Some Definitions According to International Telecommunications Union (ITU), defined as transmission speed higher than 1.5 Mb/s. Any connection fast enough

Some Definitions

• According to International Telecommunications Union (ITU), defined as transmission speed higher than 1.5 Mb/s.

• Any connection fast enough to support interactive multimedia.

• Any communications method that multiplexes a number of individual channels onto a single, high-speed channel.

Broadband

Wireline Communication

• Network connection is transmitted through physical media (copper or optical fiber).

• Data is usually sent unmodulated.

• Multiple channels are aggregated via time-division multiplexing.

Wireless Communication

• Data is transmitted over the air, modulated onto a carrier signal (e.g., FDMA, CDMA)

EECS 270C Week 1 1Prof. M. Green

Analog signal:

Bit rate is b/Ts

Digital Telephony Example

000

001

010

011

100

101

110

111

Ts

Ts

Digitized signal:(b = 3)

1 0 0 1 0 1 1 1 0


For digital telephony:

Voice quality requires ~4 kHz bandwidthTs = 125 µs (fs = 8 kHz) b = 8

1 0 0 1 0 1 1 1 0

b bits in Ts

8 kHz X 8 bits (bit rate 64 kb/s) gives “DS0” signal.

User-to-network interface:

24 X DS0

Framing bit

DS1 channel DS1 bits in each TS: 24 X 8 + 1 = 193DS1 bit rate: 193 / 125 µs = 1.544 Mb/s

28 X DS1

188 Framing bits

DS3 channel DS3 bits in each TS: 28 X 193 + 188 = 5592DS3 bit rate: 5592 / 125 µs = 44.736 Mb/s

“T-carrier” system: T1 line carries a DS1 signalT3 line carries a DS3 signal

MUX

MUX


Ethernet

• Invented in 1973 at Xerox PARC

• IEEE 802.3 standard (10 Mb/s) created in 1985

• Used to create Local-Area Networks (LANs)

IEEE ethernet identifiers:

10 BASE 5 -- (10 Mb/s, baseband transmission, 500m max. cable length)

1000 BASE T -- (1 Gb/s, baseband transmission, twisted-pair)

Gigabit/10 Gigabit Ethernet (IEEE Standard 802.3):

1 Gb/s links can be transmitted over twisted-pair copper

10 Gb/s links can be transmitted over copper (short lengths) or fiber.


Networking

Wide-Area Network (WAN):multiple LANs connected over a wide geographical area -- made possible by very high-speed optical fibers

Metropolitan-Area Network (MAN):Network connection within a metropolitan area

Storage-Area Network (SAN):Uses networking techniques to manage very large amounts of data


Synchronization Methods

TX RX

CMURef.

clock

only data, not clock, transmitted

Plesiochronous Digital Hierarchy: • Different parts of network operate at frequencies that are very close (~50 ppm), but

not identical. • Such systems require additional functions to compensate for the mismatch by

repeating or adding bits.• Reference clocks generated locally (usually with crystal oscillator).• Used in Ethernet protocol.

Synchronous Digital Hierarchy: • All parts of network operate at identical frequencies, accomplished by synchronizing

all Reference clocks to the “Stratum” global system of atomic clocks.• Additional functions not required, but jitter requirement is very rigorous.• Used in SONET/SDH protocol.


Other Protocols for High-Speed Networks

Synchronous Optical Network (SONET*):• Provides a protocol (standardized by ANSI) for long-haul (> 50km) WAN

transmission over optical fiber

Optical carrier (OC) level

Native bit rate

OC-1 51.84 Mb/s

OC-3 155.52 Mb/s

OC-12 622.08 Mb/s

OC-48 2.48832 Gb/s

OC-192 9.95328 Gb/s

OC-768 39.81312 Gb/s

OC-1536 79.62612 Gb/s

OC-3072 159.25224 Gb/s

*Also known internationally as Synchronous Digital Hierarchy (SDH).


SONET Ring

• Fiber rings can easily be deployed

• If any one link fails or is down for maintenance, data can still be transmitted.

Add/DropMUX

Add/DropMUX

Add/DropMUX

Add/DropMUX

working ring standby ring

OC-48

OC-48

OC

-48

OC

-48

OC-3

OC-3

OC-12

OC-12

OC-3

OC-3

OC-12

OC-12


Fibre Channel:

• Often used for Storage Area Networks (SAN); allows fast transmission of large amounts of data across many different servers.

• Serial bit rates of 1.0625 2.125, 4.25, 8.5 Gb/s


Some SAN Terminology

JBOD: Just a Bunch Of DisksRefers to a set of hard disks that are not configured together.

RAID: Redundant Array of Independent (or Inexpensive?) DisksMultiple disk drives that are combined for fault tolerance and performance. Looks like a single disk to the rest of the system. If one disk fails, the system will continue working properly.


Passive Optical Network (PON)

• Used to replace electronic transmission in “last mile” • Facilitates “Fiber-to-the-home (FTTH)” or “Fiber-to-the-premises (FTTP)”

GPON protocol:

• 2.5 Gb/s upstream;1.25 Gb/s downstream

• TDMA “Burst-mode” operation: Switching among fibers requires fast locking at receiver (within ~30 UI).


Open Systems International (OSI) Networking Protocol

of interest toIC designers

http://http://en.wikipedia.org/wiki/OSI_model


Characteristics of Broadband Signals & Circuits

• Standard analog circuit applications: Continuous-time operation Precision required in signal domain

(i.e., voltage or current) Dynamic range determined by noise

& distortion t

V

t0

V

Primarily digital (i.e., bilevel) operation but high bit rate (multi-Gb/s) dictates analog behavior & design techniques.

t

V

t

VH

Vt

VL

• Broadband communication circuits: Discrete-time (clocked) operation Precision required in time domain

(low jitter) Bilevel signals processed


Non-return-to-zero (NRZ) format (most common):

1 0 1 1 0 1

Return-to-zero (RZ) format:

Tb

“unit interval” (UI)

€

12Tb

• Higher bandwidth RZ signals require faster circuitry than NRZ, but are more easily synchronized due to more transitions.

Binary Data Representations (time domain)


Transition Density is the ratio of transitions to the number of unit intervals in a data stream. A high transition density is desirable in a communication system.

Some Definitions (1)

6 transitions/12 clock cycles transition density = 0.5

Equivalent to density of 0011 repeating pattern



Run Length is the maximum of consecutive 0’s or 1’s that occur in a data stream. A maximum run length is often specified in a communication system to avoid long periods where no transitions are present.

(Also known as Consecutive Identical Digit – CID)

Run length = 10 bits



Pseudo-Random Bit Sequence (PRBS) is a repeating pattern that has properties similar to random sequences.

• Parameterized by n, number of DFFs in generator. • Gives almost equal number of 1’s & 0’s• Sequence length = 2n-1; max. run length = n

1001

1100

0010

0101

1110

0111

1011

1001

D1Q3Q2Q1

...

CK

Q1 Q2 Q3D1

€

D1 =Q1 ⊕Q3

23-1 PRBSEECS 270C Week 1 17Prof. M. Green

Definitions of Common PRBS Signals

Sequence Sequence Length

Run Length

Feedback

(defined by ITU)

27-1 127 7 D1 = Q1 Q3

29-1 511 9 D1 = Q5 Q9

211-1 2 047 11 D1 = Q9 Q11

215-1 32 767 15 D1 = Q14 Q15

220-1 1 048 575 20 D1 = Q3 Q20

223-1 8 388 607 23 D1 = Q18 Q23

231-1 2 147 483 647 31 D1 = Q28 Q31

Bit error-rate testing (BERT) equipment is programmed to recognize these patterns.


Decimation Properties of PRBS

23-1 PRBS:

PRBS demuxed into 2 parallel channels

Resulting bit sequences are both also 23-1 PRBS!


Typical broadband data waveform:

Length of single bit = 1 Unit Interval (1 UI)

Eye diagram

An eye diagram maps a random bit sequence to a regular structure that can be used to analyze jitter.


Close-up of measured eye diagram:

voltage swing

1 UI(Unit Interval)

Zero crossings

trise = tfall

Zero-crossing width indicates jitter.


Types of Jitter (1)Random Jitter (RJ):

• Originates from external and internal random noise sources• Stochastic in nature (probability-based)• Measured in rms units• Observed as Gaussian histogram around zero-crossing• Grows without bound over time

Histogram measurement at zero crossing exhibiting Gaussian probability distribution


Types of Jitter (2)

Deterministic Jitter (DJ):• Originates from circuit non-idealities (e.g., finite bandwidth, offset, etc.)• Amount of DJ at any given transition is predictable• Measured in peak-to-peak units• Bounded and observed in various eye diagram “signatures”

• Different types of DJ:a) Intersymbol interference (ISI)b) Duty-cycle distortion (DCD)c) Periodic jitter (PJ)


Consider a 1 UI output pulse applied to a buffer:

If rise/fall time << 1 UI, then the output pulse is attenuated and the pulse width decreases.

a) Intersymbol interference (ISI)

€

τ <<UI

€

τ ≈UI

€

τ >UI

1UI

< 1UI


0 0 1

1 0 1

ISI (cont.)

Consider 2 different bit sequences:

t = ISISteady-state not reachedat end of 2nd bit

2 output sequencessuperimposed

ISI is characterized by a double edge in the eye diagram.


Double-edge (DJ) combined with RJ

Effect of ISI on measured eye diagram:


• Occurs when rising and falling edges exhibit different delays• Caused by circuit mismatches

b) Duty cycle distortion (DCD)

Eye diagram with DCD

Crossing offset fromnominal threshold

Nominal data sequence

Data sequence with late falling edges& early rising edges due to threshold shift

t = DCD

Tb 2Tb


c) Periodic Jitter (PJ)

Timing variation caused by periodic sources unrelated to the data pattern.Can be correlated or uncorrelated with data rate.

Clock source withduty cycle ≠50%

Synchronized dataexhibiting correlated PJ

t1 t0

€

PJ =t1 −t0

Uncorrelated jitter (e.g., sub-rate PJ due to supply ripple) affects the eye diagram in a similar way as RJ.


EECS 270C Week 1 Prof. M. Green 29

f

€

1Tb

€

2Tb

€

3Tb

P(f)

Binary Data Representations in Frequency Domain (1)

€

x(t) = bk ⋅p t−kTb( )k

∑A random data signal x(t) can be represented as:

t

€

p(t)

Tb

1

0

where is the bit sequence and p(t) is a unit-interval pulse::

€

bk ∈ −1,+1[ ]

€

Sx f( ) =1Tb

P f( )2=Tb ⋅

sin πfTb( )πfTb

⎡

⎣

⎢ ⎢

⎤

⎦

⎥ ⎥

2

If there is equal probability of low or high logic levels (i.e., dc level is 0), the power spectral density of x(t) is given by:

€

P f( ) =Tb ⋅(sin πfTb )πfTb

€

Sx f( ) =1Tb

P f( )2=Tb ⋅

sinπfTb( )πfTb

⎡

⎣

⎢ ⎢

⎤

⎦

⎥ ⎥

2

f (GHz)

€

Sx f( )

5 10 15 20 25 30repeating 0101

Example: 10 Gb/s data signals

random data

100 ps

Binary Data Representations in Frequency Domain (2)

f

€

1Tb

€

2Tb

€

3Tb

€

Sx f( )


Transmission over Copper

l

c c

lIdeal transmission line:

For l, c 0, transmission line behaves like a constant delay.

Series loss rs and shunt loss gp cause attenuation and reduce bandwidth.

l

c

rs

gp

l

c

rs

gp

Lossy transmission line:


l

c

rs

gp

l

c

rs

gp

At high frequencies, skin effect causes rs to increase with frequency:

€

H(ω) ≈e−Lα ω

And dielectric loss causes gp to increase with frequency:

€

H(ω) ≈e−Lβω

L = transmission line length; αβ are constants

€

H(ω) =exp−L α ω +βω( ) ⎡ ⎣ ⎢

⎤ ⎦ ⎥For

This results in a very steep drop in a log-log scale …

€

10 logH(ω) =−4.34L⋅α ω +βω( )


f (Hz)

|H(f)| (dB)

108 109 1010 1011

Effect of High-Frequency Loss in Copper Cable


grounded shield

inner conductor (signal)

Purpose of outer conductor:• Shields region inside from external electromagnetic fields• Provides return path

Typical loss @ 100 MHz: 9 dB/foot“ @ 1 GHz: 22 dB/foot

Coaxial cable


• Signal sent differentially.• Twisting gives each line nearly equal exposure to outside interference.• Lighter and less expensive the shielded cable.• Quality specified in # twists/foot

+_

Cat 3 unshielded twisted pair (UTP): < 16 MHzCat 5e UTP: < 100 MHzCat 6 UTP: < 250 MHz

Twisted Pair


A circuit board that allows connection of several connectors together, forming a bus. For high-speed signals, the metal traces are considered to be microstrip lines.

http://en.wikipedia.org/wiki/Industry_Standard_Architecture

Backplane


Transmission over Optical Fiber

Snell’s Law of Refraction:

€

sinθ1

sinθ2

=n2

n1

=v1

v2

incident ray

reflected ray

refracted ray

€

θ1

€

θ1

€

θ 2

n1 n2

€

n2 > n1

incident ray

reflected ray refracted ray

€

θ1

€

θ1

€

θ 2

n1 n2

€

n2 < n1


incident ray


€

θ1

€

θ1

€

θ 2

n1 n2

€

n2 < n1

Let θ2 = /2:

€

sinθ1 =n2

n1

Then

€

θ c = sin−1 n2

n1

⎛

⎝ ⎜

⎞

⎠ ⎟

For θ1 > θc, light ray is completely reflected.

Total internal reflection

Total Internal Reflection


incident ray


€

θ1

€

θ1

€

θ 2

n1 n2

€

n2 < n1

ncore ncladdingncladding

core

cladding

Total internal reflection keeps all optical energy within the core, even if the fiber bends.

€

ncladding<ncore

Optical Fiber Transmission


Advantages of Optical Fibers over Copper Cable

• Very high bandwidth (bandwidth of optical transmission network determined primarily by electronics)

• Low loss

• Interference Immunity (no antenna-like behavior)

• Lower maintenance costs (no corrosion, squirrels don’t like the

taste)• Small & light: 1000 feet of copper weighs approx. 300 lb.

1000 feet of fiber weighs approx. 10 lb.• Different light wavelengths can be multiplexed onto a single

fiber via Dense Wavelength Division Multiplexing (DWM).• 10Gb/s & 40 Gb/s transmission networks are state-of-the art.


850nm(LED) 1310nm 1550nm

Commonly-used wavelengthsFiber Loss vs. Wavelength


inexpensive; used for shorter distances; dispersion causes jitter.

Diameter 125 µm

Expensive; used for long distances

Diameter = 2~8 µm

Optical dispersion compensation; non-uniform n1

Types of Optical Fiber


Optical Signals

Dr

Modulator

40G

bps

NR

Z s

igna

l

25ps

40 80 f (GHz)-40

λ = 1550nmf = 193 THz

λ = v / f

Laser source

40GHz

193THz f

0.32

1550 λ (nm)


Chromatic Dispersion (1)

• Chromatic dispersion is due to the fact that different wavelength travel at different speeds.


Chromatic Dispersion (2)

RelativegroupDelay,

τ(ps)

λ (nm)

€

CD=dτdλ

• CD is measured in ps/nm.

• CD is proportional to fiber length:

€

CD= 17 / /ps nm m( ) ⋅L


CD=0 CD=600ps/nm CD=1600ps/nm CD=2200ps/nm

10Gb/s

CD=0 CD=40ps/nm CD=100ps/nm CD=140ps/nm

40Gb/s

Chromatic Dispersion at Different Data Rates


Polarization Mode Dispersion

• PMD is due to the fact that light travels at different speed across the two orthogonal polarization states.

• Output contains two delayed images of the input pulse.


Eye Diagrams due to PMD

DGD=0(BER<1e-15)

DGD=10ps(BER<1e-15)

DGD=15ps(BER=2e-11)

DGD=20ps(BER=2e-4)

DGD=25ps(BER=2e-2)

DGD=30ps(BER=2e-2)


Documents

Some Definitions According to International Telecommunications Union (ITU), defined as transmission speed higher than 1.5 Mb/s. Any connection fast enough