LIS508 lecture 7: introduction to networks

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LIS508 lecture 7introduction to networks

• Thomas Krichel
• 2003-11-19

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Structure

• General things about networks
• History of Internet
• LANs and Ethernet
• The TCP/IP model
• discussion mostly based on Tanenbaums computer
  networks classic book.

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Computer network

• Definition
• A computer network is a collection of autonomous
  computers
• The distributed nature of the system is apparent
  to the user
• Motivation
• Resource sharing
• Increase reliability
• Improve scalability
• Money savings through use of PCs

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Progress in computers

• Moores law the power of computers doubles
  roughly every 18 months.
• 1985 - 386 Processor - 275,000 transistors
• 1989 - 486 DX Processor - 1,180,000 transistors
• 1993 - Pentium Processor - 3,100,000 transistors
• 1997 - Pentium II Processor - 7,500,000
  transistors
• 1999 - Pentium III Processor - 24,000,000
  transistors
• 2000 - Pentium 4 Processor - 42,000,000
  transistors

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Power input in networks

• The speed of network connections has improved
  much faster than that.
• But since computer network links computers,
  progress in network speed has been held up by
  computers being slow!
• The conclusion should be that progress in network
  technology will go on and will affect more of our
  lives.
• We are only at the beginning of the wired age!

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Computer networks for communication

• Access to remote information
• Data sources
• Software
• E-commerce
• Video on demand
• Person to person communication
• Email
• Video conferencing
• Interactive television

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Types of networks by technology

• Broadcasting network
• any message issued by one computer is received by
  all computers on the network
• Point-to-point network
• Circuit switched there is one physical link that
  is being made between two machines that need to
  communicate. ex. telephone
• Packet switched the communication is broken into
  pieces. Each piece is sent individually. ex
  Internet

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Types

• LAN
• Bounded size,
• bus topology one cable from first to last
  machine
• ring topology one cable in circular for
• star topology all cables go to a central
  machine.
• High speed and reliability
• WAN
• Interconnection of a large number of hosts
• Has transmission lines and routers
• Has an irregular topology, often with subnets

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WAN example

• The university campus it Westchester has one LAN
  linking all the computers together. Student and
  office facilities are separate.
• At the center, there is a gateway machine that
  send all the traffic to the Brooklyn campus.
• There, there is another set of machines that send
  out-of-campus traffic out of campus

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an internet

• An internet is a collection of networks that can
  be used together.
• It does not have a known topology.
• Parts of it are controlled by different
  organizations.
• It uses interconnects many types of networks.
• The most famous internet is the Internet.

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Network modeling

• Usually networks are modeled as layers
• Purpose of layer is to carry out services for the
  higher layer in a way that is transparent to the
  higher layer.
• Layers communicate with their peers according to
  known protocols
• Between layers in the same machine there is an
  interface.

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Service types

• Connection oriented / connectionless
• phone conversation
• datagram
• Reliable / non-reliable
• Online video
• File transfer

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example

• http is an application protocol on the Internet.
• It is the protocol that web servers and web
  clients use
• It is also used in some other instances.
• http relies on a transport service to transport
  data from one machine to another. This transport
  protocol is called TCP. This happens on a lower
  layer.

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The Internet

• The Internet is kept together by two key
  protocols
• The Internet protocol IP.
• And the transmission control protocol TCP.
• TCP relies on IP to provide services, thus IP is
  on a lower layer than TCP.
• Both are commonly referred to as TCP/IP.

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Origins of TCP/IP

• 1957 USSR launches the Sputnik
• US worried about command and control structure
  after a nuclear attack
• Early 60s Paul Baran promotes packet switching
  rather than circuit switching.
• Mid 60s Pentagon says that it wants this, gives
  grants to ARPA.

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ARPAnet original design

• Network nodes have host computers and router
  computer
• Hosts sends messages smaller than 8061 bits
• routers breaks it up into packets smaller than
  1008 bits
• all router are connected by transmission lines
• each router connected to 2 others
• store and forward principle

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implementation

• 12k times 16 bit words memory minicomputer
  without hard disk as routers connected by 56kbps
  leased phone lines
• life with four hosts in 196912
• over 30 hosts in 197209
• protocol research leads to TCP/IP in 1974
• integrated into Berkeley UNIX, freely available
• Internet research group developing protocols
• 1979 Internet research group reorganized to
  Internet Control and Configuration Board

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More history

• 1980 MILNET split off the ARPAnet
• CSNET set up
• links researchers at non-ARPA contract
  institutions to the ARPAnet
• ran on a single box with dial-up lines since late
  70s
• 1984 NSF links adds a router to it
  supercomputers, sets up NSFnet,
• the first purely TCP/IP network, on 56kbps.
• additional funding for (eventually 20) regional
  networks connect to the backbone
• 1990 ANS (MERIT,MCI,IBM) take over NSFnet

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The Internet now

• Connects millions of computers world-wide.
• Each computer is part of a local network. This
  network is sometimes very small.
• If you have problems connecting to the Internet,
  it is most likely a local problem, rather than
  the Internet being down.

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LAN

• A LAN generally operates a broadcasting network.
• Something that is transmitted by one station is
  heard by all other stations
• An individual message is called a frame.
• This creates a media access control (MAC)
  problem. When one station issues a frame, it
  destroys a frame from another station, through
  frame collision.

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Ethernet

• comes from the term "luminiferous ether".
• Today the name for a family of LAN protocols
  implementing CSMA/CD protocol for the MAC
  problem.
• CSMA/CD stands for carrier sensitive media access
  with collision detection.
• Initially only referred to IEEE 802.3 standard
• Can run over a variety of physical devices.

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IEEE 802.3 history

• 1980 first version following work by DEC, Intel
  and XEROX
• 1982 version two released
• 1983 Novell creates its own version
• 1990 support for twisted pair cable added
• Over time, a whole set of standards have emerged
  to deal with other applications such as wireless
  devices.

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10baseT

• This is most widely used physical infrastructure
  today.
• It runs over twisted-pair cable and RJ-45 jack.
• Cables are cheap, transmission is fast, .59c
• Maximum length of cable about 150m, thus not good
  for bus architecture.

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Fiber optic cable

• This type of cable is a lot faster.
• It uses light to transmit signal, so it is almost
  as fast as the speed of light.
• It has no problems of loss of signal over long
  distances.
• But it its more expensive.
• Only used for transmissions of lots of data,
  between hubs.

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other devices

• repeater is a device that amplifies an electric
  signal so that it can travel over some more wire.
• hub is a repeater with a lot of outgoing wires.
  Hubs are dump, or smart. A smart hub can be
  inspected by a monitoring device to see what the
  traffic is doing there.
• A bridge or switch is a device that links
  different LANs together. In normal promiscuous
  mode, it receives signals from all LANs. It will
  know which MAC address is on which LAN and
  transmit echo signal to the right LAN.

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MAC address

• A physical address burned onto each network
  interface card used on a LAN.
• Forms an address for your computer on a LAN
• It is 6 bytes long, written in hex, usually
  written with each byte separated by .
• 2 power 48 addresses, that is about 11000
  addresses for every inhabitant of the planet.