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Networks Today
ISOM 591
February 28, 2000
Distributed Processing
• more than one processor is used to perform a
task
• the processors are interconnected and
communicate with each other
• architecture is multiple computers distributed
throughout the system interconnected through
networks using communications lines
Distributed Processing
• goal is to move the processing as close to
the user as possible or to use those
machines which perform a specific job best
• distributed databases can be used for
increased efficiency
Types of Distributed Systems
• hierarchy of processors in a mainframe
environment
• LAN-based systems
• LANs which communicate with mainframebased systems
• network of networks like the Internet
Client Server Computing
• special form of distributed
processing in which resources
and tasks are spread across two
or more computer systems in
which the roles of client and
server are clearly defined
• servers are shared devices like
file server
• clients are workstations or PCs
Client Server Computing
• clients' requests are performed by the
server, which can be a microcomputer, mini,
or mainframe
• processing is carried out on machines
closest to the physical location of the data
and on machines optimized to perform highspeed database processing and
computations
Client Server Computing
• Only the results of the processing are sent to
the client by the server, which results in
smaller size files which are transferred.
• Thin client model places most of the
processing power in the server
– the ultimate thin client is the dumb terminal
• thick client model places much processing
power in the client
Types of Networks
• A network is a set of connected devices (nodes)
which share resources and can access each other
• public vs. private network
– local loop is a public network
– your organization’s LAN is private
• VANS (value-added networks)
– semi-private networks which offer enhanced services
like error management and message handling
LANs, MANs, WANs
• LANs connect devices within the same
building or campus
• MANs connect devices within the same
metropolitan area and typically utilize
services provided by local phone companies
• WANs connect devices across great
distances
Types of Networks
• interorganizational vs. intraorganizational
– networks can be established between
organizations (extranets)
• ex: WalMart and its suppliers
– networks can be established for use within the
organization only
• Loyola University’s Intranet
• domestic vs. international
• network of networks
• the Internet interconnects networks
Types of Networks
• Virtual private networks (VPN)
– private network which uses public
communication lines supported by a service
company
Types of Networks
• intranet
– private network accessible to authorized users
in an organization
– can be global
• extranet
– private network accessible to authorized users
in group of organizations which need to
communicate and perform transactions with
each other
Typical Network
• client or workstation (can play the role of
sender or receiver)
• host computer or server (can play the role of
sender or receiver)
• circuit or communications channel
A LAN Example
Other LANs
Gateway / bridge
Printer
Workstation
File server
Workstation
Network Components
• terminals and workstations
– PCs, intelligent workstations, bar code readers,
telephones, mobile phones, mainframes
• transmission links
– twisted pair, coaxial cable, microwave links,
satellite, fiber optics, radio frequency (a type of
wireless transmission)
• transmission methods
– protocols for sending and receiving information
Network Components
• nodes and switches
– switches route and coordinate network traffic
– a node is a connection point on the network
– nodes often contain switches or a series of
switches
– bridges, routers, PBXs, multiplexors, gateways,
concentrators, FEPs
Network Components
• architecture and standards
– architecture is the blueprint for the structure of
the network
– examples: SNA, OSI
– standards are procedures for sending and
receiving information
– examples: X.25, X.400, ethernet, token ring
Switching
• Circuit switching
– switches are used to create a circuit to connect
sender to receiver
– ex: telephone calls
• packet switching
– a message is disassembled into packets
consisting of control data and the message data
– packets are sent independently throughout a
network and then reassembled
Architecture: A Layered
Approach
Application
Application
Network
Network
Data Link
Data Link
Physical
Physical
Architecture: A Layered
Approach
• application layer
– application software serving as the user interface
• network layer
– translates the destination of the message into an
appropriate address
– determines route through the network
– collects message accounting information
Architecture: A Layered
Approach
• data link layer
– decides when to send the message
– formats the message
– detects and corrects errors
• physical layer
– physical connection between hardware devices
An Example WAN
Client
Host
Modem
Local Loop
Switching
Central Office A
FEP
Switching
Central Office B
The Need for Standards
• Hardware needs to physically interconnect
and transfer data
• compatibility is needed in communications
protocols, transfer modes, packet sizes and
specifications, error checking
• maintain minimum levels of quality