Transcript Basic concepts

Basic Concepts
• We will define basic telecommunication
terms, such as:
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analog
digital
bandwidth
compression
protocols
codes and bits
The architecture or protocol suite is the
umbrella under which the devices
communicate with each other
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
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
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
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
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
Analog Components
• Telephones plugged into your home jacks
• Most TV signals and telephone lines from
home to provider
• Most cable drops
Digital Components
• ISDN lines
• Fiber optic lines between telephone
company offices
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
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
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
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
Analog Services
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Voice (300 -3300 Hz)
Microwave Radio (2-12 GHz)
Analog cable TV signals (54-750 MHz)
Oscillate between a specific range of of
frequencies
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
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
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
Digital Signals
• Advantages digital signals:
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higher speeds
clearer voice quality
fewer errors
less complex peripheral equipment required
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
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
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
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 endusers
Channel Banks
• Introduction of digital transmission between
central offices in 1960’s
• Analog to digital conversions necessary
• Channel banks served this purpose
• Expensive to maintain, cumbersome, and
expensive
• Led to development of digital switches
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
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
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
Codes
• ASCII code is limited to 128 characters
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upper case
lower case
numbers
punctuation
• Does not include:
– bold, underlining, font changes, tables, etc.
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
Bandwidth
• Refers to capacity
• Carrying capacity expressed differently for
analog and digital transmissions
– analog capacity measured in Hertz
– digital capacity measured in bytes
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
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
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
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
Applications
• Wideband:
– TV
– Cable
– Connections between telephone offices
• Narrowband:
– phone connection to end users
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
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?
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
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
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
Layers
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1: physical layer
2: data link layer
3: network layer
4: transport layer
5: session layer
6: presentation layer
7: application layer
Compression
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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
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
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
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
Networks
• LAN (local area network)
• WAN (wide area network)
• MAN (metropolitan area network)
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 LAN’s together
Network Terminology
• Layer 2 switch: bridges with multiple
ports, switch data between LAN segments
• Router: connects multiple LAN’s together,
more complex than bridges, handle more
protocols
• Routing Switches: fast router
• Server: centrally located computer which
houses set of files, documents, data, etc.
Bridges
• Used to connect a small number of LAN’s
• Provide one common path to connect
several LAN’s
• Easy to configure, all data sent to all
devices on a network, appropriate device
picks it up, broadcast feature
• Lack routing and congestion control
Routers
• Used to connect multiple LAN’s over large
distances (differing buildings, cities)
• More sophisticated than bridges
• Can handle differing protocols from various
LAN’s
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
Routers
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Complex to install and maintain
Must have up-to-date address labels
Slower than bridges due to their complexity
Layer 3 device
Switching Routers
• Faster than non-switching routers
• Do not look up in tables where to send data
• Address placed in the pack sent