1. Computer Networks CSE 434 Fall 2009
Sandeep K. S. Gupta
Arizona State University
Department of Computer Science
The Hong Kong University of Science & Technology
November 9, 1998
Research Experience for Undergradautes (REU) 1

2. Haiku (Thanks to AR in getting me interested in them)
“Haikus are used to communicate a timeless message often achieving a wistful, yearning and powerful insight through extreme brevity – the essence of Zen” -
Here are couple from the above web site:
The Web site you seek
Cannot be located, but
Countless more exist.
Stay the patient course.
Of little worth is your ire.
The network is down.
Send me any Haiku you come across related to the Internet – or better still make one yourself and share it with us.

3. In News
“Internet turns 40; barrier imperil its growth” The Arizona Republic, Sep 02, 09,

4. Quiz 1
Discussion – listen to the lecture audio posted on the web site for details.
Distributed grading and routing demo:
Each student (router) grades one question and passes the quiz (packet) on to the next student in “snake” or zig-zag order.
For the last question, the student also aggregates the points.
The above simple routing scheme can be used to used to broadcast a long sequence of packets to all the nodes in a network
If the quizzes were initially distributed in random order for grading:
What is the probability that a student will get his own quiz for grading initially? (ans: 1/(num of students))
What is the probability that during the entire grading exercise a student will get to grade at least one of his questions? – if you have an answer please let me know 

5. Chapter 1 Introduction A note on the use of these ppt slides:
We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:
If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)
If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.
Thanks and enjoy! JFK/KWR
All material copyright
J.F Kurose and K.W. Ross, All Rights Reserved
Computer Networking: A Top Down Approach , 5th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009.
Introduction

6. Chapter 1: Introduction
Our goal:
get “feel” and terminology
more depth, detail later in course
approach:
use Internet as example
Overview:
what’s the Internet?
what’s a protocol?
network edge; hosts, access net, physical media
network core: packet/circuit switching, Internet structure
performance: loss, delay, throughput
security
protocol layers, service models
history
Introduction

7. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
end systems, access networks, links
1.3 Network core
circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction

8. What’s the Internet: “nuts and bolts” viewPC
server
wireless
laptop
cellular
handheld
millions of connected computing devices: hosts = end systems
running network apps
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
wired
links
access
points
routers: forward packets (chunks of data)
router
Introduction

9. “Cool” internet appliances
Web-enabled toaster +
weather forecaster
IP picture frame
World’s smallest web server
Internet phones
Introduction

10. What’s the Internet: “nuts and bolts” view
protocols control sending, receiving of msgs
e.g., TCP, IP, HTTP, Skype, Ethernet
Internet: “network of networks”
loosely hierarchical
public Internet versus private intranet
Internet standards
RFC: Request for comments
IETF: Internet Engineering Task Force
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
Introduction

11. What’s the Internet: a service view
communication infrastructure enables distributed applications:
Web, VoIP, , games, e-commerce, file sharing
communication services provided to apps:
reliable data delivery from source to destination
“best effort” (unreliable) data delivery
Introduction

12. What’s a protocol? human protocols: “what’s the time?”
“I have a question”
introductions
… specific msgs sent
… specific actions taken when msgs received, or other events
network protocols:
machines rather than humans
all communication activity in Internet governed by protocols
protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
Introduction

13. What’s a protocol? a human protocol and a computer network protocol:Hi
TCP connection
request Hi
TCP connection
response
Got the
time?
Get
2:00
<file>
time
Q: Other human protocols?
Introduction

14. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
end systems, access networks, links
1.3 Network core
circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction

15. A closer look at network structure:
network edge: applications and hosts
access networks, physical media: wired, wireless communication links
network core:
interconnected routers
network of networks
Introduction

16. The network edge: end systems (hosts): client/server model
run application programs
e.g. Web,
at “edge of network”
peer-peer
client/server
client/server model
client host requests, receives service from always-on server
e.g. Web browser/server; client/server
peer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype, BitTorrent
Introduction

17. Access networks and physical media
Q: How to connect end systems to edge router?
residential access nets
institutional access networks (school, company)
mobile access networks
Keep in mind:
bandwidth (bits per second) of access network?
shared or dedicated?
Introduction

18. Dial-up Modem Uses existing telephony infrastructure
telephone
network
Internet
home dial-up
modem
ISP modem
(e.g., AOL)
home PC
central office
Uses existing telephony infrastructure
Home is connected to central office
up to 56Kbps direct access to router (often less)
Can’t surf and phone at same time: not “always on”

19. Digital Subscriber Line (DSL)
telephone
network
DSL
modem
home PC
phone
Internet
DSLAM
Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data
splitter
central
office
Also uses existing telephone infrastruture
up to 1 Mbps upstream (today typically < 256 kbps)
up to 8 Mbps downstream (today typically < 1 Mbps)
dedicated physical line to telephone central office

20. Residential access: cable modems
Does not use telephone infrastructure
Instead uses cable TV infrastructure
HFC: hybrid fiber coax
asymmetric: up to 30Mbps downstream, 2 Mbps upstream
network of cable and fiber attaches homes to ISP router
homes share access to router
unlike DSL, which has dedicated access
Introduction

21. Residential access: cable modems
Diagram:
Introduction

22. Cable Network Architecture: Overview
Typically 500 to 5,000 homes
cable headend
home
cable distribution
network (simplified)
Introduction

23. Cable Network Architecture: Overview
server(s)
cable headend
home
cable distribution
network
Introduction

24. Cable Network Architecture: Overview
cable headend
home
cable distribution
network (simplified)
Introduction

25. Cable Network Architecture: Overview
FDM (more shortly):
Channels V I D E O A T C N R L 1 2 3 4 5 6 7 8 9
cable headend
home
cable distribution
network
Introduction

26. Fiber to the Home OLT Optical links from central office to the home
ONT
OLT
central office
optical
splitter
optical fiber
optical fibers
Internet
Optical links from central office to the home
Two competing optical technologies:
Passive Optical network (PON)
Active Optical Network (PAN)
Much higher Internet rates; fiber also carries television and phone services

27. Ethernet Internet access
100 Mbps
1 Gbps
server
Ethernet
switch
Institutional
router
To Institution’s ISP
Typically used in companies, universities, etc
10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet
Today, end systems typically connect into Ethernet switch

28. Wireless access networks
shared wireless access network connects end system to router
via base station aka “access point”
wireless LANs:
802.11b/g (WiFi): 11 or 54 Mbps
wider-area wireless access
provided by telco operator
~1Mbps over cellular system (EVDO, HSDPA)
next up (?): WiMAX (10’s Mbps) over wide area
router
base
station
mobile
hosts
Introduction

29. Home networks Typical home network components: DSL or cable modem
router/firewall/NAT
Ethernet
wireless access
point
wireless
laptops
to/from
cable
headend
cable
modem
router/
firewall
wireless
access
point
Ethernet
Introduction

30. Physical Media Twisted Pair (TP) two insulated copper wires
Category 3: traditional phone wires, 10 Mbps Ethernet
Category 5: 100Mbps Ethernet
Bit: propagates between transmitter/rcvr pairs
physical link: what lies between transmitter & receiver
guided media:
signals propagate in solid media: copper, fiber, coax
unguided media:
signals propagate freely, e.g., radio
Introduction

31. Physical Media: coax, fiber
Fiber optic cable:
glass fiber carrying light pulses, each pulse a bit
high-speed operation:
high-speed point-to-point transmission (e.g., 10’s-100’s Gps)
low error rate: repeaters spaced far apart ; immune to electromagnetic noise
Coaxial cable:
two concentric copper conductors
bidirectional
baseband:
single channel on cable
legacy Ethernet
broadband:
multiple channels on cable
HFC
Introduction

32. Physical media: radio Radio link types:
terrestrial microwave
e.g. up to 45 Mbps channels
LAN (e.g., Wifi)
11Mbps, 54 Mbps
wide-area (e.g., cellular)
3G cellular: ~ 1 Mbps
satellite
Kbps to 45Mbps channel (or multiple smaller channels)
270 msec end-end delay
geosynchronous versus low altitude
signal carried in electromagnetic spectrum
no physical “wire”
bidirectional
propagation environment effects:
reflection
obstruction by objects
interference
Introduction

33. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
end systems, access networks, links
1.3 Network core
circuit switching, packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security
1.7 History
Introduction

34. The Network Core mesh of interconnected routers
the fundamental question: how is data transferred through net?
circuit switching: dedicated circuit per call: telephone net
packet-switching: data sent thru net in discrete “chunks”
Introduction

35. Network Core: Circuit Switching
End-end resources reserved for “call”
link bandwidth, switch capacity
dedicated resources: no sharing
circuit-like (guaranteed) performance
call setup required
Introduction

36. Network Core: Circuit Switching
network resources (e.g., bandwidth) divided into “pieces”
pieces allocated to calls
resource piece idle if not used by owning call (no sharing)
dividing link bandwidth into “pieces”
frequency division
time division
Introduction

37. Circuit Switching: FDM and TDM
4 users
Example:
FDM
frequency
time
TDM
frequency
time
Two simple multiple access control techniques.
Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling.
As we will see, used in AMPS, GSM, IS-54/136
Introduction

38. Numerical example
How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?
All links are Mbps
Each link uses TDM with 24 slots/sec
500 msec to establish end-to-end circuit
Let’s work it out!
Introduction

39. Answer
Each circuit gets 1/24 of the total bandwidth. Therefore each circuit has bandwidth of (1.536 Mbps)/24 = 64kbps
(640,000 bits)/64kbs = 10sec
Add 500msec of ckt establishment time

40. Network Core: Packet Switching
each end-end data stream divided into packets
user A, B packets share network resources
each packet uses full link bandwidth
resources used as needed
resource contention:
aggregate resource demand can exceed amount available
congestion: packets queue, wait for link use
store and forward: packets move one hop at a time
Node receives complete packet before forwarding
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
Introduction

41. Packet Switching: Statistical Multiplexing
100 Mb/s
Ethernet C A
statistical multiplexing
1.5 Mb/s B
queue of packets
waiting for output
link D E
Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical multiplexing.
TDM: each host gets same slot in revolving TDM frame.
Introduction

42. Packet-switching: store-and-forwardL R R R
takes L/R seconds to transmit (push out) packet of L bits on to link at R bps
store and forward: entire packet must arrive at router before it can be transmitted on next link
delay = 3L/R (assuming zero propagation delay)
Example:
L = 7.5 Mbits
R = 1.5 Mbps
transmission delay = 15 sec
more on delay shortly …
Introduction

43. Packet switching versus circuit switching
Packet switching allows more users to use network!
1 Mb/s link
each user:
100 kb/s when “active”
active 10% of time
circuit-switching:
10 users
packet switching:
with 35 users, probability > 10 active at same time is less than .0004
N users
1 Mbps link
Q: how did we get value ?
Introduction

44. Computing the Prob. Of Greater than k users active out of N users:
p: probability that a user is active
1-p: probability a user is not-active
N: total number of users
Probability that m out of N users active: P(N,m) = C(N,m)(1-p)N-mpm, where C(N,m) is the number of different ways to select m items from N items.
Probability that less than equal to k users are active ALTE(k) = Sum0<=i<=kP(N,i)
Probability that more than k users active = 1 – ALTE(k)

45. What’s Next?
Next Class: More on Statistical Multiplexing, Bottleneck Bandwidth, Security
HW 2 - posted on the class web site
Continue reading: Chapter 1 (Ross Kurose (R&K) + Peterson Davie (P&D)) 45