Download Lecture Notes on Computer Networks

Internet & Home networking
Prof. J. Won-Ki Hong
[email protected]
Dept. of Computer Science & Engineering
POSTECH
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Internet & Home Networking
Contents
Data Communication Network
Internet & World Wide Web
Home Networking
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Data Communication Network
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Brief History of Computer Networks
• 1960’s – “How can we transmit bits across a
communication medium efficiently and reliably?”
• 1970’s – “How can we transmit packets across a
communication medium efficiently and reliably?”
• 1980’s – “How can we provide communication
services across a series of interconnected
networks?
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• 1990’s – “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?
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A Communication Model
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Sender
Input
Information
m
Input
Device
3
Input data g
or signal
g(t)
Transmitted
signal
s(t)
Transmitter
Source System
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5
Received
signal
r(t)
Output data g’
or signal
g’(t)
’
Transmission
medium
Receiver
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Output
Information
m’
Output
Device
Receiver
1
Destination System
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Common Communication Tasks
Data encoding: the process of transforming input data or
signals into signals that can be transmitted
Signal generation: generating appropriate electromagnetic 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
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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
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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
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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
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• Communications Media
– twisted pairs
– coaxial cables
– line-of-sight transmission: lasers, infra-red, microwave,
radio
– satellite links
– fiber optics
– Power line
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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
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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
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Types of Communication Networks
• Local Area Networks (LANs)
–
–
–
–
< 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
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POSTECH LAN (1998.6)
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POSTECH LAN (1999. 3)
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• Metropolitan Area Networks (MANs)
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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
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• Wide Area Networks (WANs)
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–
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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), CA*NET, NSFNET,
KREONET, BoraNet, KORNET, INET, Internet
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Internet in Korea (1995.5)
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Internet in Korea (1999.6)
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Growth of Internet Users in Korea
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Growth of Internet Hosts in Korea
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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
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• 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
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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
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• 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
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OSI Stack
OSI Stack
OSI Stack
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
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Functions of the OSI Layers
1. Physical layer – responsible for the electromechanical 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.
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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.
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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
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Relation Between Layers at an Interface
IDU
ICI
Layer N + 1
SDU
SAP
ICI
Interface
Layer N entities
exchange N-PDUs
in their layer N
Protocol
Layer N
SDU
SDU
SAP = Service Access Point
IDU = Interface Data Unit
SDU = Service Data Unit
PDU = Protocol Data Unit
ICI = Interface Control Information
Header
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• 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).
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• 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.
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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
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The Anarchistic
Network Model
Application
The OSI Model
Application
Presentation
Operating
System
The TCP/IP Model
Application
Session
Transport
Network
Transport
Controller
Data Link
Data Link
Physical
Physical
Physical
Network
the network
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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
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• 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
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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
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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
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Internet and World Wide Web
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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.
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Definitions
• A network of networks
• Based on TCP/IP (Transmission Control
Protocol/Internet Protocol)
• A variety of services and tools
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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 today’s computers are connected via
Internet
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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
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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
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E-Mail
Usenet
FTP
Gopher
Telnet
World Wide Web
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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.
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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
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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
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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
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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:
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File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Network News Transfer Protocol (NNTP)
etc.
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URL
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•
•
•
a standardized addressing scheme for Internet resources
used to link documents on the Internet
the browser knows where to go to get the document
basic format of an URL
type-of-resource:// domain.address:port/path/filename
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ftp://ftp.postech.ac.kr/pub/welcome.txt
file:///C|/My Documents/resume.htm
news:han.protocol.http
telnet://vision.postech.ac.kr
http://www.postech.ac.kr/index.html
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Home Networking
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Definition
the collection of technologies and services that make
it possible to connect
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•
•
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PCs
Network devices
Appliances
Security equipment
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Why now?
Building “Internet” into consumer products is now possible
• Standardization has occurred
• Costs are low
Low-cost, high-speed LAN and routers
• Ethernet, IEEE 1394, Phone Wire, PLC, RF, etc.
• Video rate networks - IEEE 1394,Gigabit Ethernet
Modem and broadband networking are becoming ubiquitous
Golden age of networking
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Technology Enablers
ADSL and HFC (cable) networks
• Enable broadband Internet to the home
LANs, power line carrier, phone line networks, and wireless
• Enable ubiquitous connectivity
Internet connection sharing
• Brings the Internet to everything in the home
The communications software infrastructure has been
determined:
The Web and TCP/IP
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Analogous History
•
•
•
•
Single to multiple cars per family
One to multiple phones per household
Multiple phone lines per house
One to multiple TVs per house
MegaTrend: From one Internet
device per home to MANY
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Roles for Home Networking
Data
• Extension of current use of Internet by PDAs, tablets,
multiple PCs
Communications
• Telephony, videophone, chat, conferencing
Entertainment
• Games, TV, high-fidelity audio
Control
• Lights, HVAC, security, appliances
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Connecting Everything
Public networks
PSTN, Internet
Network
camera
HomePNA
Phone line network
Power line
network
Hub
Web
phone
Printer
IEEE 1394
HomeRF
Communications
and control
Camera
Entertainment
Center
Scanner
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Challenges for deployment of home network
Ease of installation
• There are no Net admins at home…
Network configuration has to be automatic
• There are no Net admins at home…
Network health and recovery
• There are no Net admins at home…
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Home Network Architecture
Public networks
PSTN, Internet
Internet
Connection
Sharing
End to end
broadband
New media support
Camera
Printer
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Architecture for The Future
Leveraging Web technologies
Great standards exist today
• IETF: TCP/IP, DNS, DHCP, HTTP, SSL, LDAP, IPSEC
• W3C: HTML, XML
Great services exist today
• Today: eCommerce, search
• Early Stages: Internet audio/video,
IP Telephony - much like early 1950s TV
• Billions of Web hits served daily
Internet exists and it works
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TCP/IP and Web is the software infrastructure
Web is evolving
• HTTP v1.1 for performance improvements
• XML extends Web for software applications
– “Pages” can now be simply data
– Internet Explorer 5.0 has XML support
Easy to wrap existing programs/tools/systems in Web
• Programming language neutral
• Contents neutral
• Operating system neutral
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Web for “Devices”
Device or service
specific code
Application specific size
Embedded web
server
20 ~ 80K bytes code
30 ~ 90K gates on silicon
TCP/IP stack
30 ~ 90K bytes code
30 ~ 80K gates on silicon
Ethernet, 1394 or
PPP/async driver
Device specific size
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Example Web Devices
Refrigerator PC: Sharewave
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Example Web Devices
Internet-on-a-chip design from Toshiba Semiconductor
• Features:
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Network Stack - TCP, IP, UDP and PPP
General Sockets - 4 - Email - SMTP, POP3 and MIME
Web - HTTPv1.0 and HTMLv3.2 (text only)
Japanese and English character support
• Interfaces:
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CPU Interface (Generic 80x86 CPU Interface)
SRAM Interface
Physical Layer Interface (RS232C & parallel port)
Decoder Interface
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Example Web device
Interactive TV from Spyglass
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Example Web devices
Internet Router from POSTECH
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Conclusion
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