Physical Layer

1
Physical Layer

• Concerned with Transmission of Unstructured Bit
  Stream Over Physical Medium.
• Data Transmission

m
Input Device
Source System
g(t)
Transmitter
s(t)
Medium
r(t)
Receiver
Destination System
Simplified Communication Block Diagram
g(t)
Output Device
m
2
Concepts Terminology

• Medium (Simplex, Halfduplex, Fullduplex)
• Hardware --- Signal is Physically Confined.
• Twisted-pair Wires,
• Coaxial Cables,
• Fiber Optics.
• Software --- Signal is Not Physically Confined.
• Propagation Through Air,
• Seawater.

3
Frequency, Spectrum, and Bandwidth

• Signal
• Continuous (or Analog)
• Discrete (or Digital)
• Periodic -- Shape is Repeated
• Aperiodic -- Shape is Not Repeated

4
Frequency, Spectrum, and Bandwidth (cont.)

• Three Attributes
• Frequencies -- Number of Cycles per Second (Hertz
  (Hz) 1 CPS)
• Amplitude -- Instantaneous Value of The Signal
  During a Cycle.
• Phase -- Part of a Cycle That a Signal Has Passed
  When It Is Measured Or a signal That Advanced a
  Certain Number of Degrees Pass The Reference
  Points.

5
Frequency, Spectrum, and Bandwidth (cont.)

• All Signals Used In These Examples Will Be
  Sinusoidal Can Be Described By
• V(t) A sin(2pft q)
• where A is Maximum Amplitude, f is Frequency,
  t is Instant of Time,
• and q is Phase.

6
Examples

• Sine wave representation of a signal (periodic
  signal)

Aperiodic Analog Signal (e.g., Human Voice)
Amplitude
10V
Time
Aperiodic Analog Signal (e.g., Human Voice)
7
Examples(cont.)

• Aperiodic Discrete Signal

Continuous Signal
8
Examples(cont.)

• Note
• A period represents one full cycle
• A cycle represents 360o (2p radians)
• Angular velocity of the wave number of radians
  that the wave completes in a second
• Total angle a sine wave completes in time t is
  q wt 2pft

9
Examples(cont.)

• Discrete Signal(Digital Representation of Sine
  Wave)

Note Both Examples Have Frequency of 3Hz or
(3(2p) 3(360o) 1080o
10
Frequency Domain Concepts

• So Far, We Have Viewed a Signal As a Function of
  Time. But Any Signal Can Also Be Viewed As a
  Function of Frequency
• Example
• s(t) sin(2pft) 1/3 sin3(2pf)t 1/5
  sin5(2pf)t
• The Components of This Signal Are Just Sine Waves
  of Frequencies f, 3f, and 5f. Using Fourier
  Analysis, It Can Be Shown That Any Signal Is Made
  Up of Components at Various Frequencies, Where
  Each Component is a Sinusoid.

11
Frequency Domain Concepts (cont.)

• s(t) sin(2pft) 1/3 sin3(2pf)t 1/5 sin5(2pf)t

s(t)
Frequency Domain For Signal
1
f
f1
3f1
5f1
12
Frequency Domain Concepts (cont.)
13
Frequency Domain Concepts (cont.)
Amp
1
0.5
0
-0.5
-1
0
Time
1/3 sin 3(2pf1)t
14
Frequency Domain Concepts (cont.)
Amp
1
0.5
0
-0.5
-1
0
Time

• 1/5 sin 5(2pf1)t

15
Frequency Domain Concepts (cont.)
sin(2pf1)t 1/3 sin 3(2pf1)t 1/5 sin 5(2pf1)t
16
Frequency Domain Concepts (cont.)

• Spectrum of Signal -- range of frequencies. From
  example above spectrum extends from f1 to 5f1.
• Bandwidth -- Width of Spectrum or 4 f1
• Relationship Between Bandwidth Data Rate. The
  Higher The Data Rate, The Greater The Bandwidth.
• Example (Refer to Previous Examples)
• Let a Positive Pulse Represent a Binary 1 and a
  Negative pulse Represent a Binary 0 Then The
  Signal Represents The Binary Stream 1010...

17
Frequency Domain Concepts (cont.)

• The Pulse Duration is 1/ (2 f1), Thus The Data
  Rate is 2 f1 Bits Per Second.
• For f1 1000 Hz, The Data Rate 2000 bps The
  Bandwidth 4000 Hz

18
Fourier Series
A Way of Representing Any Periodic Function As a
Sum of Harmonically Related Sinusoids.
Where f 1/T is The Fundamental Frequency, an
and bn are The Sine And Cosine Amplitudes of The
nth Harmonics. Coefficients Are
19
Fourier Series (cont.)
sin(2pkft) for f 1/2p , or T 2p with
different k
20
Fourier Series (cont.)

• Multiplication of two sine waves with different k

21
Fourier Series (cont.)
22
Fourier Series (cont.)
23
Fourier Series (cont.)
Note The maximum value of sin(x) and cos(x) is 1
and the minimum value is -1. The maximum and
minimum values of cos(x1) - cos(x2) cos(x3) -
cos(x4) and sin(x1) - sin(x2) sin(x3) - sin(x4)
are 4 and -4, respectively. Hence,an and bn
converge to zero when n becomes infinite.
24
Fourier Series (cont.)
25
Fourier Series (cont.)
26
Definition

• Digital Signal -- A Sequence of Discrete
  Discontinuous Voltage Pulses. Each Pulse is a
  Signal Element
• Baud -- Number of Signal Elements Per Second.
• Note -- Baud Rate is Not Necessarily The Same As
  Bit Rate.

27
Example

• Given a bit rate of b bits/sec, the time required
  to send 8 bits (for example) is 8/b sec, so the
  frequency of the first harmonic is b/8 Hz. An
  ordinary telephone line, often called a voice
  grade line, has an artificially introduced cutoff
  frequency near 3000 Hz. This restriction means
  that the number of the highest harmonic passed
  through is 24000/b, roughly (the cutoff is not
  sharp). For some commonly used data rates, the
  numbers work out as follows

28
Example (cont.)

• Bps T(msec) First Harmonic
  (Hz) Harmonic (Hz) sent
• 300 26.67 37.5 80
• 600 13.33 75 40
• 1200 6.67 150 20
• 2400 3.33 300 10
• 4800 1.67 600 5
• 9600 0.83 1200 2
• 19200 0.42 2400 1
• 38400 0.21 4800 0

29
Maximum Data Rate of a Channel

• Signal-to-Noise Ratio
• Signal Power
• (S/N)dB 10 log10
• Noise Power
• Expresses The Amount In Decibels(dB) That The
  intended signal exceeds the noise level.
• A high S/N
• Þ High Quality Signal a Low Number of
  Required Intermediate Repeaters.

30
Maximum Data Rate of a Channel (cont.)

• Shannon's Major Result
• Maximum Number of Bits/Sec H log2 (1S/N),
  Where H is The Bandwidth of The Channel In Hertz.
• Example
• Consider a Voice Channel Being Used Via Modem
  to Transmit Digital Data. Assume Bandwidth
  3100 Hz, S/N 30dB or a Ratio of 10001 Þ
• C 3100 log2 (1 1000)
• 30,894 bps Theoretical Maximum

31
Shannon Theorem (Additional Comments)

• For a Given Data Rate, We Would Expect That a
  Greater Signal Strength Would Improve The Ability
  To Correctly Receive Data In The Presence of
  Noise.
• Key Parameter (S/N).
• Theoretical Maximum Only Much Lower Rate is
  Achievable.
• Only Assume Thermal Noise.
• Capacity --- Error Free Transmission.

32
Relation Between Data Rate, Noise, and Error.

• Noise Can Corrupt 1 or More Bits.
• If The Data Rate is Increased, Then The Bits
  Become Shorter', So More Bits Are Affected By a
  Given Pattern of Noise.
• Thus, At a Given Noise Level, The Higher The Data
  Rate, The Higher The Error Rate.

33
Nyquist's Result (Assumed Noiseless Channel)

• Maximum Data Rate 2 H log2V bits/sec.
• For a System With Bandwidth H, The Maximum Data
  Rate Using Binary Signaling Elements (2 Voltage
  Levels) is 2H. So, For H 3100 Hz, C 6200
  bps
• Now, Suppose The Signal Has 8 Discrete Levels We
  Have
• C 2 (3100Hz) log2(8) bits/sec
• 18,600 bps

34
Nyquist's Result (Assumed Noiseless Channel)

• Note
• 1. An Increase in Data Rate Increases Bit Error
  Rate.
• 2. An Increase in S/N Decreases Bit Error Rate.
• 3. An Increase in Bandwidth Allows An Increase in
  Data Rate.

35
Nyquist's Result (Assumed Noiseless Channel)

• Noise figure
• Types of Noise
• Thermal Noise
• Intermodulation Noise
• Crosstalk
• Impulse Noise

36
Local Network Transmission Media

• Baseband Coaxial Cable
• Digital Signaling
• Entire Bandwidth Consumed By Signal
• Bidirectional Signal Inserted at Any Point
  Propagates in Both Directions
• Generally Uses Special-Purpose 50W Cable
• Broadband Coaxial Cable
• Analog Signaling
• FDM Possible
• Unidirectional
• Uses Standard 75 W CATV Cable

37
Transmission Media

• Magnetic Media
• Magnetic Tape
• Floppy Disk
• Twisted Pair (Most Common)
• Used
• Telephone System
• Networks
• Note Can Run Several Km Without Amplification
• Either Digital or Analog Data
• Bandwidth Depends on Thickness of The Wire and
  The Distance

38
Baseband Coax

• Bandwidth is a Function of The Cable Length.
  eg. 1km Þ 10Mbps
• Used For
• LANs
• Telephone System
• Connecting to Computers
• T Junction
• Vampire TAP
• Signaling
• Straight Binary
• Manchester Encoding
• Diff. Manchester Encoding

39
Broadband Coax (Several Channels)

• Note Can Be Used Up to 300MHz, To Support a Data
  Rate of 150Mbps.
• Types of Broadband System
• Dual Cable
• Midsplit Cable
• Note Both Use a Device, Headend
• Broadband Requires Skilled Radio Freq. Engineers
  to Plan The Cable and Amplifier Layout and
  Install System.

40
Which Media?

• Twisted Pair
• Most Cost Effective
• For Single Building, Low Traffic LAN
• Cable
• Best For High Traffic, Lots of DP Devices.
• Fiber
• Many Advantages, Cost-Effectiveness Improvements
  Needed.
• Microwave, Laser, Infrared
• Good Choices For Point-to-Point Links Between
  Buildings.

41
Three Different Encoding Techniques
42
Fiber Optics

• Three Components
• Transmission Medium
• Light Source (LED)
• Detector (Photodiode)
• Unidirectional System That Accepts an Electrical
  Signal, Converts Transmit It By Light Pulses,
  and Then Reconverts The Output to An Electrical
  Signal at The Receiving End.
• Multimode Fiber
• Single Mode (Up to 1000 Mbps)

43
Fiber Optics (cont.)

• (a) Three examples of a light ray from inside a
  silica fiber impinging on the air/silica boundary
  at different angles. (b) Light trapped by total
  internal reflection.

44
Fiber Optics (cont.)

• A fiber optic ring with active repeaters

45
Fiber Optics (cont.)

• A passive star connection in a fiber optics
  network

46
Telephone System

• (a) Fully interconnected network. (b) Centralized
  switch. (c) Two level hierarchy.

47
Example of Circuit Route

• Typical circuit route for a medium-distance call.

48
Modems

• Transforms a Digital Bit Stream Into an Analog
  Signal.
• Related Terms
• Modulation -- The Process of Varying Certain
  Characteristics of a Signal, Called a Carrier.
• Carrier -- A Continuous Frequency Capable of
  Being modulated with a second signal (Information
  Carrying).
• Note Signals Used at Local Loops Are DC,
  Limited by Filters to The Frequency Range 300 Hz
  to 3k Hz. This is Too Slow For Digital Signaling.
  Therefore, AC Signaling is Used.

49
AC Signalings

• A Continuous Tone in The Range of 1000Hz to
  2000Hz is Introduced (Sine Wave Carrier)
• Now, We Must Use An Encoding Technique,
  Modulation (An Operation On 1 or More of The
  Three Characteristics of a Carrier Signal)
• Amplitude (ASK)
• Frequency (FSK)
• Phase (PSK)
• This Produces a Signal Which Occupies a Bandwidth
  Centered on The Carrier Frequency.

50
AC Signalings (cont.)

• Note
• ASK -- On Voice Grade, Up to 1200 bps Used Over
  Fiber.
• FSK -- Less Susceptible to Error, Up to 1200 bps.
  Can Be Used For Higher Frequencies.

51
AC Signalings (cont.)

• ASK 2 Different Binary Values Are Represented By
  2 Different Amplitudes of The Carrier Frequency.
• FSK 2 Different Binary Values Are Represented By
  2 Different Frequencies Near The Carrier
  Frequency Offset From The Carrier By Equal But
  Opposite Amounts.
• PSK The Phase of The Carrier Signal is Shifted
  to Represent Data. A Binary 0 Þ Sending A Signal
  Burst of The Same Phase as The Previous Phase.
  A Binary 1 Þ Sending A Signal Burst of
  Opposite Phase to The Preceding One.

52
AC Signalings (cont.)
(a) A binary signal (b) Amplitude
modulation (c) Frequency Modulation (d) Phase
modulation
53
AC Signalings (cont.)
(a) A talking to B (b) B talking to A
54
Encoding Techniques
55
Encoding Techniques (cont.)
(a) original signal
(b) PAM pulses
(c) PCM pulses
(d) PCM output
011001110001011110100 (d) PCM output
56
TDM

• Synchronization is Needed Over The Trunk Circuit
• Example
• Bell Telephone T1 Carrier System.
• 24TDM Channels,
• Sampling Rate of 8000 samples/sec.,
• 8 Pulses/Sample (7 Standard levels Plus 1 For
  Synchronization),
• Frame Consists of 24 8 192 Bits Plus 1 Extra
  Bit For Framing. Yielding 193 Bits Every 125
  msec., Gross Data of 1.544 Mbps (CCITT Standard).

57
TDM (cont.)
The Bell system T1 carrier (1.544 Mbps).
58
Wireless Transmission

• The Electromagnetic Spectrum-when electrons move,
  they create electromagnetic waves.
• By attaching an antenna to an electrical circuit,
  the electromagnetic waves can be broadcast
  efficiently received via receiver some distance
  away.
• In a vacuum, all electromagnectic waves travel at
  the same speed 3 (10)8 m/sec.

59
Wireless Transmission (Cont.)

• The radio, microwave, infrared, and visible
  portion of the spectrum can all be used for
  transmitting info by modulating the amplitude,
  frequency, or phase of the waves.
• The FCC allocates spectrum for AM and FM, TV,
  Cellular Phones, police, Military, Telephone
  Companies, Government, etc.

60
Radio Transmission

• Radio waves are omnidirectional. They are easy
  to generate, can travel long distances, penetrate
  buildings easily, thus widely used for
  communication (both indoor and outdoor).
• Typically frequency ranges from 30 MHZ to 1 GHZ.

61
Radio Transmission (Cont.)

• For digital data communication, the low frequency
  range implies that only lower data rates are
  achievable (i.e., in the kilobit rather than the
  megabit range).
• Example ALOHA, bandwidth 100kHz, data rate 9600
  bps.

62
Microwave Transmission

• Waves travel in a straight line (above 100 MHZ),
  and can be narrow focused.
• Transmitting receivers and transmitters must be
  accurately aligned.
• Microwave (two types) Terrestrial and Satellite
• Terrestrial typical antenna is parabola dish,
  about 10 ft in diameter, usually located at
  heights above the ground level.

63
Microwave Transmission (Cont.)

• Primary Uses
• long-haul telecommunication services, as an
  alternative to coaxial cable for transmitting TV
  and voice, short point-to-point link between
  buildings for closed-circuit TV or a data link
  between networks.
• Example Microwave Communications, Inc. (MCI)
• Common Frequency Range 2 to 40 GHz.

64
Satellites

• A Communication Satellite -- A microwave Relay
  Station, Used to Link 2 or More Ground-Based
  Microwave Transmitters/Receivers.
• Satellite Receives Transmissions On One Frequency
  Band (Uplink), Amplifies/Re- peats It on Another
  Frequency (Downlink).
• Frequency Bands -- Transponder Channels or
  Transponders.
• Altitude 36,000km, The Satellite Period is 24
  Hours.

65
Communication Satellite (Cont.)

• Uses
• TV Distribution (e.g., PBS).
• Long-distance telephone transmission.
• Private business networks.
• Mobile Satellite Service (FCC has allocated the L
  Band 1.65 GHz-Uplink 1.55 GHz-Downlink)

66
Communication Satellite (Cont.)

• Spacing Standard gt 4o Apart In The 4/6 GHz Band,
  gt 3o Spacing at 12/14 GHz.
• Optimum Frequency Range 1-10GHz.
• Point-to-Point Bandwidth 4/6 GHz.
• Round Trip Propagation Delay 240 - 300 ms.
• TDM Used For Accessing Channel.

67
Communication Satellite (Cont.)

• Point-to-point link via satellite microwave

68
Communication Satellite (Cont.)

• Broadcast link via satellite microwave

69
Communication Satellite (Cont.)

• A Two-antenna
• satellite (a)

70
Communication Satellite (Cont.)

• A Two-antenna
• satellite (b)

71
Encoding for satellite

• Typical Satellite Splits Its 500 MHz Bandwidth
  Over a Dozen Transponders, Each With a 36 MHz
  Bandwidth. Each Transponder can Encode a Single
  50Mbps Data Stream, 800 64Kbps Digital Voice
  Channels, or Other Combinations.
• Satellite vs Terrestrial
• T1 (1.544Mbps) vs 1000 Times This Via
  Rooftop-to-Rooftop Transmission.
• Fiber Has More Potential Bandwidth.

72
Transmission and Multiplexing

• FDM
• Effective Bandwidth of 3000 Hz (From 350 to 3350
  Hz) Can be theoretically divided into ten 300 Hz
  channels.
• Disadvantage Limited Number of Low-Bandwidth Can
  Be Multiplexed to Share A High-Bandwidth Circuit.
• Advantage Reliability and Simplicity of
  Equipment. Also, Bit-Level Synchronization is Not
  Needed.
• Note Filters Are Used At Both The Transmitting
  and receiving station to separate one frequency
  from another.
• TDM
• Divides The Channel Into Discrete Time Slot.

73
Multiplexing

• cosa cosb 1/2 cos(a b) cos(a - b)
• Note As shown in the equation above, multiplying
  two cosine functions yields a new signal with two
  new cosine components.
• s(t)cosa cosa s(t) (cosa)2 s(t) (1
  cos2a)/2
• s(t)/ 2 s(t) cos2a / 2
• Note By multiplying the original signal with a
  cosine function (i.e. carrier signal) twice, we
  get the original signal plus some additional
  signal. Multiplication is applied once in the
  transmitter and once in the receiver.

74
Example

• Let the original signal s(t) 4 cos (2p
  10t) 8 cos(2p 50t)
• Let the carrier signal be cos(2p 70t)
• Therefore, the result of the multiplication in
  the transmitter is
• s(t)cos(2p 70t) 2cos(2p 80t)
• 2cos(2p 60t)
• 4cos(2p 120t)
• 4cos(2p 20t)

75
Example (cont.)
Amplitude
70
4
4
2
2
Hz
0
20
60
80
120

• With a filter of 70 Hz and above, the signal
  between 0Hz and 70Hz will be erased. The new
  signal 2 cos(2p80t) 4cos(2p 120t) , which is
  shifted 70Hz of original signal, will be
  transmitted.

76
Hardware Diagram

77
Hardware Diagram (cont.)

78
Hardware Diagram (cont.)
Note The typical range of human voice is
between 300 and 3100 Hz. However, we wish to
allow for a range of 0 to 4 KHz, in order to
avoid signal interference
79
Example

• Telephone line with human voice (usually in the
  range 300 to 3100Hz)

80
Example (cont.)

81
Definition of Digital Signal Encoding Formats

• Nonreturn-to-Zero-Level (NRZ-L) 0 high
  level 1 low level
• Nonreturn to Zero Inverted (NRZI) 0 no
  transition at beginning of interval (one bit
  time) 1 transition at beginning of
  interval
• Bipolar-AMI 0 no line signal
  1 positive or negative level, alternating for
  successive ones

82
Definition of Digital Signal Encoding Formats
(cont.)

• Pseudoternary 0 positive or negative
  level, alternating for successive zeros
  1 no line signal
• Manchester 1 transition from high to
  low in middle of interval 0 transition
  from low to high in middle of interval
• Differential Manchester Always a transition in
  middle of interval 0 transition at
  beginning of interval 1 no transition at
  beginning of interval

83
Definition of Digital Signal Encoding Formats
(cont.)

• B8ZS Same as bipolar AMI, except that any
  string of eight zeros is replaced by a string
  with two code violations
• HDB3 Same as bipolar AMI, except that any
  string of four zeros is replaced by a string
  with one code violation

84
Definition of Digital Signal Encoding Formats
(cont.)
85
Interfacing

• Most Digital Data Processing Devices Have Limited
  Data Transmission Capability. Typically Generate
  NRZ-L Digital Signals. The Distance Across Which
  They Can Transmit Data is Also Limited. Hence,
  The More Common Case is

Bit-serial transmission medium
Signal and control leads
Digital data transmitter/ receiver
Transmission line interface device
Transmission line interface device
Digital data transmitter/ receiver
.
.
.
.
.
.
.
.
Data terminal equipment(DTE)
Data circuit-terminating equipment (DCE)
Generic interface to transmission medium
86
Interfacing (cont.)

• DTE Data Terminal Equipment
• Examples terminals, workstations
• DTE's are rarely directly connected to
  transmission media such as coaxial or fibers.
• Reason?
• Signal Strength
• Bit-serial Transmission Media are widely used
• Solution DCE (Data Circuit-terminating
  Equipment)

87
Characteristics of Interfacing

• Four Characteristics
• mechanical DTE/DCE connectors
• electrical voltage, coding schemes
• functional assignment of meanings to interchange
  wires
• procedural protocol (state transmissions)
• Most Popular Standards
• EIA-232-D (de facto)
• X.21 (CCITT Physical Layer under X.25)
• ISDN Physical Interface

88
EIA-232

• EIA Electronic Industries Association
• Variations 232-C(1969), 232-D(1987)
• Target Media voice-grade telephone lines
• Connector DB25, a 25-pin connector standard
• Signaling Digital Signals are used
• Data -3V bit 1, gt 3V bit 0
• Control -3V OFF, gt 3V On
• Data Rate 20kbps

89
EIA-232 (cont.)

• Interchange Circuits
• Data(4) Support full-duplex traffic
• Control(15) transmission, testing, quality
  monitoring
• Timing(3)
• Ground/Shield(2)
• The procedural definition concerns
• call set-up
• data transfer
• call clearing

90
X.25 (international Standard)

• Defines the Interface Between the Host (DTE) and
  the Carrier's Equipment (DCE)
• X.25 Has 3 Layers
• Physical (X.21 and X.21 bis)
• Frame
• Packet
• Will Look at Digital Interface (X.21). 15 pins

91
Interfacing

• RS-232C
• RS-449/442-A/423-A
• X.21 (15 pins)

92
Interfacing (cont.)

• Signal lines used in X.21

T (Transport)
C (Control)
R (Receive)
I (Indication
DCE
DTE
S (Signal, i.e. bit timing)
B (Byte timing) optional
Ga (DTE common return)
G (Ground)
93
Interfacing (cont.)

• An example of X.21 usage.
• DTE DCE
• Step C I Event in telephone analog sends
  on T sends on R
• 0 Off Off No connection-line idle T
  1 R 1
• 1 On Off DTE picks up phone T 0
• 2 On Off DCE gives dial tone
  R...
• 3 On Off DTE dials phone number T
  address
• 4 On Off Remote phone rings
  Rcall progress
• 5 On On Remote phone picked up
  R 1
• 6 On On Conversation
  T data R data
• 7 Off On DTE says goodbye T
  0
• 8 Off Off DCE says goodbye
  R 0
• 9 Off Off DCE hangs up
  R 1
• 10 Off Off DTE hangs up
  T 1

94
SONET / SDH

• SONET(Synchronous Optical NETwork)/ SDH(Synchrono
  us Digital Hierarchy)
• Motivated by break up of ATT
• Local telephone company had to connect to
  multiple long distance carriers
• Standards needed
• Started in Bell-Core
• Joined by CCITT

95
SONET Design Goals

• Enable different carriers to interwork
• Unify the U.S., European, and Japanese digital
  systems
• Provide a way to multiplex digital channels
  together
• Provide support for operations, administrations,
  and maintenance.
• Note SONET (A Synchronous system uses TDM)

96
A SONET path
Source Multiplexer
Destination Multiplexer
Repeater
Multiplexer
Repeater
Section
Section
Section
Section
Line
Line
Path
97
Basic SONET Frame

• 810 bytes put out every 125msec.
• 8000 frames/sec (matches the sampling rate of the
  PCM channels used in telephone system
• 8 810 6480 bits are transmitted, and 8000
  times per sec Þ Gross data rate 51.84Mbps, STS-1
  (Synchronous Transport Signal). All SONET trunks
  are multiples of STS-1.
• Hence, we have OC-3, OC-12, etc.
• View a sonet as a rectangle of bytes (90 9).
  After factoring out overhead, 87 9 8 8000
  50.112 Mbps user data.

98
Two back-to-back SONET frames
3 Columns for overhead
87 Columns
Sonet frame (125msec)
.....
9 Rows
Sonet frame (125msec)
Section overhead
Line overhead
Path overhead
SPE
99
Multiplexing in SONET
T1
Electro-optical converter
T1
Scrambler
STS-1
STS-3

T1
STS-1
STS-3
STS-12
OC-12
T3
STS-3
T3
STS-1
STS-3
31 Multiplexer
41 Multiplexer
100
SONET and SDHmultiplex rates

• SONET SDH Data rate(Mbps)
• Electrical Optical Optical Gross SPE User
• STS-1 OC-1 51.84 50.112
  49.536
• STS-3 OC-3 STM-1 155.52
  150.336 148.608
• STS-9 OC-9 STM-3 466.56
  451.008 445.824
• STS-12 OC-12 STM-4 622.08
  601.344 594.432
• STS-18 OC-18 STM-6 933.12
  902.016 891.648
• STS-24 OC-24 STM-8 1244.16
  1202.688 1188.864
• STS-36 OC-36 STM-12 1866.24
  1804.032 1783.296
• STS-48 OC-48 STM-16 2488.32
  2405.376 2377.728

101
Information Switching
Physical copper connection set up when call is
made.
Switching Office
packets queued up for subsequent transmission
Computer
(a) Circuit switching (b) Packet switching
102
Information Switching (cont.)(Timing of events)
(a) Circuit Sw. (b) Message Sw.
(c) Packet Sw.
103
Circuit Switching

• Circuit Switching Dedicated Path Between 2
  Stations.
• Circuit Establishment
• Data Transfer
• Circuit Disconnect
• Advantage Good for Applications Which Require
  Continuous Data Flow (e.g. Voice)
• Disadvantage Unused Bandwidth

104
Message Switching

• Message Switching (Store-And-Forward)
• Exchange Blocks of Data Between IMPs With no
  Limit on Block size.
• Disadvantage Large Buffer Required and IMP-IMP
  Line May be Tied Up Too Long.

105
Packet Switching

• Packet Switching
• Long Message are Subdivided into ShortPackets,
  and Packets are Transmitted Between IMPs.
• Advantage Suited for Handling Interactive
  Traffic
• Disadvantage Proper Routing Problem

106
ISDN Concept

• Principles of ISDN
• Support of Voice and Non-Voice Applications
• Support for Switched and Nonswitched Applications
• Reliance on 64Kbps Connections
• Intelligence in the Network
• Layered Protocol Architecture
• Variety of Configuration

107
Evolution of ISDN

• Evolution From Telephone IDN's
• Transition of One or More Decades
• Use of Existing Networks
• Interim User Network Arrangements
• Connections at Other Than 64kbps

108
Objectives of ISDN

• Standardization
• Transparency
• Separation of Competitive Function
• Leased and Switched Services
• Cost-Related Tariffs
• Smooth Migration
• Multiplexed Support

109
Comments of Service

• Videotex - Interactive Access to Remote Database.
  Example - On-line Telephone Book
• Teletex -- A Form of Electronic Mail For Home and
  Business Use Note May Need Written Copies
  Via Fax
• Telemetry or Alarm Example -
  Electronic Meter Reading, - Smoke Detectors

110
Candidate Services for Integration

• Service
• Bandwidth Telephony Data Text Image
• Digital Telephone Packet-switched Telex
• voice Circuit-switched Teletex
• (64Kbps) Leased Leased circuits Leased
  circuit
• circuits Telemetry Videotex
• Information Funds transfer Facsimile
• retrival (by
• voice and Information Information Informat
  ion
• synthesis) retrieval retrieval
  retrieval
• Mailbox Mailbox Surveillance
• Electronic mail Electronic mail
• Alarms

111
Candidate Services for Integration

• Service
• Bandwidth Telephony Data Text Image
• Wide Music High-speed TV
• band Computer conferencing
• (gt64Kbps) Communication Teletex
• Videophone
• Cable TV
• distribution

112
Comments on ISDN Architecture

• Digital Bit Pipe (64Kbps)
• Support Multiple Independent Channels by TDMing
  of The Bit Stream
• Two Principal Standards - Low Bandwidth (Home
  Use) - High Bandwidth (Businesses)

113
Comments of Service
114
ISDN Architecture Continue

• NT1 -- Network Terminating Device, Connected to
  The ISDN Exchange.
• Has Connectors For a Passive Bus Cable
• Up to 8 ISDN Devices can be Connected
• Has Electronics For Network Adm., Monitoring,
  Performance, Contention Resolution, \etc

115
ISDN Architecture Continue

• NT2 (PBX) -- Needed by Businesses to Handle More
  Traffic Simultaneously
• Need Adapter For Non-ISDN Devices Example
  RS-232C Terminal
• CCITT Has Defined Four Reference Points R, S,
  T, and U U is Two-wire Copper Twisted Pair,
  But Will Be Replaced By Fiber.

116
ISDN Architecture Continue
(a) Example ISDN system for home use
117
ISDN Architecture Continue
(b) Example ISDN system with a PBX for use in
large business
118
Block Structure of a digital PBX
Line module for ISDN devices
Control unit
Trunk module
Line module for RS-232-C terminals
To ISDN exchange
Switch
Line module for analog telephones
Service unit
119
ISDN Architecture Continue
Interface
Interface
Customers equipment
Carriers equipment

• A - 4kHz analog telephone channel
• B - 64 kbps digital PCM channel for voice or data
• C - 8 or 16 kbps digital channel

120
ISDN Architecture Continue

• D - 16 or 64 kbps digital channel for out-of-band
  signaling
• E - 64 kbps digital channel for internal ISDN
  signaling
• H - 384, 1536, or 1920 kbps digital channel

121
ISDN Architecture Continue

• It is not CCITT's intention to allow an arbitrary
  combination of channels on the digital bit pipe.
  Three combinations have been standardized so far
• 1. Basic rate 2B 1D
• 2. Primary rate 23B 1D (U.S. and Japan) or 30B
  1D (Europe)
• 3. Hybrid 1A 1C