ENGS 4 - Lecture 3 Technology of Cyberspace Winter 2004 Thayer School of Engineering Dartmouth College

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ENGS 4 - Lecture 3 Technology of Cyberspace
Winter 2004Thayer School of EngineeringDartmouth
College

• Instructor George Cybenko, x6-3843
• gvc_at_dartmouth.edu
• Assistant Sharon Cooper (Shay), x6-3546

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Basic Terminology - bits

• bit basic unit of information, having two
  possible values, 0 or 1.
• example if b is a bit, then either b0 or b1
• b1b2 are two bits, then the possible values are
  00, 01, 10, 11.
• b1b2b3 could be 000,001,010,011,100,101,110,111
• b1b2b3b4 could have how many values?
• k bits could have 2k values
• information transfer rates are measures in bits
  per second

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Basic Terminology - bytes

• byte 8 bits, so 256 possible values.
• 26 characters, lower and upper case 52
• 10 digits, 521062
• add punctuation, control characters, etc
• 128 traditional characters (ASCII characters)
• typically, one typed character is stored in 8
  bits 1 byte
• storage and memory sizes are expressed in units
  of bytes

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kilo, mega, tera, peta

• kilo is Greek prefix for 1000
• 10 bits can have 210 values ( 1024)
• a kilobit is 1024 bits, kilobyte is 1024 bytes
• mega is Greek prefix for 1,000,000
• 220 bits 1 megabit, 220 bytes 1 megabyte
• 230 bits 1 terabit, 230 bytes 1 terabyte

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Some simple examples

• Google home page has about 4000 bytes
• 4000 bytes 32,000 bits
• Internet has to move 32,000 bits for a user to
  see the Google home page.
• Internet has to move 3,200,000 bits for 100 users
  to see Google, IE, about 3 megabits
• Dartmouth has 10,000 people on campus

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Basic Web Browsing
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Network fabric hubs, switches, routers
Hub
Router
Hub
Switch
Router
Printer
Router
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Network fabric hubs, switches, routers

• MAC address hardware address assigned by
  manufacturer
• IP address 32 byte address used for all
  devices attached to the Internet (4 billion
  addresses)
• hub broadcasts all data to all ports
• switch directs data to ports according to the
  IP to hardware/MAC address correspondence
• router directs data to other routers for
  deliver based on IP addresses
• aggregated data transfer requirements are huge

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Bandwidth and latency

• bandwidth measured in bits per second
• example dialup modem has bandwidth of 56kbps
  56 kilobits per second 56 x 1024 bits per
  second
• wireless ethernet has nominal bandwidth of 11
  megabits per second
• wired ethernet has 10 or 100 megabits per second
  bandwidth
• latency is the time required to move to move the
  first bit from one point to another

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Bandwidth versus latency

• Truck load of DVDs driven from Hanover to Boston
  2 hour drive
• 10,000 DVDs in truck, each DVD stores 4.7
  gigabytes of data 4.7x 8 Gb 37.6 gigabits
  about 3.8 x 1014 bits
• 7,200 seconds in 2 hours
• bandwidth is 3.8 x 1014 bits/ 7.2 x 103
• 38 x 1013 / 7.2 x 103 5 x 1010 bps 50 gbps
• latency is 2 hours

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Bandwidth versus latency

• 400,000 bits per web page
• 10,000 users
• 4,000,000,000 bits 4 gigabits
• if the 10,000 users get their web pages in 1
  second, then the network has to offer at least 4
  gigabits per second bandwidth
• observed latency is only a second or so
• Quality of Service (QOS) guaranteed latency and
  bandwidth

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Cisco Systems
Leading manufacturer of high performance routers
and switches for the Internet Founded in late
1980s Stanford spinoff, based on software
developed there Huge growth in 1990s Internet
tech collapse in 2000
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Cisco Stock 1999- now
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Engineering Challenges of Different Content Types
Content
Bandwidth Bursty QoS?
Web, data Medium Yes
No
Voice Low Yes
Yes
TV, video High No
Yes
Monitoring Variable No
No
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Homework 1 Due Jan 20

1. Estimate the number of bytes in the ORC
   (2003-2004 edition, printed)
2. How much time would downloading it require on a
   56 kbps modem line?
3. How much time would downloading it require on a
   10 mbps ethernet?
4. How much time would downloading it require on a
   100 mbps ethernet?
5. What is the bandwidth and latency of the NASA
   Mars Rover to earth channel?
6. Create a web page with the answers to these
   questions on the webpage.

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Homework 1 Due Jan 20

• Create a web page with the answers to these
  questions on the webpage.