Public Management Information Systems Communications and World Wide Web

greydullNetworking and Communications

Oct 30, 2013 (4 years and 10 days ago)

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Public Management Information Systems


Communications and World Wide Web


Wednesday, October 30, 2013

Hun Myoung Park,
Ph.D.



Public Management & Policy Analysis Program

Graduate School of International Relations

2

Communication Basics


Sender encodes (converts) his message.


Receiver decodes (translates) the
received message.


Message to be sent


Media or channel through which the
message travels (air, radio, TV, phone,
Internet, etc.)


Feedback (error checking)

3

Transmission Methods 1


Analog signals: continuous


Frequency


Amplitude


Digital signals: discrete


Modem (modulator/demodulator)


Dial
-
up connection


Bps (bit per second)


Baud (pulses per second) or modulation rate


Emulation software: check errors (parity bit)

4

Transmission Methods 2


Frequency (Hz), the number of times a
signal makes a complete cycle per
second. KHz, MHz, GHz


Bandwidth (bps) is ranges of frequencies.
The difference between the highest and
lowest frequency transmitted (or amount of
data transmitted) per second. Kbps, Mbps.


Wavelength: from long (low frequency) to
short (high frequency

UHF, cell phone).

5

Transmission Methods 3


Serial versus parallel transmission


Direction of transmission:


Simplex: transmitted in a single direction only


Half
-
duplex: one direction at a time


Full
-
duplex: both directions at the same time


Timing of transmission


Synchronous: blocks of data are transferred


Asynchronous: start and stop bits to
distinguish one byte from the others.

6

Transmission Methods 4


Circuit versus packet switching


Circuit switching establishes a connection
(physical path and circuit) that cannot be use
by others. PSTN (telephone network)


Packet switching sends data in a series of
packets and then assembles them in the
destination. Paul Baran, Donald Davies,
Leonard Kleinrock in the 1960s. PSDN


Wired (faster and more secure) versus
wireless network

7

Packet Switching of Internet


Data are split into small chunks, “packets”


Each packet has a header with information
about its sequence number and the
destination


Each packet may independently travel a
different routes to get to the destination
and be buffered and queued depending on
network traffic. No order in transmission.


The packet header at the destination is
stripped off and then packets are put
together (assemble) in the proper order.

8

Communication Media 1


Twisted
-
pair wire: RJ
-
45 (LAN) and RJ
-
11


Coaxial cable (coax) in the cable TV
industry. More expensive, faster, less
susceptible to interference (by shield
blocking electro
-
magnetic signals)


Optical fiber cable uses light pulse sent by
a laser device thought the cable. Super
-
fast and in turn expensive. Used for
backbone (telephone) network.

9


10

Communication Media 2


Radio frequency (RF) transmission


Infrared (IR) transmission


Cellular radio: cell, cellular tower, mobile
telephone switching office (MTSO). G3.


Microwave (“line
-
of
-
sight”) and comm.
satellite use microwave stations
(microwave antennas) and satellite dishes.


Global positioning systems (GPS), Wi
-
Fi,
Bluetooth

11


12

Communication Media 3


Telephone lines


Conventional dial
-
up connection


ISDN (Integrated Services Digital Network)
ADSL (Asymmetric Digital Subscriber Line)
and DSL use higher frequency than voce
phone call on telephone lines.


Cable access (cable TV).


Satellite and fixed wireless access need
modems and transceivers.

13


14

Communication Media 4


Wired Ethernet (T1, T3)


Broadband over fiber (BoF)


Cellular broadband or mobile wireless
(laptops, smart phones)


Wi
-
Fi (Wireless Fidelity) is wireless
networking standards (wireless Ethernet)


IEEE 802.11


802.11g and 802.11n

15

Network (Physical) Topologies


Star network has a central hub (router)
connected by other devices.


Ring network: devices are connected from one
node to the next. One
-
way direction of
transmission. IBM’s Token Ring Network


Bus network has a central bus line to which
devices (nodes) are attached.


Mesh network: each device is connected to
multiple devices in a network.


Hybrid network combines above typologies.

16


17

Network Architecture


Client
-
server network


Most common architecture


Servers process clients’ request and provide services
to clients. Not particular machines but functions.


Depending on tasks, network, file, mail, Web, DNS,
printer, license servers and others are available.


A single machine can run more than one servers.


Uploading and downloading (polling & addressing)


Peer
-
to
-
peer (P2P) network


Direct access to other devices without servers.


Internet P2P computing for sharing resources online.

18

Types of Network 1


Sharing programs, data, and devices


Access to databases and better security


LAN (Local Area Network)


Covers small geographical area


Bridge for same types of networks


Router for different networks (layer 3)


Gateway, bridge + router + etc.

19

Types of Network 2


WAN (Wide Area Network)


MAN (Metropolitan Area Network)


VPN (Virtual Private Network) allows
remote and secure access to the network
(intranet) through encrypted “tunneling”


Intranets versus extranets: private
networks used for employees. Authorized
outsiders can access extranets.

20

Internet History


Systems of interconnected computer networks


ARPAnet (Advanced Research Project Agency)
of Department of Defense in 1969


Packet switching as a method of network
communications in the 1960s.


FTP in 1971 and email in 1973


Open Systems Interconnection (OSI) in 1977


TCP/IP (Transmission Control Protocol/Internet
Protocol) Protocol Suite in 1983


World Wide Web in 1991

21

TCP/IP (Internet Protocol Suite)


Replaced ISO’s OSI w/o session and
presentation layers under applications


Communication protocol for Internet


Five layers (from the lower one)

1.
Physical layer converts bits into signals on media

2.
Data link: node
-
to
-
node delivery of frames

3.
Network (delivery of packets by routing and
Internet Protocol (IP). IPv4 and IPv6

4.
Transport (logical delivery of messages)

5.
Application (provide services to users)

22


23

E
-
mail Address


Types of email addresses


User_ID@domain.root_domain_type


User_ID@domain.domain_type.country


User_ID@subdomain.domain.domain_type


Subdomain and domain names


Root domain: com, edu, gov, org, net, etc.


Domain type: .ac, .co, .re, .go


Country: .us, .jp, .kr, .fr

24

Web Address


Uniform Resource Locator (URL) as a URI
(Uniform Resource Identifier)


http://www.iuj.ac.jp/faculty/kucc625/or.html


Protocol or scheme (http, https, ftp, etc.)


Domain name, domain type, country


Port number (http://www.iuj.ac.jp:80)


Directory or path (forward slash / not
\
)


Document name and arguments of CGI

25

Internet Address: IP Address


IP address is a numerical label assigned
to devices wired on Internet


Network interface identification and
location addressing under TCP/IP


IPv4 (32bits); 2
8
.2
8
.2
8
.2
8
=4,294,967,296


Scarcity of domain names in IPv4


Move toward IPv6 (128bits) supporting up
to 2
128

in 1998

26

Domain Name Systems


DNS is a hierarchical naming systems
translates a human friendly name to it IP
address


Domain names registrations controlled by
Internet Corporation for Assigned Names
and Numbers (ICANN), nonprofit
organization


Domain name servers (DNS)


Root domain, domain types

27

Internet Services (Applications) 1


E
-
mail (Electronic mail)


SMTP (Simple Mail Transfer Protocol)


MIME (Multipurpose Internet Mail Extension)


POP (Post Office Protocol)


IMAP (Internet Mail Access Protocol)


FTP (Filer transfer protocol), secured FTP


Telnet (Terminal Network) for establishing
remote connection. Secured telnet


Gopher, browsing and searching services

28

Internet Services (Applications) 2


Usenet (user network) newsgroup


Listservs, e
-
mail based discussion groups


WWW (World Wide Web) integrates other
Internet services using hyperlinks


Web servers and browsers


HTTP (Hypertext Transfer Protocol)


Static and dynamic documents (HTML)


CGI (Common Gateway Interface)


Plug
-
in or applets (Java applets)

29

Web Servers


Process requests from Web browsers and
send the result back to the browsers


Use CGI to generate dynamic documents


Apache (HTTP/Tomcat), IIS (Microsoft),
other vendors’ products (IBM, Oracle, etc.)


Virtual hosting


Load limits and overload


Server
-
side scripts (SSI)

30

Web Browsers


Interpret markup languages (HTML/XML)


Plug
-
ins (add
-
ons) to improve connectivity


Web standards: Mozilla and Firefox


Web compatible: Safari, Google chrome


Others: Opera, Konqueror


Text
-
based: Lynx


Microsoft Internet Explorer (MSIE) and
ActivX do not comply with Web standards

31

Web Features and Web 2.0


Interface for input and output of text,
image, audio, video, and others


Replacing or integrating existing Internet
services like FTP, Gopher, Listservs


Push technology (Webcasting) for
information delivery by software


Improved interactivity

Web 2.0


Internet radio, television, podcasting