chapter 6 networks and telecommunications

Chapter 6Chapter 6Networks and TelecommunicationsNetworks and Telecommunications

The StrategicManagement of

InformationTechnology

Transaction Processing Transaction Processing SystemSystem

Input OutputProcess

Information

Communication

Systems Development

Local Area NetworksLocal Area Networks

Local Area Networks: Local Area Networks: A DefinitionA 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

Local Area Networks:Local Area Networks:ReasonReason

Performance Change Management Systems Management Network Management Direct Communication Ease in Installation and Maintenance

Network ProtocolsNetwork Protocols

1. Physical Layer– Interfaces between Network Medium and Network Drives– Defines Electrical and Mechanical Characteristics of

Network– Bad Plug

Network ProtocolsNetwork Protocols 2. Logical Link Layer

– Frames Packets

– Controls Physical Layer Data Flow

– Data Colision 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

Network ProtocolsNetwork 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

Communication according to the Open Communication according to the Open System Interconnection Reference ModelSystem Interconnection Reference Model

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Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Physical LayerPhysical Layer

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Physical Layer

Hardware Description:The interface to the physical cable mediumis described; layout of connectors, signalson each connector, voltage levels.The physical connection to the network, how connections are established and maintained,and how error conditions in data medium arehandled.

Data Link LayerData Link Layer

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Data Link Layer

Software Description:Transmit blocks of data from the data link layerin one computer to another.Detect errors in data blocks and either correctthe errors or ensure retransmissions of theeffected data blocks.

ProtocolsProtocols 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.

ProtocolsProtocols 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.

TopologiesTopologies Star Topology Bus Ring Physical Star, Logical Ring

TopologiesTopologies 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.

TopologiesTopologies Bus Topology

– One cable passed throughout entire implementation and to which each unit is connected.

– Network cannot be centrally controlled.

BUS

TopologiesTopologies 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


– 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 INFOFC FCSSADA RI ED FS


– 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.

TopologiesTopologies 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.

WiringWiring

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

Cost-effective ways to increase accessCost-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

Cost-effective ways to increase access:Cost-effective ways to increase access:Multiple Access UnitsMultiple 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

Cost-effective ways to increase access:Cost-effective ways to increase access:FDDI and APPNFDDI 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 comunicating 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.

Cost-effective ways to increase access:Cost-effective ways to increase access:Bridges, Gateways, and RoutersBridges, 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.

Network LayerNetwork Layer

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Network Layer

Responsible for buffering and routing packets throughout the network. (Virtual Circuits)Essential in Wide Area Networks, not used in bus-topology LANs.

Network LayerNetwork Layer

Novell

UNIX

Microsoft/NT

OS/2

Network Operating System

DefaultPrtocol

Wide AreaNetwork

IPX/SPX

TCP/IP

Net/BIOS

NDS

DCE

Internet Packet Exchange/Sequence Packet Exchange(lower/higher)

Transmission Control Protocol/Internet Protocol(higher/lower)

Basic In Out System

Naming Convention

Addtitional Security

Transport LayerTransport Layer

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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 bu the network.Above it, messages are the information units.

Session LayerSession Layer

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Session Layer

Responsible for providing a communicationsession between two user processes running on two separate network nodes. Responsible for determining whether a session can begin, be maintained, or terminated.

Presentation LayerPresentation Layer

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Presentation Layer

Converts user messages from the form used bu the application layerto that used by all lower layers. Below this layer, the meaning of data fields of messages and packets does not influence their processing.

Application LayerApplication Layer

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Boundary between the OSI networkand the application (user) processes.If a LAN operates as a distributedsystem, the application layer is responsible for direct communicationwith elements of the distributedoperating system.

Architectural Layers and TiersArchitectural Layers and TiersArchitectural Layers

Network Server

UserInterface

Function Set

DatabaseAccess

DataPartitioning

DataTransport

TranslationLayer

CommunicationProtocol

Data Objects

Data Dictionary

Client

Architectural Layers and TiersArchitectural Layers and TiersTiered-Architecture

Processing DataPresentation

Client

Client

FunctionalityServer

FunctionalityServer

FunctionalityServer

FunctionalityServer

DatabaseRemoteProcedureCalls

Database

Architectural Layers and TiersArchitectural 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

Architectural Layers and TiersArchitectural 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

Local Area NetworksLocal Area Networks

Important Mechanism to Integrate:– Hardware– Software– Application Development Environment

Communication according to the Open Communication according to the Open System Interconnection Reference ModelSystem Interconnection Reference Model

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Presentation Layer

Session Layer

Transport Layer

Network Layer

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Physical Layer

Changes In The MarketplaceChanges 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

Cooperative ProcessingCooperative 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.

Attributes of Cooperative Attributes of Cooperative ProcessingProcessing

Distributed processing Connectivity among processors Distributed databases System-wide rules

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

Connectivity ElementsConnectivity Elements

Building Cooperative Building Cooperative Processing SystemsProcessing 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.

Components Of Cooperative Components Of Cooperative Processing SystemsProcessing 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.

Forms Of Cooperative Forms Of Cooperative ProcessingProcessing

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.

Cooperative ProcessingCooperative 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

Guidelines For Building Guidelines For Building NetworksNetworks

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.

Network Connectivity Network Connectivity ComponentsComponents

Bridges– Link two similar networks together

Routers– provide additional translation and route

selection features Gateways

– link dissimilar networks Smart hubs

Network ArchitectureNetwork 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

OSI’s Seven LayersOSI’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

Broadband Broadband TelecommunicationsTelecommunications

Where more than one signal travels over a communication medium at one time. As organizations put more kinds of data on computers, they need greater bandwidth to whip this data around.

How a Telecommunications System Is How a Telecommunications System Is Analagous To a Highway SystemAnalagous To a Highway System

The Flows - The flow of information within and between the corporate office, departments, and individuals is analogous to the traffic flow in the highway system within and between cities.

Building of Systems - Information systems departments are responsible for designing, building, and maintaining the information system in the same way that governments are responsible for building and maintaining streets, roads, and highways for cars and trucks.

Managed by Users - Once built, both systems are managed not by builders but by users or drivers.

Standards - Government agencies provide standards and laws for regulating the flow of highway traffic, that are enforced by police. Similarly, the information systems function develops and enforces the telecommunications standards for message traffic.

““Facts of Life” in the Telecommunications Facts of Life” in the Telecommunications IndustryIndustry

Organizations have a multitude of networks The reach of networks is expanding organizationally The telecommunications industry is being destabilized Global network services are emerging New technologies are improving bandwidth utilization The focus of network designers is now

interconnecting LANs Electronic mail provides a new communication

infrastructure

Murray’s Eight Phases to a Totally Distributed SystemMurray’s Eight Phases to a Totally Distributed System

Phase 1: The first phase is characterized by host-based, real-time query and update. This phase is traditional on-line information system processing, where dumb terminals access host-based applications to view and update data

Phase 2: The second phase provides additional query capabilities through file transfers to PCs.

Phase 3: The third phase adds batch updating form PC data. This phase reverses the philosophy of Phase 2 by making the PC database the master.

Phase 4: The forth phase enables real-time query and update from either host or PC. This phase extends the capabilities of the PCs by allowing them to update the host on-line.

Phase 5: The fifth phase introduces homogeneous cooperative processing without two-phase commit, that is, like databases run on the same hardware and system software platforms. This phase adds true distributed databases, across similar or identical platforms.

Phase 6: The sixth phase moves to heterogeneous cooperative processing without two-phase commit, that is, databases run on a mix of platforms. This phase extends the previous one by permitting distributed databases across mixed platforms.

Phase 7: This seventh phase adds the all-important two-phase commit capability (to homogeneous databases), going a system a true distributed database.

Phase 8: This phase extends Phase 7 to heterogeneous databases.

Personal Communications Personal Communications NetworksNetworks

Permit person-to-person rather than location-to-location. Each person will have his or her own personal phone number

associated with a lightweight telephone that he or she carries around.

Each person will not only transmit telephone conversations but also computer-based information, voice mail, electronic messaging, call screening, and other personal from anywhere.

Important technology for– emergencies

natural disasters– special events

political conventions and sporting events

Wireless LANs Will Likely be Wireless LANs Will Likely be the Best Alternativethe Best Alternative

Wireless LANs have the advantage in hazardous environments, in historic buildings where wiring ducts are full, for disaster recovery, and in temporary installations. Furthermore, there are many instances where temporary communications are needed, and wireless are much easier to reconfigure. Wireless LANs use either light (in the form of infrared) or radio (in the form of narrowband or spread spectrum) technologies to transmit signals.

T-Carriers Hierarchy and T-Carriers Hierarchy and DifferenceDifference

A T1 line is equivalent to a group of 24 voice grade lines, which means its capacity is 1.544 million bits per second (mbps).

A T2 trunk has a capacity of 96 voice circuit equivalent (6.312 mbps), T3 has a 672 voice circuit equivalent (44.736 mbps) and T4 has a 4,032 voice circuit equivalent (139.264 mbps).

T-carriers are used mainly to carry analog voice signals that have been digitized, while the nomenclature of DS represents the arrival of true end-to-end digital circuits.

Fast Packet Switching Fast Packet Switching TechnologiesTechnologies

Frame relay uses variable-length packets and is slated to replace the workhorse of today’s data networks, X.25. It is most appropriate for sending large bursts of data.

Cell relay is faster than frame relay because it transmits fixed-length packets, which require less processing. It is most appropriate for transmitting packets that must be received in sequence and at standard intervals, such as voice and video.

Network ComponentsNetwork Components Network File Server Network Operating System Network Interface Card Workstation Software Connection Network Wiring Hub Backup Device

Network AdvantagesNetwork Advantages Sharing Printers and Other Devices Providing Mass Storage Sharing Data Providing Network Security Providing Communication Services Sharing Software Facilitating Group Interaction Permitting Distributed Processing Enhancing Software Support and Training

Key Client/Server IssuesKey Client/Server Issues

Ability to Build Graphical User Interfaces Compenent Re-Use Team Development Deployment Scalability Cross Platform Delivery Adaptability Design/Integration

Key IssuesKey Issues

Strategic Business Objectives Software Fit Software Customization User Productivity Information Access Flexibility and Adaptability Software Implementation System Performance Customer Service Cost of Ownership

Client/Server EvaluationClient/Server Evaluation Object-Oriented Technology Integration of Third Party Components Application Partitioning Interpreted or Compiled Code Multiplatform GUI and Operating Systems Team Development Ease in Application Maintenance Open Connectivity to Multiple Databases On-Line Transaction Processing Applications

SONETSONETThe transport network for broadband services will

be SONET (synchronous optical network), a set of international standards for transmission over fiber-based networks at speeds of 51.84 mbps (above T3) to a shopping 13 gigabytes per second. its importance lies with the fact that SONET will allow networks to use equipment from different vendors due to its “mid-span meet”-an information model and messages sets for making translations among equipment.

FDDIFDDI

FDDI (fiber distributed data interface) is an international standard for operating a fiber optic cable network at 100 mbps (nearly T4 speed). It is most appropriate for backbone networks that link LANs in a building or between buildings, because it can support up to 500 workstations up to two kilometers (1.2 miles) apart.

chapter 6 networks and telecommunications

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