Liveness Protocol provides the desired service all the time Protocol has no deadlocks no process waits forever for an event to occur Proving one may depend on the other Spring 2003 UCSC CMPE150 13 Protocol Performance Average delay Throughput or capacity Time between transmission of an information bit and reception of the bit at the receiver Number of information bits sent divided by the time between transmission of first bit and delivery of the last bit Computations will make strong assumptions in most cases results of analytical model provide only a rough approximation Most effective for comparative analysis Spring 2003 UCSC CMPE150 14 Basic Network Services S 1 2 1 2 D All data flow along same path Shared network resources Connection oriented service Reliable data transfer In order delivery no duplicates or missing data Flow control Do not congest the receiver Congestion control Do not congest the network s Spring 2003 UCSC CMPE150 15 Basic Network Services S 1 2 2 2 2 1 1 2 1 1 D Data may take different paths to destination 1 Shared network resources Connection oriented service Reliable data transfer In order delivery no duplicates or missing data Flow control Do not congest the receiver s Congestion control Do not congest the network s Spring 2003 UCSC CMPE150 16 Basic Network Services S 1 2 3 2 1 3 D Shared network resources Connectionless service No delivery guarantees needed from the network Any connection oriented service to application is provided by end to end protocol Spring 2003 UCSC CMPE150 17 Switching Methods S D Shared network resources Allocation of shared network resources to the transport of user data Circuit switching and packet switching are the two main types we will consider Spring 2003 UCSC CMPE150 18 S Circuit Switching D call request call accept DATA call termination termination ack Portion of physical resource is assigned to a single connection Delay and signaling overhead in establishing and ending connections Spring 2003 UCSC CMPE150 19 Multiplexing in Circuit Switching Share a given communication channel among multiple connections Frequency division multiplexing FDM Frequency spectrum of a link is partitioned into multiple bands and each band is assigned to zero or one connection at any given time Time division multiplexing TDM Time is divided into frames of fixed duration and each frame is divided into a fixed number of time slots A connection is assigned to a time slot and occupies the same time slot for multiple frames Spring 2003 UCSC CMPE150 20 FDM and TDM Example FDM 4 users frequency time TDM frequency
View Full Document
Unlocking...