Bài giảng Hệ điều hành nâng cao - Chapter 16: Distributed System Structures (phân phối cấu trúc hệ thống) trình bày về động cơ phân phối hệ thống, cấu trúc mạng, cơ cấu truyền thông, giao thức truyền thông và các vấn đề về thiết kế.
AMBIENT/
Chủ đề:
Nội dung Text: Bài giảng Hệ điều hành nâng cao - Chapter 16: Distributed System Structures
- Module 16: Distributed System Structures
Operating System Concepts – 8th Edition
Operating System Concepts – 8th Edition 16.1 Silberschatz, Galvin and Gagne ©2009
- Chapter 16: Distributed System Structures
s Motivation
s Types of Network-Based Operating Systems
s Network Structure
s Network Topology
s Communication Structure
s Communication Protocols
s Robustness
s Design Issues
s An Example: Networking
Operating System Concepts – 8th Edition 16.2 Silberschatz, Galvin and Gagne ©2009
- Chapter Objectives
s To provide a high-level overview of distributed systems and the
networks that interconnect them
s To discuss the general structure of distributed operating systems
Operating System Concepts – 8th Edition 16.3 Silberschatz, Galvin and Gagne ©2009
- Motivation
s Distributed system is collection of loosely coupled processors
interconnected by a communications network
s Processors variously called nodes, computers, machines, hosts
q Site is location of the processor
s Reasons for distributed systems
q Resource sharing
4 sharing and printing files at remote sites
4 processing information in a distributed database
4 using remote specialized hardware devices
q Computation speedup – load sharing
q Reliability – detect and recover from site failure, function transfer,
reintegrate failed site
q Communication – message passing
Operating System Concepts – 8th Edition 16.4 Silberschatz, Galvin and Gagne ©2009
- A Distributed System
Operating System Concepts – 8th Edition 16.5 Silberschatz, Galvin and Gagne ©2009
- Types of Distributed Operating Systems
s Network Operating Systems
s Distributed Operating Systems
Operating System Concepts – 8th Edition 16.6 Silberschatz, Galvin and Gagne ©2009
- Network-Operating Systems
s Users are aware of multiplicity of machines. Access to resources of
various machines is done explicitly by:
q Remote logging into the appropriate remote machine (telnet,
ssh)
q Remote Desktop (Microsoft Windows)
q Transferring data from remote machines to local machines, via
the File Transfer Protocol (FTP) mechanism
Operating System Concepts – 8th Edition 16.7 Silberschatz, Galvin and Gagne ©2009
- Distributed-Operating Systems
s Users not aware of multiplicity of machines
q Access to remote resources similar to access to local resources
s Data Migration – transfer data by transferring entire file, or transferring
only those portions of the file necessary for the immediate task
s Computation Migration – transfer the computation, rather than the
data, across the system
Operating System Concepts – 8th Edition 16.8 Silberschatz, Galvin and Gagne ©2009
- Distributed-Operating Systems (Cont.)
s Process Migration – execute an entire process, or parts of it, at different
sites
q Load balancing – distribute processes across network to even the
workload
q Computation speedup – subprocesses can run concurrently on
different sites
q Hardware preference – process execution may require specialized
processor
q Software preference – required software may be available at only
a particular site
q Data access – run process remotely, rather than transfer all data
locally
Operating System Concepts – 8th Edition 16.9 Silberschatz, Galvin and Gagne ©2009
- Network Structure
s Local-Area Network (LAN) – designed to cover small geographical
area.
q Multiaccess bus, ring, or star network
q Speed 10 – 100 megabits/second
q Broadcast is fast and cheap
q Nodes:
4 usually workstations and/or personal computers
4 a few (usually one or two) mainframes
Operating System Concepts – 8th Edition 16.10 Silberschatz, Galvin and Gagne ©2009
- Depiction of typical LAN
Operating System Concepts – 8th Edition 16.11 Silberschatz, Galvin and Gagne ©2009
- Network Types (Cont.)
s Wide-Area Network (WAN) – links geographically separated sites
q Point-to-point connections over long-haul lines (often leased from
a phone company)
q Speed 1.544 – 45 megbits/second
q Broadcast usually requires multiple messages
q Nodes:
4 usually a high percentage of mainframes
Operating System Concepts – 8th Edition 16.12 Silberschatz, Galvin and Gagne ©2009
- Communication Processors in a
Wide-Area Network
Operating System Concepts – 8th Edition 16.13 Silberschatz, Galvin and Gagne ©2009
- Network Topology
s Sites in the system can be physically connected in a variety of ways; they
are compared with respect to the following criteria:
q Installation cost - How expensive is it to link the various sites in the
system?
q Communication cost - How long does it take to send a message from
site A to site B?
q Reliability - If a link or a site in the system fails, can the remaining
sites still communicate with each other?
s The various topologies are depicted as graphs whose nodes correspond to
sites
q An edge from node A to node B corresponds to a direct connection
between the two sites
s The following six items depict various network topologies
Operating System Concepts – 8th Edition 16.14 Silberschatz, Galvin and Gagne ©2009
- Network Topology
Operating System Concepts – 8th Edition 16.15 Silberschatz, Galvin and Gagne ©2009
- Communication Structure
The design of a communication network must address four basic issues:
s Naming and name resolution - How do two processes locate
each other to communicate?
s Routing strategies - How are messages sent through the
network?
s Connection strategies - How do two processes send a sequence
of messages?
s Contention - The network is a shared resource, so how do we
resolve conflicting demands for its use?
Operating System Concepts – 8th Edition 16.16 Silberschatz, Galvin and Gagne ©2009
- Naming and Name Resolution
s Name systems in the network
s Address messages with the process-id
s Identify processes on remote systems by
pair
s Domain name service (DNS) – specifies the naming structure of
the hosts, as well as name to address resolution (Internet)
Operating System Concepts – 8th Edition 16.17 Silberschatz, Galvin and Gagne ©2009
- Routing Strategies
s Fixed routing - A path from A to B is specified in advance; path
changes only if a hardware failure disables it
q Since the shortest path is usually chosen, communication costs
are minimized
q Fixed routing cannot adapt to load changes
q Ensures that messages will be delivered in the order in which they
were sent
s Virtual circuit - A path from A to B is fixed for the duration of one
session. Different sessions involving messages from A to B may have
different paths
q Partial remedy to adapting to load changes
q Ensures that messages will be delivered in the order in which they
were sent
Operating System Concepts – 8th Edition 16.18 Silberschatz, Galvin and Gagne ©2009
- Routing Strategies (Cont.)
s Dynamic routing - The path used to send a message form site A to
site B is chosen only when a message is sent
q Usually a site sends a message to another site on the link least
used at that particular time
q Adapts to load changes by avoiding routing messages on heavily
used path
q Messages may arrive out of order
4 This problem can be remedied by appending a sequence
number to each message
Operating System Concepts – 8th Edition 16.19 Silberschatz, Galvin and Gagne ©2009
- Connection Strategies
s Circuit switching - A permanent physical link is established for the
duration of the communication (i.e., telephone system)
s Message switching - A temporary link is established for the duration
of one message transfer (i.e., post-office mailing system)
s Packet switching - Messages of variable length are divided into
fixed-length packets which are sent to the destination
q Each packet may take a different path through the network
q The packets must be reassembled into messages as they arrive
s Circuit switching requires setup time, but incurs less overhead for
shipping each message, and may waste network bandwidth
q Message and packet switching require less setup time, but incur
more overhead per message
Operating System Concepts – 8th Edition 16.20 Silberschatz, Galvin and Gagne ©2009
Thêm vào BST
Báo xấu
Download
Vui lòng tải xuống để xem tài liệu đầy đủ
