With statistical multiplexing, the total bandwidth available can be utilized more fully since the links are not idle when only one host is transmitting. The statistical multiplexing allows aggregation of variable bit rate traffic streams.
Module 1
Data communication components : Physical media, Packet switching, Circuit switching, Delay, loss and throughput,
Network topology, Protocols and standards, OSI model, Connecting LAN and virtual LAN
Module 3: Transport layer
Transport layer services, Multiplexing and demultiplexing, User datagram protocol, Transmission control protocol: connection, features, segment, Round-Trip Time estimation and timeout, Flow control, Congestion control, SCTP
Module 2: Application layer
Principles of network applications, Web and HTTP, File transfer protocol, Electronic mail, Domain name system, DDNS, SSH, SNMP ,Internet Applications.
Module 1
Data communication components : Physical media, Packet switching, Circuit switching, Delay, loss and throughput,
Network topology, Protocols and standards, OSI model, Connecting LAN and virtual LAN
Module 3: Transport layer
Transport layer services, Multiplexing and demultiplexing, User datagram protocol, Transmission control protocol: connection, features, segment, Round-Trip Time estimation and timeout, Flow control, Congestion control, SCTP
Module 2: Application layer
Principles of network applications, Web and HTTP, File transfer protocol, Electronic mail, Domain name system, DDNS, SSH, SNMP ,Internet Applications.
UNIT I FUNDAMENTALS & LINK LAYER 9
Building a network – Requirements – Layering and protocols – Internet Architecture – Network software – Performance ; Link layer Services – Framing – Error Detection – Flow control
Slide ini adalah copyright dari buku Computer Networking : A Top-Down Approach (5th Edition) by James F. Kurose and Keith W. Rose.
Tutorial versi video berbahasa indonesia dapat diakses di http://www.pecollege.net/ViewVideoList.aspx?list=9
Ini gratis
UNIT I FUNDAMENTALS & LINK LAYER 9
Building a network – Requirements – Layering and protocols – Internet Architecture – Network software – Performance ; Link layer Services – Framing – Error Detection – Flow control
Slide ini adalah copyright dari buku Computer Networking : A Top-Down Approach (5th Edition) by James F. Kurose and Keith W. Rose.
Tutorial versi video berbahasa indonesia dapat diakses di http://www.pecollege.net/ViewVideoList.aspx?list=9
Ini gratis
The Slides Introduction of Computer Network. All about the course will explain in the slides, read to understand what we should learn. Computer Networking is the practice of connecting computers together to enable communication and data exchange between them. In general, Computer Network is a collection of two or more computers. It helps users to communicate more easily. In this article, we are going to discuss the basics which everyone must know before going deep into Computer Networking.
A computer network is a collection of interconnected devices that can communicate with each other to share resources and information. These devices can include computers, servers, routers, switches, printers, and more. Networks can vary in size and complexity, from small local networks within a home or office to vast global networks like the internet.
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Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
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The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
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http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
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1. 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 Computer Networking:
represent a lot of work on our part. In return for use, we only ask the A Top Down Approach ,
following:
If you use these slides (e.g., in a class) in substantially unaltered form, 5th edition.
that you mention their source (after all, we’d like people to use our book!) Jim Kurose, Keith Ross
Addison-Wesley, April
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. 2009.
Thanks and enjoy! JFK/KWR
All material copyright 1996-2009
J.F Kurose and K.W. Ross, All Rights Reserved
Introduction 1-1
2. Chapter 1: Introduction
Our goal: Overview:
get “feel” and what’s the Internet?
terminology what’s a protocol?
more depth, detail
network edge; hosts, access
later in course
approach: net, physical media
use Internet as network core: packet/circuit
example switching, Internet structure
performance: loss, delay,
throughput
security
protocol layers, service models
history
Introduction 1-2
3. 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 1-3
4. What’s the Internet: “nuts and bolts” view
PC millions of connected Mobile network
server computing devices: Global ISP
wireless hosts = end systems
laptop
running network
cellular
handheld apps Home network
Regional ISP
communication links
access fiber, copper,
points
wired
radio, satellite Institutional network
links transmission
rate = bandwidth
router routers: forward
packets (chunks of
data)
Introduction 1-4
5. “Cool” internet appliances
Web-enabled toaster +
weather forecaster
IP picture frame
http://www.ceiva.com/
World’s smallest web server
http://www-ccs.cs.umass.edu/~shri/iPic.html Internet phones
Introduction 1-5
6. What’s the Internet: “nuts and bolts” view
Mobile network
protocols control sending,
receiving of msgs Global ISP
e.g., TCP, IP, HTTP, Skype,
Ethernet
Home network
Internet: “network of
networks” Regional ISP
loosely hierarchical
public Internet versus Institutional network
private intranet
Internet standards
RFC: Request for comments
IETF: Internet Engineering
Task Force
Introduction 1-6
7. What’s the Internet: a service view
communication
infrastructure enables
distributed applications:
Web, VoIP, email, games,
e-commerce, file sharing
communication services
provided to apps:
reliable data delivery
from source to
destination
“best effort” (unreliable)
data delivery
Introduction 1-7
8. What’s a protocol?
human protocols: network protocols:
“what’s the time?” machines rather than
“I have a question” humans
introductions all communication
activity in Internet
governed by protocols
… specific msgs sent
… specific actions protocols define format,
taken when msgs order of msgs sent and
received, or other received among network
events entities, and actions
taken on msg
transmission, receipt
Introduction 1-8
9. What’s a protocol?
a human protocol and a computer network protocol:
Hi
TCP connection
request
Hi
TCP connection
Got the response
time? Get http://www.awl.com/kurose-ross
2:00
<file>
time
Q: Other human protocols?
Introduction 1-9
10. 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 1-10
11. 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 1-11
12. The network edge:
end systems (hosts):
run application programs
e.g. Web, email
at “edge of network” peer-peer
client/server model
client host requests, receives
service from always-on server
client/server
e.g. Web browser/server;
email client/server
peer-peer model:
minimal (or no) use of
dedicated servers
e.g. Skype, BitTorrent
Introduction 1-12
13. 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 1-13
14. Dial-up Modem
modem (e.g., AOL)
PC modem
dial-up
home ISP
home
network Internet
telephone
office
central
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”
15. Digital Subscriber Line (DSL)
PC
home
office
modem central
DSL
splitter network
telephone
DSLAM
phone downstream data
home upstream data; 50KHz-1MHz
0-4KHz phone; 4-50KHz
Existing phone line: Internet
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
16. 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 1-16
18. Cable Network Architecture: Overview
Typically 500 to 5,000 homes
cable headend
home
cable distribution
network (simplified)
Introduction 1-18
19. Cable Network Architecture: Overview
server(s)
cable headend
home
cable distribution
network
Introduction 1-19
20. Cable Network Architecture: Overview
cable headend
home
cable distribution
network (simplified)
Introduction 1-20
21. Cable Network Architecture: Overview
FDM (more shortly):
C
O
V V V V V V N
I I I I I I D D T
D D D D D D A A R
E E E E E E T T O
O O O O O O A A L
1 2 3 4 5 6 7 8 9
Channels
cable headend
home
cable distribution
network
Introduction 1-21
22. Fiber to the Home
ONT
central office splitter
optical
OLT
fiber
optical
ONT
fibers
Internet optical
ONT
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
23. Ethernet Internet access
100 Mbps Institutional
router
Ethernet To Institution’s
switch ISP
100 Mbps
1 Gbps
100 Mbps
server
Typically used in companies, universities, etc
10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet
Today, end systems typically connect into Ethernet
switch
24. Wireless access networks
shared wireless access
network connects end system
to router router
via base station aka “access
point”
base
wireless LANs: station
802.11b/g (WiFi): 11 or 54 Mbps
wider-area wireless access
provided by telco operator
~1Mbps over cellular system
mobile
(EVDO, HSDPA)
hosts
next up (?): WiMAX (10’s Mbps)
over wide area
Introduction 1-24
25. Home networks
Typical home network components:
DSL or cable modem
router/firewall/NAT
Ethernet
wireless access
point
wireless
to/from laptops
cable router/
cable
modem firewall
headend
wireless
access
Ethernet point
Introduction 1-25
26. Physical Media
Twisted Pair (TP)
Bit: propagates between two insulated copper
transmitter/rcvr pairs wires
physical link: what lies Category 3: traditional
between transmitter & phone wires, 10 Mbps
receiver Ethernet
guided media:
Category 5:
100Mbps Ethernet
signals propagate in solid
media: copper, fiber, coax
unguided media:
signals propagate freely,
e.g., radio
Introduction 1-26
27. Physical Media: coax, fiber
Coaxial cable: Fiber optic cable:
two concentric copper glass fiber carrying light
conductors pulses, each pulse a bit
bidirectional high-speed operation:
baseband: high-speed point-to-point
single channel on cable
legacy Ethernet low error rate: repeaters
broadband: spaced far apart ; immune
multiple channels on to electromagnetic noise
cable
HFC
Introduction 1-27
28. Physical media: radio
signal carried in Radio link types:
electromagnetic terrestrial microwave
spectrum e.g. up to 45 Mbps channels
no physical “wire” LAN (e.g., Wifi)
bidirectional 11Mbps, 54 Mbps
propagation wide-area (e.g., cellular)
environment effects: 3G cellular: ~ 1 Mbps
reflection satellite
obstruction by objects Kbps to 45Mbps channel (or
interference multiple smaller channels)
270 msec end-end delay
geosynchronous versus low
altitude
Introduction 1-28
29. 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 1-29
30. 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 1-30
31. 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 1-31
32. Network Core: Circuit Switching
network resources dividing link bandwidth
(e.g., bandwidth) into “pieces”
divided into “pieces” frequency division
pieces allocated to calls time division
resource piece idle if
not used by owning call
(no sharing)
Introduction 1-32
33. Circuit Switching: FDM and TDM
Example:
FDM
4 users
frequency
time
TDM
frequency
time
Introduction 1-33
34. 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 1.536 Mbps
Each link uses TDM with 24 slots/sec
500 msec to establish end-to-end circuit
Let’s work it out!
Introduction 1-34
35. Network Core: Packet Switching
each end-end data stream resource contention:
divided into packets aggregate resource
user A, B packets share demand can exceed
network resources amount available
each packet uses full link congestion: packets
bandwidth queue, wait for link use
resources used as needed store and forward:
packets move one hop
at a time
Bandwidth division into “pieces” Node receives complete
Dedicated allocation packet before forwarding
Resource reservation
Introduction 1-35
36. Packet Switching: Statistical Multiplexing
100 Mb/s
A Ethernet statistical multiplexing C
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 1-36
37. Packet-switching: store-and-forward
L
R R R
takes L/R seconds to Example:
transmit (push out) L = 7.5 Mbits
packet of L bits on to R = 1.5 Mbps
link at R bps
transmission delay = 15
store and forward:
sec
entire packet must
arrive at router before
it can be transmitted
on next link
delay = 3L/R (assuming
more on delay shortly …
zero propagation delay)
Introduction 1-37
38. 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
N users
circuit-switching: 1 Mbps link
10 users
packet switching:
with 35 users, Q: how did we get value 0.0004?
probability > 10 active
at same time is less
than .0004
Introduction 1-38
39. Packet switching versus circuit switching
Is packet switching a “slam dunk winner?”
great for bursty data
resource sharing
simpler, no call setup
excessive congestion: packet delay and loss
protocols needed for reliable data transfer,
congestion control
Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps
still an unsolved problem (chapter 7)
Q: human analogies of reserved resources (circuit
switching) versus on-demand allocation (packet-switching)? Introduction 1-39
40. Internet structure: network of networks
roughly hierarchical
at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,
Cable and Wireless), national/international coverage
treat each other as equals
Tier-1
providers
Tier 1 ISP
interconnect
(peer)
privately
Tier 1 ISP Tier 1 ISP
Introduction 1-40
42. Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs
Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISPs
Tier-2 ISP pays Tier-2 ISP also peer
Tier-2 ISP privately with
tier-1 ISP for
connectivity to Tier 1 ISP each other.
rest of Internet
tier-2 ISP is
customer of
tier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP
Tier-2 ISP Tier-2 ISP
Introduction 1-42
43. Internet structure: network of networks
“Tier-3” ISPs and local ISPs
last hop (“access”) network (closest to end systems)
local
ISP Tier 3 local
local local
ISP ISP
ISP ISP
Local and tier- Tier-2 ISP Tier-2 ISP
3 ISPs are
customers of Tier 1 ISP
higher tier
ISPs
connecting
them to rest
Tier 1 ISP Tier 1 ISP Tier-2 ISP
of Internet
local
Tier-2 ISP Tier-2 ISP
ISP
local local local
ISP ISP ISP Introduction 1-43
44. Internet structure: network of networks
a packet passes through many networks!
local
ISP Tier 3 local
local local
ISP ISP
ISP ISP
Tier-2 ISP Tier-2 ISP
Tier 1 ISP
Tier 1 ISP Tier 1 ISP Tier-2 ISP
local
Tier-2 ISP Tier-2 ISP
ISP
local local local
ISP ISP ISP Introduction 1-44
45. 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 1-45
46. How do loss and delay occur?
packets queue in router buffers
packet arrival rate to link exceeds output link
capacity
packets queue, wait for turn
A packet being transmitted (delay)
packets queueing (delay)
B
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Introduction 1-46
47. Four sources of packet delay
1. nodal processing: 2. queueing
check bit errors time waiting at output
determine output link link for transmission
depends on congestion
level of router
processing queueing
nodal
B
propagation
A
transmission
Introduction 1-47
48. Delay in packet-switched networks
3. Transmission delay: 4. Propagation delay:
R=link bandwidth (bps) d = length of physical link
L=packet length (bits) s = propagation speed in
time to send bits into medium (~2x108 m/sec)
link = L/R propagation delay = d/s
Note: s and R are very
processing queueing different quantities!
nodal
B
propagation
A
transmission
Introduction 1-48
49. Caravan analogy
100 km 100 km
ten-car toll toll
caravan booth booth
cars “propagate” at Time to “push” entire
100 km/hr caravan through toll
toll booth takes 12 sec to booth onto highway =
service car (transmission 12*10 = 120 sec
time) Time for last car to
car~bit; caravan ~ packet propagate from 1st to
2nd toll both: 100km/
Q: How long until caravan
(100km/hr)= 1 hr
is lined up before 2nd toll
A: 62 minutes
booth?
Introduction 1-49
50. Caravan analogy (more)
100 km 100 km
ten-car toll toll
caravan booth booth
Yes! After 7 min, 1st car
Cars now “propagate” at at 2nd booth and 3 cars
still at 1st booth.
1000 km/hr 1st bit of packet can
Toll booth now takes 1 arrive at 2nd router
min to service a car before packet is fully
Q: Will cars arrive to transmitted at 1st router!
2nd booth before all See Ethernet applet at AWL
cars serviced at 1st Web site
booth?
Introduction 1-50
51. Nodal delay
d nodal = d proc + d queue + d trans + d prop
dproc = processing delay
typically a few microsecs or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
= L/R, significant for low-speed links
dprop = propagation delay
a few microsecs to hundreds of msecs
Introduction 1-51
52. Queueing delay (revisited)
R=link bandwidth (bps)
L=packet length (bits)
a=average packet
arrival rate
traffic intensity = La/R
La/R ~ 0: average queueing delay small
La/R -> 1: delays become large
La/R > 1: more “work” arriving than can be
serviced, average delay infinite!
Introduction 1-52
53. “Real” Internet delays and routes
What do “real” Internet delay & loss look like?
Traceroute program: provides delay
measurement from source to router along end-end
Internet path towards destination. For all i:
sends three packets that will reach router i on path
towards destination
router i will return packets to sender
sender times interval between transmission and reply.
3 probes 3 probes
3 probes
Introduction 1-53
54. “Real” Internet delays and routes
traceroute: gaia.cs.umass.edu to www.eurecom.fr
Three delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms link
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
18 * * * * means no response (probe lost, router not replying)
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
Introduction 1-54
55. Packet loss
queue (aka buffer) preceding link in buffer has
finite capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous
node, by source end system, or not at all
buffer
(waiting area) packet being transmitted
A
B
packet arriving to
full buffer is lost
Introduction 1-55
56. Throughput
throughput: rate (bits/time unit) at which
bits transferred between sender/receiver
instantaneous: rate at given point in time
average: rate over longer period of time
link capacity
server sends bits pipe that can carry
server, with link capacity
pipe that can carry
(fluid) of F bits
file into pipe fluid at rate
Rs bits/sec Rfluid at rate
c bits/sec
to send to client Rs bits/sec) Rc bits/sec)
Introduction 1-56
57. Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
bottleneck link
link on end-end path that constrains end-end throughput
Introduction 1-57
58. Throughput: Internet scenario
Rs
per-connection
Rs Rs
end-end
throughput:
R
min(Rc,Rs,R/10)
in practice: Rc or Rs Rc Rc
is often bottleneck Rc
10 connections (fairly) share
backbone bottleneck link R bits/sec
Introduction 1-58
59. 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 1-59
60. Protocol “Layers”
Networks are complex!
many “pieces”:
hosts
Question:
routers
Is there any hope of
links of various organizing structure of
media network?
applications
protocols Or at least our discussion
hardware, of networks?
software
Introduction 1-60
61. Organization of air travel
ticket (purchase) ticket (complain)
baggage (check) baggage (claim)
gates (load) gates (unload)
runway takeoff runway landing
airplane routing airplane routing
airplane routing
a series of steps
Introduction 1-61
62. Layering of airline functionality
ticket (purchase) ticket (complain) ticket
baggage (check) baggage (claim baggage
gates (load) gates (unload) gate
runway (takeoff) runway (land) takeoff/landing
airplane routing airplane routing airplane routing airplane routing airplane routing
departure intermediate air-traffic arrival
airport control centers airport
Layers: each layer implements a service
via its own internal-layer actions
relying on services provided by layer below
Introduction 1-62
63. Why layering?
Dealing with complex systems:
explicit structure allows identification,
relationship of complex system’s pieces
layered reference model for discussion
modularization eases maintenance, updating of
system
change of implementation of layer’s service
transparent to rest of system
e.g., change in gate procedure doesn’t affect
rest of system
layering considered harmful?
Introduction 1-63
64. Internet protocol stack
application: supporting network
applications application
FTP, SMTP, HTTP
transport: process-process data transport
transfer
TCP, UDP network
network: routing of datagrams from
source to destination link
IP, routing protocols
link: data transfer between physical
neighboring network elements
PPP, Ethernet
physical: bits “on the wire”
Introduction 1-64
65. ISO/OSI reference model
presentation: allow applications to
interpret meaning of data, e.g., application
encryption, compression, machine-
presentation
specific conventions
session: synchronization, session
checkpointing, recovery of data transport
exchange
network
Internet stack “missing” these
layers! link
these services, if needed, must physical
be implemented in application
needed?
Introduction 1-65
66. message M
source
application
Encapsulation
segment Ht M transport
datagram Hn Ht M network
frame Hl Hn Ht M link
physical
link
physical
switch
destination Hn Ht M network
M application
Hl Hn Ht M link Hn Ht M
Ht M transport physical
Hn Ht M network
Hl Hn Ht M link router
physical
Introduction 1-66
67. 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 1-67
68. Network Security
The field of network security is about:
how bad guys can attack computer networks
how we can defend networks against attacks
how to design architectures that are immune to
attacks
Internet not originally designed with
(much) security in mind
original vision: “a group of mutually trusting
users attached to a transparent network”
Internet protocol designers playing “catch-up”
Security considerations in all layers!
Introduction 1-68
69. Bad guys can put malware into
hosts via Internet
Malware can get in host from a virus, worm, or
trojan horse.
Spyware malware can record keystrokes, web
sites visited, upload info to collection site.
Infected host can be enrolled in a botnet, used
for spam and DDoS attacks.
Malware is often self-replicating: from an
infected host, seeks entry into other hosts
Introduction 1-69
70. Bad guys can put malware into
hosts via Internet
Trojan horse Worm:
Hidden part of some infection by passively
otherwise useful receiving object that gets
software itself executed
Today often on a Web self- replicating: propagates
page (Active-X, plugin) to other hosts, users
Virus Sapphire Worm: aggregate scans/sec
in first 5 minutes of outbreak (CAIDA, UWisc data)
infection by receiving
object (e.g., e-mail
attachment), actively
executing
self-replicating:
propagate itself to
other hosts, users
Introduction 1-70
71. Bad guys can attack servers and
network infrastructure
Denial of service (DoS): attackers make resources
(server, bandwidth) unavailable to legitimate traffic
by overwhelming resource with bogus traffic
1. select target
2. break into hosts
around the network
(see botnet)
3. send packets toward
target from target
compromised hosts
Introduction 1-71
72. The bad guys can sniff packets
Packet sniffing:
broadcast media (shared Ethernet, wireless)
promiscuous network interface reads/records all
packets (e.g., including passwords!) passing by
A C
src:B dest:A payload
B
Wireshark software used for end-of-chapter
labs is a (free) packet-sniffer
Introduction 1-72
73. The bad guys can use false source
addresses
IP spoofing: send packet with false source address
A C
src:B dest:A payload
B
Introduction 1-73
74. The bad guys can record and
playback
record-and-playback: sniff sensitive info (e.g.,
password), and use later
password holder is that user from system point of
view
C
A
src:B dest:A user: B; password: foo
B
Introduction 1-74
75. Network Security
more throughout this course
chapter 8: focus on security
crypographic techniques: obvious uses and
not so obvious uses
Introduction 1-75
76. 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 1-76
77. Internet History
1961-1972: Early packet-switching principles
1961: Kleinrock - queueing 1972:
theory shows ARPAnet public demonstration
effectiveness of packet- NCP (Network Control Protocol)
switching
first host-host protocol
1964: Baran - packet-
first e-mail program
switching in military nets
ARPAnet has 15 nodes
1967: ARPAnet conceived
by Advanced Research
Projects Agency
1969: first ARPAnet node
operational
Introduction 1-77
78. Internet History
1972-1980: Internetworking, new and proprietary nets
1970: ALOHAnet satellite
Cerf and Kahn’s internetworking
network in Hawaii principles:
1974: Cerf and Kahn - minimalism, autonomy - no
architecture for internal changes required
interconnecting networks to interconnect networks
best effort service model
1976: Ethernet at Xerox
PARC stateless routers
decentralized control
ate70’s: proprietary
architectures: DECnet, SNA, define today’s Internet
XNA architecture
late 70’s: switching fixed
length packets (ATM
precursor)
1979: ARPAnet has 200 nodes
Introduction 1-78
79. Internet History
1980-1990: new protocols, a proliferation of networks
1983: deployment of new national networks:
TCP/IP Csnet, BITnet,
1982: smtp e-mail NSFnet, Minitel
protocol defined 100,000 hosts
1983: DNS defined connected to
for name-to-IP- confederation of
address translation networks
1985: ftp protocol
defined
1988: TCP congestion
control
Introduction 1-79
80. Internet History
1990, 2000’s: commercialization, the Web, new apps
Early 1990’s: ARPAnet Late 1990’s – 2000’s:
decommissioned more killer apps: instant
1991: NSF lifts restrictions on messaging, P2P file sharing
commercial use of NSFnet network security to
(decommissioned, 1995)
forefront
early 1990s: Web
est. 50 million host, 100
hypertext [Bush 1945, Nelson
million+ users
1960’s] backbone links running at
HTML, HTTP: Berners-Lee
Gbps
1994: Mosaic, later Netscape
late 1990’s:
commercialization of the Web
Introduction 1-80
81. Internet History
2007:
~500 million hosts
Voice, Video over IP
P2P applications: BitTorrent
(file sharing) Skype (VoIP),
PPLive (video)
more applications: YouTube,
gaming
wireless, mobility
Introduction 1-81
82. Introduction: Summary
Covered a “ton” of material!
You now have:
Internet overview
context, overview,
what’s a protocol?
“feel” of networking
network edge, core, access more depth, detail to
network follow!
packet-switching versus
circuit-switching
Internet structure
performance: loss, delay,
throughput
layering, service models
security
history
Introduction 1-82
Editor's Notes
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