Review: The physical layer'

1

• Review The physical layer.
• Bandwidth/Capacity
• bit rate/baud rate
• How to determine the number of bits per symbol?
• Relation between the bandwidth and capacity
• Nyquists theorem maximum baud rate for
  noiseless channel.
• max baud rate 2 Bandwidth
• Shannon's theorem maximum bit rate for noisy
  channel.
• C Bandwidth log_2 (1 S/N)
• Data encoding
• digital data to digital signals
• digital data to analog signals
• amplitude modulation, frequency modulation and
  phase modulation.

2

• Simplex/half-duplex/duplex communication
• Multiplexing when it is needed?
• Time Division Multiplexing, Frequency division
  Multiplexing, Code division multiplexing.

3

• A physical layer protocol RS-232-C.
• Four components
• mechanical interface
• electrical interface
• functional interface
• procedureal interface
• Terminology
• DTE (data terminal equipment) computer
• DCE (data circuit-terminating equipment) modem

4

• mechanical interface
• 25-pin connector
• 47.04-0.13mm wide
• top row 1-13
• bottom row 14-25 .....,
• cable 15m
• electrical interface
• 1 lt -3V
• 0 gt 4V
• bit rate up to 20kbps

5

• functional interface which circuit should
  connect to which pin (Fig 2-21).
• 1 protective ground
• 2 transmit
• 3 receive
• 4 request to send
• 5 clear to send
• 6 data set ready
• 7 common return
• 8 carrier detect
• 20 data terminal ready

(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(20)
6

• procedural interface legal sequence of events.
• Example
• DTE requests to send,
• DCE clear to send.