Net CECS 327
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This 30 page Class Notes was uploaded by Zackary Cronin on Monday October 5, 2015. The Class Notes belongs to CECS 327 at California State University - Long Beach taught by Jeho Park in Fall. Since its upload, it has received 37 views. For similar materials see /class/218750/cecs-327-california-state-university-long-beach in Computer Science and Engineering at California State University - Long Beach.
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Date Created: 10/05/15
What is Netcentric Computing 0 Google it on the Web and the top result is 0 Cole March 2001 By quotnetcentric computingquot I mean connected computing Netcentric computing isn39t communications or networking per se although it certainly includes both Bernard Cole is the author of The Emergence of NetCentric Computing The article can be found at httpWWW embedded com coumnsnetcentricvie W99000 77 Distributed Computing An Introduction week 1 Different Forms of Computing Monolithic Computing single computersingle user no network or timesharing multiuser terminal mainframe Distributed Computing multiple networked computer workstation user you Parallel Computing multiple processing units for a single program Cooperative ComputingGrid Computing search for ET using surplus CPU cycle Distributed system distributed computing 0 Early computing was performed on a single processor Uniprocessor computing can be called centralized computing 0 A distributed system is a collection of independent computers interconnected via a network capable of collaborating on a task 0 Distributed computing is computing performed in a distributed system Distributed Computing An Introduction week 1 Distributed computing 0 WWW Email FTP etc network services 0 Ecommerce auction chatrooms VoIP and network games etc network applications Distributed Computing An Introduction week 1 Distributed systems an example work stati Ons I a network host Distributed Computing An Introduction week 1 Centralized vs Distributed Computing Why distributed computing 0 Economics distributed systems allow the pooling of resources including CPU cycles data storage inputoutput devices and services 0 Reliability a distributed system allow replication of resources andor services thus reducing service outage due to failures 0 The Internet has become a universal platform for distributed computing The Strengths and Weaknesses of Distributed Computing The affordability of computers and availability of network access 0 Multiple Points of Failures Resource sharing 0 Security Concerns Scalability Fault Tolerance Summary on basics really What is Netcentric Computing Different forms of computing Distributed system distributed computing Advantage and disadvantage of distributed computing For the next class you will 0 read Chapter 1 0 find a joke or two about Netcentric computing CECSS27 Spring 2009 The Client Server Paradigm 5 Instructor Dr Jeho Park Iterative servers Vs Concurrent servers Concurrent Server 0 A connection oriented server can be threaded so that it can service multiple clients concurrently Such a server is said to be a concurrent server 0 An unthreaded connection oriented server is said to be an iterative server A Concurrent Connection oriented Server A client process at the head of the connection queue server host concurrert server process 5 k the server connection queue n 39n e 39n the main thread accepts39c39mnections T a child thread processes i the protocol for a A chent process Whose connectlon has been accepted client process A client process whose connection has been accepted Sequence diagram EchoServer3 gm mr pue wmm wow B me Q m n B l l l l l l l l l l l l l l l l l l l l l l l l a u gt m C E A Q n B l l l l l l l l l l l l l Ellllllll l l C gt gt m C e E w l o S h e m m llll mllllllltll llll s N N lt lt I I I I I I I I I I I I I I I I I I II s om e W e Ill II I I I I I I I I I I I I I I I I I I I I I I II S m C E EchoSenerS concurrent excerpt ServerSocket myConnectionSocket new ServerSocketCserverPort while true forever loop MyStreamSocket myDataSocket new MyStreamSocketCmyConnectionSocketacceptC D Thread theThread new Threaanew ServerThreadeyDataSocket theThreadstart end while forever SenerThreadjava excerpt class ServerThread implements Runnable static Final String endMessage quotquot39 MyStreamSocket myDataSocket EchoServerThreadCMyStreamSocket myDataSocket thismyDataSocket myDataSocket public void run boolean done False String message try put in here the logic For each client session while done message myDataSocketreceiveMessageC iF messagetrimequals endMessage myDataSocketclose done true end if else myDataSocketsendMessageCmessage end else end while done end try catch Exception ex end run end class Server Thread Class template class ServerThread implements Runnable static Final String endMessage quotquot MyStreamSocket myDataSocket ServerThreadCMyStreamSocket myDataSocket thismyDataSocket myDataSocket public void run boolean done False String message try add code here end try catch Exception ex SystemoutprintlnquotException caught in thread ex end run end class Stateful servers vs Stateless servers Stateful server 0 A stateful server maintain arirnii on each active client lGlobaI state information Session state information I 0 State information can reduce the data exchanged and thereby the response time Global State Information State information maintained by the server for all the clients throughout the lifetime of a server Eg counter protocol Session State Information For some protocols or applications a server must maintain information specific to a client during its service session Consider a network service such as file transfer ftp A file is typically transferred in blocks reguiring several rounds of data exchanqes to complete the file transfer The dialog during a session proceeds roughly as follows Client Please send me the file foo in directory someDir Server Okay Here is block1 of the file Client Got it Server Okay Here is block2 of the file Client Got it Stateless vs Stateful server diagram Stateless Server Stateful Server 4 le ID le ID le pos1t1on le position GET le name GET le name le ID gt ready lt gt send le ID block 0 send next block data from week 0 Of le data from block 0 of file lt gt send le ID block 1 send next block data from block 1 of le gt data from block 1 of le no V 0 Stateless vs Stateful server 0 Stateless server is straightforward to code servers process each request in the same manner 0 Stateful server is harder to code but the state information maintained by the server can reduce the data exchanqed and allows enhancements to a basic service 0 Maintaining stateful information is difficult in the presence of failures Stateless vs Stateful server FIP Client le ID le position GET le name ready send next block data from block 0 of le data is lost due to network failure send next block client resubmits request data from block 1 of le client receives data as block 0 of le on the true block 0 is missed Session State Information 2 Another example of a stateful protocol is one for a shoopinq cart application Each session must maintain state data that keeps track of the identify of the shopper and the cumulative contents of the shopping cart Stateful vs stateless server 0 In actual implementation a server may be Stateless Stateful A hybrid wherein the state data is distributed on both the server side and the client side Which type of server should be chosen is a design issue Summary of ClientServer Paradigm The difference between the clientserver system architecture and the clientserver distributed computing paradigm Definition of the paradigm and why it is widely adopted in network services and network applications The issues of service sessions protocols service location interprocess communications data representation and event synchronization in the context of the clientserver paradigm The threetier software architecture of network applications Presentation logic application logic and service logic Connectionless server versus connectionoriented server Iterative server versus concurrent server and the effect on a client session Stateful server versus stateless server In the case of a stateful server global state information versus session state information
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