18-345: Introduction to Telecommunication Networks Lectures 1


Course Overview • Administrivia

18-345: Introduction to Telecommunication Networks Lectures 1: Course Overview

• Objective • People, course communications • Grading, course policies

• Why are networks important? • A whirlwind tour of the course

Peter Steenkiste Spring 2015 www.cs.cmu.edu/~prs/nets-ece




Course Goals

• Instructor.

• Become familiar with the principles and practice of data networking

• Peter Steenkiste • [email protected], Gates Hall 9107

• Routing, transport protocols, naming, ...

• Teaching assistant.

• Learn how to write applications that use the network

• Antonio Rodriguez

• Use web and peer-to-peer style applications

• Course secretary

• Get some understanding about network internals in a hands-on way

• Kathy McNiff, Gates 9213

• Implementing different types of protocol, error recovery, conformance with standards, etc.

Page 1

Course Format

Course Materials •

• ~28 lectures

Textbook: Computer Networks – A Systems Approach, L. Peterson and B. Davie, Morgan Kaufmann References

• Cover the “principles and practice”

• 6 homework assignments • Practice for tests – not graded

• 4 programming projects

• Computer Networking – A Top-Down Approach, by J. Kurose and K. Ross, Addison Wesley • Computer Networks, Wetherall and Tanenbaum • Communication Networks, by A. Leon-Garcia and I. Widjaja, , Second edition, McGraw-Hill. • Data and Computer Communications, W. Stalling, MacMillan Publishing Company, New York.

• How to use and build networks / networked applications • Larger, open-ended group projects. Start early!

• 6 in class quizzes • Short in-class tests on the last block of lectures

• Midterm and final • Two 2-hour in class tests


Projects and Recitation Sections

Getting Questions Answered • Administrative: start with web site

• Key objective: system programming • Different from what you’ve done before!

• If the answer is not there, please send us email

• Can use C or Java • Often designed to run indefinitely – must handle all errors! • Interfaces specified by documented protocols • Concurrency involved (inter and intra-machine) • Must have good test methods

• Course material: class, office hours • Typically requires a discussion – piazza or email often does not work well

• Projects: piazza, office hours

• Recitations to provide project background, discuss programming tools and skills

• Piazza: others might have the same question • Office hours for more complicated issues 7

Page 2

Administrative Stuff


• Watch the course web page

• Roughly equal weight in projects and testing

• http://www.cs.cmu.edu/~prs/nets-ece/ • All handouts, readings, project information, .. • If something is missing on the web site, please let us know asap

• 35% for projects • 15% for quizzes • 50% for two exams

• This course does not use blackboard • Read bboard - piazza

• You MUST demonstrate competence in both projects and tests to pass the course

• E-mail on things like grades should go to instructor (do not use piazza for this!)

• Fail either and you fail the class!

• Office hours will be posted on web page • Changes will be posted in the “News” section of the web page

Policy on Late Work, Regrading, Exam & Quiz coverage

Policy on Collaboration • Working together is important • Discuss course material in general terms • Work together on program debugging, .. • Final submission must be your own work • Projects are done in teams of two • Collaboration, group project skills • Both students must understand the project • What we don’t want to have to say: we run all projects through cheat-checkers comparing with other old and new submissions … • All cases of cheating will be reported

• Assignments must be handed in on time • Only exception is documented illness and family emergencies

• Regrading requests must be submitted in writing with secretary within 1 week • Entire exam or quiz will be regraded.

• Exam and Quiz coverage: • All materials right before the exam/quiz • Details will be on the web page 12

Page 3

The Slides

Course Overview

• The slides are a resource that is shared by many instructors

• Administrivia • Why are networks important?

• Also some sharing with 15-441

• What is a network? • What is the Internet • Internet design

• They include contributions from Peter Steenkiste, Hyong Kim, Srini Seshan, Dave Andersen, Hui Zhang, and others

• A whirlwind tour of the course


What is a Network?

Basic Building Block: Links

• An infrastructure that allows (distributed) “users” to communicate with each other

• Simplest example: 2 nodes • Sender changes voltage, frequency, … • Or maybe it is optical or wireless?

• People, devices, … • By means of voice, video, text, … • Focus on electrical/optical/RF/.. (not trucks)




• But receiver must “understand” sender – protocols • More on this later

• It is assumed that the infrastructure is shared by many users

• Okay… what about more nodes?

• Point to point link is not very interesting • Value increases with the number of users!

• How about a million?



Page 4

Scaling the Network

Communication Network Architecture • Network architecture: the plan that specifies how the network is built and operated • Architecture is driven by the network services • Overall communication process is complex • Network architecture partitions overall communication process into separate functional areas called layers - more on this later Next we will trace evolution of three network architectures: telegraph, telephone, and computer networks

Or one wire (N2)

Wires for everybody!

But First a bit of History

Or how about …


Network Architecture Trends

Network Architecture Evolution

Information transfer per second

• Telegraph Networks • Message switching & digital transmission



• Telephone Networks

1.0E+12 1.0E+10

• Circuit Switching • Analog transmission → digital transmission → mobile

1.0E+08 1.0E+06 1.0E+04 1.0E+02

• Internet

1.0E+00 1850

Telegraph networks




Telephone networks




Internet, Optical & Wireless networks

• Packet switching & computer applications • Increasingly faster, more diverse edge & apps

Next Generation Internet

• Next generation Internet ???

Page 5

Telegraphs & Long-Distance Message Communications

Message Switching Architecture • Network nodes were created where several optical telegraph lines met (Paris and other sites) • Store-and-Forward Operation:

• Courier: physical transport of the message • Messenger pigeons, pony express, FedEx

• Telegraph: message is transmitted across a network using signals – much faster!

• Messages arriving on each line were decoded • Next-hop in route determined by destination address of a message • Each message was carried by hand to next line, and stored until operator became available for next transmission

• Drums, beacons, mirrors, smoke, flags, • Light, electricity

East line South line

Bell’s Telephone

Electric Telegraph Networks

• Alexander Graham Bell (1875) working on harmonic telegraph to multiplex telegraph signals • Discovered voice signals can be transmitted directly

• Electric telegraph networks exploded • Message switching & Store-and-Forward operation • Key elements: Addressing, Routing, Forwarding

• Microphone converts voice pressure variation (sound) into analogous electrical signal • Loudspeaker converts electrical signal back into sound

• Optical telegraph networks disappeared Message

Network North Node line West line

• Telephone patent granted in 1876 • Bell Telephone Company founded in 1877

Message Message

Signal for “ae” as in cat

Source Message




Electrical signal



Page 6


Three Phases of a Connection

Circuit Switching • Source first establishes a connection (circuit) to the destination • Each switch along the way stores info about connection (and possibly allocates resources)

• Source sends the data over the circuit


Telephone network


Telephone network


Telephone network

Connection set up

• No need to include the destination address with the data since the switches know the path

• The connection is explicitly torn down

Dial tone.

Dial number


Telephone network

• Example: telephone network (analog) Information transfer

Pick up phone


Telephone network

Network selects route; Sets up connection; Called party alerted

Exchange voice signals

Connection release 6. 25

Links and Switches in Early Telephone Networks

Telephone network

Hang up.

Circuit Switching Discussion • Circuits have some very attractive properties. • Fast and simple data transfer, once the circuit has been established • Predictable performance since the circuit provides isolation from other users • E.g. guaranteed bandwidth

• But it also has some shortcomings. • How about bursty traffic? • Do you need a permanent circuit to Facebook? • Circuit will be idle for significant periods of time

• How about users with different bandwidth needs?



Page 7

Contrast this with Message (Packet) Switching (our emphasis)

And Some More Examples …

• Source sends information as self-contained messages that have an address.

• Television network • Over the air • Cable TV • Satellite

• Source may have to break up single message in multiple packets

• Each packet travels independently to the destination host. • Switches use the address in the packet to determine how to forward the packets • Store and forward

• Radio broadcast • Various private networks

• Analogy: a letter in surface mail.

• E.g., for first responders, military, ..



Today’s Lecture

What about the Internet • An inter-net: a network of networks.

• Administrivia

• Networks are connected using routers and other devices, e.g., for security, accounting, … • Networks can use diverse technologies • Typically managed by different organization

• Why are networks important? • What is a network? • What is the Internet • Internet design


• The Internet: the interconnected set of networks of the Internet Service Providers (ISPs) • About ~23,000 “transit” ISPs make up the Internet • Many more “edge” networks

• A whirlwind tour of the course 32


Page 8

What is the Objective of the Internet?

Packet Switching – Statistical Multiplexing

• Enable communication between diverse applications on diverse devices (“computers”)


• Web, peer-to-peer, video streaming, distributed processing, video and audio conferencing, …

• Over very diverse infrastructures • The “Internet”, WiFi and cellular, data center networks, corporate networks, dedicated private networks, …

• In contrast: previous networks were special purpose and fairly homogeneous in terms of technology

• Switches arbitrate between inputs • Can send from any input that’s ready

• Must understand application needs/demands (Thursday) • Traffic data rate and loss sensitivity • Traffic pattern (bursty or constant bit rate) • Traffic target (multipoint or single destination, mobile or fixed)

• Links are never idle when there is traffic to send • (Efficiency!) 34



Internet Design • In order to inter-operate, all participating networks must follow a common set of rules • Example: requirements for packets:

• Need to share network resources

• Address format, header information, packet size limit, ..

• But also: routing, error reporting, billing, … • Also: what is the “service model”, i.e., the commitment made to applications

• How? Switched network

• Party “A” gets resources sometimes • Party “B” gets them sometimes

• Interior nodes act as “Switches”

• Internet: best-effort – packets can get lost, etc. • But some applications need reliable data delivery, a minimal bandwidth guarantee, low latency, …

• Many challenges: fairness, efficiency, … 36


Page 9

Networks Juggle Many Goals

Must also Deal with “Real World”

• Support rich set of applications • Efficiency – resource use; cost • The “ilities”:

• Economics and public policy play a big role in the design of the Internet

• • • •

• ISPs are competing for customers but they must also work together • They must make money – no ISPs, no Internet

Evolvability Managability Security (securability, if you must) Ease of:

• Public policy looks after user interests and tries to promote competition and innovation • Users will only use the network if they get value out of it

• Deployment, management • Creating useful applications

• Concerns such as privacy can stifle use

• Scalability 38


Success Factors for New Services

Transmission Technology • Relentless improvement in transmission • High-speed transmission in copper pairs

• Technology not only factor in success of a new service • Three factors considered in new telecom services

• DSL Internet Access

• Higher call capacity in cellular networks Technology

Can there be demand for the service?

Market New Service

• Lower cost cellular phone service Can it be implemented costeffectively?

• Enormous capacity and reach in optical fiber • Plummeting cost for long distance telephone

• Allows innovation in applications, services • E-mail  chat  audio  video • Peer to peer, cloud computing


Is the service allowed?

Page 10

Processing Technology

Moore’s Law

• Relentless improvement in processing & storage • Moore’s Law: doubling of transistors per integrated circuit every two years • RAM: larger tables, larger systems • Digital signal processing: transmission, multiplexing, framing, error control, encryption • Network processors: hardware for routing, switching, forwarding, and traffic management • Microprocessors: higher layer protocols and applications • Higher speeds and higher throughputs in network protocols and applications

Transistor count


P4 Pentium III

1.0E+07 486 DX



1.0E+05 8086

1.0E+04 1.0E+03

8080 4004

0 1972


Pentium II Pentium Pro Pentium Intel DX2

10 1982

20 1992

30 2002

The S Curve

• The network effect: usefulness of a service increases with size of community

Service Penetration & Network Effect • Telephone: T=30 years

• Metcalfe's Law: usefulness is proportional to the square of the number of users • Phone, fax, email, ICQ, …

• city-wide & inter-city links

• Automobile: T=30 years

• Economies of scale: per-user cost drops with increased volume

• roads

• Others

• Cell phones, PDAs, PCs • Efficiencies from multiplexing

• S-curve: growth of new service has S-shaped curve, challenge is to reach the critical mass


Page 11

• • • •

Fax Cellular & cordless phones Internet & WWW Napster and P2P


Regulation & Competition

• New technologies very costly and risky • Standards allow players to share risk and benefits of a new market

• Telegraph & Telephone originally monopolies • Extremely high cost of infrastructure • Profitable, predictable, slow to innovate

• Competition feasible with technology advances

• • • •

• Long distance cost plummeted with optical tech • Alternative local access through cable, wireless • Radio spectrum: auctioned vs. unlicensed

Reduced cost of entry Interoperability and network effect Compete on innovation Completing the value chain • Chips, systems, equipment vendors, service providers

• Internet supports multiple applications • Innovation leads to new appls and usage models • Regulation needed to ensure competition and universal access

• Example: • 802.11 LAN, IP, HTTP/SMTP/…

Today’s Lecture

Standards Bodies • Internet Engineering Task Force

• Administrivia

• Internet standards development • Request for Comments (RFCs): www.ietf.org

• Why are networks important?

• International Telecommunications Union • International telecom standards

• What is a network? • What is the Internet • Internet design

• IEEE 802 Committee • Local area and metropolitan area network standards

• Industry Organizations • MPLS Forum, WiFi Alliance, World Wide Web Consortium

• A whirlwind tour of the course 49

Page 12

Whirlwind Tour of the Course


• Infrastructure: hardware (or close to it) • Core networking protocols: IP, dealing with errors and congestion, routing, … • Optimizing performance: QoS techniques, caching, CDNs, peer-peer, … • Making it work well: security, management, … • IP everywhere: the Internet, last mile, wireless, mobility, data center, video, IP-TV, skype, … • Focus is on today’s Internet but also trends

• Why do we have different types of “wires”? • And why do I care?

• Ethernet is very old, so why is it so fast? • Can’t they find something better?

• What are the limits of some of the technologies? • Both physical and protocol limits

• What will the Internet look like in 10, 20, 30 years? 50


Core Networking Protocols

Optimizing Performance

Think: traffic on the roads • How do I found a path to my destination • How do I specify addresses • What if my car breaks down? • How do I deal with traffic jams • …

• Intuitively: lots of bandwidth! • But there is more to it: • Latency is often more critical! • How voice and video – can I offer guarantees? • Can I beat the speed of light? • Hint: this can make you rich

• Why did we use peer to peer networks? • And why did they (mostly) go away?



Page 13

Making the Network Work Well

IP Everywhere • Using IP technology has become attractive

• Good technology is only a small part of the puzzle – deployment and management issues are equally (or more) critical

• Cheap commodity hardware, lots of tools, people trained in the technology, end-to-end support, …

• The (public) Internet: our focus

• Involves many people, high cost

• How do you optimize “the web”: CDNs, caching, …

• Data centers: very special requirements

• How do I secure my network?

• Map-reduce, 3-tier business apps, load balancing, …

• Lots of bad guys: DOS, compromised hosts, privacy leaks, botnets, …

• IP TV, voice/video conferencing: • Very high QoE expectations

• How I manage resources, reduce operator errors, deal with failures, …

• Wireless and mobile apps • For many users, primary way of accessing Internet

• And how does it differ in LAN, WAN, wireless, …

• Residential networking 54


Page 14


18-345: Introduction to Telecommunication Networks Lectures 1

Course Overview • Administrivia 18-345: Introduction to Telecommunication Networks Lectures 1: Course Overview • Objective • People, course communic...

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