© 2001 by Prentice Hall7-1 Local Area Networks, 3rd Edition David A. Stamper Part 3: Software Chapter 7 LAN System Software

© 2001 by Prentice Hall 7-2 Chapter Preview Generic LAN system software functions Workstation system software functions Server system software functions Printer software Backup software In this chapter you will study:

© 2001 by Prentice Hall 7-3 Server/Workstation Communications The first problem the workstation must address is connecting to a server. Once a client has a server connection, the user at the client can log onto the network. Depending on the LAN OS being used, a user can log onto a single server, a collection of resources called a domain, or the entire corporate network. Regardless of the environment—single server, domain, or network directory—the user’s network software must find a server resource that can authenticate the logon request.

© 2001 by Prentice Hall 7-4 Server/Workstation Communications (cont.) The address of the server with which the workstation must communicate is essential because the address is part of the data link message header. The network layer protocols determine the format of addresses. Leading transport/network layer protocols include the transmission control protocol/internet protocol (TCP/IP) used on the Internet, and the sequenced packet exchange /internet packet exchange (SPX/IPX) protocol used on many Novell and Microsoft LANs.

© 2001 by Prentice Hall 7-5 IP and IPX Header Formats Version IP Header Length Destination Address Source Address Header Checksum Type of Service Packet Length IdentificationFlags Fragment Offset Time to Live Protocol Checksum Source Socket Source Node Source Network Length Transport Control Packet Type Destination Network Destination Node Destination Socket IP Header IPX Header

© 2001 by Prentice Hall 7-6 Services Advertising Protocol In Novell NetWare LAN implementations, the services advertising protocol (SAP) is implemented at the OSI application layer. Inherent in this protocol is the presence of a server table in each server and router. When the server is initiated, one of its startup functions is to broadcast a SAP message. A broadcast message has a distinct destination address that allows it to be accepted by all nodes. The SAP message identifies the server’s name, address, and the types of services it can provide.

© 2001 by Prentice Hall 7-7 A Generic Server Table MktgSvr AcctSvr SWDevSvr HRSvr MfgSvr RanDSvr ExOffL Unused File SQL File Printer A12B634A DDC3958B DD84A124 A12C583D 29837CAB 834AB3E7 5602C0A1 Server NameAddressServer TypeHops

© 2001 by Prentice Hall 7-8 The Network Directory In a large LAN with hundreds of users, hundreds of addresses, dozens of printers, and 5 to 10 servers, keeping track of the names and locations of people and equipment is a significant effort. A network directory is fundamentally a database of LAN objects, properties of those objects, and values for properties.

© 2001 by Prentice Hall 7-9 Possible Contents of a Network Directory Server User Printer Disk volume Network address Full name Location Print server Server name Manufacturer Location Telephone address Operator name Capacity Name Login name Address Name Print queues Name Interface ObjectProperties

© 2001 by Prentice Hall 7-10 Client/Server Dialogue Once the client and server have connected, a client/server dialogue can begin. When an application requests a service from the OS, it does so by issuing a signal called an interrupt. The redirector reacts to the interrupt and decides whether it is a LAN request or a local request. The redirector must know which interrupts to intercept. Once the redirector has the request, it must formulate a server message to indicate which service is to be provided. It formats a message with the proper request codes and sends the message to the LANCom process.

© 2001 by Prentice Hall 7-11 Redirector Implementations Client Operating System Redirector LANCom Application Program Redirector receives application requests and routes local request to the client OS and network request to LAN communication process.

© 2001 by Prentice Hall 7-12 Redirector Implementations (cont.) Client Operating System Redirector LANCom Application Program Client OS gets request and sends network requests to the redirector.

© 2001 by Prentice Hall 7-13 LAN Operating System Functions Optimized I/O – One of the main services provided by a server is disk access. Disk access consists of three components: seek, latency, and transfer. I/O optimization attempts to reduce one or more of these disk access components. Disk Configurations – One of the functions of an OS is to implement a file system. This involves allocating and deallocating disk space and keeping track of space allocated to each file. – Partitioning sometimes it is beneficial to divide a single disk drive in two or more partitions; each partition can be managed separately

© 2001 by Prentice Hall 7-14 LAN Operating System Functions (cont.) – Single Disk Volume a volume is a logical disk (a partition or collection of partitions) or physical disk that has been formatted and can be used to store data by an OS. – Multiple Disk Volumes or Volume Sets Most LAN OSs allow multiple partitions or disks to be combined to form a single logical partition. A volume created from multiple partitions is called a volume set. – RAID Level 0—Striping without parity Another capability provided with some LAN OSs is called a Redundant Array of Inexpensive Disks (RAID) Level 0 or striping without parity. Multiple partitions on different disks can be combined to proved a single logical disk; striping with parity differs from a volume just described in that data is written to all partitions simultaneously.

© 2001 by Prentice Hall 7-15 Fault Tolerance A LAN with fault tolerance allows the server to survive some failures that would ordinarily be disabling. Fault tolerance usually is provided by a combination of backup hardware components and software capable of using the backup hardware. A level of fault tolerance also can be provided by using redundant arrays of inexpensive disks (RAID). There are six levels of RAID, but for fault tolerance we are concerned only with RAID Level 1 and RAID Level 5.

© 2001 by Prentice Hall 7-16 Mirrored Disk Drives Controller 1Controller 2 File 1 File 2 Duplexed Controllers 1 2

© 2001 by Prentice Hall 7-17 Raid Level 5 Technology File 1 Part 1File 1 Part 3File 1 ParityFile 1 Part 2 File 2 Part 2File 2 Part 3File 2 Part 1File 1 Parity Server 1 234

© 2001 by Prentice Hall 7-18 A Fault-Tolerant Duplexed Server Dedicated High-Speed Connection Duplexed Servers Disk Drive Mirrored Disk Drives

© 2001 by Prentice Hall 7-19 Logical and Physical Printers In discussing the operation of a printing environment, we need to make a distinction between logical printing and physical printing. The application’s job stream is sent to a logical printer. Logical printers collect print streams from one or more applications. Logical printers are connected to zero, one, or several physical printers that Microsoft call a printing device.

© 2001 by Prentice Hall 7-20 LAN Printing Configurations Because printing requirements vary among companies using LANs, a wide range of implementation options exist. Among these are: – Private printers attached to a user’s computer and not shared – Shared printers attached to file servers – Shared printers attached to users’ workstations – Shared printers attached to computers that are dedicated to the printing task – Shared printers attached to special-purpose print servers – Shared printers attached directly to the LAN via an on-board LAN adapter and print server

© 2001 by Prentice Hall 7-21 Some Spooler Options Collect printed output Hold hobs in disk queue after printing View jobs on hold in print queue Delete jobs from print queue Se/change job priorities Start/stop printers Print banners Print statistical reports Direct print jobs to designated printers Hold jobs in disk queue before printing Set number of print copies Attach/detach printers from print queue Add/delete printers Start/stop spooler process Close print jobs based on time- out interval

© 2001 by Prentice Hall 7-22 Backup Software The software used to perform the backups is as important as the hardware. Backup software is responsible for reading the files being backed up and writing them to the backup device. Backup devices often come with a backup/restore program (both capabilities are contained on one program), and most LAN system software includes a backup/restore module. Some LAN administrators choose to purchase a separate, more functional backup system than the LAN or backup device versions.