Transcript Systemic Semiotic Design Practice:
BUSS 909 Office Automation & Intranets
Lecture 2
Data Communication Technologies
Clarke, R. J (2001) L909-02: 1
Notices
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Clarke, R. J (2001) L909-02: 2
Agenda L909-02
Data Communications Principles and Technologies
in this lecture we
consider only the Data Communications technologies relevant to Office Automation
we will revisit this topic
lectures in subsequent Clarke, R. J (2001) L909-02: 3
Agenda T909-01
Writing for Commerce: Essays and Case Studies (differs from the published schedule) Clarke, R. J (2001) L909-02: 4
Office Automation Overview
Clarke, R. J (2001) L909-02: 5
Office Automation
the greatest proportion of work involves information in textual form:
procedures
reports
memoes
applies to:
service industries, bureaucracies, public sector organisations, and small large private sector organisations Clarke, R. J (2001) L909-02: 6
Office Automation
additionally, decision making (work about work) in any organisation is conducted in groups
these groups almost always are involved in language activities (reading, writing etc)
board room meetings
brainstorming sessions
formal reviews
shareholders meetings Clarke, R. J (2001) L909-02: 7
Office Automation
technologies called OA systems have been developed since the mid-1970s to cope with these kinds of work
generally these systems are based on networks of various kinds (we review the various types and some standard terminology used to describe them this lecture) Clarke, R. J (2001) L909-02: 8
Office Automation
these technologies at that time were very expensive (special hardware and software)
the leader was Wang Computers
by the mid 80s experimental systems were being researched to support
group-based activities
- this research is still ongoing (Nunamaker et al 1991 40-61) Clarke, R. J (2001) L909-02: 9
Office Automation
OA systems were augmented with systems that had similar functionality
other names that can be found include: OIS- Office Information Systems; EMS- Electronic Meeting Systems; Collaborative Management Systems Clarke, R. J (2001) L909-02: 10
Office Automation
much of this has been superceded by developments in the marketplace including
proprietary integrated software
eg. Lotus Notes; Microsoft Office97
also the WWW and graphical browsers provide a way for organisations to transform
desktop computing
to
webtop computing
Clarke, R. J (2001) L909-02: 11
Office Automation
but the research that led to these systems is still relevant as we try to implement the same functionality in the form of
intranets and extranets
(private networks based on Internet technology) Clarke, R. J (2001) L909-02: 12
Office Automation
an additional trend is to create the
virtual organisation
, which again is based on theory and principles established and developed during the mid-1970s
telework, remote work, mobile data systems etc Clarke, R. J (2001) L909-02: 13
Network Processing & Topologies
Clarke, R. J (2001) L909-02: 14
Network Terms
topology
= pattern of a network
circuit
transmission facility provides =>1 channels of communication eg/ phone line, microwave signal, optical cable
node
point in a network where circuits are interconnected by one or more units
may be other computers Clarke, R. J (2001) L909-02: 15
Network Processing
(1) Timesharing Networks
oldest approach
introduced in 3rd generation
consists of a single computer
performance limited to the computer Clarke, R. J (2001) L909-02: 16
Network Processing
(2) Distributed Processing
when minicomputers became popular
companies started distributing minis and micros throughout the organisation
when interconnected the technique is called
distributed computing
or
distributed data processing (DDP)
Clarke, R. J (2001) L909-02: 17
Network Processing
(3) Client/Server Computing
some functions are best handled locally and some are best handled centrally
blend of timesharing approach (central use) and distributed processing (local)
usually LANs but can be WANs
client
: user has access to network by means of desktop computer
server
: computer of any size which provides control of network function Clarke, R. J (2001) L909-02: 18
Network Topologies
(1)
describes how multiple computers are connected together (eg/
distributed processing, client/server computing
) on a network
several different topologies are available Clarke, R. J (2001) L909-02: 19
Network Topologies
(2)
Star Network
central computer called the
central node
guarentees centralised control
failure on central node causes failure over entire network Clarke, R. J (2001) L909-02: 20
Network Topologies
(3)
Ring Network
does not include a central node
control is distributed throughout network
failure in any link causes problem for network
Hybrid Network
star & rings can be used together
when this occurs the topology is referred to as a Hybrid Topology Clarke, R. J (2001) L909-02: 21
Network Management, Planning & Control
Clarke, R. J (2001) L909-02: 22
Network Management
(1)
often critical to firms
network failures can be catastropic
require planning and control
need to be managed
What would happen if a your banks ATM data comms network fails ?
Clarke, R. J (2001) L909-02: 23
Network Management
(2)
in large companies
network manager
network analysts
software analysts
datacom technicians
in small companies
LAN manager Clarke, R. J (2001) L909-02: 24
Network Management
(3) Network Manager
:
responsible
for
planning
implementing
operating
controlling
responsible
to
CIO Clarke, R. J (2001) L909-02: 25
Network Management
(4) Network Analyst
perform same function as systems analysts
restricted to communication-oriented systems
Software Analysts
program & maintain datacom software Clarke, R. J (2001) L909-02: 26
Network Management
(5) Datacom technicians
concerned with hardware and operations
LAN Manager
found in smaller organisations
members of information services
generally a member of using organisation
may perform all of the duties of network manager Clarke, R. J (2001) L909-02: 27
Network Planning
all activities that aim to anticipate firms networking needs Capacity planning
analyses & plans for traffic volumes
Staff planning
people to manage network & skills
Performance monitoring
analyse response times and potential changes Clarke, R. J (2001) L909-02: 28
Network Control
day-to-day monitoring
of the network
involves
fault detection
,
fault
isolation, network restoration
firm needs
standard procedures
to implement network control Clarke, R. J (2001) L909-02: 29
Network Architectures
Clarke, R. J (2001) L909-02: 30
Network Architectures
(1)
variety of hardware & software
products available from:
computer manufacturers
common carriers
data coms specialist companies
many suppliers & standards is a ‘mixed blessing’ Clarke, R. J (2001) L909-02: 31
Network Architectures
(2)
network architectures specify
protocols
rule for interfacing (interconnecting) various units
all data coms devices will follow specific protocols
variety of units led to a small number of
‘industry’ standards
Clarke, R. J (2001) L909-02: 32
Network Architectures
(3)
Industry standards include:
SNA (IBM)
BNA (Burroughs)
DSE (Honeywell)
One of the most common data coms standards is called OSI
Clarke, R. J (2001) L909-02: 33
Network Architectures
(4)
SNA
Systems Network Architecture
developed by IBM because it marketed 200 different data coms products
one of the first standards developed
a
proprietary
standard Clarke, R. J (2001) L909-02: 34
Network Architectures
(5)
SNA:
defines all activities involved in transmitting data through a network
transmitted from a user node
transmitted to a host node
transmitted through one or more
intermediate nodes
Clarke, R. J (2001) L909-02: 35
Network Architectures
(6)
separates
physical activities
that transmit data
and
logical activities
transmission that control Clarke, R. J (2001) L909-02: 36
Network Architectures
(7)
SNA
classifies logical activities into
layers
layers insulate users from changes in the datacom hardware and software
layers have become a common strategy in other datacoms standards Clarke, R. J (2001) L909-02: 37
OSI Model
Clarke, R. J (2001) L909-02: 38
OSI Model
(1)
OSI = Open Systems Interconnection
almost all Network rely upon this Model to organise communications between Clients and Servers
uses layers like SNA to define physical and logical layers
7 layers are used; all nodes have them Clarke, R. J (2001) L909-02: 39
OSI Model
(2)
A layer at one node (user) ‘talks’ to its corresponding layer at the other (host) end
Layers 1-3 needed at every node; Layers 4-7 at host & user nodes only Clarke, R. J (2001) L909-02: 40
OSI Model
(3)
1: Physical Layer
Transmits the data from one node to another
eg./ RS232c
2: Data Link Layer
Formats the data into a record called a frame
Performs error detection Beginning Flag Address Control Message Frame Check Ending Flag Clarke, R. J (2001) L909-02: 41
OSI Model
(4)
3: Network Layer
causes the physical layer to transfer the frames from node to node
4: Transport Layer
enables user and host nodes to communicate with each other
synchronizes fast- and slow- speed equipment as well as overburdened and idle units Clarke, R. J (2001) L909-02: 42
OSI Model
(5)
5: Session Layer
initiates, maintains and terminates each session
sessions consist of all frames that comprise an activity, and all signals that identify beginning and end
eg./ log-on and user id routines to initiate sessions Clarke, R. J (2001) L909-02: 43
OSI Model
(6)
6: Presentation Layer
formats data for presenting to user or host
eg./ information to be displayed on users screen is formatted into proper number of screen lines and characters per line
7: Application Layer
controls user input from the terminaland executes the user’s application program Clarke, R. J (2001) L909-02: 44
OSI Model
(7)
Eg./ User needs host software
L7 (application) takes request
L6 (presentation) changes input data to correct format for transmission
L5 (session) starts the session on the host machines
L4 (transport) selects route from user to host
L3 & 2 (network & data link) cause data to be transmitted through L1 (physical) Clarke, R. J (2001) L909-02: 45
USER
High Low
OSI Model
(8) 7: Application Layer
consists of application programs that use the network
6: Presentation Layer
standardises data presentation to applications
5: Session Layer
manages sessions between applications
4: Transport Layer
provides end-to-end error detection and correction HOST
High 3: Network Layer
manages connections across the network for the upper layers
2: Data Link Layer
provides reliable data delivery across the physical link
1: Physical Layer Low
defines the physical characteristics of the network media Clarke, R. J (2001) L909-02: 46
User Actions Terminal Software or ROM Routines Protocols
User Node
OSI Model
(9) Intermediate Nodes Host User Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1
P P P AP SP
3 2
SP SP/P P P
3 2 1
P
1
P P P
Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1
Host Front-end or switching Node Front-end Processor Channel Devices
Front-end processor Cluster Control Unit
Clarke, R. J (2001) L909-02: 47
Web Clients & Servers
Source: Yeager & McGrath (1996, 11-16) Clarke, R. J (2001) L909-02: 48
Internet
Internet (=Internetworking)
collection of computer networks and to allow interoperability between them
networks can consist of many types of network technologies, protocols, and computers
Several protocols are required for transmitting data across the Internet (TCP/IP) Clarke, R. J (2001) L909-02: 49
Internet
Internet Protocol
IP manages the
transfer of data across physically distinct networks
transfers data into
packets ‘envelope’
within an that describing its source and destination
a message is in effect shattered into pieces, packaged as packets in envelopes, and burst transmitted to the destination
IP looks after delivering these packages one packet at a time! Clarke, R. J (2001) L909-02: 50
Internet
Transmission Control Protocol
networks are unreliable and IP does not guarantee that all pieces arrive (no notion of a
connection
)
TCP defines conventions that make sure the pieces arrive in the correct order
- by specifying another envelope around the data packets
IP layer moves packets, TCP manages the connection
Clarke, R. J (2001) L909-02: 51
Internet
Other Services & Protocols
the
layering
or
encapsulation
which is a characteristic of OSI also works in much the same way with other services supported by the Internet (TCP/IP)
File Transfer Protocol
defines the conventions which describe how computers can cooperate in order to copy files from one computer to another on the Internet- it uses TCP/IP to do this Clarke, R. J (2001) L909-02: 52
Internet
Other Services & Protocols Internet Protocol; Transmission Control Protocol; File Transfer Protocol FTP TCP IP FTP Physical Network TCP IP Clarke, R. J (2001) L909-02: 53
Internet
Web Services & Protocols
the web is just another internet service!
Hypertext Transfer Protocol (HTTP) is the set of rules for making and fulfilling web requests
however, the web is also designed to encapsulate other protocols including FTP, Gopher, WAIS, telnet and NNTP- we will talk about these services latter Clarke, R. J (2001) L909-02: 54
Internet
Web Services
works as a
client-server
- in terms of services not necessarily hardware
differs from other
network models
(terminal to mainframe; and peer-to peer) because client and server are independent, fully functional computer systems in their own right Clarke, R. J (2001) L909-02: 55
Mainframe & Terminal
Internet
Web Services Typing Printing Client-server Request Reply Peer-to-Peer
Send Message Send Message Clarke, R. J (2001) L909-02: 56
Intranets & OA
Success of WWW- Open Standards
machines on the Internet are effectively decentralised
an important aspect of the web is that it is a set of open (not proprietary) protocols:
Uniform Resource Locators URLs
Hypertext Transfer Protocol (HTTP)
Hypertext Markup Language (HTML) Clarke, R. J (2001) L909-02: 57
Intranets & OA
Success of WWW- Specific Issues
web protocols are general enough to be implemented on any computer
web application are the ‘topmost’ layer in the Internet protocol hierarchy
complex processes of transfer of data are ‘hidden’ from the web application developer and user
as a consequence there is a great variety of web applications available Clarke, R. J (2001) L909-02: 58
Web Servers & Clients
Source: Yeager & McGrath (1996, 11-16) Web Web FTP TCP IP FTP Physical Network TCP IP Clarke, R. J (2001) L909-02: 59
Summary
Clarke, R. J (2001) L909-02: 60
Intranets & OA
Failure of OA- Proprietary Technologies
OA did not become very important because they were based on
proprietary technologies
implies ‘closed’ technologies and markets- ultimately counter-productive!
slow development time, large market lags, small client bases, under utilised technology, increased expense in setup, use, maintenance, upgrade Clarke, R. J (2001) L909-02: 61
Intranets & OA
Failure of OA- Specific Issues
data sometimes had to be
re-entered
proprietary technologies mean that other vendors don’t have the technical information needed to write transfer routines
had to rely on the vendor to keep the technology current- there development team is the only one available to service your needs
incompatibilities
can’t supplement the OA vendors equipment with other vendors products Clarke, R. J (2001) L909-02: 62
From OSI to TCP/IP
OSI 7: Application Layer 6: Presentation Layer 5: Session Layer 4: Transport Layer 3: Network Layer 2: Data Link Layer 1: Physical Layer TCP/IP
4: Application Layer
consists of applications and processes that use the network
3: Host-to-Host Transport Layer
provides end-to-end data delivery services
2: Internet Layer
defines the datagram and handles the routing of data
1: Network Access Layer
consists of routines for accessing physical networks Clarke, R. J (2001) L909-02: 63
Next Week
Lecture (L909-03):
Office Automation Systems Computer supported Cooperative Work/Groupware
Tutorial (T909-02):
Search Engines & Techniques (differs from Tutorial Schedule) Clarke, R. J (2001) L909-02: 64