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PC Networks 2 Elements of a PC Network


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PC Networks 2 Elements of a PC Network

  1. 1. PC Networks
  2. 2. Elements of a PC Network Client PC Client PC Client PC
  3. 3. Client PCs <ul><li>Sit on desks of ordinary managers, professional, or clerical workers </li></ul><ul><li>Usually begin life as stand-alone PCs </li></ul><ul><li>Add a Network Interface Card (NIC) </li></ul><ul><li>If operating system is not network-capable, must add client shell software </li></ul><ul><li>Do not confuse with client process </li></ul>
  4. 4. Client Operating System <ul><li>Some PC operating systems are already network-capable </li></ul><ul><ul><li>Windows 95, NT </li></ul></ul><ul><ul><li>No need to add additional software </li></ul></ul><ul><li>Other client operating systems are not network-capable </li></ul><ul><ul><li>Add client shell software </li></ul></ul>
  5. 5. Servers <ul><li>Provide services to client PCs </li></ul><ul><li>Usually High-End PCs </li></ul><ul><ul><li>Add NIC </li></ul></ul><ul><ul><li>Add Server Operating System </li></ul></ul><ul><ul><li>Add service software </li></ul></ul><ul><li>Can be low-end PCs for light services </li></ul><ul><li>Can be a UNIX workstation server </li></ul><ul><li>Can even be a mainframe or minicomputer </li></ul>Examples : Dell , HP , Sun
  6. 6. Server Specialization <ul><li>Most PC networks have multiple servers </li></ul><ul><ul><li>In a network with 200 client PCs, there are likely to be 10-20 servers of different types </li></ul></ul><ul><li>Why so many? Because servers are usually specialized by services </li></ul><ul><ul><li>Optimized for needs of each service (power, disk drive access, etc.) </li></ul></ul><ul><ul><li>Less expensive than using single large server </li></ul></ul><ul><ul><li>If one crashes, all do not crash </li></ul></ul>
  7. 7. Server Specialization <ul><li>However, some offer multiple services </li></ul><ul><ul><li>File storage </li></ul></ul><ul><ul><li>Remote printing </li></ul></ul><ul><ul><li>E-mail, etc. </li></ul></ul><ul><li>The decision of how much to specialize each server is a matter of tradeoffs between the cost of adding a new server and the benefits of specialization. </li></ul>
  8. 8. Main Types of Servers <ul><li>File Server </li></ul><ul><ul><li>Stores program and data files (acts like large hard disk drive) </li></ul></ul><ul><ul><li>Programs run via file server program access </li></ul></ul><ul><ul><ul><li>E-mail </li></ul></ul></ul><ul><ul><ul><li>Word processing, etc. </li></ul></ul></ul><ul><ul><li>Also handles remote printing </li></ul></ul><ul><ul><li>Usually a fairly high-end PC </li></ul></ul>
  9. 9. Main Types of Servers <ul><li>Application Server </li></ul><ul><ul><li>Runs server program in client/server processing </li></ul></ul><ul><ul><li>May be a workstation server rather than a PC, because client/server processing is platform-independent </li></ul></ul><ul><ul><li>Database </li></ul></ul><ul><ul><li>Webserver </li></ul></ul>Example : Oracle
  10. 10. Main Types of Servers <ul><li>Communication Server </li></ul><ul><ul><li>For communication into, out of the PC network </li></ul></ul><ul><ul><li>Dial in from home </li></ul></ul><ul><ul><li>Go out to the Internet, a remote host computer, etc. </li></ul></ul>
  11. 11. Main Types of Servers <ul><li>Directory Server </li></ul><ul><ul><li>Knows locations of all resources on all servers </li></ul></ul><ul><ul><li>Can be used to search for resources </li></ul></ul><ul><ul><li>Can give user access to resources for which the user has access rights </li></ul></ul>Example : Novell
  12. 12. Server Operating System <ul><li>Servers Need Operating Systems </li></ul><ul><ul><li>Service applications run on these OSs </li></ul></ul><ul><ul><li>Optimized for running server services </li></ul></ul><ul><ul><li>Different optimization needs than client OSs </li></ul></ul><ul><li>Usually Bundled with Some Applications </li></ul><ul><ul><li>Email, webserver, etc. may be included </li></ul></ul><ul><li>Usually Bundled with Management Software </li></ul><ul><ul><li>May buy more from third parties </li></ul></ul><ul><li>Server licenses </li></ul>
  13. 13. Server Operating Systems <ul><li>Novell NetWare </li></ul><ul><ul><li>Old market leader, less than 40% market share </li></ul></ul><ul><ul><li>New sales: Netware 30%, Windows 40%, UNIX/Linux 30% </li></ul></ul><ul><ul><li>Strong in directory service </li></ul></ul><ul><ul><ul><li>NetWare Directory Services </li></ul></ul></ul><ul><ul><ul><li>NetWare strongest in mid-sized firms </li></ul></ul></ul><ul><ul><li>Newest versions called InterNetware </li></ul></ul><ul><ul><li>Limited to PC servers </li></ul></ul>NetWare
  14. 14. Server Operating Systems <ul><li>UNIX/Linux </li></ul><ul><ul><li>70% of market for webservers, database application servers </li></ul></ul><ul><ul><li>Can run on workstation servers </li></ul></ul><ul><ul><li>Weak in file service </li></ul></ul><ul><ul><li>Difficult to administer: must hire new staff or retrain existing staff </li></ul></ul><ul><ul><li>Dominant in large size organizations </li></ul></ul>UNIX
  15. 15. Server Operating Systems <ul><li>Microsoft Windows NT/2000 Server </li></ul><ul><ul><li>Relatively new </li></ul></ul><ul><ul><li>Easy to use, because based on Windows </li></ul></ul><ul><ul><li>Priced attractively (Linux a threat) </li></ul></ul><ul><ul><li>Can run on PCs or workstation servers </li></ul></ul><ul><ul><li>Webserver software included </li></ul></ul><ul><ul><li>Growing rapidly </li></ul></ul><ul><ul><li>Now has directory service needed for large firms </li></ul></ul><ul><ul><li>Strongest in small firms, department servers </li></ul></ul>Windows NT Server
  16. 16. Server Operating Systems <ul><li>A single PC network may have servers with different OSs </li></ul><ul><ul><li>NetWare file servers </li></ul></ul><ul><ul><li>NetWare directory servers </li></ul></ul><ul><ul><li>Windows webserver </li></ul></ul><ul><ul><li>UNIX database server </li></ul></ul>NetWare Windows Server UNIX
  17. 17. Service Application Software <ul><li>The heart of PC networking </li></ul><ul><li>File service (store, retrieve files) </li></ul><ul><li>Electronic mail service </li></ul><ul><li>Database service </li></ul><ul><li>Web service </li></ul><ul><li>Communication service </li></ul><ul><li>Costs much more than the NOS </li></ul>Examples: Microsoft BackOffice and IBM Lotus Software
  18. 18. Transmission Network <ul><li>Need not be a LAN </li></ul><ul><ul><li>Can be a local internet or enterprise internet </li></ul></ul><ul><ul><li>It may link thousands of client PCs and hundreds of servers </li></ul></ul><ul><ul><li>So PC networking is not the same as local area networking </li></ul></ul>
  19. 19. Independent Server Operating System Client A Database Server X File Server Y File Server Z Login to Server X Simultaneous Login to Server Y File A
  20. 20. Independent Server Operating System <ul><li>Servers do not even know that others exist </li></ul><ul><li>Easy on network administrators, who do not have to manage all information on an integrated basis </li></ul><ul><li>Hard for users who have to know what server holds a target file, then log into that server </li></ul><ul><li>Hard for users who have to know what server runs what service, then log into that server </li></ul>
  21. 21. Synchronized Server Operating System Client A Directory Server X File Server Y File Server Z Synchronized Server Network Synchronizing Messages Single Login to Directory Server File A
  22. 22. Synchronized Server Networks <ul><li>Directory server maintains list of all resources </li></ul><ul><li>Easy on user: login once, to directory server. Access to all resources. </li></ul><ul><li>Easy on user: no need to ask which server has the file or service </li></ul><ul><li>Harder on network administrator, who must plan and manage an integrated directory </li></ul>
  23. 23. Communication Between Client PC and Server LAN Internetting Transport Application LAN Internetting Transport Application LAN Protocol IP or IPX TCP or SPX Service Windows PC Server PC networking is an application layer issue
  24. 24. Communication with Three Servers Client PC Windows NT Server Server UNIX Server NetWare File Server IPX/SPX TCP/IP TCP/IP ODI NDIS NFS
  25. 25. Communication with Multiple Servers Adaption Layer Software NIC Printing through NetWare Server Request for data to UNIX server Multiplexes Transmissions Places inside subnet (802.2, 802.3)frames SPX, NCP IPX TCP IP IPX/SPX Protocol Stack TCP/IP Protocol Stack
  26. 26. File Service Local Drives A: B: C: Virtual Drives F: S: Y: Z: File Save and Retrieve Commands; Disk Management Commands Client PC File Server File Save and Retrieve Commands; Disk Management Commands Virtual drives are directories on the file server’s hard disk drives
  27. 27. Data File Storage: Backup A C File Server B Network Administration PC Tape Backup Unit File Saves Backup
  28. 28. Backup <ul><li>End users rarely back up their hard disks </li></ul><ul><li>File servers usually are backed up nicely </li></ul><ul><li>Storing files on a virtual drive means that they will be backed up </li></ul><ul><li>A real problem in large installations (think about UBmail with 5,000 user accounts) </li></ul>Tape backup
  29. 29. Virtual Drive Access from Anywhere Own Desktop PC Notebook in Car or Hotel PC at Home Files On Virtual Drive H: PC in Another Office File Retrieval
  30. 30. Shared Virtual Drive Haraj Sidhu Tod Kimura Shared Virtual Drive (S:) Luz Ochoa No Access X Save Retrieve
  31. 31. Shared Virtual Drives <ul><li>Potential Problem </li></ul><ul><ul><li>First A retrieves and edits the file </li></ul></ul><ul><ul><li>Then B retrieves and edits the file </li></ul></ul><ul><ul><li>Then A saves </li></ul></ul><ul><ul><li>Then B saves </li></ul></ul><ul><ul><li>Whose changes are now in the file? </li></ul></ul><ul><li>Locking </li></ul><ul><ul><li>When one person starts to use a file, it is locked </li></ul></ul><ul><ul><li>Nobody can change it </li></ul></ul><ul><ul><li>Others, however, can read the old version </li></ul></ul>
  32. 32. Program Storage on a File Server Single Copy of Program Stored On Virtual Drive Z Small &quot;Stub&quot; Program on Client PC Download for Execution vs Winstal l
  33. 33. Program Execution Via File Server Program Access Network Client PC RAM and Processor Program Client PC Hard Disk Drive File Server Hard Disk Drive Server RAM and Processor Copy from Server Disk to Client RAM for Execution Client PC File Server
  34. 34. Redirection in a Network-Capable Operating System Network-Capable Operating System Application Program 2. Calls for Local Drives (C:) are Handled by the Client Operating System PC Hardware Network Interface Card 1. Call to access data file (includes name of drive)
  35. 35. Redirection in a Network-Capable Operating System Application Program 3. Calls for Virtual Drives (F:) are Redirected to the File Server PC Hardware Network Interface Card File Server via Network Network-Capable Operating System
  36. 36. Print Service Client PC Printer File Server with Print Queue Network Print Server Printout goes from the client PC to a print queue on the file server, not to the print server. A print queue is a directory with associated control software Printout goes from the print queue to a print server . Network Printers
  37. 37. Client/Server Processing Network Client PC Application Server (need not be a PC) Client Program (Excel) Server Program (Oracle) Request Response Application Layer Interactions Concepts: introduction and details
  38. 38. Program Processing <ul><li>File Server Program Access </li></ul><ul><ul><li>Processing is done only on client PC </li></ul></ul><ul><ul><li>File server stores program </li></ul></ul><ul><ul><li>Limited to small programs </li></ul></ul><ul><li>Client/Server Processing </li></ul><ul><ul><li>Processing shared by client PC and server </li></ul></ul><ul><ul><li>Application server rather than file server </li></ul></ul><ul><ul><li>Good for larger applications </li></ul></ul><ul><ul><li>Platform independent </li></ul></ul>
  39. 39. Remote Access Server Remote Client PC Remote Access Server Modem Modems Telephone Line Remote Access Software LAN NT FAQ - RAS
  40. 40. Remote Access <ul><li>Remote Control Software </li></ul><ul><ul><li>Remote control server acts like a PC attached to the network locally. Processing is done on access server. </li></ul></ul><ul><ul><li>What appears on the remote access server “screen” appears on the remote screen </li></ul></ul><ul><ul><li>Simple but very slow: screen images must travel across network </li></ul></ul>Example : pcAnywhere PC Network Remote PC Access Server
  41. 41. Remote Access Server <ul><li>Remote Node Service </li></ul><ul><ul><li>Remote PC is a full network node </li></ul></ul><ul><ul><li>Processing is done on the remote PC, for fast screen changes </li></ul></ul><ul><ul><li>File opens and saves cause file transfers over network </li></ul></ul>PC Network Access Server File Server Remote PC outside of the network
  42. 42. Gateway Server 53 IBM Mainframe Synchronous Communication Gateway Server SNA Communication IPX/SPX Communication Gateways translate between networks with different standards architectures -- in this case, IPX/SPX and SNA Client PC inside the network
  43. 43. Internet Access <ul><li>Client PC connects to router </li></ul><ul><ul><li>Connection is via TCP/IP </li></ul></ul><ul><ul><li>Router links user to the Internet </li></ul></ul>Router TCP/IP Communication Connection to the Internet
  44. 44. Connecting to the Internet <ul><li>Firewall </li></ul><ul><ul><li>Stands between Internet and the company </li></ul></ul><ul><ul><li>Limits unauthorized access </li></ul></ul>Router TCP/IP Communication Connection to the Internet