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Basic Concepts

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Title: Basic Concepts


1
Basic Concepts
  • We will define basic telecommunication terms,
    such as
  • analog
  • digital
  • bandwidth
  • compression
  • protocols
  • codes and bits

2
  • The architecture or protocol suite is the
    umbrella under which the devices communicate with
    each other

3
Congestion
  • All networks are limited in how many peripherals
    they can support without experiencing too much
    degradation
  • Today more and more peripherals are being added
    to networks
  • New ways to eliminate congestion on a network
    have been developed

4
Eliminating Congestion
  • Multiplex
  • to transmit two or more signals over a single
    channel
  • Compression
  • reducing the representation of the information,
    but not the information itself
  • reducing the bandwidth or number of bits needed
    to encode information or a signal

5
Multiplexing
  • Several devices can share a telephone line
  • T-1 telephone line will carry 24 communication
    paths on one high-speed link
  • T-3 provides 672 communication paths on one link

6
Compression
  • Applications such as graphics, x-ray images,
    video are bit intensive
  • Thus require high bandwidth when transmitting
  • Compression reduces the number of bits needed to
    transfer

7
Analog and Digital
  • Telephone system developed to transmit speech
  • Spoken words are transmitted as analog sound
    waves
  • People speak in an analog format, in waves
  • Telephone system was completely analog until 1960

8
Analog Components
  • Telephones plugged into your home jacks
  • Most TV signals and telephone lines from home to
    provider
  • Most cable drops

9
Digital Components
  • ISDN lines
  • Fiber optic lines between telephone company
    offices

10
Analog Signals
  • Move down telephone lines as electromagnetic
    waves
  • The way it travels is expressed in frequency
  • Frequency refers to the number of times per
    second that a wave oscillates or swings back and
    forth in a complete cycle from its starting point
    to its ending point

11
Analog Signals
  • A complete cycle occurs when a wave starts at a
    zero point of voltage, goes to the highest
    positive point of the wave, down to the negative
    voltage portion, and then back to zero voltage

12
Analog Signals
  • The higher the speed or frequency, the more
    complete cycles of a wave are completed in a
    period of time
  • This speed or frequency is measured in Hertz
  • Hertz a measurement of frequency in cycles per
    second, 1 hertz is 1 cycle p/sec

13
Hertz
  • A wave that oscillates or swings back and forth
    10 times per second has a speed of 10 hertz or
    cycles per second
  • Bandwidth or range of frequencies a service
    occupies is determined by subtracting the lower
    range from the higher range
  • 300-3300Hz (voice) 3300-300 3000Hz

14
Analog Services
  • Voice (300 -3300 Hz)
  • Microwave Radio (2-12 GHz)
  • Analog cable TV signals (54-750 MHz)
  • Oscillate between a specific range of of
    frequencies

15
Analog versus Digital
  • Analog system can no longer handle the increase
    in the number of calls that are being generated,
    was designed for lower volume
  • Digital networks are faster, have more capacity,
    and are more reliable

16
Impairments on Analog Services
  • Analog signals loose their power the longer they
    travel
  • Signal meets resistance in the media (copper,
    coaxial cable, air), causes fading of the signal
    or attenuation of the signal
  • Analog signals also pick up noise or electrical
    energy while travelling from power lines, light
    sources, and electrical machinery
  • Requires amplification to inhibit attenuation

17
Amplification
  • To overcome resistance in a signal, analog
    signals are amplified while they travel over a
    medium
  • Drawbacks amplification
  • also increases level of noise in signal

18
Digital Signals
  • Advantages digital signals
  • higher speeds
  • clearer voice quality
  • fewer errors
  • less complex peripheral equipment required

19
Digital Signals
  • No waves are transmitted
  • Digital signals are transmitted in the form of
    binary bits
  • Binary being composed of two parts
  • In telecommunications this means only on or off,
    one or zero piece(s) of information transmitted

20
Digital Signals
  • Less error, because on-off easier to recreate
    than an analog signal or sine wave
  • Easier to repair than analog signals
  • When digital signals fade, are easy to REGENERATE
    (not amplify) over distance
  • Noise is discarded along the digital path

21
Digital TV
  • Great example of how digital transmission
    enhances clarity, because
  • noise in signal eliminated
  • error detection high in digital systems, so
    distance from signal not a factor
  • signal lost altogether if it is not in range
  • provides studio quality voice and image
  • began in 1998, 100 in 2006

22
Digital Phone Services
  • Digital technology first implemented in 1962 in
    the long distance network
  • 1975 Northern Telecom introduces the first
    digital telephone switch (PBX)
  • 1976 ATT 4ESS toll office switch
  • 1977 NT installs first digital switch
  • 1982 5ESS calls digitally switched to end-users

23
Channel Banks
  • Introduction of digital transmission between
    central offices in 1960s
  • Analog to digital conversions necessary
  • Channel banks served this purpose
  • Expensive to maintain, cumbersome, and expensive
  • Led to development of digital switches

24
Basics
  • Computers exchange bits to communicate with each
    other
  • Bits are arranged in a predefined format to make
    them readable
  • ASCII American Standard Code for Information
    Interchange
  • EBSDIC Extended Binary Coded Decimal
    Interexchange

25
Basics
  • Baud rate is a measure of transmission speed
    over an analog phone line
  • Baud rate measured differently than bit rate
  • Bits are measured in seconds
  • Baud rate measures the number of changes per
    second in an analog sine wave signal

26
Baud and Bit Rates
  • A baud is one analog electrical signal
  • One wave or cycle equals one baud
  • 1200 baud line means that the analog wave
    completes 1200 cycles in one second
  • 56,000 bits per second lines, carry 56,000 bits
    in one second, or 56Kbps

27
Codes
  • ASCII code is limited to 128 characters
  • upper case
  • lower case
  • numbers
  • punctuation
  • Does not include
  • bold, underlining, font changes, tables, etc.

28
Attachments
  • Word processors add their own codes to perform
    fancy word processing
  • Easier to send the entire documents as attachment
    than to come up with coding schemes for all such
    specialized documents
  • MIME (multipurpose mail extension) mail protocol
    used send attachments

29
Bandwidth
  • Refers to capacity
  • Carrying capacity expressed differently for
    analog and digital transmissions
  • analog capacity measured in Hertz
  • digital capacity measured in bytes

30
Hertz
  • Measure of frequency of analog services
  • Example
  • Co-axial cable with bandwidth of 400 MHz
  • means 400 million cycles per second
  • difference between lowest and highest frequency,
    within which the medium carries traffic

31
Hertz
  • Cabling which carries between 200MHz and 300 MHz
    has a bandwidth or frequency of 100 MHz
  • The greater the difference between highest and
    lowest frequency the greater the bandwidth or
    capacity of the medium

32
Bits
  • ISDN, T-1, T-2, ATM are digital services
  • speed is stated in the number of bits transmitted
    per second
  • T-1 1.54 million bits p/s (Mbps)
  • ISDN 64Kbps
  • ATM 622 Mbps, or 13.22 Gbps

33
Narrow/Wideband
  • Narrowband
  • T-1 at 1.54Mbps
  • Analog phone lines at 3,000 Hz
  • BRI ISDN at 64Kbps
  • Wideband
  • Broadcast TV 6MHz per channel
  • Cable TV 700MHz
  • ATM at 13.22 Gbps
  • SONET up to 13.22G
  • T-3 at 44.7Mbps

34
Applications
  • Wideband
  • TV
  • Cable
  • Connections between telephone offices
  • Narrowband
  • phone connection to end users

35
Protocols
  • Enable computers to communicate with each other
  • Spell out the rules of interaction between two or
    more computers
  • Handle error detection and correction and file
    transmission

36
Examples of Protocols
  • Who transmits first?
  • What is the structure of the addresses of devices
    such as computers?
  • How are errors fixed?
  • How long to wait before disconnecting?
  • How to package data to be sent?

37
Architecture
  • Ties computers and peripherals together into a
    coherent whole
  • Forms the network which connects all devices
    together
  • Layers within architectures have protocols to
    define functions such as routing, error checking
    and addressing

38
Examples of Architectures
  • SNA developed by IBM to tie together all their
    devices
  • OSI Open Standards Interconnection, developed by
    International Standards Organization, to allow
    devices from various vendors to communicate with
    each other

39
OSI
  • Not widely implemented
  • Laid foundation for the concept of open
    communications among vendors
  • Basic concept of layering of groups of functions
    into 7 layers
  • Each layer can be changed and developed
    independently

40
Layers
  • 1 physical layer
  • 2 data link layer
  • 3 network layer
  • 4 transport layer
  • 5 session layer
  • 6 presentation layer
  • 7 application layer

41
Compression
  • White spaces redundant images removed
  • Letter abbreviation
  • Only changed part of image transmitted
  • Many types of compression methods
  • Based on mathematical algorithms
  • Codec (coder/decoder) devices used to perform the
    algorithm

42
Streaming Media
  • Software used to speed up transmission of video
    and audio over the Internet
  • When graphics and text sent to your screen, text
    immediately available, graphs later
  • Important feature of browsers to make material
    available as it downloads
  • MPEG standards are used for streaming

43
Streaming Media
  • ITU formed the Moving Picture Experts Group
    (MPEG) in 1991 to develop compression standards
  • Made standard that more processing power needed
    to encode than to decode material
  • RealNetworks Inc.
  • Microsoft Corporation

44
Multiplexing
  • Combines traffic from multiple telephones or data
    devices into one stream
  • Allows many devices to share the same
    communication path
  • Makes more efficient use of telephone lines
  • Does not alter actual data sent
  • Consists of special equipment, hardware

45
Networks
  • LAN (local area network)
  • WAN (wide area network)
  • MAN (metropolitan area network)

46
Network Terminology
  • Hub wiring center to which all devices are
    connected within a segment of a LAN, connections
    with twisted pair cabling
  • Switching Hub allows multiple transmissions on a
    LAN segment
  • Backbone connects hubs together
  • Bridge connects multiple LANs together

47
Network Terminology
  • Layer 2 switch bridges with multiple ports,
    switch data between LAN segments
  • Router connects multiple LANs together, more
    complex than bridges, handle more protocols
  • Routing Switches fast router
  • Server centrally located computer which houses
    set of files, documents, data, etc.

48
Bridges
  • Used to connect a small number of LANs
  • Provide one common path to connect several LANs
  • Easy to configure, all data sent to all devices
    on a network, appropriate device picks it up,
    broadcast feature
  • Lack routing and congestion control

49
Routers
  • Used to connect multiple LANs over large
    distances (differing buildings, cities)
  • More sophisticated than bridges
  • Can handle differing protocols from various LANs

50
Routers
  • Capabilities
  • flow control if path congested holds data until
    capacity is available
  • path optimization selects best available path
    with use of tables
  • sequencing sends data in orderly packets
  • receipt acknowledgement receiver send a message
    back to verify receipt of file

51
Routers
  • Disadvantages
  • Complex to install and maintain
  • Must have up-to-date address labels
  • Slower than bridges due to their complexity
  • Layer 3 device

52
Switching Routers
  • Faster than non-switching routers
  • Do not look up in tables where to send data
  • Address placed in the pack sent
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