Lecture1a - University of Hong Kong– lecture notes and supplementary readings – assignment...

Dr. Ka-Cheong Leung CSIS 7304 The Wireless Internet and Mobile Computing Slide 1

CSIS 7304The Wireless Internet and

Mobile ComputingDr. Ka-Cheong Leung

(http://www.cs.hku.hk/~c7304)


Class Structure

• Instructor: Dr. Ka-Cheong Leung– E-mail: [email protected]– Office Hours: Wednesdays 5:00 – 6:00 p.m. or

by appointment

• Web page: http://www.cs.hku.hk/~cs7304– lecture notes and supplementary readings– assignment handouts and lecture recordings– announcements


Course Readings• Required textbook

– Mobile CommunicationsJochen Schiller, Second Edition, Addison Wesley, 2003

• Reference textbook– Wireless Communications and Networks

William Stallings, Second Edition, Prentice Hall, 2005

• Additional readings on wireless TCP– will be available on the class web page


Grading• Written assignments 9%• Midterm Examination (12 July 2006) 26%• Final Examination 65%

• Assignments– submit electronically via

http://msccs.cs.hku.hk/intranet2005/default.asp– due at 7 p.m. on the designated due dates– no late assignments accepted for credit


Policies• Advised to acquire the required textbook and

possess a copy of any required readings– need to read any supplementary readings– not all details covered in class

• responsible to fill in any missing background– Prerequisite

• basic understanding of computer systems and networking protocols

• Read ahead the readings to aid your understanding of lectured materials and engage class discussions


Policies• No extension granted for the assignments• No make-up midterm and final examination• Academic Integrity Policy prohibits plagiarism

– all work submitted for credit must be done on your own– work or ideas developed by someone else must be properly

cited in your coursework

When scholastic dishonesty is suspected, the case will be reported to the University Disciplinary Committee.


Acknowledgement• Some lecture slides adopted from:

– presentation slides of “Mobile Communications” (our required textbook) authored by Dr. Jochen Schiller

– lecture notes used at the University of Southern California and evolved over many years, with contributions from Dr. Deborah Estrin, Dr. Ramesh Govindan, Dr. Christos Papadopoulos, Dr. John Heidemann, and Dr. Bill Cheng

• I do introduce and modify some of the slides to fit in our class. Please give credit to the contributors and raise any “bug” reports to me ☺

• All course materials are copyrighted. Any use or redistribution outside this course is prohibited without prior permission from all contributors.


Course Topics

• Wireless transmission basics• Medium access control• GSM and UMTS• Wireless LANs• Mobile IP and DHCP• Mobile transport layer• Support for mobility


Focus of the Class• Goal: “Learn how to learn”

– skills acquired for your life, not just for this class– learn the interplay between human and systems

• Protocols and mechanisms– will not deal with how bits move in physical media– did this in your undergraduate class

• We will deal with:– protocol rules and algorithms for wireless

communications– investigate mechanism tradeoffs– why this way and not another?


The Internet, Circa 1969


A Recent Internet ISP Map


The Internet, on a Poster, Circa 2000

[data courtesy of UCSD’s caida]


Internet Development Mantra

Quote from a t-shirt commonly worn at IETF meetings:

“We reject kings, presidents and voting. We believe in rough consensus and running code.” (Dave Clark)


Glimpses of the Future?

http://www.picoweb.net/(an 8-bit web server with Ethernet)

UCB mote:an 8-bit sensor nodewith non-IP basednetworking

a sensor network(tracking the truck)


Some Definitions

• Host: computer, PDA, light switch, ...• Link: path followed by bits

– Wire or wireless– Broadcast or switched (or both)

• Switch: moves bits between links– Packet switching: stateless, store & forward– Circuit switching: stateful, cut through


Networks

…

Point-to-Point

Multiple Access

Wireless…


Switched Networks

– two or more nodes connected by a link, or

– two or more networks connected by two or more nodes

• A network can be defined recursively as...


What Is the Problem?


What Is the Problem?


But What to Scale?Always define what kind of“scale” you mean

– Number of hosts, globally routable– Network should support many link layers– Geographic distance– Many versions of software, hardware technologies– Range of bandwidths– Different application needs (QoS, etc.)– Levels of trust / administrative boundaries– Range of price points for hardware

Lots of dimensions of “scaling” to consider


Applications Rule!• Sometimes easy to forget in this course

• Aside: What are the implications of global connectivity?– Technological issues– Societal issues– Economic issues– Security issues– etc.


Application Considerations

• Application input to network– Traffic data rate– Traffic pattern (bursty or constant bit rate)– Traffic target (multipoint or single

destination, mobile or fixed)• Network service delivered to application

– Delay sensitivity– Loss sensitivity


Reliable File Transfer

• Loss sensitive• Not delay sensitive relative to round trip

times• Point-to-point or multipoint• Bursty


Remote Login

• Loss sensitive• Delay sensitive

– Subject to interactive constraints– Can tolerate up to several hundreds of

milliseconds

• Bursty• Point to point


Network Audio

• Relatively low bandwidth– Digitized samples, packetized

• Delay variance sensitive• Loss tolerant• Possibly multipoint, long duration

sessions– Natural limit to number of simultaneous

senders


Network Video

• High bandwidth• Compressed video, bursty• Loss tolerance function of compression• Delay tolerance a function of

interactivity• Possibly multipoint• Larger number of simultaneous sources


Web

• Transactional traffic– Short requests, possibly large responses

• Loss (bug?) tolerant• Delay sensitive

– Human interactivity

• Point-to-point (multipoint is asynchronous)


Disruptive Applications

• Applications that “disrupt” business as usual• Not easy to predict: multicast case in point• Web was arguably the first, and not many

saw that coming• Napster is the poster child• Gnutella, Kazaa, Morpheus (?)• Others? What’s next?


The Global Network


Getting Started

• Host configuration• Network configuration• ISP• Computers meeting computers• Computers exchanging data


Host Configuration

• Host configuration needs:– a physical network cable (Ethernet, etc.)– an IP address– a network mask– a gateway– a DNS server (and other servers)

• Automated with DHCP


A Network

• Network configuration needs:– wires (from the phone or cable company)– Router(s)– a firewall?– an ISP to connect to the Internet– network addresses (e.g. 192.168.1.xxx)– servers


An ISP

• ISP needs:– a (big?) block of addresses– connections to one or more other ISPs, peerings– multiple routers, probably at exchange points– servers for your users: mail, web, etc.– servers for you: monitoring, etc– competent network admins (recommended)– an AUP (Acceptable Use Policy)– a lawyer


What Is….

• Structure• Metrics• Failure modes• Functions


Idealized Network Structure

Backbones

Regionals

Campus LANs


How Do Computers Find Each Other?

Internet

Computer1 Computer 2


What Are the Different Kinds of Addresses?

• Have domain name (e.g., www.hku.hk)– Global, human readable name

• DNS translates name to IP address (e.g. 147.8.145.50)– Global, understood by all networks

• Finally, we need local net address– e.g., Ethernet (08-00-2c-19-dc-45)– Local, works only on a particular network


Domain Naming System (DNS)

LocalDNS server

What’s the IP address for www.hku.hk?

Computer 1

It is 147.8.145.50

DNS address manually configured into OS

Packets have IP address information=> DNS server knows Computer 1’s address


Finding Ether Address: Address Resolution (ARP)

Ethernet

Broadcast: who knows the Ethernet address for 147.8.145.50?

Ethernet

Broadcast: I do, it is08-00-2c-19-dc-45


Sending a Packet Through the Internet

R

R

R

RRHH

H

H

H

R

RH

R

Routers send a packet to next closest point

H: Hosts

R: Routers


How Do the Routers Know Where to Send Data?

• Forwarding tables at each router populated by routing protocols

• Original Internet: manually updated• Routing protocols update tables based

on “cost”– Exchange tables with neighbors or

everyone– Use neighbor leading to shortest path


Network Metrics

• Bandwidth– Transmission capacity (a.k.a. How many

bits can fit in a section of a link?)• Delay

– queueing delay– Propagation delay (limited by c)

• Delay-bandwidth product– Important for control algorithms


Network Failures

• Packet loss– Queue overflows– Line noise

• Node or link failures• Routing transients or failures• Application level service failures• Some failure is expected (e.g. congestive

loss), but too much failure is bad


Some Backsliding about Robustness

• NAT boxes• Application-level gateways• Layer-3 caches• User tweaking

• All violate the end-to-end principles– Reduce robustness


Lack of Security in the Network• Eavesdropping

– credit card numbers or passwords in packets• Using other people’s resources

– worms, DDoS• Breaking into machines

– software bugs, poor configuration, trojan horses• Other things

– physical security, social engineering

• But, strong security is possible– requires all of good protocols, implementation, and people


Engineering Trade-offs

Network can be engineered to provide:• Reliability• Low delay• Cost

Pick any two

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