Understanding Operating Systems Sixth Edition

Understanding Operating SystemsSixth Edition Chapter 9Network Organization Concepts

Learning Objectives After completing this chapter, you should be able to describe: • Several different network topologies—including the star, ring, bus, tree, and hybrid—and how they connect numerous hosts to the network • Several types of networks: LAN, MAN, WAN, and wireless LAN • The difference between circuit switching and packet switching, and examples of everyday use that favor each Understanding Operating Systems, Sixth Edition

Learning Objectives (cont'd.) • Conflict resolution procedures that allow a network to share common transmission hardware and software effectively • The two transport protocol models (OSI and TCP/IP) and how the layers of each one compare Understanding Operating Systems, Sixth Edition

Network Organization Concepts • When computer facilities are connected together by data-communication components, they form a network of resources to support the many functions of the organization. • Networks provide an essential infrastructure for members of the information-based society to process, manipulate, and distribute data and information to each other. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • A Network is a collection of loosely coupled processors interconnected by communication links using cables, wireless technology, or a combination of both. • A common goal of all networked systems is to provide a convenient way to share resources while controlling users’ access to them. • These resources include both hardware and software. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • There are two general configurations for OSs for networks. • The oldest added a networking capability to a single-user OS. • Network operating system (NOS): • With this configuration, users are aware of the specific assortment of computers and resources in the network and can access them by logging on to the most appropriate host or by transferring data from the remote computer to their own. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • With the second configuration, users don’t need to know where and how each machine is connected to the system. • They can access remote resources as if they were local resources. • A distributed operating system (D/OS) • Provides good control for distributed computing systems and allows their resources to be accessed in a unified way. • Represents a total view across multiple computer systems for controlling and managing resources without local dependencies. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • A Distributed Operating System (D/OS) • Composed of the same four managers previously discussed but with a wider scope. • At a minimum, it must provide the following components: • Process or Object Management; • Memory Management; • File Management; • Device Management; • Network Management. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • Distributed operating system (D/OS) (cont'd.) • Comprised of four managers with a wider scope Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • A Distributed Operating System (D/OS) offers several important advantages over older Oss and NOSs: • Easy and reliable resource sharing; • Faster computation; • Adequate load balancing; • Good reliability; • Dependable electronic communications among the network users. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • In a distributed system, each processor classifies the other processors and their resources as Remote. • Considers its own resources Local. • The size, type, and identification of processors vary. • Processors are referred to as sites, hosts, and nodes depending on the context in which they’re mentioned. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • A Distributed Operating System (D/OS): • “Site” indicates a specific location in a network containing one or more computer systems. • “Host” indicates a 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 a network to identify it to other computers in the network. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology • A Distributed Operating System (D/OS): • Typically, a host at one site (server) has resources that a host at another site (client) wants to use. • Hosts can alternate being client or servers depending on their requirements. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsBasic Terminology Understanding Operating Systems, Sixth Edition

Network Organization ConceptsNetwork Topologies • Sites in any networked system can be physically or logically connected to one another in a certain topology. • The geometric arrangement of connections (cables, wireless, or both) that links the nodes. • The most common geometric arrangements are • Star • Ring • Bus • Tree • Hybrid. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsNetwork Topologies • In each topology there are tradeoffs between: • The need for fastcommunication among all sites; • The tolerance of failure at a site or communicationlink; • The cost of long communication lines; • The difficulty of connecting one site to large number of other sites. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsNetwork Topologies • The physical topology of a network may not reflect its logical topology. • A network that is wired in a star configuration can be logically arranged to operate as if it is a ring. • It can be made to manipulate a token in a ring-like fashion even though its cables are arranged in a star topology. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsNetwork Topologies • When deciding which configuration to use, the network designer should keep in mind four basic criteria: • Basic cost • The expense required to link the various sites in the system. • Communications cost • The time required to send a message from one site to another. • Reliability • The assurance that many sites can still communicate with each other even if a link or site in the system fails. Understanding Operating Systems, Sixth Edition

Network Organization ConceptsNetwork Topologies • When deciding which configuration to use, the network designer should keep in mind four basic criteria: • User environment: • The critical parameters that the network must meet to be a successful business investment. • The key to choosing the best design is to understand the available technology, as well as the customer’s business requirements and budget. Understanding Operating Systems, Sixth Edition

Network TopologiesStar • Sometimes called a hub or centralized topology, is a traditional approach to interconnecting devices in which all transmitted data must pass through a central controller when going from a sender to a receiver. • Advantages • Permits easy routing because the central station knows the path to all other sites; • Because there is a central control point, access to the network can be controlled easily; • Priority status can be given to selected sites. Understanding Operating Systems, Sixth Edition

Network TopologiesStar • Disadvantages • This centralization of control requires that the central site be: • Extremely reliable; • Able to handle all network traffic, no matter how heavy. Understanding Operating Systems, Sixth Edition

Network TopologiesStar Understanding Operating Systems, Sixth Edition

Network TopologiesRing • All sites are connected in a closed loop with the first connected to the last (Figure 9.4). • Can connect to other networks via the bridge or gateway, depending on the protocol used by each network. • The protocol is the specific set of rules used to control the flow of messages through the network. • If the other network has the same protocol, a bridge is used to connect the networks. • If the other network has a different protocol, a gateway is used. Understanding Operating Systems, Sixth Edition

Network TopologiesRing Understanding Operating Systems, Sixth Edition

Network TopologiesRing • Data is transmitted in packets that also contain source and destination address fields. • Each packet is passed from node to node in one direction only. • The destination station copies the data into a local buffer. • The packet continues to circulate until it returns to the source station, where it is removed from the ring. • There are some variations to this basic topology such as the double loop network (Figure 9.5), and a set of multiple rings bridged together (Figure 9.6). • Both variations provide more flexibility, but at a cost. Understanding Operating Systems, Sixth Edition

Network TopologiesRing Understanding Operating Systems, Sixth Edition

Network TopologiesRing • Although ring topologies share the disadvantage that every node must be functional for the network to perform properly, rings can be designed that allowed failed nodes to be bypassed. • A critical consideration for network stability. Understanding Operating Systems, Sixth Edition

Network TopologiesBus • All sites are connected to a single communication line running the length of the network (Figure 9.7). • Devices are physically connected by means of cables that run between the devices, but the cables don’t pass through a centralized controller mechanism. • Messages from any site circulate in both directions through the entire communication line and can be received by all other sites. • Because all sites share a common communication line, only one of them can successfully send messages at any one time. Understanding Operating Systems, Sixth Edition

Bus (cont'd.) Understanding Operating Systems, Sixth Edition

Network TopologiesBus • A control mechanism is needed to prevent collisions. • In this environment, Data may: • Pass directly from one device to another; • May be routed to an end point controller at the end of the line. • If the data reaches an end-point controller without being accepted by a host, the end point controller turns it around and sends it back so the message can be accepted by the appropriate node on the way to the other end point controller. Understanding Operating Systems, Sixth Edition

Network TopologiesBus • With some busses, each message must always go to the end of the line before going back down the communication line to the node to which it’s addressed. • Other bus networks allow messages to be sent directly to the target node without reaching and end point controller. Understanding Operating Systems, Sixth Edition

Network TopologiesTree • A collection of busses. • The communication line is a branching cable with no closed loops (Figure 9.8). • The tree layout begins at the head end, where one or more cables start. • Each cable may have branches that may, in turn, have additional branches. • Using bridges as special fitters between busses of the same protocol and as translators to those with different protocols allow designers to create networks that can operate at speeds more responsive to the hosts in the network. Understanding Operating Systems, Sixth Edition

Network TopologiesTree Understanding Operating Systems, Sixth Edition

Network TopologiesTree • In a tree configuration, a message from any site circulates through the communication line and can be received by all other sites, until it reaches the endpoints. • If a message reaches an end point controller without being accepted by a host, the end point controller absorbs it. • It isn’t turned around as it is when using a bus topology. • One advantage of bus and tree topologies is that even if a single node fails, message traffic can still flow through the network. Understanding Operating Systems, Sixth Edition

Network TopologiesHybrid • A hybrid topology is some combination of any of the four topologies. • A hybrid can be made by replacing a single host in a star configuration with a ring (Figure 9.9). Understanding Operating Systems, Sixth Edition

Network TopologiesHybrid • The objective is to select among the strong points of each topology and combine them to meet that system’s communication requirements most effectively. Understanding Operating Systems, Sixth Edition

Network TopologiesHybrid Understanding Operating Systems, Sixth Edition

Network Types • It’s often useful to group networks according to the physical distances they cover. • Network are generally divided into: • Local area networks (LAN) • Metropolitan area networks (MAN) • Wide area networks (WAN) • In recent years the wireless local area network has become ubiquitous. Understanding Operating Systems, Sixth Edition

Network TypesLocal Area Network (LAN) • Defines a configuration found within a single office building, warehouse, campus, or similar enclosed environment. • Generally owned, used, and operated by a single organization and allows computers to communicate directly through a common communication line. • Although a LAN may be physically confined to a well-defined local area, its communications aren’t limited to that area because the LAN can be a component of a larger communication network and can provide easy access to other networks through a bridge or a gateway. Understanding Operating Systems, Sixth Edition

Network TypesLocal Area Network (LAN) • Bridge • A device and the software to operate it, that connects two or more geographically distant LANs that use the same protocols. • Bridge connecting two LANs using Ethernet • Gateway • A more complex device and software used to connect two or more LANs or systems that use different protocols. • Translates one network protocol into another; • Resolves hardware and software incompatibilities; • SNA gateway connecting a microcomputer network to a mainframe host. Understanding Operating Systems, Sixth Edition

Network TypesLocal Area Network (LAN) • High-speed LANs have a data rate that varies from 100 Mbps to morethan 40 Gbps. • Because the sites are close to each other, bandwidths are available to support very high-speed transmission for fully animated, full-color graphics and video, digital voice transmission, and other high data-rate signals. • Star, ring, bus, tree, and hybrid topologies are normally used to construct LANs. Understanding Operating Systems, Sixth Edition

Network TypesLocal Area Network (LAN) • The transmission medium used may vary from one topology to another. • Factors to be considered when selecting a transmission medium: • Cost • Data rate • Reliability • Number of devices that can be supported • Distance between units • Technical limitations. Understanding Operating Systems, Sixth Edition

Network TypesMetropolitan Area Network (MAN) • Defines a configuration spanning an area largerthan a LAN, ranging from several blocks of buildings to an entire city. • Notexceeding 100 km circumference. • In some instances MANs are owned and operated as public utilities providing the means for internetworking several LANs. • A high-speed network often configured as a logical ring. Understanding Operating Systems, Sixth Edition

Network TypesMetropolitan Area Network (MAN) • Depending on the protocol used, messages are either transmitted: • In one direction only using only one ring (Figure 9.4); • In both directions using two counter-rotating rings (Figure 9.5). • One ring always carries messages in one direction, and the other ring always carries messages in the opposite direction. Understanding Operating Systems, Sixth Edition

Network TypesWide Area Network (WAN) • Defines a configuration that Interconnects communication facilities in different parts of a country or the world. • Could be operated as part of a public utility. • WANs Use the common carriers’ communications lines which are government-regulated private companies. • Telephone companies that already provide the general public with communication facilities. • WANs use a broad range of communication media, including satellite and microwaves. Understanding Operating Systems, Sixth Edition

Network TypesWide Area Network (WAN) • The speed of transmission is limited by the capabilities of the communication line. • WANs are generally slower than LANs. • The first WAN, ARPANET, was developed in 1969 by the Advanced Research Projects Agency (ARPA). • Responsibility for its operation was transferred in 1975 to the Defense Communications Agency. • Its successor, the Internet, is the most widely recognized. • There are other commercial WANs that exist. Understanding Operating Systems, Sixth Edition

Network TypesWireless Local Area Network (WLAN) • A LAN that uses wirelesstechnology to connect computers or workstations located within the range of the network. • The Institute of Electrical and Electronics Engineers (IEEE) has specified several standards for wireless networking, each with different ranges (Table 9.1). • WLAN can provide easy access to a larger network or the Internet (Figure 9.11). • A WLAN poses security vulnerabilities because of its open architecture and the inherent difficulty of keeping out unauthorized intruders. Understanding Operating Systems, Sixth Edition

Network TypesWireless Local Area Network (WLAN) Understanding Operating Systems, Sixth Edition

Network TypesWireless Local Area Network (WLAN) • The IEEE mobile WiMAX standard (802.16), approved in 2005 by the IEEE, promises to deliver high-bandwidth data over much longer distances (up to 10 miles) than the current Wi-Fi standard. Understanding Operating Systems, Sixth Edition

Understanding Operating Systems Sixth Edition