COMP 421 /CMPET 401
COMMUNICATIONS and NETWORKING
CLASS 5 (4B)
TRANSMISSION MEDIA
Overview
Guided - wire
 Unguided - wireless
 Characteristics and quality determined by
medium and signal
 For guided, the medium is more important
 For unguided, the bandwidth produced by
the antenna is more important
 Key concerns are data rate and distance

Design Factors

Bandwidth
– Higher bandwidth gives higher data rate

Transmission impairments
– Attenuation
Interference
 Number of receivers

– Major factor in guided media
– More receivers (multi-point) introduce more
attenuation
Electromagnetic Spectrum
Guided Transmission Media





The transmission capacity depends on the distance
and on whether the medium is point-to-point or
multi-point
Medium
Freq
Range
Twisted Pair
Twisted Pair
Coaxial cable
Optical fiber
– Multi-mode
0 - 3.5KHz
– Single Mode
Typical Typical Repeater
Atten. Delay Spacing
0.2dB/km 50us/km
2km
0 - 1.0MHz 3.0dB/km 5 us/km
2km
0 - 500MHz 7.0dB/km 4 us/km
1-9km
180-370THz 0.5dB/km 5 us/km
2km
180-370THz 0.2dB/km 5 us/km
40km
Twisted Pair



Consists of two insulated copper wires arranged in a regular
spiral pattern to minimize the electromagnetic interference
between adjacent pairs
Often used at customer facilities and also over distances to
carry voice as well as data communications
Low frequency transmission medium
Twisted Pair - Applications
Most common medium
 Telephone network

– Between house and local exchange (subscriber
loop)

Within buildings
– To private branch exchange (PBX)

For local area networks (LAN)
– 10Mbps or 100Mbps
Twisted Pair - Pros and Cons

Cheap

Easy to work with

Low data rate

Short range
Twisted Pair - Transmission
Characteristics






Analog
– Amplifiers every 5km to 6km
Digital
– Use either analog or digital signals
– repeater every 2km or 3km
Limited distance
Limited bandwidth (1MHz)
Limited data rate (100MHz) using different modulation
& signaling techniques
Susceptible to interference and noise
Unshielded and Shielded TP


Unshielded Twisted Pair (UTP)
– Ordinary telephone wire
– Cheapest
– Easiest to install
– Suffers from external electromagnetic interference
(EM)
Shielded Twisted Pair (STP)
– the pair is wrapped with metallic foil or braid to
insulate the pair from electromagnetic interference
– More expensive
– Harder to handle (thick, heavy)
UTP Categories

Cat 3
– up to 16MHz
– Voice grade found in most offices
– Twist length of 7.5 cm to 10 cm

Cat 4 (least common)
– up to 20 MHz

Cat 5
– up to 100MHz
– Commonly pre-installed in new office buildings
– Twist length 0.6 cm to 0.85 cm
Category 5E and 6
Today, cables and related components are available in more grade
categories than the industry standards specify. You can choose from Cat 5,
Cat 5e, Cat 5e+, Cat 6 and yes, even Cat 6+. While there is plenty of hype
and confusion surrounding these implied categories
CAT 6 Features
Cat 6 more than doubles the bandwidth of Cat 5e, from 100 MHz to
250 MHz, supporting future emerging applications
Improved EMC performance to reject outside noise from TVs,
wireless, and other adjacent applications.
Full backwards compatibility to support all legacy applications
Simpler and less costly installations, due to reduction in electronics
needed for echo and NEXT (Near End Cross Talk) cancellation.
Equations for CAT 6 Parameters
Attenuation (dB) = 1.991*sqrt(f) + 0.01785*f + 0.21/sqrt(f)
pr-pr NEXT (dB) = -20log( 10^( -0.05(74.3-15log(f)) ) + 2*10^( -0.05(94.0-20log(f)) ) )
PSNEXT (dB) = -20log( 10^( -0.05(72.3-15log(f)) ) + 2*10^( -0.05(90.0-20log(f)) ) )
pr-pr FEXT (dB) = -20log( 10^( -0.05(67.8-20log(f)) ) + 4*10^( -0.05(83.1-20log(f)) ) )
PSFEXT (dB) = -20log( 10^( -0.05(72.3-20log(f)) ) + 4*10^( -0.05(90.0-20log(f)) ) )
Return loss (dB) = 19 at 1-20 MHz; 19-10*log(f/20) at 20-250 MHz
Phase Delay (ns) = 546 + 34/sqrt(f)
Delay skew (ns) = 50
pr-pr
freq
PS
pr-pr
PS
return phase delay
atten NEXT NEXT ELFEXT ELFEXT loss
(MHz) (dB) (dB)
(dB)
100
21.7 39.9
37.1 23.2
20.2
12.0
549.4 50.0
250
36.0
30.2 17.2
14.2
8.0
548.2 50.0
33.1
(dB)
(dB)
(dB)
delay skew
(ns)
(ns)
The RJ 45 Connector
To identify the RJ-45 cable type, hold the two ends of the cable next to each
other so you can see the colored wires inside the ends

Straight-through — the colored wires are in the same sequence at both ends of the cable.
Crossover — the first (far left) colored wire at one end of the cable is the third colored wire at the other end of the cable
Understanding USOC & RJ
8-Wire Jack
(10BaseT Data Connections)
8-Wire Jacks
(USOC RJ31X Through RJ37X)
6-Wire Jack
(USOC - RJ14W)
Understanding USOC & RJ
8-Wire Jack
(IBM Token Ring Connections)
8-Wire Jacks
(USOC RJ41 Through RJ48)
Also TIA 568B
(TIA 568A Swaps Pairs 2 & 3)
6-Wire Jack Modified Jack
(DEC MMJ)
Twisted Pair Advantages

Inexpensive and readily available

Flexible and light weight

Easy to work with and install
Twisted Pair Disadvantages

Susceptibility to interference and noise

Attenuation problem
– For analog, repeaters needed every 5-6km
– For digital, repeaters needed every 2-3km

Relatively low bandwidth
LEVEL 5 CABLING
PER Specification TSB-36 for UTP cable connections for LEVEL 5:
- A terminal jack can be 90M (295ft) from the wiring closet.
- A device can be 10M from a terminal jack at the users location.
- There can be up to 6M of cross-connect patch cords in the wire closet
- Termination of cables must obey the following:
- Twists of actual pairs must be maintained to half-inch of terminatio
- Cable sheath should be stripped only as far as necessary to termina
- Cables bundles should not nopt tightly bound or cinched
- Cable bundles should not be placed under stress or tension
- Cable bend radii should not be less than 8 times the cable diameter
Coaxial Cable
Coaxial Cable Applications
Most versatile medium
 Television distribution

– Aerial to TV
– Cable TV

Long distance telephone transmission
– Can carry 10,000 voice calls simultaneously
– Being replaced by fiber optic
Short distance computer systems links
 Local area networks

Coaxial Cable - Transmission
Characteristics

Analog
– Amplifiers every few km
– Closer if higher frequency
– Up to 500MHz

Digital
– Repeater every 1km
– Closer for higher data rates
Coax
The outer shield protects the inner conductor from outside
electrical signals. The distance between the outer conductor
(shield) and inner conductor plus the type of material used for
insulating the inner conductor determine the cable properties or
impedance. Typical impedances for coaxial cables are 75 ohms
for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The
excellent control of the impedance characteristics of the cable
allow higher data rates to be transferred than with twisted pair
cable.
Coax Advantages

Higher bandwidth
– 400 to 600Mhz
– up to 10,800 voice conversations

Can be tapped easily (pros and cons)

Much less susceptible to interference than
twisted pair
Coax Disadvantages

High attenuation rate makes it expensive
over long distance

Bulky
CABLE SUBSITUTION DATA
TYPE
CM
CL2
CL3
FPL
MP
PLTC
Communication wires & cables
Class 2 remote control, signaling, & power-limited cables
Class 3 remote control, signaling, & power-limited cables
Power limited fire protective signaling cables
Multi-purpose cables
Power limited tray cable
xxR
xxP
Indicates a RISER cable
Indicates a PLENUM cable
Plenum is highest grade. Order is
Riser is next higher grade. Order is
General Purpose is next. Order is
Residential is lowest. The order is
: MPP -> CMP -> CL3P -> CL2P; FPLP -> CL3P & 2P
: MPR -> CMR -> CL3R -> CL2R; FPLR -> CL3R & CL2R
: MP -> CM -> CL3 -> CL2 : FPL or PLTC -> CL3 & CL2
: CMX -> CL3X -> CL2X
THE CATEGORIES OF CABLE
WIRE LEVEL
1
Level 1 cable is for basic comm & power limited circuits. VOICE GRADE ONLY.
2
Level 2 cable is similar to IBM Type 3 cable for 2 to 25 twisted pair cable. 1MHz max.
8db/1000ft attenuation @ 1MHz; 4db/1000ft @ 256KHz. DIGITAL DATA GRADE
3
Level 3 cable is Unshielded Twisted Pair (typical telephone wire). 16MHz max frequency.
7.8db/1000ft attenuation @ 1MHz; 4db/1000ft @ 256KHz. 10Mpbs ENET/ 4Mpbs TR
4
Level 4 cable is Low Loss Premises Telecommunication cable, shielded/unshielded, 20Mhz m
6.5db/1000ft attenuation @ 1MHz; 31db/1000ft @ 20MHz for 24AWG wire
4.5db/1000ft atten @ 1MHz; 24db/1000ft @ 20MHz for 22AWG wire. 16Mbps TR.
5
Level 5 cable is DATA GRADE up to 100Mbit
IBM CABLE TYPE
1
1P
2
2P
3
5
6
8
9
9P
9R
Dual pair STP 22AWG solid, non-plenum data cable, used for long runs in walls of buildings
Dual pair STP 22AWG, plenum data cable
Dual pair STP 22AWG data, 4 pair UTP 24AWG solid, telephone(voice) non-plenum cable
Dual pair STP 22AWG data, 4 pair 22AWG telephone plenum cable
Multi-pair (usually 4) UTP 22 or 24 AWG solid data & voice cable for runs in walls
Two 100/140 micrometer optical fiber in a single sheath
Dual pair 26AWG non-plenum patch panel data cable, used for patch panels. Attn=1.5xType1
One flat STP of 26AWG stranded wire for under carpet
Dual pair STP 26AWG solid non-plenum data cable, Low grade dual pair. Attn=1.5xType1
Dual pair STP 26AWG plenum data cable
Dual pair STP 26AWG riser data cable
Based on general description of cable per IBM definitions
Optical Fiber
Optical Fiber - Benefits

Greater capacity
– Data rates of hundreds of Gbps
Smaller size & weight
 Lower attenuation
 Electromagnetic isolation
 Greater repeater spacing

– 10s of km at least
Attenuation
Optical Fiber - Applications
Long-haul trunks
 Metropolitan trunks
 Rural exchange trunks
 Subscriber loops
 LANs

Optical Fiber - Transmission
Characteristics




Act as wave guide for 1014 to 1015 Hz
– Portions of infrared and visible spectrum
Light Emitting Diode (LED)
– Cheaper
– Wider operating temp range
– Last longer
Injection Laser Diode (ILD)
– More efficient
– Greater data rate
Wavelength Division Multiplexing
Fiber Optic Types

Multimode step-index fiber
– the reflective walls of the fiber move the light pulses
to the receiver

Multimode graded-index fiber
– acts to refract the light toward the center of the fiber
by variations in the density

Single mode fiber
– the light is guided down the center of an extremely
narrow core
Optical Fiber
Optical fiber
Optical fiber consists of thin glass fibers that can carry information at frequencies in the visible light
spectrum and beyond. The typical optical fiber consists of a very narrow strand of glass called the core.
Around the core is a concentric layer of glass called the cladding. A typical core diameter is 62.5 microns
(1 micron = 10-6 meters). Typically Cladding has a diameter of 125 microns. Coating the cladding is a
protective coating consisting of plastic, it is called the Jacket.
Refraction in Fiber
An important characteristic of fiber optics is
refraction. Refraction is the characteristic of a
material to either pass or reflect light. When light
passes through a medium, it "bends" as it passes
from one medium to the other. An example of this is
when we look into a pond of water.
Angle of Incidence
If the angle of incidence is small, the light rays are reflected and do not
pass into the water. If the angle of incident is great, light passes through
the media but is bent or refracted.
Optical fibers work on the principle that the core refracts the light and the
cladding reflects the light. The core refracts the light and guides the light
along its path. The cladding reflects any light back into the core and stops
light from escaping through it - it bounds the medium!
Optical Fiber Transmission Modes
Step Index
Step index has a large core, so the light rays tend to bounce around
inside the core, reflecting off the cladding. This causes some rays to take
a longer or shorter path through the core. Some take the direct path with
hardly any reflections while others bounce back and forth taking a longer
path. The result is that the light rays arrive at the receiver at different
times. The signal becomes longer than the original signal. LED light
sources are used. Typical Core: 62.5 microns.
Step Index Mode
Graded Index
Graded index has a gradual change in the core's refractive index. This
causes the light rays to be gradually bent back into the core path. This is
represented by a curved reflective path in the attached drawing. The result
is a better receive signal than with step index. LED light sources are used.
Typical Core: 62.5 microns.
Graded Index Mode
Single Mode
Single mode has separate distinct refractive indexes for the cladding
and core. The light ray passes through the core with relatively few
reflections off the cladding. Single mode is used for a single source of
light (one color) operation. It requires a laser and the core is very small:
9 microns.
Single Mode
Comparison of Optical Fibers
Loose Tube Fiber
Non-armored
Armored
FIBER OPTIC LINK SUMMARY
Wavelenght
Fiber
850nm
62.5/125
Output
Receive
-18dBm
-38 dBm
FIBER OPTIC LINK SUMMARY
Max Range
5km
1300nm
9/125
-18dBm
-40 dBm
20km
1300nm
w laser
9/125
-12dBm
-40 dBm
50km
Cable Type:
Fiber Type:
Single
# of Fibers:
12/cable
Wavelenght: 1300nm
Tempurature: -30 to 60C
Max Attn:
1.5dB/km
Application:
Direct Burial
Jacket:
Armored
RADAR
CONTROL CENTER/TOWER
Radar to Control Center Link
Fiber
Jumpers
Interduct
Radar
Mux
ST
2 DUPLEX
JUMPERS
ST
ST
12 STRANDS
ST
FIBER
BOX
Radar (6 - RS232)
Interduct
WALL
MT.
FIBER
DIST. ST
BOX
ST
2 DUPLEX
JUMPERS
Rack
MT.
Dist.
BOX
Control
Center
MUX
Voice (2 phones)
LAN line
Fiber
Jumpers
4.0km HURGHADA
3.5km SHARM
2.5km LUXOR
5M
20M
AIS Room
OTHER LINKS
E1
LAN 1
LAN 2
T3
FIBER
MUX
ST
12 STRANDS
FIBER
BOX
FIBER
BOX
350m SHARM
LAN 1
LAN 2
T3
FIBER
MUX
ST
ADOC
LAN 1
LAN 2
E1
T3
FIBER
MUX
12 STRANDS
LAN 1
LAN 2
T3
FIBER
MUX
ST
FIBER
BOX
FIBER
BOX
E1
LAN 1
LAN 2
500m HURGHADA
50m
E1
MUX
E1
5M
50m
E1
T3
FIBER
MUX
ST
5M
5M
50m
ST
12 STRANDS
FIBER
BOX
ST
FIBER
BOX
3.0km LUXOR
T3
FIBER
MUX
E1
E1
MUX
Voice
RS-232
LAN 1
LAN 2
EFIBSUM.vsd
A Fiber Connector
Fiber Connectors
Splicing
Splicing Technologies
Splicing technologies may be
divided into two basic categories:
fusion and mechanical.
Avg. Splice Loss (dB)
Fusion Splicing 0.10 dB
Rotary Mechanical* 0.20 dB
Mechanical Splice 0.20 dB
Mechanical methods may include
products that use mechanical
means to align two cleaved fibers
or products that require polishing
of the fiber ends.
Return Loss
Return loss is the measure of the
level of signal reflected by the
splice back to the source. Return
loss of 40 dB or better is needed
to assure proper performance for
analog video transmission over
fiber.
DWDM
DWDM works by combining and transmitting multiple signals
simultaneously at different wavelengths on the same fiber. In effect,
one fiber is transformed into multiple virtual fibers. So, if you were to
multiplex eight OC -48 signals into one fiber, you would increase the
carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. Currently,
because of DWDM, single fibers have been able to transmit data at
speeds up to 400Gb/s. And, as vendors add more channels to each
fiber, terabit capacity is on its way.
A key advantage to DWDM is that it's protocol and bit-rate
independent. DWDM-based networks can transmit data in IP,
SONET/SDH, Ethernet, and handle bit-rates between 100 Mb/s and
2.5 Gb/s. Therefore, DWDM-based networks can carry different
types of traffic at different speeds over an optical channel.
Fiber Optic Advantages

Greater capacity (bandwidth of up to 2 Gbps)

Greater distance—can run fiber as far as several
kilometers.

Smaller size and lighter weight

Lower attenuation - The light signals meet little resistance, so data
can travel farther.

Immunity to environmental interference

Highly secure due to tap difficulty and lack of signal
radiation
Fiber Optic Disadvantages

Expensive over short distance

Requires highly skilled installers

Adding additional nodes is difficult
Fiber Testing
Testing and certifying fiber optic cable.
It's easy to certify fiber optic cable because of its immunity to electrical interference.
You only need to check a few measurements:
Attenuation (or decibel loss)—Measured in dB/km, this is the decrease of signal
strength as it travels through the fiber optic cable.
Return loss—This is the amount of light reflected from the far end of the cable back
to the source. The lower the number, the better. For example, a reading of -60 dB is
better than -20 dB.
Graded refractive index—Measures how much light is sent down the fiber. This is
commonly measured at wavelengths of 850 and 1300 nm. Compared to other
operating frequencies, these two ranges yield the lowest intrinsic power loss. (NOTE:
This is valid for multimode fiber only.)
Propagation delay—This is the time it takes for a signal to travel from one point to
another over a transmission channel.
Time-domain reflectometry (TDR)—Transmits high-frequency pulses so you can
examine the reflections along the cable and isolate faults.
Fiber Design Considerations
•Maximum 150 to 160 kilometers between repeaters
•Determined by loss budget
•Typical installation 60 to 80 kilometer between repeaters
•0.25 dB loss per kilometer for fiber
•Lasers
•Transmitters have output from 0 to +10 dBm
•Receivers have -30 dBm average receiver sensitivity
•Repeater amplifiers consume 100 watts per fiber
•Under 2.5 Gigabits/sec per fiber pair is no longer state of art
Wireless Transmission
Unguided media
 Transmission and reception via antenna
 Two techniques are used:
 Directional

– Focused beam
– Careful alignment required

Omnidirectional
– Signal spreads in all directions
– Can be received by many antennas
Frequencies



2GHz to 40GHz
– Microwave
– Highly directional
– Point to point
– Satellite
30MHz to 1GHz
– Omnidirectional
– Broadcast radio
3 x 1011 to 2 x 1014
– Infrared
– Local
Wireless Examples
Terrestrial microwave transmission
 Satellite transmission
 Broadcast radio
 Infrared

Troposcatter Antenna Configuration
Terrestrial Microwave

Uses the radio frequency spectrum, commonly from 2 to 40 Ghz

Transmitter is a parabolic dish, mounted as high as possible

Used by common carriers as well as by private networks

Requires unobstructed line of sight between source and receiver

Curvature of the earth requires stations (called repeaters) to be
~30 miles apart
Microwave Transmission
Applications

Long-haul telecommunications service for
both voice and television transmission

Short point-to-point links between
buildings for closed-circuit TV or a data
link between LANs
Microwave Transmission
Advantages

No cabling needed between sites

Wide bandwidth

Multi-channel transmissions
Microwave Transmission
Disadvantages

Line of sight requirement

Expensive towers and repeaters

Subject to interference such as passing
airplanes and rain
LOS Radio
Fresnel Zones
So, in a nutshell, to visualize what happens to radio waves when they
encounter an obstacle, we have to develop a picture of the wavefront after
the obstacle as a function of the wavefront just before it (as opposed to
simply tracing rays from the distant source). Now we're in a position to talk
about Fresnel zones. A Fresnel zone is a simpler concept once you have
some understanding of diffraction: it is the volume of space enclosed by an
ellipsoid which has the two antennas at the ends of a radio link at its foci.
The surface of the ellipsoid is defined by the path ACB, which exceeds the
length of the direct path AB by some fixed amount. This amount is n /2,
where n is a positive integer. For the first Fresnel zone, n = 1 and the path
length differs by /2 (i.e., a 180 phase reversal with respect to the direct
path). For most practical purposes, only the first Fresnel zone need be
considered.
Fresnel Zone
The two-dimensional representation of a Fresnel zone is
In order to quantify diffraction losses, they are usually expressed in terms of a
dimensionless parameter , given by:
where d is the difference in lengths of the straight-line path between the
endpoints of the link and the path which just touches the tip of the diffracting
object (see Fig. 7, where d = d1 + d2 - d). By convention, is positive when
the direct path is blocked (i.e., the obstacle has positive height), and negative
when the direct path has some clearance ("negative height").
Diffraction
“Knife edge" diffraction means that the top of the obstacle is small in terms of
wavelengths. This is sometimes a reasonable approximation of an object in the real
world, but more often than not, the obstacle will be rounded (such as a hilltop) or have a
large flat surface (like the top of a building), or otherwise depart from the knife edge
assumption. In such cases, the path loss for the grazing case can be considerably more
than 6 dB - in fact, 20 dB would be a better estimate in many cases. So, Fresnel zone
clearance can be pretty important on real-world paths. And, again, keep in mind that the
Fresnel zone is three-dimensional, so clearance must also be maintained from the sides
of buildings, etc. if path loss is to be minimized. Another point to consider is the effect
on Fresnel zone clearance of changes in atmospheric refraction, as discussed in the last
section. We may have adequate clearance on a longer path under normal conditions
(i.e., 4/3 earth radius)
Ground Reflections
One common source of reflections is the ground. It tends to be more of a
factor on paths in rural areas; in urban settings, the ground reflection path
will often be blocked by the clutter of buildings, trees, etc. In paths over
relatively smooth ground or bodies of water, however, ground reflections
can be a major determinant of path loss. For any radio link, it is
worthwhile to look at the path profile and see if the ground reflection has
the potential to be significant. It should also be kept in mind that the
reflection point is not at the midpoint of the path unless the antennas are
at the same height and the ground is not sloped in the reflection region just the remember the old maxim from optics that the angle of incidence
equals the angle of reflection
Other Sources of Reflections
On long links, reflections from objects near the line of the direct path will almost
always cause increased path loss - in essence, you have a permanent "flat fade" over a
very wide bandwidth. Reflections from objects which are well off to the side of the
direct path are a different story, however. This is a frequent occurrence in urban areas,
where the sides of buildings can cause strong reflections. In such cases, the angle of
incidence may be much larger than zero, unlike the ground reflection case. This means
that horizontal and vertical polarization may behave quite differently When the
reflecting surface is vertical, like the side of a building, a signal which is transmitted
with horizontal polarization effectively has vertical polarization as far as the reflection
is concerned. Therefore, horizontal polarization will generally result in weaker
reflections and less multipath than vertical polarization in these cases.
Effects of Rain, Snow and Fog
The loss of LOS paths may sometimes be affected by weather conditions
(other than the refraction effects which have already been mentioned).
Rain and fog (clouds) become a significant source of attenuation only
when we get well into the microwave region. Attenuation from fog only
becomes noticeable (i.e., attenuation of the order of 1 dB or more) above
about 30 GHz. Snow is in this category as well. Rain attenuation
becomes significant at around 10 GHz, where a heavy rainfall may cause
additional path loss of the order of 1 dB/km.
Attenuation from Trees and
Forests
Trees can be a significant source of path loss, and there are a number of variables
involved, such as the specific type of tree, whether it is wet or dry, and in the case of
deciduous trees, whether the leaves are present or not. Isolated trees are not usually a
major problem, but a dense forest is another story. The attenuation depends on the
distance the signal must penetrate through the forest, and it increases with frequency.
According to a CCIR report [10], the attenuation is of the order of 0.05 dB/m at 200
MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz, 0.3 dB/m at 2 GHz and 0.4 dB/m at 3
GHz. At lower frequencies, the attenuation is somewhat lower for horizontal
polarization than for vertical, but the difference disappears above about 1 GHz. This
adds up to a lot of excess path loss if your signal must penetrate several hundred meters
of forest! Fortunately, there is also significant propagation by diffraction over the
treetops, especially if you can get your antennas up near treetop level or keep them a
good distance from the edge of the forest, so all is not lost if you live near a forest
Link Analysis
Some PDH to SDH Comparisons
PDH
(Plesiochronous Digital Hierarchy)
Asynchronous
Bit Interleaving - Requires
Complete Demux of Data
Stream to Extract a Single
Channel
Relatively Low Bandwidths
1960’s Technology
Limited Network
Management
SDH
•SDH (Synchronous Digital Hierarchy)
Synchronous
Byte Interleaving (Requires
Much Demux to Extract a
Single Channel
Relatively High Bandwidths
1980’s - 1990’s Technology
Robust Network
Management
SDH Features
•Modern and Digital
•Equipment Availability for 15 Years Expected
•SDH Allows Drop and Insert Without Complete Demultiplexing
•SDH Allows Multiplexing of Tributaries That Have Different Bit Rates
•SDH Overhead Is Structured to Provide Access at Section, Line
and Path Layers Allows Enhanced Maintenance, Control,
Performance and Administration at Each Laye
•Digital Radio limits the dependence on Trans Atlas routing
Satellites
Communications satellites are radio relays
in the sky. They receive signals transmitted
from earth-based antennas, amplify the
signals, and return the signals to earth. Satellites
are extremely useful because they can
handle large amounts of different types of traffic,
they offer almost worldwide coverage, and
they can be installed independently and relatively
quickly.
Satellites
Satellite systems, which consist of specialcase beyond-LOS equipment, consist of
three parts: the space segment, which includes
the satellite; a ground segment comprising
simple to complex communications terminal
equipment; and a control segment that performs
satellite station-keeping chores and directs
allocation of satellite bandwidth between users.
Satellites
Satellite systems use different frequencies
for transmitting and receiving information.
A ground terminal transmits the signal on the
uplink frequency; the satellite retransmits the
signal on the downlink frequency to the ground
receiver terminal. A transponder device within a
satellite receives the incoming signal, amplifies
it, changes the signal frequency, and retransmits
it to the receiving terminal. Satellite
uplink and downlink frequencies are usually
referred to in pairs, like 6/4 GHz with the first
number the uplink frequency and the second
number the downlink frequency.
Satellites
Most commercial satellites have more
than one transponder, with bandwidth differing
among various designs. Contemporary C-band
commercial satellites have as many as 34 transponders
each. Each transponder can relay
one color television channel with program sound,
1200 voice channels, or a data rate of up to 50
Mbps. The number of channels a satellite can
provide is related to the available bandwidth
and how it is used. This number may be increased
by improving the efficiency of the transponder
or increasing its power. However, because
more power requires more weight, the
number of channels is related to the satellite’s
size and weight.
Satellite

A microwave relay station in space

Satellite receives on one frequency, amplifies or repeats
signal and transmits on another frequency

Geostationary satellites
– remain above the equator at a height of 22,300 miles
(geosynchronous orbit)
– travel around the earth in exactly the time the earth
takes to rotate
Satellite Transmission Links

Earth stations communicate by sending
signals to the satellite on an uplink

The satellite then repeats those signals on a
downlink

The broadcast nature of the downlink
makes it attractive for services such as the
distribution of television programming
Satellite Transmission Process
satellite
transponder
Signal Delayed
0.25ms each way
dish
dish
22,300 miles
uplink station
downlink station
Satellite Transmission Applications

Television distribution
– a network provides programming from a
central location using direct broadcast
satellites (DBS)

Long-distance telephone transmission
– high-usage international trunks

Private business networks
Principal Satellite Transmission Bands

C band: 4(downlink) - 6(uplink) GHz
– the first to be designated
–

Ku band: 12(downlink) -14(uplink) GHz
– rain interference is the major problem

Ka band: 19(downlink) - 29(uplink) GHz
– equipment needed to use the band is still very
expensive
Communications Satellite Frequency
Bands
Satellite Lettered Bands
Classes of Satellites
The technical/operational performance characteristics that are to be used in
conjunction with the possible services are:
1. Standard T-2
Earth Stations having a nominal G/T of 37 dB/K and operating in the 11/14 GHz frequency bands via the
EUTELSAT II satellite system for international public telephony and high quality television transmissions or
international public telephony only. (Note: The T1 standard applied to TDMA transmissions on EUTELSAT-I h
been replaced by the T2 standard)
2. Standard V-1
Earth Stations having a nominal G/T between 26 dB/K and 30.5 dB/K (depending upon location) and
operating in the 11/14 GHz frequency bands via the EUTELSAT II satellite system for international
high quality television transmissions only.
3. Standard S-1
Earth Stations having a nominal G/T of 30 dB/K and operating in the 12/14 GHz frequency bands via the
EUTELSAT I/II satellite system for international SMS services (SMS Open Network).
Satellites
Generally, commercial systems operate
within different parts of the UHF and SHF bands
than do military systems. The accompanying
chart shows the relation of frequency bands
with letter frequency designators used in the
telecommunications industry. L-, C-, and Kuband
systems are currently available for lease;
all can provide communications services to most
of the world. Wide geographic coverage by Cband
is more prevalent than that by Ku-band
because Ku-band satellites tend to use very
narrow beam antennas to support high population
density regional locations. L-band, which is
associated with small terminals and mobile applications,
is used by INMARSAT and is available
worldwide.
Satellite Communication Access and Topology
•Multi-Channel Per Carrier
•Time Division Multiplex
•Demand Assigned Multiple Access (DAMA) Technology
•Provides Better Utilization of Bandwidth
•Adaptable to Traffic Needs of a Mission
•Topology Can Be a Star or Mesh Depending on Mission
Requirements
•Controlled From Command Center
•Secondary Sites Are Slaves to Command Center
Multiple Access Control Techniques for
Satellite Communications
Multiplexing
FDMA (Frequency Division Multiple
Access): A static multiple access technique
where transponder bandwidth is subdivided into
smaller frequency bands, or sub-channels, in which
each subchannel is assigned to a specific user.
TDMA (Time Division Multiple Access):
A static multiple access technique where
the transponder bandwidth is assigned to each
user during a specific time slot in a cyclic time
frame.
ACCESS TECHNIQUES
CDMA (Code Division Multiple Access):
A dynamic multiple access technique,
also known as spread spectrum, where total
transponder bandwidth employs a separate and
distinct code for each user to access a traffic
channel at any instant of time in sharing the
overall bandwidth with other users.
Polling (Roll Call and Round Robin):
A dynamic multiple access technique where
total transponder bandwidth is made available
to a user for the duration of time the user
requires. Upon transmission completion, channel
access is passed to the next user on the
polling list in a cyclic manner.
DAMA (Demand Assigned Multiple Access):
A family of dynamic multiple access
techniques where each user reserves channel
space based upon individual need.
Communications
Architecture Considerations

Single Channel per Carrier (SCPC)
– Dedicated point to point communications

Demand Assign Multiple Access (DAMA) And
Time Division Multiple Access (TDMA)
– Support multiple users on a as needed basis
– Very bandwidth efficient
Satellite Communication Access & Topology
• Demand Assigned Multiple Access (DAMA)
Technology
– Provides Better Utilization of Bandwidth
– Adaptable to Traffic Needs of a Mission
• Topology Can Be a Star or Mesh Depending on
Mission Requirements
– Controlled From Command Center
– Secondary Sites Are Slaves to Command Center
CONTENTION
Contention: A family of dynamic multiple
access techniques where users compete
with each other for channel space by transmitting
when required. If separate transmissions
collide, the corrupted transmissions are re-attempted
after a random delay.
Each of the multiple access channel
control techniques has advantages and disadvantages.
The selection of a multiple access
technique depends upon network application,
traffic generation profiles for each network subscriber,
and user tolerance to traffic throughput
delays.
Summary of Techniques
Currently, FDMA and TDMA techniques
are static and do not adapt readily to changing
traffic loads. Polling techniques are not suitable
for networks with exceptionally large numbers
of users due to the time needed to cycle through
the polling list. CDMA has an inherent electronic
countermeasure resistance, but is expensive
to implement. DAMA is most efficient
for networks of users with varying traffic loads,
but the automated reservation (control) system
technology is complex.
Antenna Diameter Vs. G/T
The signal level on any contour line is
derived from the satellite’s EIRP at that location,
with values of EIRP measured in decibels
referenced to one watt of power or dBw. The
higher the EIRP value, the better the signal
quality. For example, the EIRP level of a satellite
signal could range from 18 dBw at beam
edge to 21 dBw at beam center. The G/T gain-tonoise temperature ratio of the ground station
determines the quality of the received signal.
Satellite Terminal Parameters
Satellite Communication
To achieve successful satellite communications,
several technical considerations must
be satisfied. Considerations include the
geolocation of the terminal with respect to the
satellite beam coverage or “footprint” on the
earth’s surface, the frequency band, the signal
bandwidth, the antenna transmit gain expressed
as its Effective Isotropic Radiated Power (EIRP),
the size of the antenna dish, and the antenna
receive performance “figure of merit,” expressed
as G/T (the ratio of antenna receive gain to
system noise temperature in decibels per degrees
Kelvin, or dB/K).
Technical Constraints
Basic technical constraints affect system
performance and dependability of satellite
communications. Antenna size and polarization
influence system performance in terms of
radio receiver sensitivity G/T and transmitter
output power EIRP. Besides these physical
characteristics, other factors such as atmospheric
“noise” and temperature play significant
roles.
EIRP
The EIRP of an earth terminal is a key
parameter in determining system performance.
The EIRP required depends on the communications
traffic that the earth terminal needs to
support. The recently introduced micro earth
terminals and very small aperture terminals
(VSAT) with low ElRPs are not able to support
the communications traffic volume that a large
earth terminal with a high EIRP can support.
There is a trade-off in a communications link
between the transmit EIRP and the receive G/T
required to support a given data rate. There is
also a trade-off in available power versus bandwidth
allocated by the satellite resource manager,
as well as between transmitter power and
antenna gain.
Satellites and Noise
Noise is the principal enemy of a
satellite receiver because it affects the receiver’s
ability to accurately separate the downlink radio
signal from ever-present random electrical energy.
Noise can be natural cosmic background
static, can come from heat generated by the
antenna’s own amplifier, or can originate from
other electronic parts of the receiver. Noise is
also caused by the sun’s RF energy falling on
the antenna. Fortunately, this phenomenon is
relatively short-lived, amounting to several minutes
a day and occurring seasonally in the fall
and spring, when, during the solar equinoxes,
the sun’s transit contributes to these disturbances.
Sun spots and solar flares can also
affect receiver performance at any time.
VSAT TERMINALS
Examples of Satellite Terminals
•
3.8-meter Trailerized Antenna
Current Area Beam Coverage - Arabsat II
Ku-Band EIRP Coverage
C-Band High EIRP Coverage
C-Band Medium EIRP Coverage
TYPICAL SATELLITE INTERFACE
Link Budget
Determines the dish
size, output power,
frequency, and other
physical radio parameters
SYNC. DATA
RADAR
SYNC. DATA
ASYNC. DATA
Modem
Modem
Modem
P
A
Electronics
Telephone
Resources Determine
• Interfaces Type
• Interface Quantity
• Bit Rates
VOICE
LNA
Modem
Satellite Interface
• Combines lines
• Compresses Data
• Buffers Transmission
Terminal Equipment
Physical Transmission
& Reception of
Combined Data
Link Budget & Timing
• The first step to a design/cost is a Link Budget
• The Link Budget will provide design requirements for:
•Operating Band
•Antenna size
•Transmitter power
•Satellite availability
•All these will help define the system Cost
• There is a 252 ms delay in the receipt of data over a
satellite link
Satellite Data Sheet
FROM: DURRES
TO: BELGIIUM
REQUIREMENTS
---------------------------------*Availability
(%):
99.900
*Required Eb/No
(dB):
5.50
*Bit Error Rate
:
E-08
*Modulation Type
:
QPSK
*Info. Rate
(Kbps): 256.00
*FEC Rate
:
0.69
*Spread Spectrum Factor :
1.00
*Modem Step Size
(kHz):
1.00
SATELLITE
---------------------------------*Satellite
INTELSAT 705
Satellite West Long
:
18.0
*Transponder
SPOT-SPOT
!Usable Trnspndr BW (MHz):
72.00
!SFD @ 0 dB/K
(dBW/M^2): -97.10
*Transponder Atten
(dB):
12.0
TRANSMIT E/S
---------------------------------North Lat: 41.3
West Long: 39.0
Frequency
(GHz):
14.20
*Satellite G/T
(dB/K):
4.20
*Antenna Diameter
(m):
2.4
Antenna Gain
(dBi):
49.40
Antenna Elevation (Deg):
37.69
Carrier EIRP
(dBW):
43.72
*Power Control
(dB):
0.00
*Output Circuit Loss (dB):
0.00
Path Loss
(dB): 207.11
Other Losses
(dB):
0.70
(other loss = atm,pol,ant point)
RECEIVE E/S
---------------------------------North Lat: 51.0 West Long: 23.0
Frequency
(GHz):
11.20
*Satellite EIRP
(dBW):
42.10
*Antenna Diameter
(m):
3.8
Antenna Gain
(dBi):
51.80
Antenna Elevation (Deg):
31.42
*LNA Noise Temp
(K):
65.00
*Loss betw.LNA & Ant.(dB):
0.06
System Noise Temp.
(K): 107.94
Station G/T
(dB/K):
31.47
Path Loss
(dB): 205.16
Other Losses
(dB):
0.60
Satellite Data Sheet
INTERFERENCE
---------------------------------------------------------------------------C/Io Adj Sat U
(dB-Hz):
71.92
#C/Io Intermod
(dB-Hz):
75.41
C/Io Adj Sat D
(dB-Hz):
78.52
C/No Thermal Up
(dB-Hz):
68.71
C/Io Crosspol
(dB-Hz):
80.28
C/No Thermal Dn
(dB-Hz):
69.62
C/Io Adj Channel (dB-Hz):
79.42
C/Io Total
(dB-Hz):
68.79
C/Io Adj Trans
(dB-Hz):
83.67
C/No Therm Total (dB-Hz):
66.13
C/Io Microwave
(dB-Hz):
N/A
C/No Total
64.25
(dB-Hz):
RAIN ATTENUATION
---------------------------------------------------------------------------Overall Link Margin (dB):
Uplink Availability
Rain Margin
Dnlink Availability
Rain Margin
G/T Degradation
4.67
(%):
99.912
(dB):
4.67
(%):
99.988
(dB):
4.47
(dB):
4.36
*Rain Model
: CRANE
*Uplink Rain Zone
: D2
*Dnlink Rain Zone
: C
TRANSPONDER
H.P.A
----------------------------------
----------------------------------
*Number of Carriers
*Total OPBO
: MULTIPLE
(dB):
3.50
*Number of Carriers
:
1.0
*Total HPA OPBO
:
0.00
Total IPBO
(dB):
7.00
HPA Power/Carrier
(dBm):
24.32
Carrier OPBO
(dB):
26.78
Required HPA Size
(dBW):
-5.68
Carrier IPBO
(dB):
30.29
Required HPA Size
(W):
0.27
FCC Req: 1) Uplink Flange Density
(dBW/4kHz):
(@46.0) 2) Downlink EIRP Density
(dBW/4kHz):
Transponder BW Used Per Carrier
(x1.35)
Transponder Power Used Per Carrier
Transponder Bandwidth Allocation
-22.34
File:
I705DBE
2.56
(%):
0.35
# = deltas used
(%):
0.47
! = modif. default
0.251
* = user's input
(MHz):
Satellite as a Cost Effective
Solution
Advances in Satellite Hardware has:
•Lowered Hardware Cost
•Decreased Large Hub Station Requirements
•Systems Available in Transportable Configurations
•Lease Minimal of Space Segment;
•Full Period
•Occasional Use
Satellite Advantages

Can reach a large geographical area

High bandwidth

Cheaper over long distances
Satellite Disadvantages

High initial cost

Susceptible to noise and interference

Propagation delay
UHF/VHF Radio
RADIO COVERAGE REQUIREMENTS
ENROUTE
130NM
freq 128.1MHz
121.9
GND CNTL
CNTL
TWR
119.7
TOWER TMA
CONTROL
CENTER
118.1
TMA
128.1 ENROUTE
128.8 ENTOUTE
121.5
TMA
RADIO HORIZON IS
150NM AT 15,000ft
213NM AT 30,000ft
BASED ON:
Freq.= 126 MHz
RF FEED LOSS = 2.5dB
ANTENNA GAIN = 0dBd
TRANS. ERP = 14W
RCVR SENSIT.= -90dBm
TMA
ENROUTE
130NM
freq 128.8MHz
NOTE: DISTANCE TO HORIZON IS
1.228xHeight
RADIO HORIZON
AT 15,000'
N
HF Radio Systems
Harris
Transmitter/Receiver
Transworld
Transceiver
Sunair
Transmitter/Receiver
Harris
Transceiver
Antennas




Compact Rooftop RLPA
Frequency range 2 to 30 MHz
Radius of rotation 8.7 m
Gain
– 7dBi @ 6.2 MHz
– 12dBi @ 30 MHz


Range of rotation ± (n x 360°)
Efficiency
–
–
–
–
6.2-30
5.4-6.2
4.4-5.4
2.0-4.4
90-98
50-90
25-50
5-25
HF Whip Antenna Patterns
Radiation Pattern between Sites
A Complete HF System
Broadcast Radio
Omnidirectional
 FM radio
 UHF and VHF television
 Requires line of sight
 Suffers from multipath interference

– Reflections
Infrared

Achieved using transceivers that modulate
noncoherent infrared light

Requires line of sight (or reflection)

Blocked by walls
– e.g. TV remote control, Infrared port
Protocol Layers
A Laser Infrared Unit
System Block Diagram
Range
Lens
This lens provides a beam divergence of
0.5 degrees, giving a large beam footprint.
This is to avoid problems of loss of signal
due to building movement, atmospheric
distortions, ease of installation and longterm reliability. A coarse optical filter is
placed in front of the lenses to reduce the
effect of sunlight on the APD.
System
Range
200m
100 x 100mm
500m
100 x 100mm
1000m
150 x 150mm
2000m
150 x 150mm
The size of the transmit aperture provides
a wide area of emission to avoid safety and
scintillation problems.
4000m
200 x 200mm
Beam Width
END Class
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