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Transcript
Chapter 9 Network Organization Concepts CIS106 Microcomputer Operating Systems Gina Rue CIS Faculty Ivy Tech State College Northwest Region 01 Introduction Network Organization Concepts • Stand-alone computers linked together through communication systems to form networks transmit & process data & information among users in the system • Goal of networked systems are to provide a way to share resources: – hardware: CPU, memory, printers, tape, and disk drives – software: programs & data files See Fig. p.199 2 Introduction Network Organization Concepts OS Types for Networking • OS built for the network is built on top of the existing local computer OS is referred to as a Network Operating System – users can access resources by: – logging on to a remote host – transferring data from the remote computer to their own 3 Introduction Network Organization Concepts • The Distributed OS provides good control for distributed computing systems & allows their resources to be accessed in a unified way – advantages: easy & reliable resource sharing, improved computation performance, adequate load balancing, dependable electronic communications among users 4 Basic Terminology • Network is a collection of processors interconnected by a communication network • In a distributed system each processor classifies the other processors & their resources as remote & considers its own resources as local 5 Basic Terminology • Size, type, and identification of processors varies • Processors are referred to as sites, hosts, & nodes – site is a specific location on the network containing one or more computers – host is a specific computer system found at a site whose services & resources can be used from remote locations – node refers to the name assigned to a computer connected to the network 6 Basic Terminology • Typically a host at one site is called the server & has resources that a host at another site, called the client wants to use • Hosts can alternate between being clients or servers depending on the requirements 7 Network Topologies – Networks can be physically or logically connected in a variety of topologies • Common arrangements are: – star, ring, bus, tree – Each topology has tradeoffs • need for fast communication among all sites • tolerance of failure at a site or communication link • difficulty of connecting one site to a large number of other sites 8 Network Topologies – Deciding which configuration to use, system designers should consider 3 criteria: • Basic cost – expense required to link the various sites in the system • Communication cost – time required to send a message from one site to another • Reliability – assurance that many sites can still communicate with each other even if a link or site in the system fails 9 Network Topologies – Star • sometimes called a “hub” or “centralized” approach to interconnect devices • data must pass through a central controller when going from sender to receiver • permits easy routing, central station knows the path to all other sites • central points makes access to the network easy to control and priority status • central site must be extremely reliable & able to handle heavy network traffic See Fig. 9.1 p.201 10 Network Topologies – Ring • all sites are connected in a closed loop • data is transmitted in packets also contain source & destination address fields • a data packet is passed in one direction from node to node to a local buffer on the destination node • a packet will continue to move through the ring & returns to the source then removed from the ring • several variations with more flexibility but at a cost See Fig. 9.2 p.202 11 Network Topologies – Bus • all sites are connected to a single communication line running the length of the network • physically connects the devices by cables that run between them • only one node can send a message successfully at one time • data may pass directly from one device to another or may be routed to an end point controller See Fig. 9.5 p.206 12 Network Topologies – Tree • a collection of busses • communication line is branching cable with no closed loops • tree layout begins at the “head end” one or more cables start • each cable may have branches that may additional branches • bridges are used to translate different protocols See Fig. 9.6 p.206 13 Network Topologies – Hybrid • combination of any of the four topologies • Objectives – select among the strong points of each topology – combine topologies to meet the that system’s communication requirements most cost effectively See Fig. 9.7 & 9.8 p.207 14 Network Types Often used to group networks according to the physical distances they cover – Local Area Network (LAN) – Metropolitan Area Network (MAN) – Wide Area Network (WAN) 15 Network Types Local Area Network (LAN) – configuration found in a single office building, warehouse, campus, lab • generally owned, used, & operated by a single organization • LAN can be a component of a larger network – Bridge is a device & software that connects two or more LANs that use the same protocols – Gateway is a more complex device & software used to connect two or more LANs that use different protocols 16 Network Types Local Area Network (LAN) – operates at speeds from one MB per second to one GB per second – bandwidths are available to support highspeed transmission for graphics, video, digital, & voice – transmission medium varies from one topology to another - cable, wire, fiber-optic – transmission medium considerations are cost, data rate, reliability, number of devices, distance, & technical limitations 17 Network Types Metropolitan Area Networks (MAN) – defines configurations spanning an area larger than a LAN, ranging from several blocks to an entire city, not exceeding 100 kilometers – may be owned & operated by a single or many individuals & organizations or by public utilities providing means for connecting LANS • typically configured as a ring for one direction transmission or dual ring transmitting in two 18 directions Network Types Wide Area Network (WAN) – configuration that interconnects communication facilities in different parts of the country or world, or operates as part of a public utility – use communication lines of “common carriers” such as telephone companies • use broad range of media, satellites, microwaves & high-speed transmission • generally slower than LANs • Internet is the most widely recognized WAN • ARPnet, Telenet 19 Software Designing Issues Network designers must address four issues: – How do sites use addresses at other sites? – How are messages routed & how are they sent? – How do processes communicate with each other? – How are conflicting demands for resources resolved? 20 Software Designing Issues Addressing Conventions – sites need to be uniquely identified by using names, addresses & routes • local name refers a name each unit is known by on its own system • global name refers to a name each unit is known by outside its own system – Domain Name Service (DNS) protocol a general purpose distributed data query service that resolves Internet addresses 21 Software Designing Issues Routing Strategies – allows data to get from one point on the network to another • requires each destination be uniquely identified • forwards data between networks – each router records a table of addresses of the networks that are connected • variety of message formats • two most common routing protocols, routing information protocol & open shortest path first 22 Software Designing Issues Routing Strategies – Routing Information Protocol (RIP) • chooses the best path for data transfer with the smallest number of “hops” • distance vector algorithm is easy to implement but may not choose the most reliable path – Open Shortest Path First (OSPF) • if an intermediate hop is malfunctioning it is eliminated from consideration until it is restored • topological database data structure is maintained by OSPF & updated when failure occurs 23 Software Designing Issues Connection Models – not concerned with data content, but with moving data from one point to another – network designed to minimize costs – provides full connectivity among attached devices – data entering the network at one point is routed to its destination by switching from node to node, whether by • circuit switching • packet switching 24 Software Designing Issues Connection Models – Circuit Switching • communication model where a dedicated communication path is established between 2 hosts • the path is a connected sequence of links • connection between points only exists until one is disconnected • telephone system a good example • once connection is complete, transparent to users • information transmitted at a fixed rate 25 Software Designing Issues Connection Models – Packet Switching • store-and-forward technique • message is divided into multiple equal-sized units called packets • packets reaching a destination are reassembled • effective for long-distance transmission • flexible to different transmission rates • no guarantee data will arrive in physical sequential order • allows users to set priorities to their messages 26 Software Designing Issues Connection Models – Packet Switching, two methods of selecting a path • datagrams – destination & sequence number of the packet is added, a route is selected as it is accepted into the network • virtual circuit – destination & packet sequence number are not added because complete path from sender to receiver is established before transmission starts 27 Software Designing Issues Conflict Resolution – Because networks consist of devices sharing a common transmission capability, a method to control access is necessary to facilitate equal & fair access to this common resource 28 Software Designing Issues Conflict Resolution – Access Control Techniques • Round Robin – Allows each node to use the communication medium for a certain amount of time • Reservation – Access time on the medium is divided into slots & nodes can reserve future time • Contention – no attempt is made to determine whose turn it is to transmit so nodes compete for access to the medium 29 Software Designing Issues Conflict Resolution – Medium Access Control Procedures • Carrier Sense Multiple Access (CSMA) – contention-based protocol – a node on the network will listen to, or test, the communication medium before sending a message – prevents collision with another node currently transmitting • Carrier Sense Multiple Access with Collision Detection (CSMA/CD) – Ethernet most widely known – reduces the number of collisions See Fig. 9.9 p.216 30 Transport Protocol Standards In the early 1980s network usage grew & the need to integrate dissimilar network devices & their complexity • To allow multi-vendor interoperability, two standards were developed – International Organization for Standardization (ISO) – Transmission Control Protocol/Internet Protocol (TCP/IP) 31 Transport Protocol Standards International Organization Standardization (ISO) – makes technical recommendations about data communication interfaces – Open System Interconnect (OSI) reference model is the frame work for defining the services that a network should provide to its users – 7 layers are used to group localized functions so redesigning layers & protocol to take advantage of changing services 32 Transport Protocol Standards ISO-OSI reference model Layer 1 - Physical Layer Layer 2 - Data Link Layer Layer 3 - Network Layer Layer 4 - Transport Layer Layer 5 - Session Layer Layer 6 - Presentation Layer Layer 7 - Application Layer See Fig. 9.10 p.218 33 Transport Protocol Standards Transmission Control Protocol/Internet Protocol (TCP/IP) – oldest & most widely used protocol developed by U.S. Dept. of Defense’s ARPAnet – provides efficient & error-free transmission between different systems – file-transfer protocol (FTP) allows large files to be sent across unreliable networks error-free – Three main components: • processes, hosts, networks See Fig. 9.11 p.221 34 Transport Protocol Standards Transmission Control Protocol/Internet Protocol (TCP/IP) Layer 1 - Network Access Layer 2 - Internet Layer 3 - Host-Host Layer 4 - Process/Application 35 Summary • Network operating systems (NOS) include functions of the four managers – memory – processor – device – file • NOS need to coordinate all functions among network hardware & software, no matter where they are physically located 36 Summary • NOS success must meet reliability requirements of its owner, NOS must detect: – node failure – changing routing instructions to avoid that node – make sure lost messages are retransmitted until successfully received 37 Summary • Introduced basic network organization concepts: – common terminology – network topologies – types of networks – software design issues – transport protocol standards 38