Introduction to Networks

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Introduction to Networks
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The library

• Computer networks allow us to
• Order books online
• Receive access to online databases
• Receive software updates

• Use networked computers to
• Create or download catalog records for our
  holdings
• Create electronic bibliographies

A system view
Environment
U s e r s
Inputs
Outputs
Transformational process
energy money materials personnel information
products services
Many of our products and services are delivered
to our users via computer network
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Connectivity of Public Libraries
Information Use Management Policy Institute
http//www.ii.fsu.edu/plinternet_findings.cfm
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Computers in libraries
Stand-alone pc or Mac
Mainframe "dumb" terminals
Networked computers and peripherals
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Local Area Network (LAN)
A communication network used by a single
organization over a limited distance which
permits users to share information and resources.
Schatt, Stan. 1992. Understanding local area
networks. 3rd ed. Carmel, Indiana SAMS.
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Local Area Network elements

• Transmission medium - type of wire or other medium

Network topology - architecture
Transmission protocol - rules followed when
sending signals
Software
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Transmission media (1)

• Unshielded twisted pair (UTP)
• Least expensive
• Four pairs grouped in plastic sheath
• Each pair consists of two insulated wires twisted
  together
• Limited range - 10BASE-T max 100 meters (328 feet)

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Twisted pair (cont.)

• Category 3 up to 10 Mbps

Category 5 up to 100 Mbps
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Transmission media (2)

• Coaxial cable
• Copper conductor surrounded by insulation
• Span distance of 185 meters (607 feet) for thin
  Ethernet 10BASE-2)

Copper conductor
Plastic insulation layer
Braided metal shield
Cable jacket
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Transmission media (3)

• Fiber-optic cable
• Expensive
• Immune to electromagnetic or radio-frequency
  interference
• Capable of sending signals several miles
• Fast

Coating
Glass Core
Cladding
Strengthening fibers
Cable jacket
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Fiber optic transmission
Glass Core
Cladding
Cladding (light-refracting)
Light source
Cut-away view
Glass fiber (light-transmitting)
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Transmission media (4)

• Wireless
• Radio waves
• Can travel long distances ? interference
• Can penetrate buildings
• Omnidirectional
• Low bandwidth
• Microwaves
• Travel in straight line
• Good signal to noise ratio
• Do not penetrate buildings well
• Light waves
• Unidirectional - require laser and photodetector
  on both ends for two-way transmissions
• Line of sight--requires precise alignment of
  sender and receiver
• High bandwidth

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Network architecture - star topology
OPAC
printer
OPAC
Circulation
OPAC
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Network architecture - ring topology
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Ring topology
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FDDI (Fiber Distributed Data Interface)
Bidirectional token ring network
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Network architecture - bus topology
OPAC
Circulation Server
Bus
OPAC
OPAC
printer
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Network architecture - bus topology using switch
or hub
Hub
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Network protocol - token ring
Token passes from node to node
IEEE Std. 802.5 ISO/IEC 8802-5
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Network protocol - Carrier-Sense Multiple Access
with Collision Detection (CSMA/CD)

• User's workstation generates a signal to send
• Listens to detect a carrier signal from any other
  user
• If no other signal is detected, first user's
  message is sent
• User listens for message collision. If detects
  collision, waits random period of time, then
  restarts process

IEEE Std. 802.3 ISO/IEC 8802-3
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EtherNet frame (packet) format
FRAME CHECK SEQUENCE
DESTINATION ADDESS
SOURCE ADDRESS
PREAMBLE
TYPE
DATA
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Mix and match wiring and control topologies
Star wiring with token passing
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Network of networks
Bridge
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Adding wireless
Access point for wireless
IEEE Std. 802.11 ISO/IEC 8802-11
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Wide Area Networks (WANs)

• Component entities can be miles apart
• Often consist of multiple local area networks
  linked together
• Largest WAN is the Internet

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Internet (1)

• Late 1950s - Department of Defense communications
  went through public telephone network, considered
  vulnerable
• DOD wanted command-and-control network that could
  survive nuclear war

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Internet (2)
Switching office
Toll office
Toll office
Barans proposed distributed switching system

• Telephone system

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Internet (3)

• ARPANET (Advanced Research Projects Agency
  Network - U.S. Dept. of Defense Program)

First connections 1. UCLA (hooked up 9/2/69)
2. Stanford Research Institute (10/1/69) 3.
UCSB (11/1/69) 4. Univ.of Utah (12/69)
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Internet (2)

• Highly redundant network (many ways to get from
  point A to point B)

Uses packet switching
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Switched telephone network
Switchboard
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Long distance telephone switching
Trunk line
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If roads were like telephones
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Traffic flow
Beretania
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Packet switching

• Each message divided into packets
• Source
• Destination
• Packet number of how many packets
• Data

Packet switches (nodes on Internet) use
distributed adaptive routing
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Packet-switched network
switch
switch
switch
switch
switch
switch
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Network redundancy
switch
switch
switch
X
switch
switch
switch
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Required in order to be on the Internet

• Physical connection to someone who is already
  part of the Internet
• Utilize Internet Protocol
• Suite of software telnet, ftp, etc.
• IP address

hypatia.slis.hawaii.edu 128.171.58.11
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Surfing the 'Net
Server
Request messages
Text, graphics, error messages
Client
Webserver application responds to requests from
client
Browser application sends requests to server
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Getting a Web page

• Get numerical IP address
• Establish connection with machine running server
• Send request for file to server
• Server sends file
• Release connection
• Display text
• Repeat above steps to request images

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Universal Resource Locator (URL)
http//www.cool.com/mystuff/myfile.html
machine
directory
file name
protocol
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Getting the IP address
What is numerical address of www.cool.com?
Domain Name Server
Browser
123.157.78.99
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nslookup command on UNIX

• Tashi delek nslookup www.ala.org
• Server dns1.hawaii.edu
• Address 128.171.3.13
• Non-authoritative answer
• Name www.ala.org
• Address 66.158.92.67

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The IP address
128.171.94.192
Network class
No. of Network Bytes
Example
A
1
8.0.0.0
B
2
128.171.0.0
C
3
199.1.1.0
University of Hawaii is a Class B network
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The IP address
128.171.94.192
UH Network
Subnet
Machine
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Establish a connection
Client sends connection request to server
Server sends connection accepted response to
client
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Requesting receiving file
Client sends "GET /mystuff/myfile.html" command
to server
Server looks in mystuff directory
Server sends myfile.html to client
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Release connection
Client sends disconnect request to server
Server closes connection
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Display text and images
Browser displays text and images in accordance
with directions in HTML tags
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Reference models
OSI
TCP/IP
Application
Presentation
Application
Session
Transport
Transport
Internet
Network
Subnet (Host-to-network)
Data link
Physical
TCP Transmission Control Protocol/Internet
Protocol
OSI Open Systems Interconnection
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Networked communication
Client
Server
Application
Application
Transport
Transport
TCP/IP
Internet
Internet
Data link Physical
Data link Physical
OSI
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TCP/IP Layered standards architecture
Application
HyperText Transfer Protocol (HTTP). Browser
requests Web pages Webserver sends text,
graphics, or error messages
Transport
Transmission Control Protocol (TCP). Session
control divides msgs into segments adds header
to each segment with no. (e.g. 1 of 5) error
correction
Internet
Internet Protocol (IP). Adds header to each
segment containing routing information. Now
called packets.
Subnet
Data link - Transmission control for LAN. Now
called frames. Physical - Wiring, voltage,
connectors
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Sending out a request
Software at each layer adds header/trailer
Application
HTTP
Transport
TCP-H
Segment
Internet
IP-H
TCP-H
Packet
Data link Physical
DL-H
TCP-H
IP-H
Frame
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Receiving a request
Software at each layer strips off header/trailer
Application
HTTP req.
TCP-H
Transport
Internet
IP-H
TCP-H
Data link Physical
DL-H
TCP-H
IP-H
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Server responds
Client
Server
Application
Application
Transport
Transport
Internet
Internet
Data link Physical
Data link Physical
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Routing
Client
Server
Application
Application
Router
Transport
Transport
Internet
Internet
Internet
Data link Physical
Data link Physical
Data link Physical
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Standards organizations
IEEE - Institute of Electrical and Electronics
Engineers http//www.ieee.org/portal/site IETF -
Internet Engineering Task Force
http//www.ietf.org/ ISO International
Standards Organization http//www.iso.org/iso/en/I
SOOnline.frontpage NISO National Information
Standards Organization http//www.niso.org/
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IEEE - Institute of Electrical and Electronics
Engineers standards
802.3 Ethernet 802.5 Token ring 802.11 Wireless
LAN 802.15 Wireless personal area networks
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Internet2
High-speed applications, prioritizing packets,
etc.