CHAPTER 12: WAN System Software

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CHAPTER 12 WAN System Software

• MIS 3523 Business Data Communications
• Dr. Segall
• Spring 2002
• REVISED FOR FINAL EXAM!!!

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CHAPTER OBJECTIVES

• 1. Describe the functions of the OSI session
  layer.
• 2. Discuss the functions provided by an operating
  systems and device drivers.
• 3. Compare database and telecommunications access
  methods.
• 4. Explain the capabilities of a teleprocessing
  monitor.
• 5. Trace the flow of a transaction through a
  system.

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OSI SESSION LAYER

• OSI (Open Systems Interconnection)
• Recall OSI Reference Model from Benjamin-Cummings
  Module Session 1-Chapter 1.
• Recall 7 Layers in OSI Reference Model
  1.Physical, 2.Data Link, 3.Network, 4.Transport,
  5.Session, 6.Presentation, 7.Application.
• In this chapter, we will primarily address
  functions in the 5th or Session Layer.

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INTRODUCTION

• SYSTEM SOFTWARE
• software that supports applications in carrying
  out their tasks.
• Examples include
• Operating Systems software
• Data Communications software.
• Software exists at each of the layers of the OSI
  Reference Model upward from Data Link layer.

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Software Overview

• Types of Software
• 1. Application Software examples are
  manufacturing software, ORACLE
• 2. System Software includes Operating System
  (OS) software that supports applications in
  carrying out their tasks. Examples of OS include
  Novell, Windows NTS.
• Figure 12-1 on page 343 gives a Generic Software
  Configuration.The data communications portions of
  that environment are discussed in this Chapter.

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Software Overview

• Two major components of Networking Software
• 1. Access Methods
• Provides interface with terminals devices and
  application independence.
• 2. Transaction Control Processes (TCP)
• Also provides interface between terminal and
  application independence.
• Functions provided by TCP interfacing
  applications devices go beyond those provided
  by the typical access method. These added
  capabilities include
• Data edits
• Message switching
• Data formatting
• Transaction definition and recovery.

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Operating System

• The overall manager of the computing system that
  performs all of its functions, transparent to the
  application program and the programmer.
• See Table 12-1 on page 344 for OS Functions of
• Interface Functions
• Provides interface to I/O system
• Process Functions
• Management Functions
• Manages I/O system devices using I/O Drivers.
• File Management Functions

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SOFTWARE OVERVIEW

• I/O Drivers
• Part of OS that manages the I/O subsystem by
  providing low-level access to devices.
• As can be seen from Figure 12-1 on page 343, on
  the database side (Top part of Figure 12-1) the
  low-level devices are Disks, and on the data
  communications side (Bottom of Figure 12-1) the
  low-level devices are Communication Lines.

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SOFTWARE OVERVIEW

• Access Methods
• Exist for both database and data communication
  systems as shown on Figure 12-1.
• Subsystem that provides I/O services as an
  interface between an application and its
  associated devices.
• Essentially functions as a black box to translate
  user request into requests tailed to the file or
  device being accessed.
• Database access methods allow users to retrieve
  data.
• Data communications access methods allow users to
  display data on a terminal.

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Database and File Management Systems

• DBMS (Database Management Systems)
• A system that organizes data into records into
  files.
• Examples ORACLE, MS Access
• Uses DATA access methods to provide multiple
  paths to data.
• FMS (File Management System)
• A system that provides a SUBSET of a DBMS
  capabilities.
• Oriented toward ONE FILE hence does NOT provide
  file relationships,
• Provides functions such as storage allocation
  file access methods for a SINGLE file.

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Transaction Control Process (TCP)

• Also called a teleprocessing monitor or.
  message control system.
• Do NOT confuse with TCP/IP of Chapter 6 for
  Transmission Control Protocol/Internet
  Protocol!!!
• Enables different terminals to interface with
  multiple applications and removes an application
  from details such as discussed in text on page
  345.
• Uses different TERMINAL access methods to give
  access to multiple terminal types.

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An Example of Transaction Flow

• An illustration of how the software components
  cooperate in processing a transaction.
• Transaction Example in text on pages 346-8 is
  that of admitting a patient to a hospital.
• STEP 1 User selects the admit patient
  transaction from menu. The selection is
  transmitted to the TCP.
• STEP 2 The TCP responds to the users selection
  by displaying a patient ID form on the terminal
  and issues a read request for the terminal. The
  user completes the form and transmits it to the
  TCP.

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An Example of Transaction Flow

• STEP 3 TCP receives the transaction from the
  terminal.
• STEP 4 The TCP sends the patients ID to an
  application with a request to find a patient
  record that matches the requested ID.
• STEP 5 A database read request is made to obtain
  patient record with ID indicated.
• STEP 6 The application returns the result to the
  TCP.
• STEP 7 TCP receives all data necessary for
  admitting patient.
• STEP 8 Data checks edits.

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An Example of Transaction Flow

• STEP 9 TCP writes transaction log.
• STEP 10 Modify database per transaction log.
• STEP 11 Determination of application(s)
  processes.
• STEP 12 Application selected begin processing.

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An Example of Transaction Flow

• STEP 13 Application requests DBMS and acts on
  it.
• STEP 14 DBMS inserts the patient record and
  returns result status to the application.
• STEP 15 Formats a reply message returns it to
  the TCP.
• STEP 16 TCP determines if another application
  process must become involved in the transaction.
• STEP 17 Application process completed and
  indicates system readiness to accept another
  transaction.

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Data Communication Access Methods

• Allow system users easier access to terminal
  devices.
• Application-Terminal Connection
• One of the functions of an access method.
• May be accomplished by having a pool of
  applications and a pool of available terminals as
  shown in Figure 12-2 on page 349.
• Access method serves as a switch to connect
  terminal requests with the proper applications.

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Data Communication Access Methods

• Accessing a Terminal
• Can be used with or without a TCP as shown in
  Figure 12-3 on page 350.
• With a TCP
• Access method performs fewer functions because
  TCP performs some functions such as message
  routing data editing.
• See Figure 12-3(b) on page 350.

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Data Communication Access Methods

• Without a TCP
• Access method makes the connection between an
  application program and a terminal.
• Could be Static in which the application
  terminal are attached to each other the
  terminal can run only the transaction provided by
  that particular application.
• VTAM (Virtual Telecommunications Access Method)
  by IBM provides several methods for
  terminal-applications connections.

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Transaction Control Process

• TCP Configuration
• Serves as a SWITCH between applications
  terminals. See Figure 12-4 on page 351.
• Must be aware of
• 1. Terminals attached to it.
• 2. Transactions that can be submitted.
• 3. Applications responsible for processing those
  transactions.
• Implementation
• Can be MONOLITHIC as in Figure 12-5(a) on page
  352
• Can be MULTIPLE process as in Figure 12-5(b) on
  page 352.

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Single Threading vs. Multiple Threading

• Single Threading only ONE operation is processed
  at a time.
• See Figure 12-6(a) on page 353.
• Analogy ONE customer processed processed in
  grocery market until total order has been
  tabulated money collected before processing
  next customer.
• Multithreading MULTIPLE operations are processed
  concurrently.
• See Figure 12-6(b) on page 353. INCREASE in
  number of PROCESSES, INSTRUCTIONS EXECUTED, and
  TOTAL MEMORY REQUIREMENTS .
• Example waiter or waitress in restaurant.
• Analogy EVERY customer in line would receive
  attention as time allows. Price check holding up
  processing of one customer would transfer
  processing time to next customer in line. While
  check is being written, another customer would be
  served.

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Maintaining Context

• Context Data
• requirement of multithreaded processes that keeps
  track of completed parts as well as the parts yet
  to be worked on, and ensuring that an interrupted
  transaction is restarted at the correct point.
• SUMMARY OF EXAMPLE from text
• 4 Terminals (T1 to T4) and 3 Applications (A1 to
  A3)
• Chronological record of the TCPs activities are
  listed in Table 12-2 on page 354.
• Consists of ACCEPT..., WRITE ..., ACCEPT ....,
  ROUTE ..., etc.

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TCP (Continued)

• Memory Management
• Functions provided by the TCP that manage context
  information and accept data from both terminals
  and applications.
• Can handle multiple messages that may be queued
  up simultaneously.
• Transaction Routing
• Routing of a transaction received from a terminal
  to 1 or more application programs.
• See Figure 12-7 on page 355 for Transaction
  Routing in a TCP of a BANK.

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TCP (Continued)

• Transaction Log
• Records all of the data received and is used in
  recovering from failures and in system auditing.
• In some systems could be synchronized with the
  database logging function so that transaction
  such as to a bank account would be reprocessed in
  the correct sequence of events in the advent of
  system failure.
• Security Statistics
• Statistics could be necessary to effectively
  manage a network system and collected in a TCP
  such as
• number of transactions from all terminals
• types of transactions
• number of characters transmitted from all
  terminals

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TCP (Continued)

• Message Priorities
• Priorities could be assigned by TCP according to
  source and type of message.
• Application Development
• TCP can provide features to make testing
  debugging easier such as the ability to trace or
  examine transactions received by the TCP.
• The TCP should allow concurrent running of
  production applications and test applications

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TCP (Continued)

• Operation Interface
• Allows network administrator the ability to
  monitor control the TCP environment such as
• Adding terminals applications
• Starting or stopping devices
• Reconfiguring the system
• See Figure 12-8 on page 358 for TCP-Operation
  Interface.
• See Page 357 for list of List of Operation
  Interface Capabilities.

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TCP (Continued)

• List of Operation Interface Capabilities
• TCP Interface
• Defining lines, terminal, or applications
• Stopping lines, terminals, or applications
• Deleting lines, terminals or applications
• Displaying statistics

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TCP (Continued)

• List of Operation Interface Capabilities
• TCP shutdown
• Starting lines, terminals, or applications
• Adding lines, terminals, or applications
• Enabling/disabling statistics
• Moving lines, terminals, or applications from one
  TCP to another

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TCP (Continued)

• Other TCP Functions
• Start Stop Applications
• Load Balancing
• See Table 12-3 on page 358 for a summary of TCP
  Activities.

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Exercise 6 on page 359 Compare and contrast the
functions of a local area network file server and
a TCP. 
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P E 6 on page 359COMPARE AND CONTRAST THE
FUNCTION OF A LOCAL AREA NETWORK FILE SERVER
TCP.A LAN server and a TCP have several common
capabilities. Some of these are 1.
multi-threading 2. receives inputs from a
variety of requesters 3. manages queues, memory,
and buffers The primary differences are1.
Servers often run in a dedicated processor, TCPs
operate in a shared environment2. Servers have
multiple requesters but relatively few servers
while a TCP will likely have many terminal
requesters and many application servers 3.
TCPs deal mainly with messages and transactions
while file servers deal mostly with downloading
files.
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WAN System Software

• THE END!!!