Title: Introduction to Networks
1Introduction to Networks
2The library
- Use networked computers to
- Create or download catalog records for our
holdings - Create and distribute electronic bibliographies
- Computer networks allow us to
- Order books online
- Receive access to online databases
- Receive software updates
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
via computer network (e.g., virtual reference)
3Connectivity of Public Libraries
Information Use Management Policy Institute
http//www.ii.fsu.edu/plinternet_findings.cfm
4Computers in libraries
Stand-alone pc or Mac
Mainframe "dumb" terminals
Networked computers and peripherals
5Local 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.
6Local Area Network elements
- Transmission medium - type of wires or other media
Network topology - architecture
Transmission protocol - rules followed when
sending signals
Software
7Transmission 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)
8Twisted pair (cont.)
- Category 5 up to 100 Mbps
Category 6 up to 1000 Mbps
9Transmission 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
10Transmission 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
11Fiber optic transmission
Glass Core
Cladding
Cladding (light-refracting)
Light source
Cut-away view
Glass fiber (light-transmitting)
12Transmission media (4)
? ? c
- 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
109 Hz
1011 Hz
1015 Hz
13Network architecture - star topology
OPAC
printer
OPAC
Circulation
OPAC
14Network architecture - ring topology
15Ring topology
16FDDI (Fiber Distributed Data Interface)
Bidirectional token ring network
17Network architecture - bus topology
OPAC
Circulation Server
Bus
OPAC
OPAC
printer
18Network architecture - bus topology using switch
or hub
Hub
19Network protocol - token ring
Token passes from node to node
Token
Msg.
Token
IEEE Std. 802.5 ISO/IEC 8802-5
Msg. Rec.
20Network 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
21EtherNet frame (packet) format
FRAME CHECK SEQUENCE
DESTINATION ADDESS
SOURCE ADDRESS
PREAMBLE
TYPE
DATA
22Mix and match wiring and control topologies
Star wiring with token passing
23Network of networks
Bridge
24Adding wireless
Access point for wireless
IEEE Std. 802.11 ISO/IEC 8802-11
25Wide Area Networks (WANs)
- Component entities can be miles apart
- Often consist of multiple local area networks
linked together - Largest WAN is the Internet
26Internet Two tales converge
- Late 1950s - Department of Defense communications
went through public telephone network, considered
vulnerable - DOD wanted command-and-control network that could
survive nuclear war
27A robust proposition
Switching office
Toll office
Toll office
Barans proposed distributed switching system
28Internet 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)
29Internet characteristics
- Highly redundant network (many ways to get from
point A to point B) - (Barans idea)
Uses packet switching (Clarks idea)
30Switched telephone network
A
B
Switchboard
31Long distance telephone switching
B
A
Trunk line
32If roads were like telephones
33Traffic flow
Beretania
34Packet switching
- Each message divided into packets
- Source
- Destination
- Packet number of how many packets
- Data
Packet switches (nodes on Internet) use
distributed adaptive routing
35Packet-switched network
switch
switch
switch
switch
switch
switch
36Network redundancy
switch
switch
switch
X
switch
switch
switch
37Required 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
38Surfing the 'Net
Server
Request messages
Text, graphics, error messages
Client
Webserver application responds to requests from
client
Browser application sends requests to server
39Getting 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
40Universal Resource Locator (URL)
http//www.cool.com/mystuff/myfile.html
machine
directory
file name
protocol
41Getting the IP address
What is numerical address of www.cool.com?
Domain Name Server
Browser
123.157.78.99
42nslookup 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
43The 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 Hawaii is a Class B network
44The IP address
128.171.94.192
UH Network
Subnet
Machine
45Establish a connection
Client sends connection request to server
Server sends connection accepted response to
client
46Requesting receiving file
Client sends "GET /mystuff/myfile.html" command
to server
Server looks in mystuff directory
Server sends myfile.html to client
47Release connection
Client sends disconnect request to server
Server closes connection
48Display text and images
Browser displays text and images in accordance
with directions in HTML tags
49Sending data
Client sends "GET /mystuff/myfile.html" command
to server
msg
msg
msg
1
2
3
50Sending data
Client sends "GET /mystuff/myfile.html" command
to server
msg
1
To 123.157.78.99
51Reference 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
52Networked communication
Client
Server
Application
Application
Transport
Transport
TCP/IP
Internet
Internet
Data link Physical
Data link Physical
OSI
53TCP/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
54Sending 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
55Receiving 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
56Shannon-Weaver Communication Model
Network medium
Channel
coded
decoded
Transmitter
Receiver
Your browser
Server
Source
Destination
57Server responds
Client
Server
Application
Application
Transport
Transport
Internet
Internet
Data link Physical
Data link Physical
58Routing
Client
Server
Application
Application
Router
Transport
Transport
Internet
Internet
Internet
Data link Physical
Data link Physical
Data link Physical
59Standards 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/
60IEEE - Institute of Electrical and Electronics
Engineers standards
802.3 Ethernet 802.5 Token ring 802.11 Wireless
LAN 802.15 Wireless personal area networks
61A Few Internet Issues
62Problem
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
63ICANN
64IP Version 4 Address
256
256
256
256
4,294,967,296 Possible IP addresses
3,700,000,000 Available IP addresses
65Address Needs
66IP Version 6 (IPv6) Number
- 20010DB800002F3B02AA00FFFE289C5A
340,282,366,920,463,463,374,607,431,768,211,456 Possible IP addresses
67The Domain Name System
68Visiting the MIT Library Website
http//libraries.mit.edu
69Visiting the MIT Library Website
http//libraries.mit.edu
70Universal Resource Locator (URL)
http//libraries.mit.edu
machine
protocol
Human-readable address
71Getting the IP (numerical) address
What is numerical address of libraries.mit.edu?
Where does the local Domain Name Server get the
numerical address?
Local Domain Name Server
Our Computer
Address 18.51.0.23
72Domain Name System Hierarchy
Root
libraries.mit.edu?
.com
.org
.edu
.gov
.af
.al
...
Top-Level Domains
Our Local DNS
73The DNS hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
Generic Top-Level Domains (gTLDs)
Country-Code Top-Level Domains (ccTLDs)
http//www.iana.org/domains/root/db/
74The DNS hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
United States Generic Top-Level Domains (also
.mil)
75The DNS hierarchy
Root
address for .edu server
.com
.org
.edu
.gov
.af
.al
...
Our Local DNS
76The DNS hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
libraries.mit.edu?
Our Local DNS
77The DNS hierarchy
Root
address for mit.edu server
.com
.org
.edu
.gov
.af
.al
...
hawaii.edu
mit.edu
ucsd.edu
Our Local DNS
cornell.edu
berkeley.edu
78The DNS hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
libraries.mit.edu?
hawaii.edu
mit.edu
ucsd.edu
Our Local DNS
18.51.0.23
cornell.edu
berkeley.edu
79Getting the IP (numerical) address
What is numerical address of libraries.mit.edu?
Local Domain Name Server
Our Computer
Address 18.51.0.23
80The DNS hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
hawaii.edu
mit.edu
ucsd.edu
18.51.0.23 (authoritative answer)
Our Local DNS
cornell.edu
berkeley.edu
81Using the nslookup command
nslookup
www.google.com
Server 128.171.3.13 Address
128.171.3.1353 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
82Caching DNS
www.google.com?
Cache
Non-authoritative answer 74.125.53.103 74.125.53.
104 74.125.53.105
Our Local DNS
Time to Live
3600
3599
3598
3597
3596
3595
0003
0002
0001
DNS Record
83The DNS hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
hawaii.edu
mit.edu
ucsd.edu
cornell.edu
berkeley.edu
84The DNS hierarchy
Root
Top-Level Domain
.edu
Second-Level Domain
hawaii.edu
www.hawaii.edu?
128.171.224.100
UH DNS
85The IPv4 Address
Range 0-255 (256 possibilites)
128.171.224.100
256 possible nos.
256 possible nos.
Fixed for UH
256 x 256 66,536 addresses
86The DNS hierarchy
Root
.edu
hawaii.edu
Subnets
128.171.x.x
ICS Dept. 128.171.10.x
Coll. of Engin. 128.171.60.x
Physics Dept. 128.171.30.x
87Subnet Addresses
hawaii.edu
Subnets
128.171.x.x
ICS Dept. 128.171.10.x
Coll. of Engin. 128.171.60.x
Physics Dept. 128.171.30.x
256 possible addresses
128.171.10.156
UH
ICS
machine
88Domain Name System Hierarchy
Root
.com
.org
.edu
.gov
.af
.al
...
89Root servers
Root
Root
Root
Root
Root
Root
Root
90Problem
Tower of Babel
91Standards - IETF
92Problem
The China Problem
93Problem
94World Connection Density
Western Europe
US
Global Digital Divide
http//www.chrisharrison.net/projects/InternetMap/
95Packet prioritization
Telemedicine
Commerce
96Packet Prioritization
Pay for priority?
ExxonMobil
IHS
Net Neutrality
97Internet2
High-speed applications, prioritizing packets,
etc.