introduction to networks. the library a system view environment transformational process...

Introduction to Introduction to NetworksNetworks

The libraryA system view

Environment

Transformationalprocess

Inputs Outputs

energymoneymaterialspersonnelinformation

productsservices

Users

Computer networks allow us to:

• Order books online

• Receive access to online databases

• Receive software updates

Use networked computers to:

• Create or download catalog records for our holdings

• Create and distribute electronic bibliographies

Many of our products and services are delivered via computer network (e.g., virtual reference)

Connectivity of Public LibrariesInformation Use Management & Policy Institute

http://www.ii.fsu.edu/plinternet_findings.cfm

Computers in libraries

Stand-alone pc or Mac

Networked computers and peripherals

Mainframe & "dumb" terminals

Local Area Network (LAN)

A communication network used by a single organization over a limited distance which permits users to share information and resources.*

*Schatt, Stan. 1992. Understanding local area networks. 3rd ed. Carmel, Indiana: SAMS.

Local Area Network elements

Transmission medium - type of wires or other media

Network topology - architecture

Transmission protocol - rules followed when sending signals

Software

Transmission media (1)

Unshielded twisted pair (UTP)– Least expensive (CAT 5e 1,000 feet for

$260 in Spring 2011)– Four pairs grouped in plastic sheath– Each pair consists of two insulated wires

twisted together– Limited range - max 100 meters (328 feet)

Twisted pair (cont.)

Category 5 – up to 100 Mbps

Category 6 – up to 1000 Mbps

Transmission media (2)Coaxial cable

– Copper conductor surrounded by insulation

– Span distance of 185 meters (607 feet) for thin Ethernet 10BASE-2)

Cable jacket

Braided metal shield

Plastic insulation

layer

Copper conductor

Transmission media (3)Fiber-optic cable

– Expensive– Immune to electromagnetic or radio-

frequency interference– Capable of sending signals several miles– Fast

Cable jacket

Cladding

Glass Core

Strengthening fibers

Coating

Fiber optic transmission

Cladding

Glass Core

Cut-away viewLight

source

Cladding(light-

refracting)

Glass fiber(light-

transmitting)

Transmission media (4)Wireless

– Radio waves•Can travel long distances interference•Can penetrate buildings•Omnidirectional•Low bandwidth

– Microwaves•Travel in straight line•Good signal to noise ratio•Do not penetrate buildings well

– Light waves•Unidirectional - require laser and photodetector on both ends for two-way transmissions

•Line of sight--requires precise alignment of sender and receiver

•High bandwidth

109 Hz

1011 Hz

1015 Hz

ν * λ = c

Network architecture - star topology

OPAC

OPAC

OPACCirculation

printer

Network architecture - ring topology

Ring topology

FDDI (Fiber Distributed Data Interface)Bidirectional token ring network

Network architecture - bus topology

OPAC

OPACCirculation&Server

printer OPAC

Bus

Network architecture - bus topology using switch or hub

Hub

Network protocol - token ringToken passes from node to node

IEEE Std. 802.5

ISO/IEC 8802-5

TokenMsg.

Msg.Rec.

Token

Network protocol - Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)

• User's workstation generates a signal to send• Listens to detect a carrier signal from any other user • If no other signal is detected, first user's message is sent• User listens for message collision. If detects collision,

waits random period of time, then restarts processIEEE Std. 802.3

ISO/IEC 8802-3

EtherNet frame (packet) format

PREAMBLEDESTINATION

ADDESSSOURCE

ADDRESS TYPE DATAFRAMECHECK

SEQUENCE

Mix and match wiring and control topologies

Star wiring with token

passing

Network of networks

Bridge

Adding wireless

Access point for wireless

IEEE Std. 802.11ISO/IEC 8802-11

Wide Area Networks (WANs)

• Component entities can be miles apart

• Often consist of multiple local area networks linked together

• Largest WAN is the Internet

Internet – Two tales converge

• Late 1950s - Department of Defense communications went through public telephone network, considered vulnerable

• DOD wanted command-and-control network that could survive nuclear war

A robust proposition

Telephone system

Switching office

Toll office

Toll office

Baran’s proposed distributed switching

system

Internet beginning• ARPANET (Advanced Research

Projects Agency Network - U.S. Dept. of Defense Program)

First connections: 1. UCLA (hooked up

9/2/69) 2. Stanford Research

Institute (10/1/69) 3. UCSB (11/1/69) 4. Univ.of Utah (12/69)

Internet characteristics

Highly redundant network (many ways to get from point A to point B)

(Baran’s idea)

Uses packet switching

(Clark’s idea)

Switched telephone network

Switchboard

A B

Long distance telephone switching

Trunkline

AB

If roads were like telephones…

Traffic flow

Beretania

Packet switchingEach message divided into packets

– Source– Destination– Packet number of how many

packets– Data

Packet switches (nodes on Internet) use distributed adaptive routing

Packet-switched network

switch

switch

switch

switchswitch

switch

Network redundancy

switch

switch

switch

switch

switch

switch X

Required in order to be on the Internet• Physical connection to

someone who is already part of the Internet

• Utilize Internet Protocol

• Suite of software: telnet, ftp, etc.

• IP addresshypatia.slis.hawaii.edu128.171.58.11

Surfing the 'Net

Client

Server

Webserver application responds to requests from clientBrowser application

sends requests to server

Getting a Web page• Get numerical IP address• Establish connection with

machine running server• Send request for file to server• Server sends file• Release connection• Display text• Repeat above steps to request

images

Universal Resource Locator (URL)

http://www.cool.com/mystuff/myfile.html

machine

protocol

directory file name

Getting the IP address

What is numerical address of www.cool.com?

123.157.78.99

Domain Name Server

Browser

nslookup command on UNIX

Tashi delek% nslookup www.ala.orgServer: dns1.hawaii.eduAddress: 128.171.3.13Non-authoritative answer:Name: www.ala.orgAddress: 66.158.92.67

The IP address

Network class

No. of Network

Bytes Example

A 1 8.0.0.0

B 2 128.171.0.0

C 3 199.1.1.0

University of Hawai`i is a Class B network

128.171.58.11

The IP address

128.171.94.192

UH Network

Subnet

Machine

Establish a connection

Server sends “connection accepted” response to client

Client sends “connection request” to server

Requesting & receiving file

Client sends

"GET /mystuff/myfile.html" command to server

Server looks in mystuff directory

Server sends myfile.html to client

Release connection

Client sends disconnect request to server

Server closes connection

Display text and images

Browser displays text and images in accordance with directions in HTML tags

Sending data

Client sends


msg msg msg

1 2 3

Sending data

Client sends


msg 1 To: 123.157.78.99

Reference models

TCP/IP‡

OSI*

Application

Application

TransportInternet Transport

NetworkSubnet(Host-to-network)

Data link

*OSI = Open Systems Interconnection

Presentation

Session

Physical‡TCP = Transmission Control Protocol/Internet Protocol

Networked communication

Client Server

Application ApplicationTransportInternet

TransportInternet

Data link

Physical

Data link

Physical

TCP/IP

OSI

TCP/IP Layered standards architecture

ApplicationHyperText Transfer Protocol (HTTP). Browser requests Web pages; Webserver sends text, graphics, or error messages

Transport

Internet

Transmission Control Protocol (TCP). Session control; divides msgs into segments; adds header to each segment with no. (e.g. 1 of 5); error correction

Internet Protocol (IP). Adds header to each segment containing routing information. Now called packets.

SubnetData link - Transmission control for LAN. Now called frames.

Physical - Wiring, voltage, connectors

Sending out a request

Software at each layer adds header/trailer

Application HTTP

Transport

Internet

TCP-H

IP-H

Data link

Physical

DL-H

TCP-H

TCP-H IP-H

Segment

Packet

Frame

Receiving a request

Software at each layer strips off header/trailer

Application

Transport

Internet

Data link

Physical

HTTP req.

TCP-H

IP-H

DL-HTCP-H

TCP-H

IP-H

Shannon-Weaver Shannon-Weaver Communication ModelCommunication Model

ChannelChannel

TransmitterTransmitter ReceiverReceiver

SourceSource DestinationDestination

coded

decoded

Your browserYour browser ServerServer

Network Network mediummedium

Server responds

Client Server

Application ApplicationTransportInternet

TransportInternet

Data link

Physical

Data link

Physical

Routing

Client Server

Application Application

Transport

Internet

Transport

Internet

Data link

Physical

Data link

Physical

Internet

Data link

Physical

Router

Standards organizations

IEEE - Institute of Electrical and Electronics Engineers

http://www.ieee.org/portal/siteIETF - Internet Engineering Task Force

http://www.ietf.org/ISO – International Standards Organizationhttp://www.iso.org/iso/en/ISOOnline.frontpageNISO – National Information Standards Organizationhttp://www.niso.org/

http://www.ieee.org/portal/site

http://www.ietf.org/

http://www.iso.org/iso/en/ISOOnline.frontpage

http://www.niso.org/

IEEE - Institute of Electrical and Electronics Engineers standards

802.3 Ethernet802.5 Token ring802.11 Wireless LAN802.15 Wireless personal area

networks

A Few Internet Issues

Every business or institution on the Internet needs unique server names to be registered in the DNS

Problem

www.hawaii.edu

Every entityon the Internet

needs a unique address

128.171.224.100

IP Version 4 Address

128.171.58.11

4,294,967,296 Possible IP addresses

256256 256256* * *

~3,700,000,000 Available IP addresses

Address Needs

IP Version 6 (IPv6) Number

2001:0DB8:0000:2F3B:02AA:00FF:FE28:9C5A

340,282,366,920,463,463,374,607,431,768,211,456 Possible IP addresses

The Domain Name The Domain Name SystemSystem

Visiting the MIT Library Website

http://libraries.mit.edu

Universal Resource Locator (URL)

http://libraries.mit.edu

machineprotocol

Human-readable address

Getting the IP (numerical) address

What is numerical address of libraries.mit.edu?

Address: 18.51.0.23

Local Domain Name Server

Our Computer

Where does the local Domain Name Server

get the numerical address?

Root

Domain Name System Hierarchy

Our Local DNS

.com .org .edu .gov .af .al ...

libraries.mit.edu?

Top-Level Domains

Root

The DNS hierarchy


GenericTop-Level Domains

(gTLDs)

Country-CodeTop-Level Domains

(ccTLDs)

http://www.iana.org/domains/root/db/

http://www.iana.org/domains/root/db/

Root

The DNS hierarchy


United StatesGeneric Top-Level Domains

(also .mil)

Root

The DNS hierarchy

Our Local DNS


address for .edu server

Root

The DNS hierarchy

Our Local DNS


libraries.mit.edu?

Root

The DNS hierarchy

Our Local DNS


hawaii.edumit.edu ucsd.edu

berkeley.edu cornell.edu

address for mit.edu server

Root

The DNS hierarchy

Our Local DNS




libraries.mit.edu?

18.51.0.23

Getting the IP (numerical) address

What is numerical address of libraries.mit.edu?

Address: 18.51.0.23

Local Domain Name Server

Our Computer

Root

The DNS hierarchy

Our Local DNS



berkeley.edu cornell.edu18.51.0.23

(authoritative answer)

%Server: 128.171.3.13Address: 128.171.3.13#53

Non-authoritative answer:www.google.com canonical name = www.l.google.com.Name: www.l.google.comAddress: 74.125.53.103Name: www.l.google.comAddress: 74.125.53.104Name: www.l.google.comAddress: 74.125.53.105%

Using the nslookup command

nslookup www.google.com

Caching DNS

Our Local DNS

Cache

www.google.com?

Non-authoritative answer:74.125.53.10374.125.53.10474.125.53.105

DNS Record

Time to Live:360035993598359735963595…000300020001

Root

The DNS hierarchy




Root

The DNS hierarchy

.edu

hawaii.edu

Top-Level Domain

Second-LevelDomain

UHDNS

www.hawaii.edu?www.hawaii.edu?

128.171.224.100128.171.224.100

The IPv4 Address

128.171.224.100

Range: 0-255(256 possibilites)

FixedforUH

256possible

nos.

256possible

nos.

256 x 256 = 66,536addresses

Root

The DNS hierarchy

.edu

hawaii.edu

128.171.x.x

ICS Dept.128.171.10.x

Coll. of Engin.128.171.60.x

Physics Dept.128.171.30.x

Subnets

Subnet Addresses

hawaii.edu

128.171.x.x

ICS Dept.128.171.10.x

Coll. of Engin.128.171.60.x

Physics Dept.128.171.30.x

Subnets

128.171.10.156

UH ICS machine

256 possible addresses

Root

Domain Name System Hierarchy


Root

Root servers

Hidden Master Root Server

Root

RootRoot

Root

Root Root

Tower of Babel

Problem

Standards - IETF

The China Problem

Problem

$$$$$$$$$$$$$$

Problem

World Connection Density

http://www.chrisharrison.net/projects/InternetMap/

US

Western Europe

Global Digital DivideGlobal Digital Divide

Packet prioritization

Commerce

Telemedicine

Packet PrioritizationPay for priority?

IHS

ExxonMobil

Net NeutralityNet Neutrality

Internet2High-speed applications, prioritizing packets, etc.

introduction to networks. the library a system view environment transformational process...

Documents