Cosc 2150: Computer Organization

1
Cosc 2150Computer Organization

• Chapter 12
• Network Organization and Architecture

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Chapter 12 Objectives

• Become familiar with the fundamentals of network
  architectures.
• Learn the basic components of a local area
  network.
• Become familiar with the general architecture of
  the Internet.

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Bandwidth

• Bit (b) a unit of information, 0 or 1
• 10 bits can represent 1024 different messages
• 20 bits represent gt 1 million
• 30 bits gt 1 billion messages
• The bandwidth of a communication channel number
  of bits per second it transmits
• All channels have limited bandwidth
• One byte (B) 8 bits (an octet)
• Transmitting 1 MB at 56K bps takes 143 sec.
• 1 GB gigabyte takes 40 hours
• at 7Mbps 19 minutes at 1 Gbps takes 8 seconds)
• Latency delay from first bit transmitted to
  first received

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Progress of Technology

• Have more disk storage
• 1971 10 MB
• 2001 80,000 MB
• 2008 1,000,000 MB (1 TB)
• Higher communication speeds
• Human speech 30 bits/sec
• 1971 Modem 300 bits/sec
• 2001 Modem 56,000 bits/sec
• T1 line 1,544,000 bits/sec
• Internet 2 1,000,000,000 bits/sec
• Nortel 1,000,000,000,000 bits/sec in 1
  fiber (entire U.S. telephone
  traffic)

IMPROVEMENT 8000 x
1971-2001 IMPROVEMENT 3 BILLION x
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BANDWIDTH APPLICATION TECHNOLOGY
Experimental
1 terabit
All U.S. telephone conversations simultaneously
1 gigabit
Gigabit Ethernet
Full-motion HDTV
OC12 622 Mb
FDDI
Fiber
OC3 155 Mb
Virtual Reality, Medical Imaging
T3/E3
T3 44.7 Mb
Video Conferencing, Multimedia
ADSL
DSL 7 Mb
T1/E1
Streaming Video Voice
ISDN
128K
T1 1.544 Mb
Copper
Browsing, Audio
New Modem
56K
E-mail, FTP
19.2
In Kbps
Old Modem
Telnet
Wireless WAN
4.8
Paging
Human speech 30 bps
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Early Academic and Scientific Networks

• In the 1960s, the Advanced Research Projects
  Agency funded research under the auspices of the
  U.S. Department of Defense.
• Computers at that time were few and costly. In
  1968, the Defense Department funded an
  interconnecting network to make the most of these
  precious resources.
• The network, DARPANet, designed by Bolt, Beranek,
  and Newman, had sufficient redundancy to
  withstand the loss of a good portion of the
  network.
• DARPANet, later turned over to the public domain,
  eventually evolved to become todays Internet.

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Some humor first

• http//www.the5thwave.com/images/cartoons_computer
  /large/training/631lg.gif

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OSI - The Model

• A layered model
• Each layer performs a subset of the required
  communication functions
• Each layer relies on the next lower layer to
  perform more primitive functions
• Each layer provides services to the next higher
  layer
• Changes in one layer should not require changes
  in other layers

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OSI - The Model (2)
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OSI Layers (1)

• Transmission media (Layer 0 Hardware)
• cables between two network stations
• Physical (Layer 1 Hardware)
• Physical interface between devices
• Mechanical
• Electrical
• Functional
• Procedural
• Data Link (Layer 2 Hardware)
• Means of activating, maintaining and deactivating
  a reliable link
• Error detection and control
• Higher layers may assume error free transmission
• transmits and receives frames, MAC protocol
  belongs to this layer

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OSI Layers (2)

• Network (layer 3 Hardware)
• Transport of information
• Higher layers do not need to know about
  underlying technology
• Not needed on direct links
• Most high level Network protocols are in this
  layer
• Transport (layer 4)
• Exchange of data between end systems
• Error free
• In sequence
• No losses
• No duplicates
• Quality of service

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OSI Layers (3)

• Session (layer 5)
• Control of dialogues between applications
• Dialogue discipline
• Grouping
• Recovery
• Presentation (layer 6)
• Data formats and coding
• Data compression
• Encryption
• Application (layer 7)
• Means for applications to access OSI environment

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Network Hardware Outline

• layer 0 media
• Cabling
• Layer 1 physical
• repeaters, hubs
• Layer 2 Link layer
• bridges, switches, and Collision domains
• Layer 3 Network layer
• Router, router architecture.

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Layer 0 Transmission media

• 10BASE2 standard
• uses coax cable (like Cable TV wiring).
  component pieces include BNC T connectors and BNC
  terminators
• Segments of cable had a maximum length of 185
  meters
• Why 10BASE2? standards committee rounded 185 to
  200, then shorten it.
• The 10 is for 10Mbps (megabits per second)

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Layer 0 Transmission media (2)

• 10BASE-T
• The T is for twisted, as in twisted-pair wires
• The wire is normally called Category 3 (CAT3) or
  better like CAT5
• maximum length is 100 meters (328 feet),
• 10BASE-F
• F stands for Fiber, or fiber optic media

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Layer 0 Transmission media (3)

• 100BASE-T
• covers the entire range of 100Mbps systems, all
  twisted pair and fiber media
• 100BASE-TX, uses twisted pair cat-5 wire (100
  meters max length)
• 100BASE-FX, uses fiber.
• 1000BASE-T or Gigabit or GigE
• covers the entire range of 1000Mbps systems.
• Uses both Cat-5, Cat-5e and fiber

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Layer 0 Transmission media (4)

• Multi-Gigabit Ethernet
• 10 Gbps Standard and working on faster, 50 to 100
  Gbps standards
• Cisco Announce 1 Zettabyte edge routers (2008)
• Fiber optic cabling.
• Cable connectors for Cat3 and Cat5
• RJ-11 4 wire modular connected. Also used in
  standard telephone cables. Cat 3 wires only.
• RJ-45 8 wire connected. RJ-45 can be used to
  connect 4 wire as well.

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What if the max length is to short?

• The max length is where the signal degrades past
  the point of usefulness
• You will need to put a piece of network hardware.
• What do you use?
• Depends on where it is connecting to

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Distance Limitations

• Copper Cat 5 wiring
• MMF Multimode fiber
• SMF Single-mode fiber

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Fiber Optic

• Optical fiber supports three different
  transmission modes depending on the type of fiber
  used.
• Single-mode fiber provides the fastest data rates
  over the longest distances. It passes light at
  only one wavelength, typically, 850, 1300 or 1500
  nanometers.
• Multimode fiber can carry several different light
  wavelengths simultaneously through a larger fiber
  core.

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Fiber Optic

• Multimode graded index fiber also supports
  multiple wavelengths concurrently, but it does so
  in a more controlled manner than regular
  multimode fiber
• Unlike regular multimode fiber, light waves are
  confined to the area of the optical fiber that is
  suitable to propagating its particular
  wavelength.
• Thus, different wavelengths concurrently
  transmitted through the fiber do not interfere
  with each other.

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High Capacity Digital Links

• When an STS signal is passed over an optical
  carrier network, the signal is called OCx, where
  x is the carrier speed.

The fundamental SDH signal is STM-1, which
conveys signals at a rate of 155.52Mbps. The
SONET hierarchy along with SDH is shown in the
table.

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Ethernet

• dominant Network/LAN technology
• cheap 20 for 1000Mbs!
• first widely used LAN technology
• Simpler, cheaper than token LANs and ATM
• Kept up with speed race 10, 100, 1000 Mbps

Metcalfes Ethernet sketch
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Ethernet Interface Card

• NIC for short.
• The piece of hardware you put into your computer
  to talk to the network.
• Can be 10Mb, 100Mb, even 1Gb card now.
• 10/100Mb cards run anywhere from 20 to 100 for
  pcmcia cards.

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Ethernet Technologies 10Base2

• thin coaxial cable in a bus topology
• repeaters used to connect up to multiple segments

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Repeaters

• A hardware device that connects to segments
  together.
• repeater repeats bits it hears on one interface
  to its other interfaces
• (Layer 1) physical layer device only!

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Repeaters

• Signal attenuation is corrected by repeaters that
  amplify signals in physical cabling.
• Repeaters are part of the network medium (Layer
  1).
• In theory, they are dumb devices functioning
  entirely without human intervention. However,
  some repeaters now offer higher-level services to
  assist with network management and
  troubleshooting.

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Interconnecting LANs

• Q Why not just one big LAN?
• Limited amount of supportable traffic on single
  LAN, all stations must share bandwidth
• limited length 802.3 specifies maximum cable
  length
• large collision domain (can collide with many
  stations)

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Collision Domains

• When network devices share the same, physical
  transmission media, it is more than possible
  packets of data will collide
• Collision Domain
• Network Devices use CSMA/CD
• A devices listens to see if the media is
  available, then it been transmitting.
• More then possible two devices will attempt to
  transmit at the same time.
• This area is called a collision domain

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Hubs

• Physical Layer devices essentially repeaters
  operating at bit levels repeat received bits on
  one interface to all other interfaces
• Hubs can be arranged in a hierarchy (or
  multi-tier design), with backbone hub at its top

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Hubs (more)

• Each connected LAN referred to as LAN segment
• Hubs do not isolate collision domains node may
  collide with any node residing at any segment in
  LAN
• Hub Advantages
• simple, inexpensive device
• Multi-tier provides graceful degradation
  portions of the LAN continue to operate if one
  hub malfunctions
• extends maximum distance between node pairs (100m
  per Hub)
• can connect different Ethernet types (e.g.,
  10BaseT and 100baseT)

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Hub limitations

• single collision domain results in no increase in
  max throughput
• multi-tier throughput same as single segment
  throughput
• individual LAN restrictions pose limits on number
  of nodes in same collision domain and on total
  allowed geographical coverage

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Bridges

• ( Layer 2 ) Link Layer devices operate on
  Ethernet frames, examining frame header and
  selectively forwarding frame based on its
  destination
• Bridge isolates collision domains since it
  buffers frames
• When frame is to be forwarded on segment, bridge
  uses CSMA/CD to access segment and transmit

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Bridges (more)

• Bridge advantages
• Isolates collision domains resulting in higher
  total max throughput, and does not limit the
  number of nodes nor geographical coverage
• Transparent no need for any change to hosts LAN
  adapters
• bridges filter packets
• same-LAN -segment frames not forwarded onto other
  LAN segments
• forwarding
• how to know which LAN segment on which to forward
  frame?
• looks like a routing problem

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Backbone Bridge
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Ethernet Switches

• layer 2 forwarding, filtering using LAN addresses
• Switching A-to-B and A-to-B simultaneously, no
  collisions
• large number of interfaces
• often individual hosts, star-connected into
  switch
• Ethernet, but no collisions!

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Ethernet Switches

• Store and forward frame is completely received,
  and then sent.
• cut-through switching frame forwarded from input
  to output port without awaiting for assembly of
  entire frame
• slight reduction in latency
• Does not isolate collision domains.
• combinations of shared/dedicated, 10/100/1000
  Mbps interfaces

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Full Half Duplex

• Full Duplex
• Communication that takes place simultaneously, in
  both directions, between sender and receiver.
• No collisions possible in full duplex mode.
• Available on switches, double the speed, 100Mbps
  line can pass 200Mbps at a time.
• Half Duplex
• two-way communication occurring in only one
  direction at a time. Standard communication
  method. Line speeds are rated at half duplex
  speed.

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Auto sensing networking devices

• Most networking devices auto sense whether they
  can talk 10Mb, 100Mb, and 1Gb.
• Simple for configuration, plug it in, let the
  computer and hub/switch figure it out.
• Does not take into account transmission media
• 2 devices that can speak at 100Mbps on cat 3
  (10Mbps) will attempt to use 100Mbps.

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Routers

• Function at layer 3, network layer.
• Able to route based on IP, instead of MAC
• See previous lecture for routing.

NORTEL
3COM
CISCO
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WWF Bridges vs. Routers

• both store-and-forward devices
• routers network layer devices (examine network
  layer headers)
• bridges are Link Layer devices
• routers maintain routing tables, implement
  routing algorithms
• bridges maintain filtering tables, implement
  filtering, learning and spanning tree algorithms

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network routers

• A router is a device that operates at network
  layer or layer 3.
• Routers actually looks at the message and
  determine what to do with it.
• For broadcast traffic, it drops the message
• It allows you to design more complex networks
  with multiple network protocols.
• It also routes between multiple IP domains

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network routers

• Routers are complex devices because they contain
  buffers, switching logic, memory, and processing
  power to calculate the best way to send a packet
  to its destination.

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Routing Using Subnets
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Routers vs. Bridges

• Bridges and -
• Bridge operation is simpler requiring less
  processing bandwidth
• - Topologies are restricted with bridges a
  spanning tree must be built to avoid cycles
• - Bridges do not offer protection from broadcast
  storms (endless broadcasting by a host will be
  forwarded by a bridge)

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Routers vs. Bridges

• Routers and -
• arbitrary topologies can be supported, cycling
  is limited by TTL counters (and good routing
  protocols)
• provide firewall protection against broadcast
  storms
• - require IP address configuration (not plug and
  play)
• - require higher processing bandwidth
• bridges do well in small (a hundred hosts) while
  routers used in large networks (thousands of
  hosts)

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IEEE 802.11 Wireless LAN

• wireless LANs untethered (often mobile)
  networking
• IEEE 802.11 standard
• MAC protocol
• unlicensed frequency spectrum 900Mhz, 2.4Ghz

• Basic Service Set (BSS) (a.k.a. cell) contains
• wireless hosts
• access point (AP) base station
• BSSs combined to form distribution system (DS)

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Ad Hoc Networks

• Ad hoc network IEEE 802.11 stations can
  dynamically form network without AP
• Applications
• laptop meeting in conference room, car
• interconnection of personal devices
• battlefield
• IETF MANET (Mobile Ad hoc Networks) working
  group

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LANs and WANs

• Local Area Networks (LAN)
• A set of computer connected in a geographically
  close network, such as in the same building,
  campus or office building.
• Wide Area Networks (WAN)
• A computer network that uses long-range
  telecommunications links to connect the networked
  computers over long distances.
• The line between two is blurry, since LANs can
  cover geography then some WANs

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Network Firewalls

• Definition A system that can not be broken in
  to.
• Monitors traffic and "protects" the computers
  behind it.
• Configure so that only certain inbound and
  outbound ports are "open"
• Blocking port 6000, means that nothing can
  remotely connect to that port
• Configure so that IP are not allowed "through"
  the firewall (inbound, outbound, or both)
• Firewalls are a layer 4 device, because it works
  on Port numbers as well as IP number, and even
  MAC addresses.

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Network Firewalls (2)

• Packet Filtering
• block certain types of packets, such only
  allowing TCP packets to port 25, but block UDP
  packets.
• Blocking all ICMP packets
• Allowing only ssh packets.
• Also can provide "Zones" of security
• unrestricted access from/to internet, protected
  zones (called DMZs) from/to the internet, and no
  access zone from/to internet.
• Or other section of the local network.

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NAT

• Network Address Translation
• The internal computers have a 10.x.x.x IP numbers
• When a computer wants to access the internet, the
  NAT receives the packet, changes the IP to it's,
  then sends to the internet. On response, the NAT
  forwards it onto the computer again.
• Since the NAT is acting as a go between, the
  computer is protected.

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VPN

• Virtual Private Network
• A method to provide a secure and encrypted
  connection between two trusted networks over an
  unsecured line
• Where line could be the internet.
• Example
• A company has two locations, New York and LA.
• They could pay for a private connection between,
  which is really expensive
• Or use a VPN on each side to connect them over
  the internet.

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VPN (2)

• A VPN client connects to the VPN server.
• All networking from the client is directed to the
  server, which acts as the network gateway.
• So the client functions as if it was behind a
  firewall and could access everything like normal.
• Example
• Employee goes on a business trip. Connect up to
  an unsecured network. Connects to the VPN server
  (via the client) and now has a secure connection
  to "work" over the unsecured network.

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IDS

• Intrusion Detection System
• Detects traffic matching a signature of a known
  attack. Similar to a Anti-Virus program.
• alerts the admin to the attack
• If it a NIPS (network Intrusion Prevention
  system), then it will initiate defensive
  response.
• such as terminating the connection
• by configuring the firewall to block it.

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Putting it all together
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Web Architecture
TIER 1
TIER 2 Server
TIER 3 Applications
TIER 4 Database
SOURCE INTERSHOP
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Deploying network equipment

• Minimize collision domains where ever possible
• Put biggest switches on top or where the most
  capacity is needed
• Always! plan to bandwidth to increase.
• planning only for today, causes more problems
  tomorrow.

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Internet

• a lot of WANs and LANs connected together to form
  the global access to computers via TCP/IP.
  Connected in a very chaotic manner, no real
  order.
• At the top of the internet hierarchy are National
  Service Providers (NSPs) that form the backbone
  of the internet.
• Regional ISPs connect to an NSP.
• Network Access Points (NAPs) are switching
  centers between the NSPs. Generally referred to
  as Metropolitan area exchanges (MAEs).

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Internet hosts count

• 1981 213 1982 235 1983 562 1984 1,204
  1985 1,961 1986 5,089 1987 28,174 1988
  80,000 1989 159,000 1990 376,000 1991
  727,000 1992 1,313,000 1993 2,217,000 1994
  5,846,000 1995 14,352,000 1996 21,819,000
  1997 29,760,000 1998 43,230,000 1999
  72,398,000 2000 109,574,000 2001
  147,345,000 2002 171,638,000 2003
  233,101,000 2004 317,646,000 2005
  394,992,000 2006 433,193,000 2007
  541,677,000

Internet host 1991 to 2007 Hosts in millions
Reference http//www.gandalf.it/data/data1.htm
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Connecting to Internet Backbone
SOURCE HOWSTUFFWORKS.COM
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Structure of the Internet
MAPS
UUNET MAP
SOURCE CISCO SYSTEMS
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Satellite Access (InterSatCom)
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Home Networks

• Connecting via DSL or Cable Modem and assuming
  you are connecting 2 or more computers in your
  house.
• You may want a firewall.
• Most Cable Modem provide "no protection" from the
  internet
• Connect DSL/Cable modem, then firewall, then a
  hub or wireless hub.
• With Wireless don't forget to set the WEP,
  otherwise, you maybe providing internet access to
  your neighbors as well without your knowledge.
• For Home use, you do not need the expensive
  switches and hubs. Many wireless hubs provide
  10/100 connection as well. And may also include
  a firewall.

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References

• See References inside this lecture
• The Internet Security Guidebook, from planning to
  deployment, Ellis and Speed, Academic Press, 2001
• The CERT Guide to System and Network Security
  Practices, Allen, Addison Wesley, 2001
• TCP/IP Network Administration, Hunt, 3rd,
  O'Reilly, 2002
• How the Internet Works, Gralla, QUE, 1999
• The Essentails of Computer Organization and
  Architecture, chap12, Null
• Numerous websites

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Q
A