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Internet

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Title: Internet

1
Internet Home networking

Prof. J. Won-Ki Hong
jwkhong_at_postech.ac.kr
Dept. of Computer Science Engineering
POSTECH

2
Contents

Data Communication Network
Internet World Wide Web
Home Networking

Data Communication Network

4
Brief History of Computer Networks

1960s How can we transmit bits across a
communication medium efficiently and reliably?
1970s How can we transmit packets across a
communication medium efficiently and reliably?
1980s How can we provide communication
services across a series of interconnected
networks?

1990s How can we provide high-speed,
broadband communication services to support
high-performance computing and multimedia
applications across the globe?
2000's What do you think will dominate in the
next 10 years?

6
A Communication Model
7
Common Communication Tasks

Data encoding the process of transforming input
data or signals into signals that can be
transmitted
Signal generation generating appropriate
electro-magnetic signals to be transmitted over a
transmission medium
Synchronization timing of signals between the
transmitter and receiver when a signal begins
and when it ends duration of each signal

Error detection and correction ensuring that
transmission errors are detected and corrected
Flow control ensuring that the source does not
overwhelm the destination by sending data faster
than the receiver can handle
Multiplexing a technique used to make more
efficient use of a transmission facility. This
technique is used at different levels of
communication

Addressing indicating the identity of the
intended destination
Routing selecting appropriate paths for data
being transmitted
Message formatting conforming to the appropriate
format of the message to be exchanged
Security ensuring secure message transmission
Systems management configuring the system,
monitoring its status, reacting to failures and
overloads, and planning for future growth

10
Communication Network

A communication network is a collection of
devices connected by some communications media
Example devices are
mainframes, minicomputers, supercomputers
workstations, personal computers
printers, disk servers, robots
X-terminals
Gateways, switches, routers, bridges
Cellular phone, Pager, TRS
Refrigerator, Television, Video Tape Recorder

Communications Media
twisted pairs
coaxial cables
line-of-sight transmission lasers, infra-red,
microwave, radio
satellite links
fiber optics
Power line

12
Network Structures

Point-to-Point Networks
each communication line connects a pair of nodes
a packet (or message) is transmitted from one
node to another
intermediate nodes, in general, receive and store
entire packet and then forward to the next node
also called store-and-forward or
pack-switched
some topologies star, ring, tree

Broadcast Networks
have a single communication line shared by all
computers on the network
packets sent by a host are received by all
computers
some topologies bus, satellite, radio

14
Types of Communication Networks

Local Area Networks (LANs)
lt a few km
high data transmission rate (at least several
Mbps)
ownership usually by a single organization
e. g., Ethernet, IBM Token Ring, Token Bus, FDDI,
Fast Ethernet, ATM, Gigabit Ethernet

15
POSTECH LAN (1998.6)
16
POSTECH LAN (1999. 3)
17

Metropolitan Area Networks (MANs)
up to 50 km
fibre optics is a popular technology for MANs
may be private or public
may involve a number of organizations
e.g., cable TV networks (CATV), ATM networks

Wide Area Networks (WANs)
a few km to thousands of km
point-to-point networks (also called long-haul
networks)
lower data transmission rate than LANs
fiber optics is a popular technology for MANs
ownership usually by more than a single
organization
e.g., ARPANET, MILNET (US military), CANET,
NSFNET, KREONET, BoraNet, KORNET, INET, Internet

19
Internet in Korea (1995.5)
20
Internet in Korea (1999.6)
21
Growth of Internet Users in Korea
22
Growth of Internet Hosts in Korea
23
Computer Communication Architecture

Computer Communication the exchange of
information between computers for the purpose of
cooperative action
Computer Network a collection of computers
interconnected via a communication network

Protocol agreement required between the
communication entities and consists of three
components
Syntax data format and signal levels
Semantics control information for coordination
and error handling
Timing speed matching and sequencing
Communications Architecture a structured set of
modules that implements the communication
function

25
ISO-OSI Reference Model

International Standards Organization (ISO) Open
Systems Interconnection (OSI) Reference model is
a framework for connecting computers on a network
Motivation?
to reduce the complexity of networking software
as a step towards international standardization
of the various protocols

The main principles applied to the OSI layered
architecture are
each layer represents a layer of abstraction,
each performs a set of well-defined functions,
implementation of a layer should not affect
adjacent layers, and inter-layer communication
should be minimized

27

OSI Stack

OSI Stack

OSI Stack
Application
Application
Application
Presentation
Presentation
Presentation
Session
Session
Session
Transport
Transport
Transport
Network
Network
Network
Data Link
Data Link
Data Link
Physical
Physical
Physical
28

Functions of the OSI Layers
1. Physical layer responsible for the
electro-mechanical interface to the
communications media
2. Data link layer responsible for
transmission, framing and error control over a
single communications link.
3. Network layer responsible for data transfer
across the network, independent of both the media
comprising the underlying subnetworks and the
topology of those subnetworks.

4. Transport layer responsible for reliability
and multiplexing of data transfer across the
network (over and above that provided by the
network layer) to the level required by the
application.
5. Session layer responsible for establishing,,
and managing sessions between cooperating
applications.
6. Presentation layer responsible for providing
independence to the application process from
differences in data representation (syntax).
7. Application layer ultimately responsible for
managing the communications between applications.

How Communication Takes Place Between the Layers
communication takes place between peer entities.
a layer provides services to the layer above it.
services are available at SAPs (Service Access
Points) analogous to telephone numbers and
street addresses

31
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32

On the sending side
a layer receives a PDU (Protocol Data Unit) from
the layer above it, with some ICI (Interface
Control Information) (such as address, data size,
etc.).
the layer ads some PCI (Protocol control
Information) to the APDU and passes the enlarged
PDU to the layer below along with more ICI.
A layer may also fragment a PDU into several
smaller pieces to be passed separately to the
layer below (in this case, the peer entity at the
receiving end will reassemble the fragments).

At the receiving end
a layer receives a PDU from the layer below.
The layer strips off the PCI added by its peer,
and passes the PDU to the layer above it.
If the sending layer fragmented a PDU, its peer
is responsible for reassembling it before passing
it up.

34
Other Communication Models

The Anarchistic Network Model
have been used mostly in PCs
The TCP/IP Model
only 5 layers exist
used mostly in Internet network applications

35
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36
Communication Service Types

Connection-oriented service
modeled after the telephone system
must establish a connection before use, and
terminates the connection when finished.
FIFO guaranteed.
the path from the sender to receiver is fixed.
resources are pre-allocated at setup time

Connectionless service
modeled after the postal system
no connection required, but instead full
addressing required in each message
FIFO not guaranteed.
the path is not fixed
resources are dynamically allocated

38
Standards Organizations

ITU-T (International Telecommunication Union -
Telecommunications Sector) - formerly CCITT
(International Telegraph and Telephone
Consultative Committee), a committee within ITU,
a United Nations agency, responsible for X.25,
X.21, X.400, X.500, X.700, X.900, etc.
ISO (International Standards Organization) ISO
8073 (connection-oriented transport protocol)
ANSI (American National Standard Institute)
IEEE (Inst. of Electrical and Electronics
Engineers) IEEE 802

IETF (Internet Engineering Task Force) TCP/IP,
FTP, SNMP
W3C (World-Wide Web Consortium) HTTP, HTML, XML
ATMF (ATM Forum) - ATM related standards
TMF (TeleManagement Forum) - formerly known as
NMF, Network Management Forum

Internet and World Wide Web

41
History of the Internet

1969 - Researchers at four US campuses create the
first hosts of the ARPANET
1971 - The ARPANET grows to 23 hosts connecting
universities and research centers
1973 - The ARPANET goes international with
connections to England and Norway
1982 - The term "Internet" is used for the first
time and TCP/IP is created
1992 - Internet Society is chartered. World-Wide
Web released by CERN.

42
Definitions

A network of networks
Based on TCP/IP (Transmission Control
Protocol/Internet Protocol)
A variety of services and tools

43
Network of networks

a group of two or more networks that are
interconnected physically
capable of communicating and sharing data with
each other
able to act together as a single network
virtually all of todays computers are connected
via Internet

44
Based on TCP/IP

TCP/IP enables the different types of machines on
separate networks to communicate and exchange
information.
TCP/IP is
A suite of protocols
Rules for sending and receiving data across
networks
Addressing
Management and verification

45
Variety of services or tools

The Internet offer access to data, graphics,
sound, software, text, and people through a
variety of services and tools for communication
and data exchange
E-Mail
Usenet
FTP
Gopher
Telnet
World Wide Web

46
World Wide Web

A way to provide and access information resources
on the Internet
Using Web Browser Web Server
Based on HTML and HTTP
Multimedia
Hypertext "links" can lead to other documents,
sounds, images, databases (like library
catalogs), e-mail addresses, etc.
Non-Linear
There is no top, there is no bottom. Non-linear
means you do not have to follow a hierarchical
path to information resources.

47
Web Browser

a piece of software that acts as an interface
between the user and the Internet, specifically
the World Wide Web
The browser acts on behalf of the user. The
browser
contacts a web server and sends a request for
information
receives the information and then displays it on
the user's computer
The browser can be graphical or text-based and
can make the Internet easier to use and more
intuitive
The helper applications are automatically invoked
by the browser when a user selects a link to a
resource that requires them
A Web browser can be used on most of computers

48
Web Server

Also known as HTTP Server or HTTP Daemon
The repository of web pages of which types are
HTML and any application data with MIME type
Listens for HTTP requests from the web browsers,
serves those requests
Designed to communicate with web browsers using
HTTP protocol
Typically runs on general purpose computer

49
HTML

consists of standardized codes,or "tags", that
are used to define the structure of information
on a web page
defines several aspects of a web page including
heading levels, bold, italics, images, paragraph
breaks and hypertext links to other resources.
a sub-language of SGML (Standard Generalized
Markup Language) that defines and standardizes
the structure of documents.
standardized and portable A document that has
been prepared using HTML can be viewed using a
variety of web browsers, such as Netscape and
Lynx

50
HTTP

the set of rules, or protocol, that governs the
transfer of hypertext between two or more
computers.
Based on Client/Server paradigm
Convey variety of Internet resources HTML
documents, text files, graphics, animation and
sound
HTTP also provides access to other Internet
protocols, among them
File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Network News Transfer Protocol (NNTP)
etc.

51
URL