Introduction to
Networks
Computer networks Use networked
computers to:
allow us to:
• Create or download
• Order books
A system view catalog records for our
online
holdings
• Receive access to
• Create and distribute
online
databases
Environment
electronic
• Receive software
bibliographies
updates
The library
Inputs
energy
money
materials
personnel
information
U
s
Outputs
Transformational
e
process
products
Many
of our products
r
andservices
services are
s
delivered via computer
network (e.g., virtual
reference)
Connectivity of Public Libraries
Information Use Management & Policy Institute
http://www.ii.fsu.edu/plinternet_findings.cfm
Computers in libraries
Stand-alone pc or
Mac
Mainframe & "dumb"
terminals
Networked computers
and peripherals
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.
Local Area Network
elements
Transmission medium - type of
wires or other media
Network topology - architecture
Transmission protocol - rules
followed when sending signals
Software
Transmission media (1)
Unshielded twisted pair (UTP)
– Least expensive (CAT 5e 1,000 feet for
$260 in Spring 2011)
– Four pairs grouped in plastic sheath
– Each pair consists of two insulated wires
twisted together
– Limited range - max 100 meters (328 feet)
Twisted pair (cont.)
Category 5 – up to 100 Mbps
Category 6 – up to 1000 Mbps
Transmission media (2)
Coaxial cable
– Copper conductor surrounded by
insulation
– Span distance of 185 meters (607 feet)
for thin Ethernet 10BASE-2)
Copper
conductor
Cable jacket
Braided metal
shield
Plastic
insulation
layer
Transmission media (3)
Fiber-optic cable
– Expensive
– Immune to electromagnetic or radiofrequency interference
– Capable of sending signals several miles
– Fast
Coating
Glass Core
Cladding
Cable jacket
Strengthening
fibers
Fiber optic transmission
Glass Core
Cladding
Light
source
Cut-away view
Cladding
(lightrefracting)
Glass fiber
(lighttransmitting)
ν*λ=c
Transmission media (4)
Wireless
– Radio waves
109 Hz
•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
1011 Hz
1015 Hz
– 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
Network architecture star topology
OPAC
printer
OPAC
Circulation
OPAC
Network architecture ring topology
Ring topology
FDDI (Fiber Distributed Data
Interface)
Bidirectional token ring network
Network architecture - bus
topology
Circulation
&
Server
printer
OPAC
Bus
OPAC
OPAC
Network architecture - bus
topology using switch or hub
Hub
Network protocol - token ring
Token passes from node to node
Token
Msg.
Msg.
Rec.
IEEE Std. 802.5
ISO/IEC 8802-5
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
EtherNet frame (packet) format
DESTINATION SOURCE
PREAMBLE
ADDESS
ADDRESS
TYPE
FRAME
CHECK
DATA
SEQUENCE
Mix and match wiring and
control topologies
Star wiring
with token
passing
Network of networks
Bridge
Adding wireless
Access
point for
wireless
IEEE Std. 802.11
ISO/IEC 8802-11
Wide Area Networks
(WANs)
• Component entities can be
miles apart
• Often consist of multiple local
area networks linked together
• Largest WAN is the Internet
Internet – Two tales
converge
• Late 1950s - Department of
Defense communications went
through public telephone
network, considered vulnerable
• DOD wanted command-andcontrol network that could
survive nuclear war
A robust proposition
Switching
office
Toll
office
Toll
office
Telephone
system
Baran’s proposed
distributed switching
system
Internet beginning
• 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)
Internet characteristics
Highly redundant network (many
ways to get from point A to point B)
(Baran’s idea)
Uses packet switching
(Clark’s idea)
Switched telephone network
A
B
Switchboard
Long distance telephone
switching
B
A
Trunk
line
If roads were like
telephones…
Traffic flow
Beretania
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
Packet-switched network
switch
switch
switch
switch
switch
switch
Network redundancy
switch
switch
switch
switch
X
switch
switch
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.
hypatia.slis.hawaii.edu
• IP address
128.171.58.11
Surfing the 'Net
Server
Client
Browser application
sends requests to
server
Webserver
application
responds to
requests
from client
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
Universal Resource Locator
(URL)
http://www.cool.com/mystuff/myfile.html
machine
protocol
directory file name
Getting the IP address
What is numerical address
of www.cool.com?
Browser
Domain Name
Server
123.157.78.99
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
The IP address
128.171.58.11
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 Hawai`i is a Class B network
The IP address
128.171.94.192
UH Network
Subnet
Machine
Establish a connection
Client sends “connection
request” to server
Server sends “connection
accepted” response to client
Requesting & receiving file
Client sends
"GET /mystuff/myfile.html"
command to server
Server looks in mystuff directory
Server sends myfile.html to client
Release connection
Client sends disconnect
request to server
Server closes connection
Display text and images
Browser displays text and
images in accordance with
directions in HTML tags
Sending data
Client sends
"GET /mystuff/myfile.html" command
to server
msg
1
msg
msg
2
3
Sending data
Client sends
"GET /mystuff/myfile.html" command
to server
msg
1
To: 123.157.78.99
Reference models
OSI*
TCP/IP‡
Application
Transport
Internet
Subnet
(Host-to-network)
‡TCP = Transmission Control
Protocol/Internet Protocol
Application
Presentation
Session
Transport
Network
Data link
Physical
*OSI = Open Systems Interconnection
Networked communication
Client
Server
Application
Transport
Internet
Data link
Application
Transport
Internet
Data link
Physical
TCP/IP
OSI
Physical
TCP/IP Layered standards
architecture
Application
Transport
Internet
Subnet
HyperText Transfer Protocol (HTTP).
Browser requests Web pages; Webserver
sends text, graphics, or error messages
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 Protocol (IP). Adds header to
each segment containing routing
information. Now called packets.
Data link - Transmission control for LAN.
Now called frames.
Physical - Wiring, voltage, connectors
Sending out a request
Software at each layer adds header/trailer
Application
Transport
Internet
Data link
HTTP
TCP-H Segment
TCP-H IP-H Packet
TCP-H IP-H DL-H
Physical
Frame
Receiving a request
Software at each layer strips off header/trailer
HTTP req.
TCP-H
TCP-H IP-H
TCP-H IP-H DL-H
Application
Transport
Internet
Data link
Physical
Shannon-Weaver
Communication Model
coded
Network
Channel
medium
Transmitter
Your
browser
Source
Receiver
decoded
Server
Destination
Server responds
Client
Server
Application
Transport
Internet
Data link
Application
Transport
Internet
Data link
Physical
Physical
Routing
Client
Server
Application
Transport
Internet
Data link
Internet
Data link
Application
Transport
Internet
Data link
Physical
Physical
Physical
Router
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/ISOOnline.frontpage
NISO – National Information Standards
Organization
http://www.niso.org/
IEEE - Institute of Electrical
and Electronics Engineers
standards
802.3
802.5
802.11
802.15
Ethernet
Token ring
Wireless LAN
Wireless personal area
networks
A Few Internet Issues
Problem
Every business or institution
on the Internet needs unique server
names to be registered in the DNS
www.hawaii.edu
Every entity
on the Internet
needs a unique address
128.171.224.100
ICANN
IP Version 4 Address
128.171.58.11
256
*
256
256
* *
256
4,294,967,296
Possible IP addresses
~3,700,000,000
Available IP addresses
Address Needs
IP Version 6 (IPv6) Number
2001:0DB8:0000:2F3B:02AA:00FF:FE28:9C5A
340,282,366,920,463,463,374,607,431,768,211,456
Possible IP addresses
The Domain Name
System
Visiting the MIT Library Website
http://libraries.mit.edu
Visiting the MIT Library Website
http://libraries.mit.edu
Universal Resource Locator
(URL)
http://libraries.mit.edu
protocol
machine
Human-readable address
Getting the IP (numerical) address
What is numerical address of
libraries.mit.edu?
Where does the local
Domain Name Server
get the
numerical address?
Our
Computer
Address:
18.51.0.23
Local
Domain
Name
Server
Domain Name System Hierarchy
libraries.mit.edu?
.com
Our
Local
DNS
.org
Root
.edu .gov
.af
Top-Level Domains
.al ...
The DNS hierarchy
Root
.com
.org
.edu .gov
.af
.al ...
Generic
Country-Code
Top-Level Domains Top-Level Domains
(gTLDs)
(ccTLDs)
http://www.iana.org/domains/root/db/
The DNS hierarchy
Root
.com
.org
.edu .gov
.af
.al ...
United States
Generic Top-Level Domains
(also .mil)
The DNS hierarchy
address for .edu
server
.com
Our
Local
DNS
.org
Root
.edu .gov
.af
.al ...
The DNS hierarchy
Root
.com
.org
.edu .gov
libraries.mit.edu?
Our
Local
DNS
.af
.al ...
The DNS hierarchy
Root
address for
mit.edu server
.com
.org
mit.edu
Our
Local
DNS
.edu .gov
hawaii.edu
berkeley.edu
.af
.al ...
ucsd.edu
cornell.edu
The DNS hierarchy
Root
.com
.org
.edu .gov
.af
.al ...
libraries.mit.edu?
mit.edu
hawaii.edu
Our
18.51.0.23
Local
berkeley.edu
DNS
ucsd.edu
cornell.edu
Getting the IP (numerical) address
What is numerical address of
libraries.mit.edu?
Our
Computer
Address:
18.51.0.23
Local
Domain
Name
Server
The DNS hierarchy
Root
.com
.org
mit.edu
Our
Local
DNS
.edu .gov
hawaii.edu
.af
.al ...
ucsd.edu
18.51.0.23
berkeley.edu
(authoritative cornell.edu
answer)
Using the nslookup command
% nslookup www.google.com
Server:
Address:
128.171.3.13
128.171.3.13#53
Non-authoritative answer:
www.google.com canonical name = www.l.google.com.
Name: www.l.google.com
Address: 74.125.53.103
Name: www.l.google.com
Address: 74.125.53.104
Name: www.l.google.com
Address: 74.125.53.105
%
Caching DNS
www.google.com?
Non-authoritative
answer:
74.125.53.103
74.125.53.104
74.125.53.105
Cache
Our Local
Time to Live:
3595
3596
3597
3598
3599
3600
0001
0002
0003
…
DNS
DNS Record
The DNS hierarchy
Root
.com
.org
mit.edu
.edu .gov
hawaii.edu
berkeley.edu
.af
.al ...
ucsd.edu
cornell.edu
The DNS hierarchy
Root
.edu Top-Level Domain
hawaii.edu
UH
DNS
Second-Level
Domain
The IPv4 Address
Range: 0-255
(256 possibilites)
128.171.224.100
Fixed
for
UH
256
256
possible possible
nos.
nos.
256 x 256 = 66,536
addresses
The DNS hierarchy
Root
.edu
hawaii.edu
Subnets
ICS Dept.
128.171.10.x
128.171.x.x
Coll. of Engin.
128.171.60.x
Physics Dept.
128.171.30.x
Subnet Addresses
hawaii.edu
Subnets
128.171.x.x
ICS Dept.
128.171.10.x
Coll. of Engin. Physics Dept.
128.171.60.x
256
possible128.171.30.x
addresses
128.171.10.156
UH
ICS machine
Domain Name System Hierarchy
Root
.com
.org
.edu .gov
.af
.al ...
Root servers
Hidden Master
Root Server
Root
Root
Root
Root
Root
Root
Root
Problem
Tower of Babel
Standards - IETF
Problem
The China Problem
Problem
$$$$$$$$$$$$$$
World Connection Density
Western Europe
US
Global Digital Divide
http://www.chrisharrison.net/projects/InternetMap/
Packet prioritization
Telemedicine
Commerce
Packet Prioritization
Pay for priority?
ExxonMobil
IHS
Net Neutrality
Internet2
High-speed applications, prioritizing
packets, etc.