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CIS 267 Transmission Efficiency Lecture Chapter 10

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Title: CIS 267 Transmission Efficiency Lecture Chapter 10


1
CIS 267 Transmission EfficiencyLecture Chapter
10
  • Vaughn L. Lucas

2
Networked Environments
  • Major source of expense is transmission cost
  • Goal is to
  • Maximize amount of information carried, or
  • Minimize transmission capacity to satisfy a given
    business communications requirement
  • Two approaches to do the above is
  • Multiplexing
  • Data Compression

3
Chapter Overview
  • Multiplexing
  • FDM (can be used with analog signals)
  • TDM
  • Synchronous
  • Asynchronous (Statistical)
  • Data Compression
  • Lossless
  • Lossy

4
Multiplexing
  • Several data sources share a common transmission
    medium simultaneously
  • Line sharing saves transmission costs
  • Higher data rates mean more cost-effective
    transmissions
  • Takes advantage of the fact that most individual
    data sources require relatively low data rates

5
Multiplexing Diagram
6
Data Compression
  • Process of eliminating redundancies in data
  • Reduces the size of data files to move more
    information with fewer bits
  • Used for transmission and for storage
  • jpeg
  • ZIP
  • Often combined with multiplexing to increase
    efficiency

7
Data Compression
8
Approaches to Terminal Support
  • Direct point-to-point links
  • I/O port and line for each terminal
  • Multidrop line
  • One terminal transmitting at a time at same rate
  • Polled by host for communication
  • Multiplexer
  • Integrated MUX function in host

9
Direct Point-to-Point
10
Multidrop Line
11
Multiplexer
12
Integrated MUX in Host
13
Frequency Division Multiplexing
  • Simple example - use in cable TV systems
  • FDM for voice transmission is declining rapidly
  • FDM still used almost exclusively for television
    distribution systems
  • Figure 10.3a on p.236 shows a general case

14
Frequency Division Multiplexing
15
Frequency Division Multiplexing
16
Frequency Division Multiplexing
17
Frequency Division Multiplexing
  • Requires analog signaling transmission
  • Bandwidth sum of inputs guardbands
  • Modulates signals so that each occupies a
    different frequency band
  • Standard for radio broadcasting, analog telephone
    network, and television (broadcast, cable,
    satellite)

18
FDM Example ADSL
  • ADSL uses frequency-division modulation (FDM) to
    exploit the 1-MHz capacity of twisted pair.
  • There are three elements of the ADSL strategy
  • Reserve lowest 25 kHz for voice, known as POTS
  • Use echo cancellation 1 or FDM to allocate a
    small upstream band and a larger downstream band
  • Use FDM within the upstream and downstream bands,
    using discrete multitone

19
Discrete Multitone (DMT)
  • Uses multiple carrier signals at different
    frequencies, sending some of the bits on each
    channel.
  • Transmission band (upstream or downstream) is
    divided into a number of 4-kHz subchannels.
  • Modem sends out test signals on each subchannel
    to determine the signal to noise ratio it then
    assigns more bits to better quality channels and
    fewer bits to poorer quality channels.

20
Time Division Multiplexing
  • Two variants in common use
  • Synchronous TDM
  • Statistical TDM
  • Figure 10.3b on p. 236 shows a general case

21
Time Division Multiplexing
22
Synchronous Time-Division Multiplexing (TDM)
  • Used in digital transmission
  • Requires data rate of the medium to exceed data
    rate of signals to be transmitted
  • Signals take turns over medium
  • Slices of data are organized into frames
  • Used in the modern digital telephone system
  • US, Canada, Japan DS-0, DS-1 (T-1), DS-3 (T-3),
    ...
  • Europe, elsewhere E-1, E3,

23
Synchronous TDM
24
SONET/SDH
  • SONET (Synchronous Optical Network) is an optical
    transmission interface proposed by BellCore and
    standardized by ANSI.
  • Synchronous Digital Hierarchy (SDH), a compatible
    version, has been published by ITU-T
  • Specifications for taking advantage of the
    high-speed digital transmission capability of
    optical fiber.

25
SONET/SDH Signal Hierarchy
26
STS-1 and STM-N Frames
27
Statistical Time Division Multiplexing
  • Intelligent TDM
  • Data rate capacity required is well below the sum
    of connected capacity
  • Digital only, because it requires more complex
    framing of data
  • Widely used for remote communications with
    multiple terminals

28
STDM Cable Modems
  • Cable TV provider dedicates two channels, one for
    each direction.
  • Channels are shared by subscribers, so some
    method for allocating capacity is
    needed\--typically statistical TDM

29
Cable Modem Scheme
30
Data Compression
  • Reduces the size of data files to move more
    information with fewer bits
  • Used for transmission and for storage
  • Combines w/ multiplexing to increase efficiency
  • Works on the principle of eliminating redundancy
  • Codes are substituted for compressed portions of
    data
  • Lossless reconstituted data is identical to
    original (ZIP, GIF)
  • Lossy reconstituted data is only perceptually
    equivalent (JPEG, MPEG)

31
Run Length Encoding
  • Replace long string of anything with flag,
    character, and count
  • Used in GIF to compress long stretches of
    unchanged color, in fax transmissions to transmit
    blocks of white space

32
Run-Length Encoding Example
33
Huffman Encoding
  • Length of each character code based on
    statistical frequency in text
  • Tree-based dictionary of characters
  • Encoding is the string of symbols on each branch
    followed. String Encoding TEA 10 00 010
    SEA 011 00 010 TEN 10 00 110

34
Lempel-Ziv Encoding
  • Used in V.42 bis, ZIP
  • buffer strings at transmitter and receiver
  • replace strings with pointer to location of
    previous occurrence
  • algorithm creates a tree-based dictionary of
    character strings

35
Lempel-Ziv Example
36
Video Compression
  • Requires high compression levels
  • Three common standards used
  • M-JPEG
  • ITU-T H.261
  • MPEG

37
MPEG Processing Steps
  • Preliminary scaling and color conversion
  • Color subsampling
  • Discrete cosine transformation (DCT)
  • Quantization
  • Run-length encoding
  • Huffman coding
  • Interframe compression
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