[PPT] - 04832250 Computer Networks (Honor Track) A Data Communication and PowerPoint Presentation

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04832250 – Computer Networks (Honor Track)

Prof. Chenren Xu（许辰人）

Center for Energy-efficient Computing and Applications Computer Science, Peking University chenren@pku.edu.cn http://soar.pku.edu.cn/

Module 0: Course Overview

A Data Communication and Device Networking Perspective A Data Communication and Device Networking Perspective

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Bilingual
Use Chinese when necessary
Focus on principles rather than details
Details in textbook anyway
Practice, practice, practice!
Projects might be ahead of course schedule, so learn as you do
Research/innovative projects for final examination
Breadths also matters
Get to know the state of art!

This version of honor track

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Introductory (first) course in computer/device networking
Learn principles of computer networking
Learn practice of computer networking
Internet architecture/protocols as case study

§ By the time you are finished …

Goals:
Learn a lot (not just factoids, but principles and practice)

§ Web surfing, mail server, network congestion, routing, bit error handling, edge networks

Have fun!

§ Learn how to spoof email, sniff network traffic, write cool networks apps, and more

What is this course about?

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Instructor
Prof. Chenren Xu（许辰人）

§ Assistant Professor in CS Dept. and CECA § Email: chenren@pku.edu.cn

Teaching Assistants
Mr. Shuang Jiang（姜双）

§ Master Student in CS Dept. and CECA § Email: js_eecs@pku.edu.cn

Miss Jing Wang（王婧）

§ Senior undergrad in CS Dept. and CECA § Email: jing.wang@pku.edu.cn

Course Staff & Logistics

Lectures:
Mon 13:00 pm – 14:50 pm
Thu 8:00 am – 9:50 am (double week)
Teaching Building No.2 414
Office hour:
By appointment
Class webpage:
http://soar.pku.edu.cn/teaching/CompNets/Fall16/
Content access: compnets_honor@pku:fall16

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Introductory course in computer networking
Prerequisites
System programming: Introduction to Computer Systems (Linux C/C++ programming)
Mathematical analytics: Linear Algebra, Algorithms, Signal Processing Basics
Course materials

Course Information

Recommended readings:
Textbook:
Slides credits

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20%: Class participation
In-class quiz (20%)
Bonus points for in-class presentation

discussion (10%)

30%: Midterm
Written test in English
50%: Research project
Oral presentation (20%)
Report write-up (20%)
Poster and demo (10%)
All in English

Grading policy: overall score calculation

Late penalty: 10% credits lost per day
Quiz and exam are based on lecture notes
You are welcome to explore in more detailed

and depth in textbook and recommended books

Grade will be “curved”
Your grade depends upon the performance of

the rest of the class.

One A4 cheating sheet allowed in the

exam not quiz.

Class handouts, books not allowed

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Topics

End-to-end Transport
Connection and Flow Management, Congestion

Management, Linux TCP/IP

Network Security
Crypto, VPN, Middlebox, IPSec, TLS, DDoS
Multimedia Networking
Video Streaming, QoS, RTP, Traffic Engineering
Emerging Technologies
5G Communication, IoT/Edge/Fog

Architecture, Bluetooth, 802.15.4 and ZigBee, Vehicular Networking, RFID and Localization, VLC, 802.11ah and LoRaWAN, SDN and NFV, Big Data

Computer Networks 101
Usage and Applications, Components, Socket API,

Protocol and Layering, Reference Model, History

Protocol support for Network Applications
DNS, HTTP, CDN and P2P
PHY concepts and Wireless Fundamentals
Signals Propagation, Modulation, Coding and

Multiplexing, Channels Properties, MIMO and OFDM

(W)LAN Concepts and Link Technologies
Framing, Error Control, Multiple Access and MAC,

LAN Switch, 802.11 and WiFi

Internetworking and Internet
Network Service, Addressing and Scaling, Routing

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Schedule (subject to change)

Date Day Topics Note 9/12 Mon Overview Project out 9/19 Mon Network App 9/22 Thu Network App 9/26 Mon Network App Project meeting 10/10 Mon PHY and Wireless Lab 1 out 10/17 Mon PHY and Wireless 10/20 Thu PHY and Wireless 10/24 Mon (W)LAN and Link Tech Quiz 1 11/1 Mon (W)LAN and Link Tech Project proposal due 11/3 Thu (W)LAN and Link Tech Lab 1 due, Lab 2 out 11/7 Mon Internetworking Quiz 2 Date Day Topics Note 11/14 Mon Internetworking 11/17 Thu Internetworking 11/21 Mon End-to-end Transport Quiz 3 11/28 Mon End-to-end Transport 12/1 Thu End-to-end Transport 12/5 Mon Midterm Lab 2 due, Lab 3 out 12/12 Mon Network Security 12/15 Thu Multimedia Networking 12/19 Mon Emerging Tech 12/26 Mon Emerging Tech 12/29 Thu Project Presentation Quiz 4, Lab 3 due

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You might not want to take this course if you are:
Not comfortable with English (oral, written, either or both)

§ ZERO credit for writing your quiz/exam answer in Chinese

Routine and non-aggressive in learning

§ Extra material beyond textbook

Non-cooperative as a team member

§ Everyone will need to make contribution to the course project

Already overloaded by other courses

WARNING!!!

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Computer science is dominated by major conferences
They attract top researchers from all over the word
They often only accept ~15% from the total submissions
They are often annually held in interesting international locations

Where Computer Scientists Publish Research Papers

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Archived by Google Scholar
Highly cited paper (200+ citations in recent 5 years)
Bleeding-edge thoughts (top workshop)
Cutting-edge work (top conference)
Test-of-time work (1000+ citations in past 10 years)
Published in top academic conference venues
Data Networking and Communication

§ ACM SIGCOMM, USENIX NSDI, ACM HotNets, ACM CoNext, IEEE INFOCOM

Mobile System and Wireless Networking

§ ACM MobiSys, ACM MobiCom, ACM HotMobile, IEEE INFOCOM

Sensor System and Networked Sensing

§ ACM SenSys, ACM UbiComp, ACM/IEEE IPSN, IEEE INFOCOM

Where to start from?

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Problem statement
Background, importance, goal, challenge, high-level proposed solution
Technical approach
Design ideas (system block diagram, algorithms, etc.)
Experimental Design
Evaluation metrics, equipment/testbed, etc.
Reference list
10+, most should be fresh (within 5 years)
Team background
Strength, experience

Milestone: Project proposal (due on 11/1 23:59 pm)

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Course number: 04830241
You don’t have to attend class
Project information will be announced by TA in class
Three lab projects
Lab 1: Wireshark based packet sniffing and analysis (Layer 1/2)

§ https://www.wireshark.org/ § https://wiki.wireshark.org/

Lab 2: Partial TCP/IP implementation based on Click Router (Layer 3/4)

§ http://read.cs.ucla.edu/click/click

Lab 3: Video CDN (Layer 7)
Cheating penalty: 20% credits of overall grade at a time

Computer Network Practicum（计算机网络实习）

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Peek inside the Network using Traceroute
Protocol and Layering
Reference Models
Internet History

Introduction of Today’s Internet

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Focus of the course

Three “networking” topics:
We’re in the middle

Distributed systems Networking Communications

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The Main Point

To learn how the Internet works
What really happens when you “browse the web”?
What are TCP/IP

, DNS, HTTP , NAT, VPNs, 802.11 etc. anyway?

To learn the fundamentals of computer networks

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Curiosity
Why and how
Impact on our world
Job prospects

Why learn about the Internet?

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From this experimental network …

(a) Dec. 1969. (b) July 1970.

ARPANET ~1970

Internet ~2005

(c) March 1971.

An everyday institution used at work,

home, and on-the-go

Visualization contains millions of links

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An enabler of societal change
Easy access to knowledge
Electronic commerce
Personal relationships
Discussion without censorship

The Impact of Internet

An engine of economic growth
Advertising-sponsored search
“Long tail” online stores
Online marketplaces
Crowdsourcing (e.g., O2O)

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To learn how the Internet works
What really happens when you “browse the web”?
What are TCP/IP, DNS, HTTP, NAT, VPNs, 802.11 etc. anyway?
To learn the fundamentals of computer networks
What hard problems must they solve?
What design strategies have proven valuable?

The Main Point (2)

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Why learn the Fundamentals?

Apply to all computer networks
We learn WiFi, then we can guess and quickly understand how satellite networks work
Intellectual interest
Reliable remote data transfer
Change/reinvention

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Example key problem: Reliability!
Any part of the Internet might fail
Messages might be corrupted
So how do we provide reliability?
Reliability solutions
Codes to detect/correct errors
Routing around failures …

Fundamentals – Intellectual Interest

Key problem Example solutions Reliability despite failures Codes for error detection/correction Routing around failures Network growth and evolution Addressing and naming Protocol layering Allocation of resources like bandwidth Multiple access Congestion control Security against various threats Confidentiality of messages Authentication of communicating parties

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At least a billion Internet hosts and growing …
Examples of upheavals in the past 1-2 decades
The Internet is constantly being

re-invented!

Growth over time and technology

trends drive upheavals in Internet design and usage

Today’s Internet is different from

yesterday’s

And tomorrow’s will be different again
But the fundamentals remain the same

Fundamentals – Reinvention

Growth / Tech Driver Upheaval Emergence of the web Content Distribution Networks Digital songs/videos Peer-to-peer file sharing Falling cost/bit Voice-over-IP calling Many Internet hosts IPv6 Wireless advances Mobile devices

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Traceroute
Protocol Layers
Reference Models
Internet History

Introduction of Today’s Internet

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Work:
Email, file sharing, printing, …
Home:
Movies / songs, news, calls / video / messaging, e-commerce, …
Mobile:
Calls / texts, games, videos, maps, information access …

Example Uses of Networks

What do these uses tell us about why we build networks?

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From the telephone onwards:
VoIP (voice-over-IP)
Video conferencing
Instant messaging
Social networking
Enables remote communication
Need low latency for interactivity

Human Communication and Resource Sharing

Many users may access the same

underlying resource

E.g., 3D printer, search index, machines in the

cloud

More cost effective than dedicated

resources per user

Even network links are shared via statistical

multiplexing

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Sharing of network bandwidth between

users according to the statistics of their demand

(Multiplexing just means sharing)
Useful because users are mostly idle and their

traffic is bursty

Key question:
How much does it help?

Statistical Multiplexing

Example: Users in an ISP network
Network has 100 Mbps (units of bandwidth)
Each user subscribes to 5 Mbps, for videos
But a user is active only 50% of the time …
How many users can the ISP support?
With dedicated bandwidth for each user: 20
Probability all bandwidth is used (assuming

independent users)? ISP 100 5 5 5 . . .

How about we have more users?

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With 30 independent users, still unlikely

(2% chance) to need more than 100 Mbps!

Binomial probabilities
Can serve more users with the same size

network!

Statistical multiplexing gain is 30/20 or 1.5X
p is over claimed
But may get unlucky; users will have degraded

service

Statistical Multiplexing – cont’d

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Same content is delivered to many users
Videos (large), songs, apps and upgrades, web pages, …
More efficient than sending a copy all the way to each user
Uses replicas in the network

Content Delivery

Source User User . . . Sending content from the source to 4 users takes 4 x 3 = 12 “network hops” in the example Replica But sending content via replicas takes only 4 + 2 = 6 “network hops” Source User User . . .

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To let computers interact with other computers
E.g., e-commerce, reservations
Enables automated information processing across different parties
For gathering sensor data, and for manipulating the world
E.g., webcams, location on mobile phones, door locks, …
This is a rich, emerging usage
The value of connectivity
“Metcalfe’s Law” ~1980:

§ The value of a network of N nodes is proportional to N2 § Large networks are relatively more valuable than small ones

Example: both sides have 12 nodes, but the left network has more connectivity

Computer/Device Communication and Connectivity

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Traceroute
Protocol Layers
Reference Models
Internet History

Introduction of Today’s Internet

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Parts of a Network

host app link router

Component Function Example Application, or app, user (not physical) Uses the network Skype, iTunes, Amazon Host, or end-system, edge device, node, source, sink Supports apps Laptop, mobile, desktop Router, or switch, node, intermediate system, … Relays messages between links Access point, cable/DSL modem Link, or channel Connects nodes Wires, wireless

Types of link
Full-duplex: bidirectional at the same time
Half-duplex: bidirectional, one at a time
Simplex: unidirectional

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Core Internet and Cloud Infrastructure

Home Network Enterprise Network Mobile Network

Cache Service

Mobile Device

Service Cache

Cache Service

Edge Network/ Cloud

<5 ms >50 ms

IoT Device

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access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net access net

ISP B ISP A ISP C

IXP IXP

peering link Internet exchange point

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Commonly known by type of technology or their purpose
WiFi (802.11)
Enterprise / Ethernet
ISP (Internet Service Provider)
Cable / DSL
Mobile phone / cellular (2G, 3G, 4G)
Bluetooth
Telephone
Internetworks
An internetwork, or internet, is what you get when you join networks together
The Internet (capital “I”) is the internet we all use

Example Networks and their name by scale

Scale Type Example Vicinity PAN (Personal Area Network) Bluetooth Building LAN (Local Area Network) WiFi, Ethernet City MAN (Metropolitan Area Network) Cable, DSL Country WAN (Wide Area Network) Large ISP Planet The Internet (network of all networks) The Internet!

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What part is the “network”?
What part represents an “ISP”?
Cloud as a generic network

Network Boundaries

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Between (1) apps and network, and (2) network components

Key Interfaces

Network-application interfaces define how apps use the network – Sockets are widely used in practice

host app host app

Network-network interfaces define how nodes work together – Traceroute can peek in the network

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Traceroute
Protocol Layers
Reference Models
Internet History

Introduction of Today’s Internet

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Defines how apps use the network
Lets apps talk to each other via hosts; hides the details of the network

Network-Application Interface

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Simple client-server setup
Client app sends a request to server app
Server app returns a (longer) reply
This is the basis for many apps!
File transfer: send name, get file
Web browsing: send URL, get page
Echo: send message, get it back
Let’s see how to write this app

Motivating Application

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Simple abstraction to use the network
The network service API used to write all

Internet applications

Part of all major OSes and languages;
riginally Berkeley (Unix) ~1983
Supports two kinds of network services
Streams: reliably send a stream of bytes
Datagrams: unreliably send separate messages.
Sockets let apps attach to the local

network at different ports

Socket API

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Using Sockets

socket() //make socket getaddrinfo() //server and port name //www.example.com:80 connect() //connect to server [block] … send() //send request recv() //await reply [block] … //do something with data! close() //done, disconnect socket() //make socket getaddrinfo() //for port on this host bind() //associate port with socket listen() //prepare to accept connections accept() //wait for a connection [block] … recv() //wait for request … send() //send the reply close() //eventually disconnect

Server Program Client Program

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Peek inside the Network using Traceroute
Protocol Layers
Reference Models
Internet History

Introduction of Today’s Internet

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Apps talk to other apps with no real idea of what is inside the network
This is good! But you may be curious …

Network Service API Hides Details

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Widely used command-line tool to let hosts peek inside the network
On all OSes (tracert on Windows)
Developed by Van Jacobson ~1987
Uses a network-network interface (IP) in ways we will explain later
Probes successive hops to find network path

Traceroute

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ISP names and places

are educated guesses

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Peek inside the Network using Traceroute
Protocol and Layering
Reference Models
Internet History

Introduction of Today’s Internet

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The network does much for apps:
Make and break connections
Find a path through the network
Transfers information reliably
Transfers arbitrary length information
Send as fast as the network allows
Shares bandwidth among users
Secures information in transit
Lets many new hosts be added

Networks Need Modularity

We need a form of modularity, to help manage complexity and support reuse

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Protocols and layering is the main structuring method used to divide up network functionality
Each instance of a protocol talks virtually to its peer using the protocol
Each instance of a protocol uses only the services of the lower layer

Protocols and Layers

Protocols are horizontal,

layers are vertical

Set of protocols in use is

called a protocol stack

An example protocol stack

used by mobile web browser

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Encapsulation is the mechanism

used to effect protocol layering

Lower layer wraps higher layer content,

adding its own information to make a new message for delivery

Like sending a letter in an envelope;

postal service doesn’t look inside

Message “on the wire” begins to

look like an onion

Lower layers are outermost

Encapsulation

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Normally draw message like this:
Each layer adds its own header
More involved in practice
Trailers as well as headers, encrypt/compress contents
Segmentation (divide long message) and reassembly

Encapsulation – cont’d

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Incoming message must be passed to the protocols that it uses

Demultiplexing

Done with demultiplexing keys in the headers

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Information hiding and reuse

Advantage of Layering

Using information hiding to connect

different systems

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Adds overhead
But minor for long messages
Hides information
App might care whether it is running over wired or wireless!

Disadvantage of Layering

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Peek inside the Network using Traceroute
Protocol and Layering
Reference Models
Internet History

Introduction of Today’s Internet

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What functionality should we implement at which layer?
This is a key design question
Reference models provide frameworks that guide us

A Little Guidance …

Application Presentation Session Transport Network Data Link Physical

Each layer has its functions.
In the same layer (horizontal)
Logical communication
Same data formats
Between neighboring layers (vertical)
Real communication
Interfaces

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A principled, international standard, to connect systems
Influential, but not used in practice.

OSI “7 layer” Reference Model

Provides functions needed by users
Converts different representations: encryption, compression, specific convertion
Manages task dialogs – synchronization, checkpoint, recovery
Provides end-to-end data delivery
Route packets over multiple networks between source and destination
Sends frames of information between neighboring network elements
Sends bits as signals “on the wire”

Application Presentation Session Transport Network Data Link Physical

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A four layer model based on experience; omits some OSI layers and uses IP as the

network layer.

IP is the “narrow waist” of the Internet
Supports many different links below and apps above

Internet Reference Model

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For units of data:

But …

Layer-based Names

Layer Unit of Data Application Message Transport Segment Network Packet Link Frame Physical Bit

For devices in the network:

Proxy or middlebox

r gateway

Repeater or hub Switch or bridge Router

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They are guidelines, not strict
May have multiple protocols working together in one layer
May be difficult to assign a specific protocol to a layer

A Note About Layers

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Goal and Motivation
Uses of Networks
Network Components
Sockets
Peek inside the Network using Traceroute
Protocol and Layering
Reference Models
Internet History

Introduction of Today’s Internet

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Rough Internet Timeline

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ARPANET by U.S. DoD was the precursor to the Internet
Motivated for resource sharing
Launched with 4 nodes in 1969, grew to hundreds of hosts
First “killer app” was email

The Beginning - ARPANET

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Leading up to ARPANET (1960s):
Packet switching (Kleinrock, Davies), decentralized control (Baran)

ARPANET - Influences

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In the early ARPANET
Internetworking became the basis for

the Internet

Pioneered by Cerf & Kahn in 1974, later

became TCP/IP

They are popularly known as the

“fathers of the Internet”

ARPANET – Influences (2)

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ARPANET Geographical Map (Dec. 1978)

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NSFNET ’85 supports educational networks
Initially connected supercomputer sites, but soon became the backbone for all networks
Classic Internet protocols we use emerged
TCP/IP (transport), DNS(naming), Berkeley sockets (API) in ’83, BGP (routing) in ‘93
Much growth from PCs and Ethernet LANs
Campuses, businesses, then homes
1 million hosts by 1993 …

Growing Up - NSFNET

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Hierarchical, with NSFNET as the backbone

Early Internet Architecture

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After ’95, connectivity is provided by large ISPs

who are competitors

They connect at Internet eXchange Point (IXP)

facilities

Later, large content providers connect
Web bursts on the scene in ’93
Growth leads to CDNs, ICANN in ’98
Most bits are video (soon wireless)
Content is driving the Internet

Modern Internet – Birth of the Web

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Complex business arrangements affect connectivity
Still decentralize, other than registering identifiers

Modern Internet Architecture

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1961: Kleinrock - queueing theory shows effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research Projects Agency
1969: first ARPAnet node operational
1972:
ARPAnet public demo
NCP (Network Control Protocol) first host-host protocol
first e-mail program
ARPAnet has 15 nodes

Internet history of 1961-1972: Early packet-switching principles

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Cerf and Kahn’s internetworking principles:

minimalism, autonomy - no

internal changes required to interconnect networks

best effort service model
stateless routers
decentralized control

define today’s Internet architecture Cerf and Kahn’s internetworking principles:

minimalism, autonomy - no

internal changes required to interconnect networks

best effort service model
stateless routers
decentralized control

define today’s Internet architecture

Internet history of 1972-1980: Internetworking, new and proprietary nets

1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn - architecture for

interconnecting networks

1976: Ethernet at Xerox PARC
Late 70’s
proprietary architectures: DECnet, SNA, XNA
Switching fixed length packets (ATM precursor)
1979: ARPAnet has 200 nodes

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Internet history of 1980-1990: new protocols, a proliferation of networks

new national networks: Csnet,

BITnet, NSFnet, Minitel

100,000 hosts connected to

confederation of networks

new national networks: Csnet,

BITnet, NSFnet, Minitel

100,000 hosts connected to

confederation of networks

1983: deployment of TCP/IP
1982: SMTP e-mail protocol
1983: DNS defined for name-to-IP-

address translation

1985: FTP protocol defined
1988: TCP congestion control

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Early 1990’s
ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
Web:

§ HTML, HTTP: Berners-Lee (hypertext [Bush 1945, Nelson 1960’s]) § late 1990’s: commercialization of the Web (1994: Mosaic, later Netscape)

Late 1990’s – 2000’s:
more killer apps: instant messaging, P2P file sharing
network security to forefront
est. 50 million host, 100 million+ users
backbone links running at Gbps

Internet history of 1990, 2000’s: commercialization, the Web, new apps

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~1 billion traditional hosts (desktops, laptops, tablets)
4-5 billion phones about a billion of which are data capable
Aggressive deployment of broadband access
Increasing ubiquity of high-speed wireless access
Emergence of online social networks:
Facebook: ~1 billion users
Service providers (Google, Microsoft) create their own networks
Bypass Internet, providing “instantaneous” access to search, email, etc.
E-commerce, universities, enterprises running their services in “cloud”

Internet history of 2005-present

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Where all the protocols come from!
Focus is on interoperability

Standards Bodies

Body Area Examples ITU Telecom G.992, ADSL H.264, MPEG4 IEEE Communications 802.3, Ethernet 802.11, WiFi IETF Internet RFC 2616, HTTP/11 RFC 1034/1035, DNS W3C Web HTML5 standard CSS standard