CEN 4500 Network Fundamentals

1
CEN 4500 - Network Fundamentals

• To insert your company logo on this slide
• From the Insert Menu
• Select Picture
• Locate your logo file
• Click OK
• To resize the logo
• Click anywhere inside the logo. The boxes that
  appear outside the logo are known as resize
  handles.
• Use these to resize the object.
• If you hold down the shift key before using the
  resize handles, you will maintain the proportions
  of the object you wish to resize.

• Part 2
• Transmission Media

2
Transmission Media

• At the lowest level, data communications involves
  encoding data into a form of energy and then
  sending said energy across a transmission medium.
• Transmission Media consists of basically two
  types
• Cable
• Wireless

3
Transmission Media

• Cabling
• 4 types of popular cabling used
• 10Base5 thick coax
• 10Base2 thin coax
• 10BaseT twisted pair (phone line)
• 10BaseF fiber optic cable
• Note 10 means 10 Mbps capacity and Base
  means baseband signaling. The X means maximum
  100-meter segment-length (coax) or medium type
  (ie, fiber or twisted pair).

4
Transmission Media

• Cabling
• 10Base5 can be identified by its thickness
  (about same diameter as a garden hose) and the
  use of vampire tap connectors

Vampire Tap
Transceiver
5
Transmission Media

• Cabling
• 10Base5
• Maximum segment length 500 meters
• Still used but losing favor to smaller,
  easier-to-install cabling and connectors, i.e

6
Transmission Media

• Cabling
• 10Base2 Thin Coax
• Cable TV-like coaxial cabling using BNC
  connectors

Cable from previous terminal or hub
Cable to next terminal or hub
Connector to network card
BNC T Connector
7
Transmission Media

• 10Base2 Thin Coax
• Very common, used to connect stations directly to
  each other
• Maximum segment length is 200 meters

8
Transmission Media

• Cabling
• 10BaseT
• Like phone cable, but with 8 wires instead of 4
• Very popular due to ease of installation
• Uses modular RJ45 connector
• Requires the use of a hub
• Maximum segment length
• of 100 meters

9
Transmission Media

• Cabling
• 10BaseF
• Fiber Optic - very expensive, but costs dropping
  as use increases
• Flexible cable about 1/4 thick
• Maximum segment length of 2000 meters

10BaseF Connector
10
Transmission Media

• Wireless
• Radio (or terrestrial)
• aka RF (Radio Frequency)
• Of course, does not require physical connection
  between stations
• Usually of limited transmission scope (within a
  building up to a few miles) due to noise and/or
  ambient interference

11
Transmission Media

• Microwave
• Just a higher frequency of radio waves, but with
  unique characteristics
• unidirectional transmission
• higher data capacity than RF
• must be line of sight

12
Transmission Media

• Wireless
• Satellites
• Either low-earth-orbit or
• Geosynchronous (high-earth-orbit)

13
Transmission Media

• Physical Limitations Of A Transmission System
• Propagation Delay
• The time required for a signal to travel across
  media
• Example electromagnetic radiation travels
  through space at the speed of light (C3x108
  meters per second)

14
Transmission Media

• Physical Limitations Of A Transmission System
• Bandwidth
• Maximum times per second the signal can change
  (i.e., from 0 to 1)

15
Transmission of Data

• Network hardware encodes information for
  transmission
• Two types of encoding
• Analog
• Amount of energy is proportional to the value of
  the item sent
• Digital
• two levels of energy used to encode 0 or 1
• Computer networks use digital (mostly)

16
Example Digital Encoding

• Medium
• Copper wire
• Energy form
• Electric current
• Encoding used
• Negative voltage encodes a 1
• Positive voltage encodes a 0

17
Digital Encoding

• Known as a waveform diagram
• X-axis corresponds to time
• Y-axis corresponds to voltage

18
Encoding Details

• All details are specified by a standard
• Several organizations produce network-ing
  standards
• IEEE
• Internet Society
• ISO
• ITU-T (formally CCITT)
• EIA
• ATM forum

19
Why Standards?

• Required to allow for interoperability between
  equipment
• Advantages
• Ensures a large market for equipment and software
• Allows products from different vendors to
  communicate
• Disadvantages
• Freezes technology
• May be multiple standards for the same thing

20
The RS-232 Standard

• Most widely used standard for com-munication
  between a CPU and devices such as a modem or
  keyboard
• Said to be serial because bits travel on the wire
  one after the other
• Uses voltages of 15 (a 0) or -15 (a 1)
• Cable length limited to 50 feet
• Uses asynchronous communication

21
Asynchronous Communications

• Sender and receiver must adhere to same
  standards, ie
• number of bits per character (usually 7)
• the duration of each bit
• The Receiver doesnt know when a character will
  arrive
• To ensure a meaningful exchange, theres a start
  bit before the character and a stop bit just
  after

22
Start Stop Bits

• An RS-232 device never leaves 0 volts on the
  line, but instead transmits 1s to signal an idle
  line
• Accordingly, the receiver cannot use a lack of
  voltage to mark the end of one bit and the
  beginning of the next.
• Instead, both sender receiver agree on the
  exact length of time a voltage value will be held
  for each bit

23
Start Stop Bits

• When the first bit of a character arrives, the
  receiver starts a timer, and uses the timer to
  know when to measure the voltage for each
  successive bit
• But because a receiver cannot distinguish between
  an idle bit and an initial 1-bit, the standard
  requires the sender to transmit an extra 0-bit
  before the bits of the character

24
Start Stop Bits

• This extra bit is known as a Start Bit
• And since the period between the end of one
  character and the beginning of another character
  can be arbitrarily long, RS-232 requires the
  sender to leave the line idle between characters
  for a minimum time (one bit-length)

25
Start Stop Bits

• This idle-time bit must have the value of 1 and
  is referred to as a stop bit

26
Start Stop Bits

• Start Bit
• same as an 0
• not part of data
• Stop Bit
• same as a 1

27
Duration Of A Bit

• Determined by the baud rate - the number of bits
  transmitted per second
• Bit duration is 1/baud rate
• Sender and receiver must use same standard

28
Two-Way Communication

• aka Full Duplex transmission
• Requires each side to have both a transmitter and
  receiver

29
Electrical Transmission

• Bad News
• Electrical energy dissipates as it travels
• Wires have resistance, capacitance and inductance
  which all distort signals
• Ambient magnetic or electrical fields also
  distort signals
• Distortion can result in loss or
  misinter-pretation of data

30
Electrical Transmission
31
Electrical Transmission

• Consequences
• RS-232 hardware must be able to handle minor
  distortions
• takes multiple samples per bit
• tolerates less than full voltage
• Cannot use electrical current for long-distance
  transmission

32
Long-Distance Communication

• Fact an oscillating signal travels farther than
  a direct current
• For long-distance communication
• Send a sine wave (aka carrier wave)
• Change (modulate) the carrier to encode data
• Modulated carrier techniques originally developed
  for radio TV transmission

33
Long-Distance Communication

• Carrier Wave
• usually a sine wave
• oscillates continuously
• Frequency of a carrier wave is fixed

34
Long-Distance Communication

• Types of Modulation
• Amplitude Modulation (AM radio)
• Frequency Modulation (FM radio)
• Phase Shift Modulation (data)

35
Long-Distance Communication

• Amplitude Modulation
• Strength of signal encodes 0 or 1
• One cycle needed for each bit
• Data rate limited by carrier bandwidth

36
Long-Distance Communication

• Phase Shift Modulation
• Changes the timing of the carrier abruptly to
  encode X bits of data (arrows, above)
• Data rate higher than unaltered carrier bandwidth

37
Long-Distance Communication

• Phase Shift Modulation
• Because hardware can measure the amount of shift
  in an oscillating wave, phase shift can be used
  to encode more than a single bit of data per
  oscillation
• According to the transmission standard, each
  carrier cycle can be broken into shift-values,
  the number of values usually a power of 2 (i.e,
  23 8 possible shifts)

38
Long-Distance Communication

• Phase Shift Modulation
• The sender uses 3 bits of data to select which of
  the 8 shift-values to use
• The receiver, conversely, detects the shift and
  determines the value of the carrier shift, and
  deduces the 3-bit value accordingly

39
Long-Distance Communication

• So what piece of hardware wizardry can do all
  this modulating and demodulating?
• A Modem (MOdulator/DEModulator)
• contains separate circuitry for
• the modulation of the outgoing signal
• the demodulation of the incoming signal

40
Long-Distance Communication

• Types of Modems
• Dialup
• use 4 copper wires telephone system
• transmit a modulated audio tone
• Optical
• use glass fiber as transmission medium
• transmit a modulated light
• Wireless
• use air/space as transmission medium
• transmit a modulated RF wave

41
Long-Distance Communication

• A typical Dialup Modem configuration

42
Long-Distance Communication

• Modem Terminology
• A Full-duplex modem
• provides 2-way communication
• allows simultaneous transmission
• uses 4 wires
• A Half-duplex modem
• also provides for 2-way communication
• can either transmit or receive at one time
• uses 2 wires
• is utterly outdated

43
Long-Distance Communication

• Multiplexing
• based on the principle that two or more signals
  that use different carrier freq-uencies can be
  transmitted over a single medium simultaneously
  without inter-ference
• fundamental to networking

44
Long-Distance Communication

• General Concept of Multiplexing

45
Long-Distance Communication

• Two Basic Types of Multiplexing
• Time Division (TDM)
• Only one item at a time on shared channel
• Item marked to identify source
• Demultiplexor uses mark to know recipient
• Frequency Division (FDM)
• Multiple items transmitted simultaneously
• Each frequency considered a discreet channel
• when referring to fiber optics, FDM is called
  wave division multiplexing

46
Long-Distance Communication

• Transmission Schemes
• Baseband transmission
• aka narrowband
• uses small part of electromagnetic spectrum
• essentially time slices transmission system
• Broadband transmission
• uses multiple carrier frequencies
• uses broader part of electromagnetic spectrum
• achieves higher throughput
• hardware more complex and thus expensive

47
Required Reading

• Comer, Chapters 4 - 6