Understanding operating systems 5th ed ch10

Understanding Operating Systems Fifth Edition Chapter 10 Management of Network Functions

Learning Objectives The complexities introduced to operating systems by network capabilities Network operating systems (NOS) compared to distributed operating systems (DO/S) How a DO/S performs memory, process, device, and file management How a NOS performs memory, process, device, and file management Important features of DO/S and NOS Understanding Operating Systems, Fifth Edition

History of Networks Initial network creation Share expensive hardware resources Provide centralized information resource access Operating system development Network operating system first Distributed operating system followed More powerful Distributed processing Even greater centralized information access User collaboration Complete common tasks Understanding Operating Systems, Fifth Edition

Comparison of Network and Distributed Operating Systems Network operating systems (NOS) Local operating systems extend powers Handle interfacing details Coordinate remote processing Coordinate communications Between local operating systems Limitations No global control of memory management, process management, device management, file management Viewed as autonomous local functions No true distributed computing Understanding Operating Systems, Fifth Edition

Comparison of Network and Distributed Operating Systems (continued) Understanding Operating Systems, Fifth Edition

Comparison of Network and Distributed Operating Systems ( continued) Distributed operating systems (DO/S) Global assets controlled by operating system Provide unified environment Optimize whole network operations Construction Replicated kernel operating system Network and intricacies hidden from users Use network as single logical system Understanding Operating Systems, Fifth Edition

Comparison of Network and Distributed Operating Systems ( continued) Understanding Operating Systems, Fifth Edition

DO/S Development Entire network resource groups managed globally Negotiation- and compromise-based resource allocation Occurs among equally important peer sites Advantage No special server software on local machines Supports file copying, e-mail, remote printing Understanding Operating Systems, Fifth Edition

Memory Management Uses kernel with paging algorithm Tracks available memory amount Based on goals of local system Global system requirements drive local site policies and mechanisms Memory allocation and deallocation dependencies Scheduling and resource-sharing schemes that optimize network resources Understanding Operating Systems, Fifth Edition

Memory Management (continued) Extended role Memory requests: local and global source s Local level Page allocation based on local policy Global level Receives process manager memory requests for new or expanding client or server processes Uses local resources for memory garbage collection, compaction Decides most and least active processes Determines preemptive processes to provide space Understanding Operating Systems, Fifth Edition

Memory Management (continued) Functions Control demand Allocates and deallocates space requests based on network’s usage patterns Page fault handling Automatically brings requested page into memory Examine total free memory table before allocating space Understanding Operating Systems, Fifth Edition

Memory Management (continued) Functions (continued) Virtual memory management Allocates and deallocates virtual memory Reads and writes to virtual memory Swaps virtual pages to disk Locks virtual pages in memory and protects pages as needed Understanding Operating Systems, Fifth Edition

Memory Management (continued) Understanding Operating Systems, Fifth Edition

Process Management Provides policies and mechanisms Create, delete, abort, name, rename, find, schedule, block, run, synchronize processes Provide real-time priority execution if required Manages execution states READY, RUNNING, WAIT Each CPU in network Required to have own run-time kernel Understanding Operating Systems, Fifth Edition

Process Management (continued) Kernel Role Helps system reach operational goal s States Dependent on global system’s process scheduler and dispatcher System’s scheduling function (three parts) Decision mode Priority function Arbitration rule Understanding Operating Systems, Fifth Edition

Process Management (continued) Understanding Operating Systems, Fifth Edition

Process Management (continued) Decision mode Determines policies when scheduling resource Options: preemptive, nonpreemptive, round robin Priority function Scheduling algorithm policy assigning order given to processes in execution cycle Examples: most time remaining (MTR), LTR Arbitration rule Resolves conflicts between equal priority jobs Examples: last-in first-out (LIFO), FIFO Understanding Operating Systems, Fifth Edition

Process Management (continued) Job scheduling advances Theories Queuing theory Statistical decision theory Estimation theory Maximize system throughput using durations to compute and schedule optimal way to interleave process chunks Process functions Specific procedures Create, locate, synchronize, delete process Understanding Operating Systems, Fifth Edition

Process Management (continued) Process functions (continued) Create process PCB with additional information identifying network location Locate process Uses system directory or process searching kernel queue spaces Requires interprocess communications support Synchronize processes Uses message passing or remote procedure calls Delete or terminate process Finds PCB, accesses it, deletes it Understanding Operating Systems, Fifth Edition

Process Management (continued) DO/S design Process-based DO/S Network resources managed as large heterogeneous collection Object-based DO/S Clumps each hardware type with necessary operational software into discrete objects Manipulated as a unit Understanding Operating Systems, Fifth Edition

Process Management (continued) Process-based DO/S Process management using client/server processes Synchronized and linked together through messages and ports (channels or pipes) Emphasizes processes and messages Providing basic features essential to process management Process management Single OS copy Multiple cooperating peers Combination of two Understanding Operating Systems, Fifth Edition

Process Management (continued) Process-based DO/S (continued) High-level cooperation and sharing Actions and data Synchronization is key issue in network process management Interrupts represented as messages Sent to proper process for service Understanding Operating Systems, Fifth Edition

Process Management (continued) Object-based DO/S System viewed as collection of objects Examples: hardware (CPUs, memory), software (files, programs), or combination Objects viewed as abstract entities Objects have a set of unchanging properties Process management becomes object management Processes act as discrete objects Two process management components Kernel level and process manager Understanding Operating Systems, Fifth Edition

Process Management (continued) Kernel level Provides basic mechanisms for building OS Dynamically creating, managing, scheduling, synchronizing, deleting objects Responsibilities Maintains network’s capability list s Responsible for process synchronization and communication support Communication between distributed objects Shared data objects, message objects, control interactions Scheduler with consistent and robust mechanism Understanding Operating Systems, Fifth Edition

Process Management (continued) The Process Manager Creates own primitives If kernel does not have primitives Examples: test and set, P and V Responsibilities Creating , dispatching, scheduling objects Synchronizing object operations Object communication and deleting objects Kernel environment To perform above tasks Objects contain all their state information Understanding Operating Systems, Fifth Edition

Device Management Devices Opened, read from, written to, closed Device parameters initialized and status bits set or cleared Global, cluster, or localized basis Allocates and deallocates devices to users Only when process issues OPEN/CLOSE command Keeps global accounting of each network device Availability Understanding Operating Systems, Fifth Edition

Device Management (continued) Understanding Operating Systems, Fifth Edition

Device Management (continued) Process-based DO/S Resources controlled by servers Called “guardians” or “administrators” Responsibilities Accepting requests for service on individual devices they control Processing each request fairly Providing service to requestor Returning to serve others Understanding Operating Systems, Fifth Edition

Device Management (continued) Process-based DO/S (continued) Systems have clusters of resources Group control Configured around complex server processes Administrator process configured as Device Manager Includes software Accepts local and remote service requests Deciphers meaning, acts on them Server process One or more device drivers, Device Manager, network server component Understanding Operating Systems, Fifth Edition

Device Management (continued) Object-based DO/S Each device managed same way throughout network Physical device considered an object Surrounded by software layer Physical device manipulated by set of operations, mobilizing device to perform designated functions Objects assembled to communicate and synchronize If local device manager cannot satisfy user request, request sent to another device manager Understanding Operating Systems, Fifth Edition

Device Management (continued) Object-based DO/S (continued) Users No need to know if centralized or distributed network resources Device Manager object at each site Maintains current directory of device objects at all sites Understanding Operating Systems, Fifth Edition

File Management Provide transparent mechanisms Find, open, read, write, close, create, delete files Subset of database managers Distributed database management implementation Part of LAN Tasks Concurrency control Data redundancy Location transparency and distributed directory Deadlock resolution or recovery Query processing Understanding Operating Systems, Fifth Edition

File Management (continued) Understanding Operating Systems, Fifth Edition

File Management (continued) Concurrency control System ability to perform concurrent reads and writes Provided actions do not jeopardize database Provides serial execution view on database Data redundancy Makes files faster and easier to read Allows process to read copy closest or easiest to access Read request split into several different requests for larger file Understanding Operating Systems, Fifth Edition

File Management (continued) Data redundancy (continued) Advantage: disaster recovery easy Disadvantage: keeping multiple copies of same file up-to-date at all times Updates performed at all sites Location transparency and distributed directory Users not concerned with physical location of files Deal with network as a single system Provided by mechanisms and directories Map logical data items to physical locations Understanding Operating Systems, Fifth Edition

File Management (continued) Location transparency and distributed directory (continued) Distributed directory Manages data locations transparency Enhances data recovery for users Contains Definitions for stored physical data and logical structure Policies and mechanisms mapping the two Systemwide names of all resources and addressing mechanisms for locating and accessing them Understanding Operating Systems, Fifth Edition

File Management (continued) Deadlock resolution or recovery Critical issues in distributed systems Most important function Detect and recover from a circular wait Complex and difficult to detect because it involves multiple processes and multiple resources Strategies used by distributed system Detection, prevention, avoidance recovery Understanding Operating Systems, Fifth Edition

File Management (continued) Deadlock resolution or recovery (continued) Recognize circular waits System uses directed resource graphs Looks for cycles Prevent circular waits Delays transaction start until it has all resources Avoid circular waits Allows execution if transaction can run to completion Recovery System selects best victim, kills victim, reallocates its resources to the waiting processes Understanding Operating Systems, Fifth Edition

File Management (continued) Query processing Function of processing requests for information Increases effectiveness Global query execution sequences Local site processing sequences Device processing sequences Ensures consistency of entire system’s scheduling scheme Query processing strategy Integral processing scheduling strategy part Understanding Operating Systems, Fifth Edition

Network Management Provides concurrent processes policies Intrasite and intersite communication Responsibilities Locate processes in network Send messages throughout network Track media use Reliably transfer data Code and decode messages, retransmit errors Perform parity checking, do cyclic redundancy checks, establish redundant links Acknowledge messages and replies if necessary Understanding Operating Systems, Fifth Edition

Network Management (continued) Links processes (objects) together through port When communication needed Provides routing functions Keeps network use statistics Message scheduling, fault localizations, and rerouting Aids process time synchronization Systemwide clock Understanding Operating Systems, Fifth Edition

Network Management (continued) Process-based DO/S Interprocess communication transparent to users Responsibilities Allocating ports to processes Identifying every process in network Controlling message flow Guaranteeing transmission and acceptance of messages without errors Interfacing mechanism for every process Traffic operator: accepts and interprets send and receive commands Understanding Operating Systems, Fifth Edition

Network Management (continued) Object-based DO/S Easy intermode and intramode communications among cooperative objects No need to know receiver location Only receiver’s name Provides message’s proper routing to receiver Process invokes operation part of its local object environment Services usually provided at kernel level Understanding Operating Systems, Fifth Edition

Network Management (continued) Understanding Operating Systems, Fifth Edition

NOS Development NOS runs on server Performs network services Workstations called clients Network management functions Only when system needs to use network Focus on sharing resources Not running programs Factors for best NOS choice Applications to run on server Technical support required User’s training level Understanding Operating Systems, Fifth Edition

NOS Development (continued) Understanding Operating Systems, Fifth Edition

Important NOS Features Support Standard local area network technologies Client desktop operating systems Robust architecture adapting easily to new technologies Support every operating system in corporate information network Operate wide range of third-party software applications and hardware devices Support multiuser network applications software Blend efficiency with security Understanding Operating Systems, Fifth Edition

Major NOS Functions Function Transfer files between computers Example : FTP command Not true file sharing Must copy file to local disk Duplicates and wastes space Needs version control Anonymous FTP Files available to general public Advantage: Web for FTP Users know how to use browser Understanding Operating Systems, Fifth Edition

Summary NOS No full utilization of global resources available to all connected sites DO/S specifically addressed NOS failure Specific requirements Secure from unauthorized access Accessible to authorized users Monitor available system resources Communications links Perform required networking tasks Understanding Operating Systems, Fifth Edition

Understanding operating systems 5th ed ch10

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Understanding operating systems 5th ed ch10