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
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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
The World Wide WebThe World Wide Web
• Search engines• Started in early 1990s as relatively simple software programs
using keyword indexes
• search engine marketing – major source of revenue• Keyword auctions
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
The Global Internet
The World Wide WebThe World Wide Web
• 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
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
How Google WorksHow Google Works
Figure 6-13
The Global Internet
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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.
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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
The Wireless Revolution
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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.
The Wireless Revolution
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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
The Wireless Revolution
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
Wireless Technology
Essentials of Management Information SystemsChapter 6 Telecommunications, the Internet, and
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