Chapter 9 Network Organization Concepts

1. Chapter 9Network OrganizationConcepts Understanding Operating Systems, Fourth Edition

2. Objectives You will be able to describe: • Several different network topologies—including the star, ring, bus, tree, and hybrid • Three types of networks: LAN, MAN, and WAN • The difference between circuit switching and packet switching • Conflict resolution procedures that allow a network to share common transmission hardware and software effectively Understanding Operating Systems, Fourth Edition

3. Objectives (continued) You will be able to describe: • The two transport protocol models (OSI and TCP/IP) and how the layers of each one compare Understanding Operating Systems, Fourth Edition

4. Basic Terminology • Network: Collection of loosely coupled processors interconnected by communication links using cables, wireless technology,or both • Goal:To provide a convenient way to share resources (hardware and software) while controlling users’ access to them • General configurations for OS for networks: • Network operating system (NOS) • Distributed operating system (D/OS) Understanding Operating Systems, Fourth Edition

5. Basic Terminology (continued) • Network operating system (NOS): Networking capability added to single-user operating system • Users aware of specific computers and resources in the network • Access via logon to remote host or by data transfer from remote host Understanding Operating Systems, Fourth Edition

6. Basic Terminology (continued) • Distributed operating system (D/OS):Users can access remote resources as if local resources • Good control for distributed computing systems • Allows resources to be accessed in a unified way • Represents total view across multiple computer systems for controlling and managing resources without local dependencies • Management is a cooperative process • Comprised of four managers with a wider scope Understanding Operating Systems, Fourth Edition

7. Basic Terminology (continued) • D/OS must provide the following components: • Process or object management • Memory management • File management • Device management • Network management Understanding Operating Systems, Fourth Edition

8. Basic Terminology (continued) Figure 9.1: Networked management system Understanding Operating Systems, Fourth Edition

9. Basic Terminology (continued) • Advantages of D/OS over traditional systems: • Easy and reliable resource sharing • Faster computation • Adequate load balancing • Good reliability • Dependable electronic communications among the network’s users Understanding Operating Systems, Fourth Edition

10. Basic Terminology (continued) • In distributed system each processor classifies other processors and resources as remote and considers its own resources local • Site: Indicates a specific location in a network with one or more computers • Host: Specific computer system found at a site whose services and resources can be used from remote locations • Node: Refers to the name assigned to a computer system connected to network to identify it to other computers in network Understanding Operating Systems, Fourth Edition

11. Basic Terminology (continued) Figure 9.2: Clients request data orservices from the hostserver and wait for theresponse. If the clienthost has resourcesneeded by the serverhost, the roles can bereversed Understanding Operating Systems, Fourth Edition

12. Network Topologies • Sites in any networked system can be physically or logically connected in a variety of topologies • Common topologies: star, ring, bus, tree, hybrid • In each topology there are tradeoffs between • Need for fastcommunication among all sites • Tolerance of failure at a site or communicationlink • Cost of long communication lines • Difficulty of connecting one site to a large number of other sites Understanding Operating Systems, Fourth Edition

13. Network Topologies (continued) • Four basic criteria : • Basic cost:Expense required to link the various sites in the system • Communications cost: Time required to send a message from one site to another • Reliability:Assurance that many sites can still communicate with each otherif a link or site fails • User’s environment:Critical parameters that network must meet to be asuccessful business investment Understanding Operating Systems, Fourth Edition

14. Star • All transmitted data must pass through acentral controller when going from a sender to a receiver • Advantages: • Permits easy routing • Easy access control to the network • Challenges: • Central site must be extremely reliable and able tohandle all network traffic, no matter how heavy Understanding Operating Systems, Fourth Edition

15. Star (continued) Figure 9.3: Star topology Understanding Operating Systems, Fourth Edition

16. Ring • All sites are connected in a closed loopwith the first site connected to the last • Network can be connected to other networks via a bridge (same protocols) or gateway (different protocols) • Data is transmitted in packets with source and destination address fields • Each packet is passed from node to node in one direction only • Every node must be functional, or failed node needs to be bypassed for proper operation Understanding Operating Systems, Fourth Edition

17. Ring (continued) Figure 9.4: Ring topology Understanding Operating Systems, Fourth Edition

18. Ring (continued) Figure 9.5: Double loop computernetwork using a ringtopology Understanding Operating Systems, Fourth Edition

19. Ring (continued) Figure 9.6: Multiple rings bridged together Understanding Operating Systems, Fourth Edition

20. Bus • All sites connected to a single communication line • Messages from any sitecirculate in both directions • Only one site can successfullysend messages at one time • Needs control mechanism to prevent collision • Data may pass directly from one device to another, or it maybe routed to an end point controller at the end of the line Figure 9.7: Bus Topology Understanding Operating Systems, Fourth Edition

21. Tree • Tree:A collection of busses connected by a branching cable with no closed loops • Allows users to create networks using bridges • Message from any site can be received by all other sites, until it reaches an endpoint • End point controller absorbs a message if it reaches end point controller without being accepted by a host • Advantage:Message traffic can still flow through the network even if a single node fails Understanding Operating Systems, Fourth Edition

22. Tree ( continued) Figure 9.8: Tree Topology Understanding Operating Systems, Fourth Edition

23. Hybrid Selects among the strong points of eachtopology and combines them to meet that system’s communications requirements mosteffectively Figure 9.9: Hybrid topology combining a star and a ring using a bridge Understanding Operating Systems, Fourth Edition

24. Hybrid (continued) Figure 9.10: Hybrid topology combining a star and a bus Understanding Operating Systems, Fourth Edition

25. Network Types • Grouping of networks according to physical distances they cover • Network types: • Local area networks (LAN) • Metropolitan area networks (MAN) • Wide area networks (WAN) Understanding Operating Systems, Fourth Edition

26. Local Area Network • A configuration found within a single office building, campus, or similarly enclosed environment • Owned, used, and operated by single organization • Allows computers to communicate directly through a common communication line • Communications aren’t limited to well-defined local area only • LAN can be a component of larger communication network • Provides easy access to outside through bridge or gateway Understanding Operating Systems, Fourth Edition

27. Local Area Network (continued) • Bridge: Connects two or more geographically distant LANs with same protocols • e.g., simple bridge used to connect 2 Ethernet LANs • Gateway: Connects two or more LANs or systems that use different protocols • Translates one network’s protocol into another, resolving hardware and software incompatibilities • e.g., SNA gateway can connect microcomputer network to mainframe host Understanding Operating Systems, Fourth Edition

28. Local Area Network (continued) • Data rates in LAN vary from 100 Mbps to morethan 40 Gbps • Close physical proximity allows very high-speed transmission • Star, ring, bus, tree, and hybridare normally used to construct local area networks • Transmission medium usedmay vary from one topology to another • Factors determining transmission medium include cost, data rate, reliability, number of devices that can besupported, distance between units etc. Understanding Operating Systems, Fourth Edition

29. Metropolitan Area Network • Configuration spanning an area largerthan a LAN • Ranging from several blocks of buildings to an entire city but notexceeding a circumference of 100 km • Owned and operated by a single organization • Usually used by many individuals & organizations • May be owned and operated as public utilities providing means for internetworking several LANs • MAN: high-speed network often configured as a logical ring Understanding Operating Systems, Fourth Edition

30. Wide Area Network • A configuration that interconnects communication facilities in different parts of a country or the world, or that is operated as part of public utility • Uses communications lines of common carriers (e.g., telephone companies) • Uses broad range of communication media (e.g., satellite, microwaves) • WANs are generally slower than LANs • Examples: ARPAnet (first WAN), Internet (most widely recognized WAN) Understanding Operating Systems, Fourth Edition

31. LAN that uses wirelesstechnology to connect computers or workstations located within the range of thenetwork WLAN typically poses security vulnerabilities Wireless Local Area Network WiMax (802.16) would enable wireless broadband connections over muchgreater ranges (up to 10 miles) Table 9.1: IEEEstandards for wirelessnetworks Understanding Operating Systems, Fourth Edition

32. Wireless Local Area Network (continued) Figure 9.11: Wireless Local Area Network Understanding Operating Systems, Fourth Edition

33. Software Design Issues • Software issues that must be addressed by network designers: • How do sites use addresses to locate other sites? • How are messages routed and how are they sent? • How do processes communicate with each other? • How are conflicting demands for resources resolved? Understanding Operating Systems, Fourth Edition

34. Addressing Conventions • Addressing protocols are closely related to network topology and geographic location of each site • Local name: Name by which a unit is known within its own system • Global name: Name by which a unit is known outside its own system • Must follow standard name lengths, formats, and other global conventions Understanding Operating Systems, Fourth Edition

35. Addressing Conventions (continued) • Domain Name Service (DNS) protocol • The DNS is hierarchical • Domain names are read from right to left • Rightmost portion is the top-level domain • Next level is the domain name • Next is one or more subdomain names • Leftmost portion is the host Understanding Operating Systems, Fourth Edition

36. Routing Strategies • Router:Internetworking device, primarily software driven, which directs traffic • Between two different types of LANs,or • Between two network segments with different protocol addresses • Operates at Network Layer • Role of routers changes as network designs change • Used extensively for connecting sites to each other and to Internet Understanding Operating Systems, Fourth Edition

37. Routing Strategies (continued) • Routerfunctions include: • Securing information generated in predefined areas • Choosing the fastest route from one point to another • Providing redundant network connections • Routing protocols must consider following: • Addressing • Address resolution • Message format • Error reporting Understanding Operating Systems, Fourth Edition

38. Routing Strategies (continued) • Message formats allow the protocol to perform its functions, such as • Finding new nodes on anetwork • Testing to determine whether they’re working • Reporting error conditions • Exchanging routing information • Establishing connections, and transmitting data • Most widely used routing protocols on Internet: • Routing information protocol (RIP) • Open shortest path first (OSPF) Understanding Operating Systems, Fourth Edition

39. Routing Information Protocol • Selection of a path based on immediate number of nodes, or hops, betweensource and destination • Path with smallest number of hops chosen always • Advantages: • Easy to implement • Disadvantages: • Does not take into consideration bandwidth, data priority, or type of network • Updating and reissuing of routing table every 30 seconds • Tables propagate from one router to another Understanding Operating Systems, Fourth Edition

40. Open Shortest Path First • Selection of a transmission path only afterthe state of a network has been determined • Routing update messages sent only when changes in routing environment occur • Reduces number of messages in internetwork • Reduces size of messages by not sending entire routing table • Disadvantages: • Increased memory usage • Bandwidth savings offset by higher CPU usage for shortest path calculation Understanding Operating Systems, Fourth Edition

41. Connection Models • Types of switching: • Circuit switching • Packet switching • Circuit Switching: Communication model in which dedicated communication path is established between two hosts before data transmission begins • Example: Telephone system • Disadvantage: Delay before signal transfer begins while the connection is set up Understanding Operating Systems, Fourth Edition

42. Packet Switching • A store-and-forward technique in whicha message is divided into multiple equal-sized units (packets) before sending to destination • At destination, packets are reassembled into their original longformat • A header containing pertinent information about the packet is attached to each packet before transmission • Advantages: • More flexible and more reliable than circuit switching • Provides greater line efficiency • Allows users to allocate priorities to their messages Understanding Operating Systems, Fourth Edition

43. Packet Switching (continued) Figure 9.12 : Packet switching; (a) divide the data into addressed packets; (b) send each packet toward its destination;(c) reassemble thedata at the destination Understanding Operating Systems, Fourth Edition

44. Packet Switching (continued) Table 9.2: Comparison of circuit andpacket switching Understanding Operating Systems, Fourth Edition

45. Packet Switching (continued) • Methods of selecting the path: • Datagrams • Virtual circuits • Datagrams: Destination and sequence number of packet added to information, uniquely identifying message to which packet belongs • Each packet handled independently and route is selected as each packet is accepted into network • At destination, all packets of same message are reassembled Understanding Operating Systems, Fourth Edition

46. Packet Switching (continued) • Datagrams: (continued) • Message can’t be delivered until all packets are accounted for • Receiving node requests retransmission of lost or damaged packets • Advantages: • Helps diminish congestion by sending incoming packets through less heavily used paths • Provides more reliability, because alternate paths may be set up when one node fails Understanding Operating Systems, Fourth Edition

47. Packet Switching (continued) • Virtual Circuit: Complete path from sender to receiver established before transmission starts • All packets belonging to a message use same route • Any node can have several virtual circuits to any other node • Advantage: Routing decision made once for all packets belonging to same message – speeds up transmission • Disadvantages: • If node fails, all virtual circuits using that node become unavailable • Congestion is difficult to resolve when heavy traffic Understanding Operating Systems, Fourth Edition

48. Conflict Resolution • Some method to control access is necessary to facilitate equal and fair access to network • Access control techniques: • Round robin • Reservation • Contention • Medium access control protocols: • Carrier sense multiple access (CSMA) • Token passing • Distributed-queue, dual bus Understanding Operating Systems, Fourth Edition

49. Access Control Techniques • Round Robin: A node is given certain amount of time to complete transmission, at end of which opportunity is passed to next node • Efficient when many nodes transmitting over long periods • Substantial overhead when few nodes transmit over long periods of time • Reservation: Access time on medium is divided into slots and node can reserve future time slots • Well suited for lengthy and continuous traffic Understanding Operating Systems, Fourth Edition

50. Access Control Techniques (continued) • Reservation: (continued) • Good for a configuration with several terminals connected to host computer through single I/O port • Contention: No attempt is made to determine whose turn it is to transmit; nodes compete for access to medium • Major advantage: Easy to implement • Better for short and intermittent traffic • Works well under light to moderate traffic • Performance tends to break down under heavy loads Understanding Operating Systems, Fourth Edition