Introduction - kondor.etf.rs

warmersafternoonΔίκτυα και Επικοινωνίες

23 Οκτ 2013 (πριν από 3 χρόνια και 10 μήνες)

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Aleksandra Smiljani
ć

aleks@ieee.org

Introduction

Uses of Computer Networks


Business Applications


Home Applications



Business Applications


Sharing resources


Common databases for customer
records, inventory, accounts


E
-
commerce


Video
-
conferencing


Disseminating the information, and
coordination



Home Applications


Getting the remote information


Person
-
to
-
person information


E
-
commerce


Entertainment


E
-
flea




Network Types


Local Area Networks


Metropolitan Area Networks


Wide Area Networks


Wireless Networks


Home Networks


Network Types

Classification of interconnected processors by scale.

Local Area Networks

Two LANs

(a)

Bus
-
broadcast

(b)

Ring

Metropoliten Area Networks

Two MANs

(a)

Star
-
switched

(b)

Ring

Switch

Metropolitan Area Networks

A metropolitan area network based on cable TV.

Wide Area Networks

Relation between hosts on LANs and the subnet.

Circuit switch

Wide Area Networks

A stream of packets from sender to receiver.

Wireless Networks

Categories of wireless networks:


System interconnection


Wireless LANs


Wireless WANs

Wireless Networks

(a)

Bluetooth configuration

(b)

Wireless LAN

Home Network Categories


Computers (desktop PC, PDA, shared peripherals)


Entertainment (TV, DVD, VCR, camera, stereo, MP3)


Telecomm (telephone, cell phone, intercom, fax)


Appliances (microwave, fridge, clock, furnace, airco)


Telemetry (utility meter, burglar alarm, babycam).

Network Hardware


Transmission medium


Transceivers: transmitters and receivers on the
point
-
to
-
point connections


Multiplexers, demultiplexers


Packet and circuit switches


Bridges


Routers


Servers, gateways, management units


Transmission Medium


Air: different frequency bands


Wires: twisted pairs


Coaxial cables


Optical fibers



Transceivers


Transmitters perform modulation and coding
to provide efficient and reliable
communication.


Receivers perform the reverse operations.


Depending on the medium transceivers are
electronic devices, antenas, or lasers and
photodiodes.


Multiplexers and Demultiplexers


Multiplexers receive multiple lower bit
-
rate
streams of data and according to some rule
transmit the higher bit
-
rate stream of data.


Demultiplexers do the opposite.

Circuit and Packet Switches


It does not make sense to connect every user
with every other user in the network.


Circuit and packet switches connect multiple
inputs to multiple outputs.


In circuit switches, the configuration pattern
changes on a slow time scale.


In packet switches, the configuration changes
on a packet
-
per
-
packet basis.


Servers, Gateways, etc.


Servers store various kinds of information for
users, for example DNS databases, e
-
mails,
web pages and provide it to the users.


Gateways convert data format, and negotiate
QoS with the network.

Layered Structure of Networks

Layers, protocols, and interfaces.

Protocol Hierarchies

Example information flow supporting virtual communication in layer 5.

Design Issues for the Layers


Addressing


Error Control


Flow Control


Multiplexing


Routing

Services to Protocols Relationship

The relationship between a service and a protocol.

Reference Models with Layers


A layer should have well defined function


Function of a layer should be
internatinationally standardized


The information flow between interfaces
should be minimized


Reference Models


The OSI reference model


The TCP/IP reference model


Hybrid reference model


Reference Models

The OSI
reference
model.

Reference Models

The TCP/IP reference model.

Reference Models

Protocols and networks in the TCP/IP model initially.

Comparing OSI and TCP/IP Models

Concepts central to the OSI model


Services


Interfaces


Protocols

Concept of TCP/IP


Implementation of the required
functionality with three layers

A Critique of the OSI Model and Protocols

Why OSI did not take over the world


Bad timing


Bad technology


Bad implementations


Bad politics

Bad Timing

The apocalypse of the two elephants.

A Critique of the TCP/IP Reference Model

Problems:


Service, interface, and protocol not distinguished


Not a general model


Host
-
to
-
network “layer” not really a layer


No mention of physical and data link layers


Minor protocols deeply entrenched, hard to replace

Hybrid Model

The hybrid reference model to be used in this book.

Example Networks


The Internet


Ethernet


Wireless LANs: 802.11

Example Networks


1960. Barn from RAND co. first proposal


1957 Advanced Research Project Agency (ARPA)


1967 Larry Roberts proposes ARPANET, that was
implemented by BBN co.


Interface Message Processors (IMP) were connected
by 54kbps links. Protocols: host
-
IMP, IMP
-
IMP,
host
-
host


1969 experimental network, UCLA, UCSB, Stanford
University, Yuta University

The ARPANET

(a)

Structure of the telephone system.

(b)

Baran’s proposed distributed switching system.

The ARPANET

The original ARPANET design.

The ARPANET

Growth of the ARPANET
(a)

December 1969. (
b)

July 1970.

(c)

March 1971.
(d)

April 1972.
(e)

September 1972.

TCP/IP Development


In 1974, TCP/IP model has been
established by Cerf and Kahn, and
incorporated into Berkeley UNIX.


Because of the large number of hosts,
domain name system (DNS) was created in
1980s.

NSFNET


NSF (National Science Foundation)
invested into the network for all
universities.


Backbone included supercomputers at
several universities, it is connected to
ARPANET at Carnegie
-
Mellon university.


MCI rented cables at 448kbps, and IBM
provided computers as routers.


NSFNET

The NSFNET backbone in 1988.

Further Development


1990 non
-
profit organization Advanced
Networks and Services (ANS) started
comercialization, and improved speed to
45Mbps, ANSNET started. In 1995 sold to
AOL


In nineties EuropaNET and EBONE are
developed

Internet Usage


Traditional applications (1970


1990)


E
-
mail


News


Remote login


File transfer


World Wide Web developed by CERN
physicist Tim Bernars
-
Lee, and Mark
Andressen at National Center for
Supercomputer applications

Architecture of the Internet

Overview of the Internet.

Ethernet


Bob Metacalfe graduated MIT and Harvard,
and worked on Hawaii on ALOHANET.


He designed first computer LAN at Xerox
Parc in Palo Alto.


DEC, Intel, Xerox make DIX standard that
becomes IEEE802.3


Metcalfe founds 3Com

Ethernet

Architecture of the original Ethernet.

Wireless LANs

(a)

Wireless networking with a base station.

(b)

Ad hoc networking.

Wireless LANs

The range of a single radio may not cover the entire system.

Wireless LANs

A multicell 802.11 network.

WLAN Issues


CSMA/CD may not be applicable


Multipath fading


Mobility


Network Standardization


Who’s Who in the Telecommunications World


Who’s Who in the International Standards World


Who’s Who in the Internet Standards World

ITU


Main sectors


Radiocommunications


Telecommunications Standardization


Development


Classes of Members


National governments


Sector members (AT&T, Cisco, Intel, AOL Time
Warner…)


Associate members


Regulatory agencies (FCC)

ISO


200 Technical Committees, divided into
subcommittees, and working groups
involving 100000 voluneers.


TC97 in charge for computers and
information processing.


American National Standards Institute
(ANSI) is US representative in ISO.


National standards organization
-
>
committee draft
-
>draft international standard
-
> standard

IEEE 802 Standards

The 802 working groups. The important ones are
marked with *. The ones marked with


are
hibernating. The one marked with † gave up.

Internet Standards


In 1983, Internet Activities Board (IAB) was
established.


Communication was done through “request
for comments” (RFC) documents.


IAB is moved to Internet Research Task
Force (IRTF) and Internet Engineering Task
Force.


Proposed standard
-
> draft standard
-
>
standard