CE80N Introduction to Networks & The Internet

CE80NCE80NIntroduction to NetworksIntroduction to Networks

&&The InternetThe Internet

Dr. Chane L. Fullmer

UCSC

Winter 2002

January 29, 2002 CE80N -- Lecture #8 2

Class DetailsClass Details

Web Search Assignment due today.Midterm on Thursday.

– Up to 50 questions.. (multiple choice)• Taken from book, lectures and glossary

– Section times.. Wed 7:30PM Web page submission:

– Email to [email protected]• Subject: cmpe080n-assgn4

mailto:[email protected]


Grading ScheduleGrading Schedule

AA 86-10086-100

BB 70-8570-85

CC 60-6960-69

FAILFAIL < 60< 60


Today’s ReadingToday’s Reading

Chapter 17 – – Clients + Servers = Distributed Computing

Chapter 18 –– Names For Computers


Master/Slave NetworkingMaster/Slave Networking

Early computers were large and expensive.– One computer per company– Controlling I/O devices at remote sites.

• Master-Slave networking.


Small Computer Use Networks Small Computer Use Networks To InteractTo Interact

Personal computers had processing power and acted independently.– Resulting in:

• Peer-to-peer networking• Distributed computing


Peer-to-Peer NetworkingPeer-to-Peer Networking

Peer-to-Peer networking permit communication among computers in which all computers are equal.


Distributed ComputingDistributed Computing

Distributed computing is any interaction that involves two or more computers communicating over a network.


Distributed Computing On The Distributed Computing On The InternetInternet

The Internet offers an amazing diversity of services.– Sending messages– Retrieving files– Printing documents

Also, diversity of styles of interaction.– Interacting with humans– Interacting with a computer program


Client-Server ComputingClient-Server Computing

Despite the diversity of services and differences in their use, all are client-server.


Three Basic FactsThree Basic Facts

Programs communicate.TCP/IP does not create or run

application programs.Computers can run multiple

programs.


Programs Are Clients Or ServersPrograms Are Clients Or Servers

Any program that offers a service is a server; any program that contacts a service is a client.


A Server Must Always RunA Server Must Always Run

A server program must always be ready to receive requests.

Server software starts and runs automatically.


People Prefer Names To People Prefer Names To NumbersNumbers

Names are preferred for computers instead of IP addresses.

This is possible by:– Allowing users to name their machine– Allowing users to enter alphabetic name for

their IP address– Providing a service that translates an

alphabetic name to a numeric address


Naming A Computer Can Be Naming A Computer Can Be Difficult Or FunDifficult Or Fun A name creates a sense of personality.

– Can reflect the role of the computer• Mail• Smtp

– Can reflect the name of the owner• John

– Can reflect a naming scheme (aka “naming convention”)

• I.e., chemical gases– Hydrogen, Helium, Argon, ….

Figure 18.1 The fifty most common names assigned to computers on the Internet in 2000.


Computer Names Must Be Computer Names Must Be UniqueUnique

Each computer on the Internet must have a unique name.

The Internet uses a familiar idea.– Extends name by adding strings– Appends a suffix to the name– Qualifies each name by giving the type

of organization


Names With Many PartsNames With Many Parts

The Internet naming scheme allows names to contain multiple parts.– Permits organizations to add additional

parts such as:• Groups• Departments• Locations

– www.cc.purdue.edu– www.soe.ucsc.edu

http://www.cc.purdue.edu/

http://www.soe.ucsc.edu/

http://www.soe.ucsc.edu/


Domain Names Domain Names Outside The USOutside The US

Most countries append a two-letter code to the domain name.– Allows for alternative schemes

• jp = Japan• uk = United Kingdom

– Recognized internationally


Translating A Name To An Translating A Name To An Equivalent IP AddressEquivalent IP Address

Internet communication software must use IP addresses to send and receive datagrams.– Translates names to IP addresses

automatically– Called the Domain Name System (DNS)


Computer Name Lookup Is Computer Name Lookup Is AutomaticAutomatic

Figure 18.2 To communicate with a remote computer, an application program asks a local domain name server for the remote computer’s IP address If the local domain name does not know the answer, it contacts a remote domain server automatically. Numbers on the arrows tell the order of the four step taken.


IP Addresses And Domain IP Addresses And Domain Names Are UnrelatedNames Are Unrelated

Domain names resemble IP addresses.– Can be deceiving– Look similar

An IP address is a 32 bit number divided into 4 parts.

A domain name may contain multiple parts.


Software Network ToolsSoftware Network Tools

Nslookup:– Converts name IP address

• > nslookup mit.edu• > nslookup 18.7.21.69

Traceroute (tracert in windows)– Traces path between hosts– Displays delay along path

• > tracert mit.edu• > tracert 18.7.21.69


SummarySummary

Distributed Computing Paradigm(Client-Server)– Programs communicate– TCP/IP does not create/run programs– Computers can run multiple programs

Clients contact serversServers always run 24/7…


SummarySummary

Computer naming …– Must be unique across the Internet– Name prefix added to domain suffix

Domain Name System (DNS) provides translations between names and IP address– Names are similar in style, but not

directly related to IP address


GlossaryGlossary

Client– A program that uses the Internet to contact a

remote server Client-Server Computing

– The interaction between two programs when they communicate across a network


GlossaryGlossary

Distributed Computing– Computations involving more than one

computer Peer-to-Peer Networking

– Any network system in which all computers are equal

Server– A program that offers a service


GlossaryGlossary

Domain Name – The name assigned to a computer on

the Internet. A single computer’s name can contain several strings separated by periods.

Domain Name System – (DNS) The Internet service used to look

up a computer’s name and find the computer’s IP address.

Midterm ReviewMidterm Review


The Telephone NetworkThe Telephone Network

Telephone analogy used for Internet development– 1876: Alexander Graham Bell obtains patent for the telephone

– 1927: Commercial telephone service by radio between New York and London opens for the first time

Provides Universal ServiceUbiquitousDesigned for voice transmission


Digital to Analog Digital to Analog

Analog is easy, but prone to distortion Digital is distortion free, but lossey Computers use binary numbers to encode

digital information– ASCII encodes characters

Sampling..– Nyquist theorem

Quantization– Introduces lossiness (quantization error)


Digital Telephone NetworkDigital Telephone Network

Circuit switched– circuit is limited to 64 kbps– wasteful when idle– unsuitable for multimedia services

Telephone network is now digital– Multiplexed – TDMA

• DS0, DS1 = 24 DS0, DS2 = 4 DS1…..


Introduction to NetworksIntroduction to Networks

Modulation of signalsModulator/Demodulator -- ModemEncoding of data to binary

– ASCIIError detection

– Parity, checksumLAN Technology

– Easy, cheap, reliable


The Early YearsThe Early Years

The Internet began as an ARPA research project.

The TCP/IP protocol software was developed to make the Internet operational.

The Internet is an Open System, with the technology freely available to all.

The Internet documentation is available on-line in the form of reports known as RFCs.



BSD UNIX distributed TCP/IP suite freely to universities in the early 80s

1982 US Military adopted TCP/IP as primary communication standard

Exponential growth from its inception IAB formed to coordinate development IETF - major technical development body

– Working groups



1988 – NSFNET Backbone1992 – Privatization (ANSNET)Exponential growth from its

inception– Half of the users today have been there

less than one year……IP Address 32 bit limitation


The Global InternetThe Global InternetEmail was the first killer app.EBONE brought Europe to the Internet1997 – Every continent is connected1998 – Every populated country is

connectedThe Internet is the new infrastructureTCP/IP is the key to how the Internet

works.


How Does the Network Work?How Does the Network Work?

Circuit Switching– Reserves resources

Packet Switching– Shares resources– Increased overhead – headers

• Packets are labeled with destination info

– Efficient – resources used as needed – Unreliable – packets can be dropped



Packet Switching– Store and Forward

• Packets move one hop at a time• Decisions are made at each hop

– Delay ..• Processing delay• Queueing delay• Transmission delay• Propagation delay



A router is used to interconnect networks– LANs to LANs or LANs to WANs– Routers forward packets from one network

to another• Process is called Routing

– Routers are the building blocks of the Internet



ISPs provide the connection service to access the Internet– “The Last Mile”

• Dialup• ADSL• Cable modem• Wireless

– Also may provide email, web space or other services


IP & RoutingIP & Routing

Protocols and protocol stack– Internet stack, OSI stack– Layering model

IP addressing– Class-based vs. CDIR

IP forwarding Routing

– Link State– Distance Vector


Transport LayerTransport Layer

Principles behind transport layer services:– multiplexing/demultiplexing– reliable data transfer– flow control, congestion control

Instantiation and implementation in the Internet– UDP, unreliable delivery– TCP, reliable with control


See you See you Thursday!Thursday!

Documents

CE80N Introduction to Networks & The Internet