Aleksandra Smiljanićaleks@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