N Tier Client/Server Concepts

1. N Tier Client/Server Concepts Norman White Stern School of Business Csntier.ppt

2. Agenda • Background • Hardware concepts • Data communications • TCP/IP • Physical networks • Database management systems

3. But First, Some Background • Computer Fundamentals (hardware, software) • Data Communications • Networking … For more background take B20.2317 Information and Internet Technologies

4. Hardware Components

5. Primary Hardware Components • Processor • Primary Storage (RAM) • Secondary Storage • Disk, tape etc. • Data Channel(s) • I/O Controllers • Other Peripheral devices

6. Components registers Processor R Memory (RAM) Data Channel video controller disk

7. Processor • Executes and decodes instructions • Different Processors understand different sets of instructions • Instructions are stored in primary storage and brought into the processor to execute • Processor also has local storage called registers, this is where arithmetic is done

8. Registers • How many • More registers are better • Means more info is in the processor so it can be processed faster • Sizes (bits/bytes etc..) • Larger registers mean you can manipulate more information at a time • Less need to retrieve information from memory

9. Instruction Set • Types of instructions • Instruction set is the complete set of machine language instructions that the computer understands • RISC computers (Reduced Instruction Set Computers) have very simple instructions that can be executed very quickly. Simple design means less cost, power. More software.

10. Data Channel • Used to transfer information between different system components • Most PCs have one main channel ( “the system bus”) • Mainframes have many data channels, allowing them to transfer large amounts of information between components

11. I/O Controllers • Controllers are used to manage a class of devices, like disk drives • Each type of device has its own controller (E.G. VGA card, serial card etc.) • Controllers send information to memory across the data channel • Controllers handle the idiosyncracies of different devices

12. Secondary Storage • Peripheral devices that can hold information for later retrieval • Disk, Tape, CDROM, diskettes

13. Software Concepts • Software is the program that you run on the computer • Two major types • Application Software – Accomplishes a business purpose • Examples Word, Access, Excel • Systems Software – Aids in running/developing applications • Operating Systems – Windows, NT, Unix, Linux • Languages – C, C++ Java, Cobol, Visual Basic etc. • Utilities

14. DATA COMMUNICATIONS Some Basics

15. Communication Components telephone cable satellite • SOURCE • SINK • MEDIUM MEDIUM SOURCE SINK

16. Communications Media • Telephone • Satellite • Cellular • Cable • Fiber Optic • Infrared • etc.

17. Analog / Digital • Analog • Represent information as a waveform • Music, video,voice • Digital • Represent Information as a string of bits • Digitization • Convert from analog to digital by sampling the waveform at fixed intervals • ISDN phone line 64000 bits per second • 8000 samples per second (each sample an 8 bit (0-255)) Number

18. Modems modulator/demodulator • Converts Digital signal to analog so it can be sent over phone lines • Reconverts analog to digital on other end 1 1 1 0 0 0 0 0 01110000

19. Digital Communications • ISDN - Integrated Services Digital Network • New communications will allow full digital communications, higher bandwidth, fewer errors ($30/mnth in NJ) • Cable et al. • Very high digital bandwidths to your home • Fiber Optic • Country backbone network already digital • ADSL • Asymmetric Digital Subscriber Line – uses existing copper

20. Communications Protocols • Need rules to communicate between systems • Communications protocols are the rules for a particular method of communication • Who says what, when • How are errors handled • How much information in a message • How is message routed from sender to receiver

21. Asynchronous vs. Synchronous Protocols • Asynchronous - A single character is a message • Errors sometimes detected, but no recovery • Horizontal parity used to detect single character errors • Synchronous - A group of characters constitute a message • Synchronous protocols usually recover from errors

22. Types of Synchronous protocols • Bisynchronous • Point to point conversation • Not used much any more • Each message is acknowledged as received • Multilateral protocols • Messages routed from one machine to another • Message includes address of destination • Needs to be routed by intermediate nodes

23. TCP/IP Model • Application Layer – Applications and processes that use network • Host-host Transport Level – end to end data delivery • Internet layer – defines the datagram and handles data routing • Network Access layer – routines for accessing physical networks

24. TCP/IP Protocol of the Internet

25. History • Originally developed as a protocol that would withstand wide network outages (Arpanet) • Now it has become the standard protocol for almost all data communications • Consists of two parts, IP ad TCP

26. TCPTransmission Control Protocol • Handles communications between 2 processes anywhere on internet • Guarantees correct data is received by receiver • Uses IP for delivery and routing of packets

27. Packets/Datagrams • Fixed size blocks of information that are sent using TCP • Packet includes information like • Address of host to send this to • Address of host it is coming from • Destination Port Number • Sending Port Number • MAC address of sender/receiver (hardware address) • Sequence info • Data

28. IP - Internet Protocol • Handle datagrams • Defines Internet addressing scheme • Routes datagrams to remote hosts • Performs fragmentation and reassembly of datagrams

29. IP Addressing • Every host has an address in the form of www.zzz.yyy.zzz (the “IP” address) • Each subcomponent refers to a particular breakdown of all of the machines on the internet. • 128.122.197.133 = sales.stern.nyu.edu • 128 = edu domain • 122 = nyu network • 197 = subnet at stern • 133 = address of sales computer

30. Name Resolution • The TCP/IP protocols include the concept of “name lookup”, where names like sales.stern.nyu.edu are translated into their numeric addresses • (128.122.197.133) • Hence one has to specify the locations of the “name servers” you wish to use.

31. Gateways • Gateways (also called IP routers) are the computers used to connect your network to the internet

32. Sockets and ports • TCP/IP uses “ports” to connect services between machines • The destination machine has particular ports offering different types of service • 23 = telnet , 80 = WWW etc. • Client machine uses random port • Combination of destination port and originating port = socket (i.e a destination port that is in use)

33. Standard TCP/IP Services • telnet - 23 • rlogin • ftp - 21 • NFS - Network File Service - 2049 • Talk - 517 • Ping - • Finger - 79 • Sendmail - 25

34. Other TCP/IP Services • World Wide Web (usually port 80) • Hyper media interface to internet • Connects clients and servers using HTTP • Hyper Text Transfer Protocol • Subset of the internet • Hottest area right now • Cuseeme, Netmeeting • Interactive video

35. TCP/IP Problems • Current standard has several major problems • Address space limitations • xxx.yyy.www.zzz limits number of nodes • Out of space in another year or so • No Quality of Service guarantees • Difficult to stream audio/video etc • Need client and server to be able to negotiate quality of service, especially for streamed multimedia

36. Summary • TCP/IP is the “language” of the internet • Many other services are based on the basic TCP/IP support • All of these services are “client/server” • Like the WWW • WWW uses HTTP (Hyper Text Transfer Protocol) • New Version of TC/IP IPv6 coming

37. Physical Networks

38. Types of Physical Networks • Star • All nodes connected to a central point which routs information • Inexpensive • Prone to failure • Bus • All nodes connected to a single cable • All message seen by all station simultaneously • Cheap, throughput limited at high volumes • Ring • Messages passed from on machine to the next

39. Packet Switched Networks • Problem – How do we fully connect thousands of computers together? (How many wires?) • 2 computers – 1 • 3 computers – 3 • 4 computers - 6 • 5 computers – 10 • N computers – (N*(N-1)/2) • 1000 computers – about .5 million connections • Solution • Don’t connect every computer to every other computer, instead “route” information from one computer to another

40. Packet Switched Network N - 1 Connections Add more connections for redundancy

41. Network Communication Protocols • Protocol • Rules to follow telling each computer what to send where, when • Packet switched protocols include routing of packets from source to destination • Protocols also define rules to follow if there are errors, I.e. how to recover, retransmit etc.

42. Higher level protocols • Low level protocols route packets (of bits) around the network. Packets include address • High level protocols know what the packets contain • TCP/IP client server protocols • Client sends requests over network to a “server” program running on another computer • WWW C/S application

43. Client Server Concepts • A program on one computer (the Client) can request services from a program on another computer (the Server) • Client issues requests to a server someplace on the network • Requests are specially formatted messages which can be understood by almost any type of computer • Requests are sent using a “standard” telecommunications protocol

44. CS Concepts • Server responds with a message in the “standard” format • Client receives message and processes it

45. Example – WEB Requests • In the WWW model, the client is the browser (Netscape, I.E.) running on your computer • The server is the web server running somewhere on the internet • Both the client and server must be connected through a TCP/IP communications network

46. N Tier Client Server • The situation gets more complex, if the initial (Tier 1) server in turn becomes a client and requests services from another server in order to process the web request. There are now 3 programs running on 3 different computers involved in the processing of the web request.

47. Client Server User Web Browser Web Server Data Base Server

48. Issues in Client/Server • Fast developing standards • Isolates users from mainframe architecture • Enables application specific machines • Heterogeneous software and hardware • Subtle performance issues

49. Advantages • Application code is “closer” to the user • Application/server independence • Portability • Scalability • Performance ?

50. Performance Issues • Client App needs to be optimized for C/S • Client only goes to server when necessary • Not well suited for high-update environment • Good for applications with relatively static data