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Chapter 6 Networks and Telecommunications

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  1. Chapter 6Networks and Telecommunications The Strategic Management of Information Technology

  2. Transaction Processing System Input Process Output Systems Development Communication Information

  3. Local Area Networks

  4. Local Area Networks: A Definition • Provides access to shared resources such as printers, data, and applications • Increases controllability and consistency in applications and data • Increases access to shared applications and databases in large computers with many users • Provides a vehicle for electronic mail • Shares access to external resources through communication lines

  5. Local Area Networks:Reason • Performance • Change Management • Systems Management • Network Management • Direct Communication • Ease in Installation and Maintenance

  6. Network Protocols • 1. Physical Layer • Interfaces between Network Medium and Network Drives • Defines Electrical and Mechanical Characteristics of Network • Bad Plug

  7. Network Protocols • 2. Logical Link Layer • Frames Packets • Controls Physical Layer Data Flow • Data Collision • 3. Network Layer • Addresses and Routes Packets • Handles Fragmentation and Reassembly of Data • Broadcast Storm • 4. Transport Layer • Manages Network Layer Connections • Provides Reliable Packet Delivery Mechanism • Multiple ACKS

  8. Network Protocols • 5. Session Layer • Provides Remote Procedure Call Support • Reports Lower-Layer Errors • Protocol Error • 6. Presentation Layer • Specifies Architecture-Independent Data Transfer Format • Encodes and Decodes Data; Encrypts and Decrypts Data; Compresses Data • Misdirected Data • 7. Application Layer • Provides Interface to End-User Processes • Provides Standardized Services to Applications • Incompatible Software

  9. Communication according to the Open System Interconnection Reference Model Application Layer 7 Presentation Layer 6 Session Layer 5 Transport Layer 4 Network Layer 3 2 Data Link Layer 1 Physical Layer

  10. Physical Layer Hardware Description: The interface to the physical cable medium is described; layout of connectors, signals on each connector, voltage levels. The physical connection to the network, how connections are established and maintained, and how error conditions in data medium are handled. 7 6 5 4 3 2 1 Physical Layer

  11. Data Link Layer Software Description: Transmit blocks of data from the data link layer in one computer to another. Detect errors in data blocks and either correct the errors or ensure retransmissions of the effected data blocks. 7 6 5 4 3 2 Data Link Layer 1

  12. Protocols • Token Passing (IBM) • All blocks of data carried around the network with a source and destination address • Traffic is guided physically from unit to unit around the ring • IEEE 802.5; ISO IS 8802-5 • Token Bus • Traffic is guided on a common data bus, which directly connects all units in the network • All units are part of an organized logical sequence • All units at any point in time know the address of the unit before and after in logical sequence. • CSMA/CD (ethernet) • All units connected to the common bus can come in at any point in time after the unit has tested and found out no one else is using the network. • When collisions happen, both units resend the data after a short break.

  13. Protocols • Medium Access Control • Interfaces to the actual transport media to enable applications to communicate • IEEE 802.5; ISO IS 8802-5 • Logical Link Control • Insures that all software implemented on the top five layers of the OSI Model remains independent of which physical network is implemented in the bottom of the model. • NETBIOS • Constructs, maintains, and uses a table of relations between the Token Ring addresses and the defined names of units and services in the network; this enables real names to be used. • Advanced Program to Program Comm. • Supports program to program communications between different systems through the Token Ring. • Specific implementation of the IBM Systems Network Architecture (SNA) Logical Unit (LU) 6.2 architecture.

  14. Topologies • Star Topology • Bus • Ring • Physical Star, Logical Ring

  15. Topologies • Star Topology • Connections are made from all connected machines to one central place. • Control unit controls traffic in the network. • Computer in the middle has absolute control over traffic in the machine.

  16. Topologies • Bus Topology • One cable passed throughout entire implementation and to which each unit is connected. • Network cannot be centrally controlled. BUS

  17. Topologies • Token Ring Topology • Signals in the network are passing from machine to machine. • This gives controlled and stable data traffic in the network. • No central control or configuration of the traffic. RING

  18. Topologies • Token Ring Topology • IEEE 802.5; ISO IS 8802-5 • Uses the Baseband Transmission Technique • Signal is directly on the transmission medium without modulating a carrier signal. • Information occupies entire bandwidth in the medium. • Token format: • Starting delimiter (one byte) • Access control (one bit) • Frame control • Destination address • Source address • Routing information • Information Field • Frame check sequence • Ending delimiter • Frame status • Address Recognized Bit • Frame Copied Bit SD AC FC DA SA RI INFO FCS ED FS

  19. Topologies • Token Ring Topology • 4 Millionbits/s versus 15 Millionbits/second • 16 Mbits/s is for large data transfer • Each individually attached unit can only work at its speed • The lower speed of the individual machine limits the data transfer rate.

  20. Topologies • Physical Star, Logical Ring Topology • Each cable connection consists of two wires and provides two ways for the signal to pass in the one cable. • Logical connection in a ring insures stability of the traffic. • Configuration and management from a central place.

  21. Wiring • Telephone Twisted Pair • Unshielded and susceptible to noise • Not for higher data rates or long distances • Inexpensive • Coaxial Cable • Central core with shield around it • Shield insures radio frequency noise is not generated • High data rates at long distances • Fiber Optic Cable • Light signals transmitted by light emitting diodes are immune to electrical and magnetic noise • High data rates at long distances

  22. Cost-Effective Ways to Increase Access • Multistation Access Unit (MAU) • Controlled Access Unit (CAU) • Fiber Distribution Data Interface (FDDI) • Advanced Peer-to-Peer Networking (APPN) • Bridges, Gateways, and Routers

  23. Cost-Effective Ways to Increase Access:Multiple Access Units • Multistation Access Unit (MAU) • Passive Ring Concentrator • Includes room for 8 connected units • Forms a ring segment • Passes signal back to ring • Ring Out/Ring In (can be connected in series) • Controlled Access Unit (CAU) • Active Ring Concentrator • Contains logic for control functions • Passes signal back to ring • Ring Out/Ring In (can be connected in series) • Acts as Primary Input, Primary Output, and Secondary Adapter

  24. Cost-Effective Ways to Increase Access:FDDI and APPN • Fiber Distribution Data Interface (FDDI) • 100 Million bits/second • Fiber connections enable larger geographic dispersion • Stations can attach directly to a ring or through a concentrator • Can connect to both the primary and secondary ring simultaneously • Advanced Peer-to-Peer Networking (APPN) • Programs capable of communicating with other programs running on other machines on the network can be automatically set in session with each other. • Network nodes know all APPC resources in both themselves and in end nodes • Each network node maintains a topology database of APPC resources and available routes through the network.

  25. Cost-Effective Ways to Increase Access:Bridges, Gateways, and Routers • Bridges • Connection between two local rings. • Unexpected physical breakdown in one ring will only affect this ring and not other rings. • Discourage users on one ring to use resources on another ring. • Operates in only the lowest levels of the OSI Model. • Connection between two token ring networks. • Gateways • Units that connect a Token Ring Network to a computer system or network that uses communications protocols other than Token Ring protocols. • Establish connections between units in the token ring network and units that are not directly attached to the Token Ring Network. • Handles/Requires protocol conversion • Operates in all seven layers of OSI Model. • Routers • Allow for selected higher level protocols to communicate through the network. • LAN-to-LAN WAN Program. • Remote NETBIOS Access Facility.

  26. Network Layer Responsible for buffering and routing packets throughout the network. (Virtual Circuits) Essential in Wide Area Networks, not used in bus-topology LANs. 7 6 5 4 Network Layer 3 2 1

  27. Network Layer Network Operating System Default Protocol Wide Area Network NDS IPX/SPX Novell Naming Convention Internet Packet Exchange/ Sequence Packet Exchange (lower/higher) TCP/IP DCE UNIX Transmission Control Protocol/ Internet Protocol (higher/lower) Additional Security Net/BIOS Microsoft/NT Basic In Out System OS/2

  28. Transport Layer Partitions long messages arriving from upper session layers into data packets. On the re- ceiving side, reassembles messages from collections of packets received. Below Transport Layer, a data packet is a unit of information handled by the network. Above it, messages are the information units. 7 6 5 4 Transport Layer 3 2 1

  29. Session Layer 7 6 5 Session Layer 4 Responsible for providing a communication session between two user processes running on two separate network nodes. Responsible for determining whether a session can begin, be maintained, or terminated. 3 2 1

  30. Presentation Layer 7 6 Presentation Layer 5 4 Converts user messages from the form used by the application layer to that used by all lower layers. Below this layer, the meaning of data fields of messages and packets does not influence their processing. 3 2 1

  31. Application Layer Application Layer 7 6 Boundary between the OSI network and the application (user) processes. If a LAN operates as a distributed system, the application layer is responsible for direct communication with elements of the distributed operating system. 5 4 3 2 1

  32. Architectural Layers and Tiers Architectural Layers Client Network Server Data Dictionary User Interface Communication Protocol Function Set Data Objects Translation Layer Database Access Data Partitioning Data Transport

  33. Architectural Layers and Tiers Tiered-Architecture Presentation Processing Data Functionality Server Client Database Remote Procedure Calls Functionality Server Functionality Server Client Database Functionality Server

  34. Architectural Layers and Tiers • Two-Tier Architecture • Advantages • Application Development Speed • Ability to model data and populate a database on a remote server • Robust • Disadvantages • Version control and redistribution problems • System security complications • Client tools and middleware are volatile

  35. Architectural Layers and Tiers • Three-Tier Architecture • Advantages • Separates Presentation, Processing, and Data into separate, distinct software tiers • Middle tier is programmed in portable C code • Remote Process Call for calling technique • Overall flexibility in resource allocation • Disadvantages • Lack of development tools • More code in more places

  36. Local Area Networks • Important Mechanism to Integrate: • Hardware • Software • Application Development Environment

  37. Communication according to the Open System Interconnection Reference Model Application Layer 7 Presentation Layer 6 Session Layer 5 Transport Layer 4 Network Layer 3 2 Data Link Layer 1 Physical Layer

  38. Communication according to the Open System Interconnection Reference Model Application Layer 7 Presentation Layer 6 Session Layer 5 Transport Layer 4 Network Layer 3 2 Data Link Layer 1 Physical Layer

  39. Changes in the Marketplace • The quality imperative • Consumer computing • Deregulation of some major industries • Crossing industry boundaries • Traditional customers are “leaving” • Crossing national boundaries • Production is becoming global • New product and service development cycles are shortening

  40. Cooperative Processing • Cooperative Processing means that processes on two or more geographically dispersed computers cooperate in order to complete a task. In a primitive way, we have had a form of cooperative processing with this broad definition for several years, in the form of terminals connected to host (usually mainframe) computers. • Client/Server Systems are a form of cooperative processing where client and server machines share a processing workload.

  41. Attributes of Cooperative Processing • Distributed processing • Connectivity among processors • Distributed databases • System-wide rules

  42. Connectivity Elements • Technical connectivity means that it is technically possible to interconnect two units so that they can communicate • Procedural connectivity means that procedures are in place to permit and encourage connectivity

  43. Building Cooperative Processing Systems • Benchmark and prototype new technologies to verify vendors’ claims. • An open architecture works on mission-critical applications. • Large distributed system projects need a vendor coordinator. • Use of CASE was mandatory.

  44. Components Of Cooperative Processing Systems • Operating Systems - provide the processing capabilities. They need to be designed for networking and powerful workstations to be useful in distributed systems. • Mainframes - likely to continue as the primary database servers, because their database management systems are highly sophisticated, and reliable distributed database technology is not yet available. • Workstations - the focal point in cooperative processing, because they initiate the requests for services that are provided across the networks. • Servers- generally perform specialized functions, such as image servers, electronic mail servers, video servers, voice mail servers, credit card servers, expert system servers, etc.. • Superservers - support hundreds of workstations each, performing mission-critical processing at the node and handling heavy traffic.

  45. Forms Of Cooperative Processing • Host-driven terminal emulation is where the desktop computer runs an application that connects to a host as a standard “dumb” terminal. • Host-driven front ending is where the desktop computer runs a host-based application by providing a graphical interface for the user, making the system easier to use. • Host-driven client/server computing is where the desktop runs an application that turns it into a server capable of receiving messages form the host to perform some tasks. • Desktop-driven client/server computing is where the host functions as a transaction processing server and the desktop submit queries to it. • Peer-to-peer computing is where processing occurs simultaneously on both the desktop and host, with control switching between the two.

  46. Cooperative Processing • Permits lower-cost computing • Makes the end user the focus of computing • Expands the computing universe by aiming at work groups • Supports new organizational structures via its connectivity • Increases organizational flexibility

  47. Guidelines For Building Networks • Create an overall architecture - meaning a set of company policies and rules which, when followed, are expected to lead to the network environment that is desired • Stress connectivity - the goal today is not a single, coherent network, but rather finding a means to interface many dissimilar networks • Use standards - Most complications in networking are caused by incompatibilities which can be reduced by using standards. In fact, standards should be the foundation of an overall architecture.

  48. Network Connectivity Components • Bridges • Link two similar networks together • Routers • provide additional translation and route selection features • Gateways • link dissimilar networks • Smart hubs

  49. Network Architecture • Not a diagram or a set of diagrams • Not one utopian solution for all network problems • Set of policies, principles, and guidelines that will lead to more widespread connectivity

  50. OSI’s Seven Layers • The Physical Layer • The Data Link Layer • The Network Layer • The Transport Layer • The Session Layer • The Presentation Layer • The Application Layer