Physical Layer Concerned with Transmission of Unstructured Bit

Physical Layer • Concerned with Transmission of Unstructured Bit Stream Over Physical Medium. m • Data Transmission: Input Device g(t) Transmitter Source System s(t) Medium r(t) Simplified Communication Block Diagram Receiver g’(t) Output Device Destination System m’ 1

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. 2

Frequency, Spectrum, and Bandwidth: Signal • • Continuous (or Analog) Discrete (or Digital) Periodic -- Shape is Repeated Aperiodic -- Shape is Not Repeated 3

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. 4

Frequency, Spectrum, and Bandwidth: (cont. ) • All Signals Used In These Examples Will Be Sinusoidal & Can Be Described By; V(t) = A sin(2 pft + q) where A is Maximum Amplitude, f is Frequency, t is Instant of Time, and q is Phase. 5

Examples: Sine wave representation of a signal (periodic signal) Amplitude A Time 1 Cycle 0 o 180 o 360 o Aperiodic Analog Signal (e. g. , Human Voice) Amplitude +10 V Aperiodic Analog Signal (e. g. , Human Voice) Time 6

Examples: (cont. ) Aperiodic Discrete Signal Amplitude +5 V Time -5 V Aperiodic Discrete Signal Continuous Signal Amplitude +3 V 90 o 180 o 360 o 0 o 90 o Cycle 0 o -3 V Time 270 o Period Continuous Signal 7

Examples: (cont. ) Note: – A period represents one full cycle – A cycle represents 360 o (2 p 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 = 2 pft 8

Examples: (cont. ) Discrete Signal(Digital Representation of Sine Wave) Amplitude +3 V Time -3 V Discrete Signal (Digital Representation of Sine Wave) Note: Both Examples Have Frequency of 3 Hz or (3(2 p) = 3(360 o) = 1080 o 9

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(2 pft) + 1/3 sin 3(2 pf)t + 1/5 sin 5(2 pf)t The Components of This Signal Are Just Sine Waves of Frequencies f, 3 f, and 5 f. Using Fourier Analysis, It Can Be Shown That Any Signal Is Made Up of Components at Various Frequencies, Where Each Component is a Sinusoid. 10

Frequency Domain Concepts (cont. ) s(t) Frequency Domain For Signal 1 f 3 f 1 5 f 1 s(t) = sin(2 pft) + 1/3 sin 3(2 pf)t + 1/5 sin 5(2 pf)t 11

Frequency Domain Concepts (cont. ) 1 Amp 0. 5 0 -0. 5 -1 0 Time sin(2 pf 1)t 12

Frequency Domain Concepts (cont. ) Amp 1 0. 5 0 -0. 5 -1 0 Time 1/3 sin 3(2 pf 1)t 13

Frequency Domain Concepts (cont. ) Amp 1 0. 5 0 -0. 5 -1 0 Time 1/5 sin 5(2 pf 1)t 14

Frequency Domain Concepts (cont. ) sin(2 pf 1)t + 1/3 sin 3(2 pf 1)t + 1/5 sin 5(2 pf 1)t 15

Frequency Domain Concepts (cont. ) • Spectrum of Signal -- range of frequencies. From example above: spectrum extends from f 1 to 5 f 1. • Bandwidth -- Width of Spectrum or 4 f 1 • 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. . . 16

Frequency Domain Concepts (cont. ) The Pulse Duration is 1/ (2 f 1), Thus The Data Rate is 2 f 1 Bits Per Second. For f 1 = 1000 Hz, The Data Rate = 2000 bps & The Bandwidth = 4000 Hz 17

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: 18

Fourier Series (cont. ) 0 for k ¹ n T/2 for k = n sin(2 pkft) for f = 1/2 p , or T = 2 p with different k 19

Fourier Series (cont. ) Multiplication of two sine waves with different k 20

Fourier Series (cont. ) 21

Fourier Series (cont. ) 22

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(x 1) - cos(x 2) + cos(x 3) cos(x 4) and sin(x 1) - sin(x 2) + sin(x 3) - sin(x 4) are 4 and -4, respectively. Hence, an and bn converge to zero when n becomes infinite. 23

Fourier Series (cont. ) A binary signal and its rms Fourier amplitudes. amplitude 1 0 1 1 0 0 0 1 0 0. 5 0. 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Successive approximations to the original signal 1 1 harmonic 0 1 Time Harmonic number 24

Fourier Series (cont. ) Successive approximations to the original signal 1 2 harmonies 0 1 2 1 4 harmonies 0 1 2 3 4 1 8 harmonies 0 1 Time 2 3 4 5 6 7 8 Harmonic number 25

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. 26

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: 27

Example (cont. ) Bps T(msec) 300 600 1200 2400 4800 9600 19200 38400 26. 67 13. 33 6. 67 3. 33 1. 67 0. 83 0. 42 0. 21 First Harmonic (Hz) sent 37. 5 80 75 40 150 20 300 10 600 5 1200 2 2400 1 4800 0 28

Maximum Data Rate of a Channel • Signal-to-Noise Ratio Signal Power (S/N)d. B = 10 log 10 Noise Power Expresses The Amount In Decibels(d. B) That The intended signal exceeds the noise level. A high S/N Þ High Quality Signal & a Low Number of Required Intermediate Repeaters. 29

Maximum Data Rate of a Channel (cont. ) • Shannon's Major Result: Maximum Number of Bits/Sec = H log 2 (1+S/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 = 30 d. B or a Ratio of 1000: 1 Þ C = 3100 log 2 (1 + 1000) = 30, 894 bps Theoretical Maximum 30

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. 31

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. 32

Nyquist's Result (Assumed Noiseless Channel) Maximum Data Rate = 2 H log 2 V bits/sec. For a System With Bandwidth H, The Maximum Data Rate Using Binary Signaling Elements (2 Voltage Levels) is 2 H. So, For H = 3100 Hz, C = 6200 bps Now, Suppose The Signal Has 8 Discrete Levels; We Have C = 2 (3100 Hz) log 2(8) bits/sec = 18, 600 bps 33

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. 34

Nyquist's Result (Assumed Noiseless Channel) Noise figure Types of Noise – – Thermal Noise Intermodulation Noise Crosstalk Impulse Noise 35

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 50 W Cable • Broadband Coaxial Cable – – Analog Signaling FDM Possible Unidirectional Uses Standard 75 W CATV Cable 36

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 37

Baseband Coax • Bandwidth is a Function of The Cable Length. eg. 1 km Þ 10 Mbps Used For: – LANs – Telephone System • Connecting to Computers: – T Junction – Vampire TAP • Signaling: – Straight Binary – Manchester Encoding – Diff. Manchester Encoding 38

Broadband Coax (Several Channels) Note: Can Be Used Up to 300 MHz, To Support a Data Rate of 150 Mbps. + 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. 39

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. 40

Three Different Encoding Techniques 41

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) 42

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. 43

Fiber Optics (cont. ) A fiber optic ring with active repeaters 44

Fiber Optics (cont. ) A passive star connection in a fiber optics network 45

Telephone System (a) Fully interconnected network. (b) Centralized switch. (c) Two level hierarchy. 46

Example of Circuit Route Typical circuit route for a medium-distance call. 47

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 3 k Hz. This is Too Slow For Digital Signaling. Therefore, AC Signaling is Used. 48

AC Signalings A Continuous Tone in The Range of 1000 Hz to 2000 Hz 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. 49

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. 50

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. 51

AC Signalings (cont. ) (a) A binary signal (b) Amplitude modulation (c) Frequency Modulation (d) Phase modulation 52

AC Signalings (cont. ) (a) A talking to B (b) B talking to A 53

Encoding Techniques • Amplitude-shift keying (ASK) A cos(2 pfct + qc) binary 1 s(t) = 0 binary 0 Frequency-shift keying (FSK) A cos(2 pf 1 t + qc) binary 1 s(t) = A cos(2 pf 2 t + qc) binary 0 Phase-shift keying (PSK) A cos(2 pfct + p) binary 1 s(t) = A cos(2 pfct) binary 0 54

Encoding Techniques (cont. ) (a) original signal (b) PAM pulses (c) PCM pulses 011001110001011110100 (d) PCM output 55

TDM • Synchronization is Needed Over The Trunk Circuit • Example: Bell Telephone T 1 Carrier System. 24 TDM 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). 56

TDM (cont. ) The Bell system T 1 carrier (1. 544 Mbps). 57

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. 58

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. 59

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. 60

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 100 k. Hz, data rate 9600 bps. 61

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. 62

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. 63

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, 000 km, The Satellite Period is 24 Hours. 64

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) 65

Communication Satellite (Cont. ) • Spacing Standard: > 4 o Apart In The 4/6 GHz Band, & > 3 o Spacing at 12/14 GHz. • Optimum Frequency Range 1 -10 GHz. • Point-to-Point Bandwidth: 4/6 GHz. • Round Trip Propagation Delay: 240 - 300 ms. • TDM Used For Accessing Channel. 66

Communication Satellite (Cont. ) Point-to-point link via satellite microwave 67

Communication Satellite (Cont. ) Broadcast link via satellite microwave 68

Communication Satellite (Cont. ) A Two-antenna satellite (a) 69

Communication Satellite (Cont. ) A Two-antenna satellite (b) 70

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 50 Mbps Data Stream, 800 64 Kbps Digital Voice Channels, or Other Combinations. Satellite vs Terrestrial – T 1 (1. 544 Mbps) vs 1000 Times This Via Rooftop -to-Rooftop Transmission. – Fiber Has More Potential Bandwidth. 71

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. 72

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+ cos 2 a)/2] = s(t)/ 2 + s(t)× cos 2 a / 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. 73

Example Let the original signal s(t) = 4 cos (2 p 10 t) + 8 cos(2 p 50 t) Let the carrier signal be cos(2 p 70 t) Therefore, the result of the multiplication in the transmitter is: s(t)cos(2 p 70 t) = 2 cos(2 p 80 t) + 2 cos(2 p 60 t) + 4 cos(2 p 120 t) + 4 cos(2 p 20 t) 74

Example (cont. ) Amplitude 70 4 4 2 0 20 60 2 80 120 Hz With a filter of 70 Hz and above, the signal between 0 Hz and 70 Hz will be erased. The new signal 2 cos(2 p 80 t) + 4 cos(2 p 120 t) , which is shifted 70 Hz of original signal, will be transmitted. 75

Hardware Diagram ¶ 76

Hardware Diagram (cont. ) ¶ 77

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 78

Example: Telephone line with human voice (usually in the range 300 to 3100 Hz) ¶ 79

Example: (cont. ) ¶ 80

Definition of Digital Signal Encoding Formats • Nonreturn-to-Zero-Level (NRZ-L) = high level 0 1 = low • Nonreturn to Zero Inverted (NRZI) = no transition at beginning of interval (one bit 1 = transition at beginning of interval 0 time) • Bipolar-AMI 0 = no line signal 1 = positive or negative level, alternating for successive ones 81

Definition of Digital Signal Encoding Formats (cont. ) • Pseudoternary 0 • Manchester 1 = positive or negative level, alternating for successive zeros 1 = no line signal = 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 82

Definition of Digital Signal Encoding Formats (cont. ) • B 8 ZS Same as bipolar AMI, except that any string of eight zeros is replaced by a string with two code violations • HDB 3 Same as bipolar AMI, except that any string of four zeros is replaced by a string with one code violation 83

Definition of Digital Signal Encoding Formats (cont. ) 84

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: Signal and control leads Digital data transmitter/ receiver . . Data terminal equipment(DTE) Bit-serial transmission medium Transmission line interface device . . Digital data transmitter/ receiver Data circuit-terminating equipment (DCE) Generic interface to transmission medium 85

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) 86

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 87

EIA-232 • • • EIA: Electronic Industries Association Variations: 232 -C(1969), 232 -D(1987) Target Media: voice-grade telephone lines Connector: DB 25, a 25 -pin connector standard Signaling: Digital Signals are used – Data: £ -3 V = bit 1, > +3 V = bit 0 – Control: £ -3 V = OFF, > +3 V = On – Data Rate: £ 20 kbps 88

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 89

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 90

Interfacing • RS-232 C • RS-449/442 -A/423 -A • X. 21 (15 pins) 91

Interfacing (cont. ) Signal lines used in X. 21 T (Transport) C (Control) R (Receive) DTE I (Indication DCE S (Signal, i. e. bit timing) B (Byte timing) optional Ga (DTE common return) G (Ground) 92

Interfacing (cont. ) An example of X. 21 usage. Step C 0 1 2 3 4 5 6 7 8 9 10 Off On On On Off Off I Event in telephone analog Off Off Off On On On Off Off No connection-line idle DTE picks up phone DCE gives dial tone DTE dials phone number Remote phone rings Remote phone picked up Conversation DTE says goodbye DCE hangs up DTE sends on T T=1 T=0 DCE sends on R R=1 R=“+++. . . +” T = address T = data T=0 R=call progress R=1 R = data R=0 R=1 T=1 93

SONET / SDH • SONET(Synchronous Optical NETwork)/ SDH(Synchronous Digital Hierarchy) – Motivated by break up of AT&T – Local telephone company had to connect to multiple long distance carriers – Standards needed • Started in Bell-Core • Joined by CCITT 94

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) 95

A SONET path Source Multiplexer Repeater Section Multiplexer Section Repeater Section Line Destination Multiplexer Section Line Path 96

Basic SONET Frame • 810 bytes put out every 125 msec. • 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. 84 Mbps, 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 ´ 8000 = 50. 112 Mbps user data. 97

Two back-to-back SONET frames 3 Columns for overhead 87 Columns Sonet frame (125 msec) . . . 9 Rows Sonet frame (125 msec) Section overhead Line overhead Path overhead SPE 98

Multiplexing in SONET T 1 T 1 T 3 · ·· STS-1 Electro-optical Scrambler converter STS-3 STS-12 OC-12 STS-3 T 3 STS-1 STS-3 3: 1 Multiplexer 4: 1 Multiplexer 99

SONET and SDH multiplex rates SONET SDH Electrical Optical STS-1 STS-3 STS-9 STS-12 OC-1 OC-3 OC-9 OC-12 STM-1 STM-3 STM-4 STS-18 STS-24 STS-36 STS-48 OC-18 OC-24 OC-36 OC-48 STM-6 STM-8 STM-12 STM-16 Data rate(Mbps) Gross 51. 84 155. 52 466. 56 622. 08 SPE User 50. 112 150. 336 451. 008 601. 344 49. 536 148. 608 445. 824 594. 432 933. 12 902. 016 891. 648 1244. 16 1202. 688 1188. 864 1866. 24 1804. 032 1783. 296 2488. 32 2405. 376 2377. 728 100

Information Switching Office Computer Physical copper connection set up when call is made. packets queued up for subsequent transmission (a) Circuit switching (b) Packet switching 101

Information Switching (cont. ) (Timing of events) (a) Circuit Sw. (b) Message Sw. (c) Packet Sw. 102

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 103

Message Switching • Message Switching (Store-And-Forward): Exchange Blocks of Data Between IMPs With no Limit on Block size. Disadvantage: Large Buffer Required and IMPIMP Line May be Tied Up Too Long. 104

Packet Switching • Packet Switching: Long Message are Subdivided into Short. Packets, and Packets are Transmitted Between IMPs. Advantage: Suited for Handling Interactive Traffic Disadvantage: Proper Routing Problem 105

ISDN Concept • Principles of ISDN • Support of Voice and Non-Voice Applications • Support for Switched and Nonswitched Applications • Reliance on 64 Kbps Connections • Intelligence in the Network • Layered Protocol Architecture • Variety of Configuration 106

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 64 kbps 107

Objectives of ISDN • Standardization • Transparency • Separation of Competitive Function • Leased and Switched Services • Cost-Related Tariffs • Smooth Migration • Multiplexed Support 108

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 109

Candidate Services for Integration Service Bandwidth Telephony Data Text Image Digital voice Telephone Packet-switched Telex Circuit-switched Teletex (64 Kbps) Leased circuits Information retrival (by voice and synthesis) Leased circuits Telemetry Funds transfer Leased circuit Videotex Information retrieval Mailbox Electronic mail Alarms Mailbox Electronic mail Surveillance Facsimile 110

Candidate Services for Integration Service Bandwidth Telephony Data Wide band High-speed Computer TV conferencing Communication Teletex (>64 Kbps) Music Text Image Videophone Cable TV distribution 111

Comments on ISDN Architecture • Digital Bit Pipe (64 Kbps) • Support Multiple Independent Channels by TDMing of The Bit Stream • Two Principal Standards - Low Bandwidth (Home Use) - High Bandwidth (Businesses) 112

Comments of Service 113

ISDN Architecture Continue • NT 1 -- 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 114

ISDN Architecture Continue • NT 2 (PBX) -- Needed by Businesses to Handle More Traffic Simultaneously – Need Adapter For Non-ISDN Devices Example: RS-232 C 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. 115

ISDN Architecture Continue (a) Example ISDN system for home use 116

ISDN Architecture Continue (b) Example ISDN system with a PBX for use in large business 117

Block Structure of a digital PBX Line module for ISDN devices Line module for RS-232 -C terminals Control unit Trunk module Switch To ISDN exchange Line module for analog telephones Service unit 118

ISDN Architecture Continue Interface Customer’s equipment Carrier’s equipment • A - 4 k. Hz analog telephone channel • B - 64 kbps digital PCM channel for voice or data • C - 8 or 16 kbps digital channel 119

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 120

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: 2 B + 1 D • 2. Primary rate: 23 B + 1 D (U. S. and Japan) or 30 B + 1 D (Europe) • 3. Hybrid: 1 A + 1 C 121