TIM 50 - Business Information Systems · PDF fileTIM 50 - Business Information Systems Lecture...

TIM 50 - Business Information Systems

Lecture 16

Instructors: Ram Akella and John Musacchio

UC Santa Cruz

November 17, 2015

Class Announcements

n Database Assignment 2 n Due Thursday, 11/19

n “Normal” assignment 5n To be posted by tonightn Due Tue 11/26

n Business Paper due 12/3

Zhejiang Discussion

¨ What could China Telecom (and Zhejiang Telecom) in particular do to lure customers from China Mobile?

¨ How could any of these strategies make use of the data in Zhejiang Telecom’s data warehouse?

Networks

Network Architecture

n Network architectures are layeredn Each layer

q uses the services of the layers belowq To offer more advanced services to layer above

n Allows layers to be designed independently n We will talk about 3 layers next…

Physical

Link

Network

What are some examples of communications networks?

n Public Telephone Networkn Internetn LANs (Local Area Networks)

What does a network do?

1) Transport data from one host to another.

Physical Layer: Convey bits over a wire

Bits: 010110...

Time

Voltage

0

1

0

1 1

0

SenderReceiver

Wire

TimeVoltage

1 1 1

00 0

Noise

Physical layer

n Other schemes for mapping a bit sequence to a physical sequence are possible.q These are called modulation schemes

Link Layer

n Make a Frame link out of a bit linkq Instead of endless sequence of 1s and 0s, we want

distinct “packages” of data that are separate from each other

n Say we want to send 2 Frames with dataq 01010101010111010 and 101010101011010q Concatenate them and send them as a sequence?

n How can the receiver tell where the new frame begins?

n Solution: insert a special sequence at the start of frame: for example: 01111110

Link Layer (cont’d)

n Also does error detection/correctionq Insert extra information the helps the

receiver to determine if the data has been corrupted.

q Example: parity bitn Sender adds a 1 or zero to end of data so number of

ones is always oddq 10011 or 10000

n If receiver counts an even number of ones, than it knows the data was corrupted.

More Link Layer.. -- EthernetWant to allow multiple hosts to share a link

How do they avoid talking at the same time?n Don’t transmit if you hear another host

transmittingn If there is a collision, stop wait a random amount

of time, and try againn This is a Medium Access Control (MAC) Protocol

Host A Host B Host C Host D

Ethernet Continuedn How do the hosts on this Ethernet identify each

other?

n Each host (actually each interface) q has a globally unique MAC addressq Cannot be changed

Host A Host B Host C Host D

Ethernet Hub

n Hub broadcasts packets on a link to all othersn As if all hosts connected to single link

q We say it is a Single collision domainn Only one host can talk at a time

Host AHost B Host C

Host D

HUB

Ethernet Switch

n If switch knows where the destination isq Switch forwards an incoming frame to destination only.q Otherwise, it broadcasts it to everyone.

n Thus, parallel conversations possible.

Host AHost B Host C

Host D

Switch

Network Layer

n A wants to send some data to Cq Suppose A knows C’s address

n A sends a packet towards Cq A marks his packet with C’s Address (an IP Address)

Host A

Host B

Host C

Host D

Link 1

Link 2

Link 3

128.114.60.202

Post Office Analogy

Alice Smith1156 High St

Santa Cruz 95064

Bob in New York

NY Post Office

Plane to London

Plane to SFO

SFOPost Office

Truck toSanta Cruz

Truck toSanta Rosa

Look at beginningof zip code.

Make forwarding decision

Look at addressMake forwarding

decision

Santa CruzPost Office

Truck toHigh St Truck to

41st Ave

Alice

Network Layer

Host A Host B

Host C

Host D

Link 1

Link 2

Link 3

128.114.60.200

128.114.60.201

128.114.60.202

128.114.60.203

Header Payload Data

Destination Address: 128.114.60.202

(IP Address)

Network Layer

Host A Host B

Host C

Host D

Link 1

Link 2

Link 3

128.114.60.200

128.114.60.201

128.114.60.202

128.114.60.203

Header Payload Data

128.114.60.202 n A uses Link 1 to send to Bn B looks at

q Packet Header q Routing Table

Address Next Hop128.114.60.202 Link 2128.114.60.203 Link 3

Routing in the Internet

Many feasible paths from source to destination.

Host B

Host A

Host C

Routing

Routingq Updating the routing tableq Objective: each packet gets closer to

destinationPacket forwarding

q Transmitting each packet on the appropriate output link

q Based on routing table

Routing AlgorithmsRouters talk to each other to

build their routing tables

Host B

Host A Host C

HUB114.211.1.2

114.211.1.1

114.211.1.3

114.211.1.4

“I am acceptingTraffic to 114.211.1.X”

Wild Card

Routing Table has Wild Cards

Host B

Host A Host C

HUB114.211.1.2

114.211.1.1

114.211.1.3

114.211.1.4114.211.1.X Link 1

1

200.261.19.X Link 2

2

ROUTING TABLE

Internet Routing is Hierarchical

AutonomousSystem (AS)

Backbone or NSP: (MCI, ATT)

AS

ISP or IAP(CRUZIO, AOL)

Customer AS

AS

ISP

Routing Concerns

n Long routes

n Circular routes

n Hijacking routes

n Route flapping

IP Addresses vs Mac AddressesnHierarchical

q The beginning bits tell you which network the host is on

q Ex: UCSC addresses start with 128.114.X.X

q The last bits tell you which host of the network

nChangeableq Changes with location of

Hostn 4 bytesn Only 4.2 billion

nNot Hierarchicalq Beginning bits tell nothing

useful

nNot Changeable

n6 bytesn281 Trillion

Link and Network Layer Interaction

Host A

Host B

EthernetHub Router

Router

Router

Router EthernetHub

Host C128.114.60.202

MAC address00-A4-B7-34-57-23

MACHeader IP

HeaderIP

Payload

Ethernet Frame

Strip MAC header off frame.Forward IP packet based onRouting table.

Payload

Issues In Networkingn Sharing of Limited Resources

q How Should A and B share a link with limited bit rate?

Source A

Source B

Destination A

Destination B

C bits per second

Issues In Networkingn Time Division Multiplexing

q gives each connection the use of the link a fixed fraction of time

q Fixed fraction of resources reserved for each connectionq Technology called circuit switching.

Source A

Source B

Destination A

Destination B

time

n Problemq When A is silent, A’s fraction of link goes unused.

Issues In Networkingn Statistical Multiplexing

q Link shared in such a way that connections are not assigned fixed fraction of Link.

q A and B unlikely to offer peak rate at the same time. n max( A+ B) < max(A) + max(B)

Source B

Source A Destination A

Destination B

A

B

A+B

Statistical Multiplexing

n Because resources aren’t reserved. It’s possible offered load too high.

n Packets are put into a queue.n If offered load remains too high, queue

will fill up and overflow.

Source A Destination A

Destination BSource B

Transport Protocolsn The Internet is unreliable

q It will make a “best effort” to get your packet to its destination

n Packets can be lost because ofq Congestionq Link errorsq Routing problems

Physical

Link

Network

Transport

Session

Presentation

Application

Transmission Control Protocol (TCP)

n Retransmit mechanism for reliabilityq Receiver sends acknowledgements to senderq If a packet is lost, source fails to get ACK, and then

retransmits.

n Congestion controlq If congestion perceived (by lost packets)q Source reduces its send rate

n When loss, sender reduces send rate by halfn Otherwise slowly increases

ACK

Packet 1

?Packet 2Packet 2

TCP cont’d

n TCP port numbersq TCP Header has a “port” number fieldq Helps host sort out how to route packets to

applications

Port 80 Packet

TCP Header

IP Header

Payload

Email Client

Port 80

Port 143

Your Computer

Audiocoder

AudiodecoderStream of

packets

UDP

n For some applications packet retransmissions are not worthwhileq Why?

n For those applications, we use UDPn UDP is a transport protocol that

q Does not do retransmissionsq Does not do congestion control

Congestion Control

n When networks are congested, certain sessions (Source-destination pairs) should reduce offered rates.q Today all TCP sessions slow down when they detect

packet losses.q UDP sessions do not slow down.

n What are some alternative strategies?q Have those whose applications aren’t as sensitive slow

down more?n How would we know which are less sensitive

Pricing within the Internet

n Customer pays an ISPq Often Flat Rate per month

n ISP pays a backbone ASq Often just flat rate, dependent on access link speed.q Sometimes based on total usage

n Backbone NSPs peer with each otherq Often for free if they exchange comparable amounts of

traffic.n Overall…

q Internet billing today is much more course grained than telephone billing.

ISP (Cruzio)

Backbone NSP

$Flat Rate

$

Flat Rate orsimple usage based

Backbone NSP

Peering Relationship

The Global Internet

The World Wide WebThe World Wide Web

• HTML (Hypertext Markup Language): • Formats documents for display on Web

• Hypertext Transfer Protocol (HTTP):• Communications standard used for transferring Web pages

• Uniform resource locators (URLs): • Addresses of Web pages• E.g., http://www.megacorp.com/content/features/082602.html

Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and

Wireless Technology


Wireless Technology

Domain Names

IP addresses are inconvenient for peopleq 32 bits hard to rememberq 128 bits very hard to remember

Domain namesq e.g. ucsc.edu

q Easier to remember than IP addresses

q However, we need some way of mapping domain names to IP addresses.

Domain Name System (DNS)

BerkeleyName Server

EECSName Server

RootName Server

UCSCName Server

SoEName Server

Hierarchy in Addresses vs. Names

Addresses hierarchical in topologyq Maximize “wild cards” and distribute address

administration

Names hierarchical in administrationq Single administered organizations often

distributed topologically (e.g. ibm.com)

Transport Protocolsn The Internet is unreliable

q It will make a “best effort” to get your packet to its destination

n Packets can be lost because ofq Congestionq Link errorsq Routing problems

Physical

Link

Network

Transport

Session

Presentation

Application

OSI Layers

Physical

Link

Network

Transport

Session

Presentation

Application

Modulation Schemes: QAM, OFDM, etc…

Ethernet, Wi-Fi, SONNET, …

Internet Protocol (IP), …

TCP, UDP

Internet Explorer, Outlook Email,Real Player, …

Some Typical Topologies

Home Network

DSL Modem TelephoneLine

RouterEthernet Switch

(to localOffice)

Small/Medium Business

Routerwith Firewall

T1 LineT1 Modem

EthernetSwitch

Web Site Server

To LocalOffice

ISP Topology

Telephone CompanyLocal Office

Local Loop

TelephoneSwitchLocal Loop

Local Loop

DSL Modem

DSL Modem

DSL Modem DSLA

M

LeasedLine toNAP

ToTelephoneNetwork

ISP Point of Presence

Network Service Provider

NetworkAccessPoint

NetworkAccessPoint

Large E-Business

Customers Merchandise Orders

Databases

Application Servers

Web Servers

Load Balancer

Incoming HTTPRequestsPresentation

Logic(AssemblingWeb page)

LogicFlow of

Interaction

Interconnectedwith Gigabit Ethernet or

other technology

Web Caching

n Speed up web page loading by storing previously seen components locally

http://www.ucsc.edu

Cache on Hard Drive

Webserver

The Global Internet


• Search engines• Started in early 1990s as relatively simple software programs

using keyword indexes

• search engine marketing – major source of revenue• Keyword auctions


Wireless Technology


Wireless Technology

The Global Internet


• Web 2.0

• Refers to more interactive Internet-based services enabling people to collaborate, share information, etc.

• Blogs: chronological, informal Web sites created by individuals using easy-to-use Weblog publishing tools

• RSS (Really Simple Syndication): syndicates Web content so content can be automatically placed into another setting

• Wikis: collaborative Web sites where visitors can add, delete, or modify content on the site


Wireless Technology


Wireless Technology

How Google WorksHow Google Works

Figure 6-13

The Global Internet


Wireless Technology


Wireless Technology

Major Web Search EnginesMajor Web Search Engines

Figure 6-14

Google is the most popular search engine on the Web, handling 56 percent of all Web searches.

The Global Internet


Wireless Technology


Wireless Technology

Intranets and ExtranetsIntranets and Extranets

The Global Internet

• Intranets• Use existing network infrastructure with Internet connectivity standards software developed for the Web.

• Create networked applications that can run on many types of computers.

• Protected by firewalls.• Extranets

• Allow authorized vendors and customers access to an internal intranet.

• Used for collaboration.• Also subject to firewall protection.


Wireless Technology


Wireless Technology

• Cellular systems

• 2G -- Competing standards for cellular service

• United States: CDMA• Most of rest of world: GSM

• Third-generation (3G) networks• UMTS (GSM extension) ATT

• CDMA 2000• 4G

• LTE, WiMax

The Wireless Revolution


Wireless Technology


Wireless Technology

• Wireless computer networks and Internet access

• Bluetooth (802.15)

• Links up to 8 devices in 10-m area using low-power, radio-based communication

• Useful for personal networking (PANs)

• Wi-Fi (802.11)

• Set of standard: 802.11a, 802.11b, 802.11g, 802.11n

• Used for wireless LAN and wireless Internet access

• Use access points: device with radio receiver/transmitter for connecting wireless devices to a wired LAN



Wireless Technology


Wireless Technology

How RFID WorksHow RFID Works

Figure 6-17

RFID uses low-powered radio transmitters to read data stored in a tag at distances ranging from 1 inch to 100 feet. The reader captures the data from the tag and sends them over a network to a host computer for processing.



Wireless Technology


Wireless Technology

• Wireless sensor networks

• Networks of hundreds or thousands of interconnected wireless devices embedded into physical environment to provide measurements of many points over large spaces

• Used to monitor building security, detect hazardous substances in air, monitor environmental changes, traffic, or military activity

• Devices have built-in processing, storage, and radio frequency sensors and antennas

• Require low-power, long-lasting batteries and ability to endure in the field without maintenance



Wireless Technology


Wireless Technology

Akamai Case

Akamai Case1) Akamai’s technology can be best classified as

q A) Enterprise Resource Planningq B) Content Delivery Networkq C) Thin Client

2)Akamai’s customers includedq A) Companies wanting a simple, inexpensive databaseq B) Companies with content heavy web sites q C) Home users wanting faster Internet access

3) Which is _not_ one way Akamai sold its product/sercice?q A) “Partner” firms like companies who do system integrationq B) Retailers like Fry’s and Best Buyq C) A sales force employed by Akalmai

Akamai CaseIn Class Discussion1) How does Akamai’s content distribution network

differ from web caching?

2) In what ways was the “tech-bust” of 2001-02 bad for Akamai? In what ways was it helpful?

3) How did EdgeSuite differ from Freeflow?

4) Why would marketing EdgeSuite be different than marketing Freeflow?

Internet Bottlenecks

n First Mile (Server Capacity) – 70% of website performance problems according to one study

n Backbone – Plentiful, but some shortage within metropolitan areas

n Peering – Exchange of traffic between NSPs

n Last Mile to homeq 56 K modems are slowq Shared LAN limitations

Solutions

n Expand Bandwidthq Being done

n Mirroring web citesq Put exact copy of same web page to multiple serversq Tricky to duplicate content

n Cachingq Problem: Stale Contentq Problem: Hard to count “click throughs”

n Content Distribution Networks…

LocalOffice orISP

Large Company

Web Server

Akamai Server

INTERNET

NSP 2

NSP 1

Web Page

Text….

Akamai Freeflow

Freeflow

n Deployed in 1999n Akamai Infrastructure

q 13000 servers in 954 networks by 2001n Customers –

q Large Commercial Websitesn Revenue model - $2000 per mbps served

q (For comparison, normal Internet access cost 500 mbps at time)

2000 Financialsn $196 Million Loss (Before special charges)

n $90 million revenuen %20 gross margin, after deducting

n server depreciation n payments to network partnersn Data center space

q But, most expenses of shouldn’t grow at same rate as number of customers, so margin should improve

n $201.5 million SG&A q (selling general and administrative) q (largely sales force cost)q Again, this might not grow at same rate as the number of

customers.n $40 million R&D

Competition

n Hosting firms (substitute)q Exodus

n Other CDNsq Sandpiper, Adero, Mirror Image

n Content Alliancesq Akamai’s competitors banded together to

share networks

2001 Market Changes

Badn Dot-coms bustn Customers leave

q “churn rate goes to 22% per quarter”Goodn Hosting firms go bust (exodus)n Some CDN competitors go bust.n Competing CDN alliances mired in problems

TIM 50 - Business Information Systems · PDF fileTIM 50 - Business Information Systems Lecture...

Documents

Transcript of TIM 50 - Business Information Systems · PDF fileTIM 50 - Business Information Systems Lecture...