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