# FIT5083 Network Infrastructure
###### tags: `2020S1`
> Formula Sheet: [Click](https://hackmd.io/SARy4x8_QA-EVwXZgr8Ang)
## Week 1

### Network Infrastructure
* In information technology, infrastructure is the physical and virtual (emulated through software) resources that support the flow, storage, processing and analysis of data.
* Network infrastructure mainly refers to the physical hardware used to interconnect computers/devices and users.
### Time-Domain Concepts
* Analog signal
* signal intensity varies in a smooth fashion over time
* Digital signal
* signal intensity maintains a constant level for some period of time and then changes to another constant level
* Periodic signal
* analog or digital signal pattern that repeats over time
* Aperiodic signal
* analog or digital signal pattern that doesn't repeat over time
### Frequency-Domain Concepts
* Fundamental frequency
* when all frequency components of a signal are integer multiples of one frequency, it’s referred to as the fundamental frequency
* Spectrum
* range of frequencies that a signal contains
* Absolute bandwidth
* width of the spectrum of a signal
* Bandwidth
* narrow band of frequencies that most of the signal’s energy is contained in
* Any electromagnetic signal can be shown to consist of a collection of periodic analog signals (sine waves) at different amplitudes, frequencies, and phases
* The period of the total signal is equal to the period of the fundamental frequency
### Relationship between Data Rate and Bandwidth
* The greater the bandwidth, the higher the informationcarrying capacity
### Reason for choosing Data/Signal Combinations
* Digital data, digital signal
* Equipment for encoding is less expensive than digital-to-analog equipment
* Analog data, digital signal
* Conversion permits use of modern digital transmission and switching equipment
* Digital data, analog signal
* Some transmission media will only propagate analog signals. e.g. optical fiber and satellite
* Analog data, analog signal
* Analog data easily converted to analog signal
### Analog Transmission
* Transmit analog signals without regard to content
* Attenuation(衰弱) limits length of transmission link
* Cascaded amplifiers boost signal energy for longer distances but cause distortion（失真）
* Distortion due to Imperfect amplification
* Some frequency components amplified more than others
* Some frequency components delayed
* Background noise is also amplified
* Analog data can tolerate some distortion
* But introduces errors in digital data
### Digital Transmission
* Concerned with the content of the signal
* Attenuation endangers **integrity** of data
* Digital Signal
* Repeaters achieve greater distance
* Repeaters recover the signal and retransmit
* Analog signal carrying digital data
* Retransmission device recovers digital data from signal
* Generates new “clean” analog signal
### Signal Noise
* Impulse noise
* Induced by EM impulse from nearby circuits
* Background noise
* Weak continuous high-frequency EMI
* Cross-Talk noise
* Signals induced from nearby circuits
* Thermal noise or Nyquist noise
* electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor.
### Channel Capacity(C)
* the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions
* Data Rate:
* rate at which data can be communicated (bps)
* Bandwidth (B):
* the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz)
* Noise:
* average level of noise over the communications path
* Error rate:
* rate at which errors occur
* Error = transmit 1 and receive 0; transmit 0 and receive 1
### Signal-to-Noise Ratio
* Ratio of the power in a signal to the power contained in the noise that is present at a particular point in the transmission
* Typically measured at a receiver
### Classifications of Transmission Media
* Transmission Medium:
* Guided Media
* Waves are guided alonng a solid medium
* E.g., copper twisted pair, copper coaxial cable, optical fiber
* Unguided Media
* Provides means of transmission but does not guide electromagnetic signals
* Usually referred to as wireless transmission
* E.g., atmosphere, outer space
* Transmission and reception are achieved by means of an antenna
* Configurations for wireless transmission:
* Directional
* Omnidirectional
### Terrestrial Microwave
* Description of common microwave antenna
* Parabolic "dish", 3 m in diameter
* Fixed rigidly and focuses a narrow beam
* Achieves line-of-sight transmission to receiving antenna
* Located at substantial heights above ground level
* Application
* Long haul telecommunications service
* Short point-to-point links between buildings
### Satellite Microwave
* Description of communication satellite
* Microwave relay station
* Used to link two or more ground-based microwave transmitter/receivers
* Receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink)
* Application
* Television distribution
* Long-distance telephone transmission
* Private business networks
### Broadcast Radio
* Description of broadcast radio antennas
* Omnidirectional
* Antennas not required to be dish-shaped
* Antennas need not be rigidly mounted to a precise alignment
* Application
* Broadcast radio
### Multiplexing
* Capacity of transmission medium usually exceeds capacity required for transmission of a single signal
* Multiplexing - carrying multiple signals on a single medium
* More efficient use of transmission medium
* Reason for Widespread Use of Multiplexing
* Cost per kbps of transmission facility declines with an increase in the data rate
* Cost of transmission and receiving equipment declines with increased data rate

## Week 2
### Definition
#### Speed - Distance of Comms Networks

#### Characteristics of WANs
* Covers large geographical areas
* Circuits provided by a common carrier
* Consists of interconnected switching nodes
* Traditional WANs provide modest capacity
* 64000 bps
* Business subscribers using T-1 service – 1.544 Mbps
* Higher-speed WANs use optical fiber and transmission technique known as asynchronous transfer mode (ATM)
* 10’s and 100’s of Mbps common
#### Characteristics of LANs
* LAN interconnects a variety of devices and provides a means for information exchange among them
* Traditional LANs
* 1 to 20Mbps data rates
* High-speed LANs
* 100Mbps to 10Gbps data rates
#### Differences between LANs and WANs
* Scope of a LAN is smaller
* LAN interconnects devices within a single building or cluster of buildings
* LAN usually owned by organization that owns the attached devices
* For WANs, most of network assets are not owned by same organization
* Internal data rate of LAN is much greater
#### Need for MANs
* Traditional point-to-point and switched network techniques used in WANs are inadequate for growing needs of organizations
* Need for high capacity and low costs over large area
* MAN provides:
* Service to customers in metropolitan areas
* Required capacity
* Lower cost and greater efficiency than equivalent service from telephone company
#### Switching Terms
* Switching Nodes:
* Intermediate switching device that moves data
* Not concerned with content of data
* Stations:
* End devices that wish to communicate
* Each station is connected to a switching node
* Communications Network:
* A collection of switching nodes
#### Techniques Used in Switched Networks
* Circuit switching
* Dedicated communications path between stations
* Connect phases
* Circuit establishment
* An end to end circuit is established through switching nodes
* Dedicated path for duration of connection, even when no data is being transmitted ! ?
* Information Transfer
* Information transmitted through the network
* Data may be analog voice, digitized voice, or binary data
* Circuit disconnect
* Circuit is terminated (‘teardown’)
* Each node de-allocates dedicated resources
* Characteristics of Circuit Switching
* Can be inefficient
* Once established, network is transparent to users
* Information transmitted at fixed data rate with only propagation delay
* Components of Public Telecommunications Network
* Subscribers - devices that attach to the network; mostly telephones
* Subscriber line - link between subscriber and network
* Also called subscriber loop or local loop
* Exchanges - switching centers in the network
* A switching centers that support subscribers is an end office
* Trunks - branches between exchanges
* Packet switching
* Message is broken into a series of packets
* Each node determines next leg of transmission for each packet
* Advantages:
* Line efficiency is greater
* Many packets over time can dynamically share the same node to node link
* Packet-switching networks can carry out data-rate conversion
* Two stations with different data rates can exchange information
* Unlike circuit-switching networks that block calls when traffic is heavy, packetswitching still accepts packets, but with increased delivery delay
* Priorities can be used
* Disadvantages:
* Each packet switching node introduces a delay
* Overall packet delay can vary substantially
* This is referred to as jitter
* Caused by differing packet sizes, routes taken and varying delay in the switches
* Each packet requires overhead information
* Includes destination and sequencing information
* Reduces communication capacity
* More processing required at each node
* Packet switching Networks - Datagram
* Each packet treated independently, without reference to previous packets
* Each node chooses next node on packet’s path
* Packets don’t necessarily follow same route and may arrive out of sequence
* Exit node usually restores packets to original
* Responsibility of exit node or destination to detect loss of packet and take recover action (if any!)
* Advantages:
* Call setup phase is avoided
* Because it’s more primitive, it’s more
* Datagram delivery is more reliable
* Packet Switching Networks – Virtual Circuit
* Preplanned route established before packets sent
* All packets between source and destination follow the same established route
* Routing decision not required by nodes for each packet
* Emulates a circuit in a circuit switching network but is not a dedicated path
* Packets still buffered at each node and queued for output over a line
* Only buffered, no routing..
* Advantages:
* Packets arrive in original
* Packets arrive correctly
* Packets transmitted more rapidly without routing decisions made at each node
#### Asynchronous Transfer Mode (ATM)
* Also known as Cell Relay
* Operates at high data rates in the WAN
* Resembles packet switching
* Involves data transfer in discrete chunks, like packet switching
* Allows multiple logical connections to be multiplexed over a single physical interface
* Minimal error and flow control capabilities reduces overhead processing and size
* Fixed-size cells simplify processing at ATM nodes

* Terminology - Connection address
* Virtual channel connection (VCC)
* Logical connection in ATM
* Basic unit of switching in ATM network
* Analogous to a virtual circuit in packet switching networks
* Exchanges variable-rate, full-duplex flow of fixed-size cells
* Virtual path connection (VPC)
* Bundle of VCCs that have the same end points
* Advantages of Virtual Paths
* Simplified network architecture
* Increased network performance and reliability
* Reduced processing and short connection setup time
* Enhanced network services

* ATM Cell Header Format
* Generic flow control (GFC)
* 4 bits, used only in user-network interface(UNI)
* Used to alleviate short-term overload conditions in network
* Virtual path identifier (VPI)
* 8 bits at the user-network interface (UNI), 12 bits at network-network interface (NNI)
* Routing field
* Virtual channel identifier (VCI) – 8 bits
* Used for routing to and from end user
* Payload type (PT) – 3 bits
* Indicates type of information in information field
* Cell loss priority (CLP) – 1 bit
* Provides guidance to network in the event of congestion
* Header error control (HEC) – 8 bit
* Error code
* ATM Service Categories
* Real-time service
* Constant bit rate (CBR)
* Real-time variable bit rate (rt-VBR
* Examples:
* Videoconferencing
* Interactive audio – e.g., telephony
* Audio/video distribution – e.g., television, distance learning, pay-per-view
* Audio/video retrieval – e.g., video-on-demand, audio library
* Non-real-time service
* Non-real-time variable bit rate (nrt-VBR)
* Available bit rate (ABR)
* Unspecified bit rate (UBR)
* Examples:
* Text/data/image – transfer, messaging, distribution, retrieval
* Remote terminal – e.g., telecommuting
* deciBels

## Week3
### Introduction to Antennas
### Type of Antennas
* Isotropic antenna (idealized)
* Radiates power equally in all directions
* Dipole antennas
* Half-wave dipole antenna (Hertz antenna)
* Quarter-wave vertical antenna (Marconi antenna)
* Parabolic Reflective Antenna

### Antenna Gain
* Antenna gain:
* Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna)
* Effective area
* Related to physical size and shape of antenna
### Propagation Modes
* Ground-Wave propagation
* Follows contour of the earth
* Can Propagate considerable distances
* Frequencies up to 2 MHz
* e.g. AM radio
* Sky-Wave propagation
* Signal reflected from ionized layer of atmosphere back down to earth
* Signal can travel a number of hops, back and forth between ionosphere and earth’s surface
* Reflection effect caused by refraction
* Frequencies between 2-30 MHz
* e.g. "short wave" radio. amateur radio, CB radio
* Line-of-sight propagation or Direct-wave
* Antennas must be within line of sight
* Refraction – bending of microwaves by the atmosphere
* Frequencies larger than 30 MHz
* Line-of-sight wireless transmission impairments:
* Attenuation and attenuation distortion
* Free space loss
* Noise
* Impulse noise
* Induced by EM impulse from nearby circuits
* irregular pulses or noise spikes

* Intermodulation noise
* occurs if signals with different frequencies share the same medium
* Cross-Talk noise
* Signals induced from nearby circuits
* unwanted coupling between signal paths
* Thermal noise or Nyquist noise
* Present in all electronic devices and transmission media
* cannot be eliminated
* function of temperature
* Particularly significant for satellite communication
* Atmospheric Absorption
* water vapour and oxygen contribute to attenuation
* Multipath
* – obstacles reflect signals so that multiple copies with varying delays are received
* Refraction
* bending of radio waves as they propagate through the atmosphere
* Thermal noise

### Attenuation
* Strength of signal falls off with distance over transmission medium
* Attenuation factors for unguided media:
* Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal
* Signal must maintain a level sufficiently higher than noise to be received without error
* Attenuation is greater at higher frequencies, causing distortion
### Multipath Propagation
* Reflection
* occurs when signal encounters a surface that is large relative to the wavelength of the signal
* Diffraction
* occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave
* Scattering
* occurs when incoming signal hits an object whose size is nearly equal to or less than the wavelength of the signal
### The Effects of Multipath Propagation
* Multiple copies of a signal may arrive at different phases
* If phases add destructively, the signal level relative to noise declines, making detection more difficult
* Inter-Symbol Interference
* One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit

### Types of Fading
* Fast fading
* Slow fading
* Flat fading
* Selective fading
* Rayleigh fading
* Rician fading
### Error Compensation Mechanisms
* Forward error correction
* Transmitter adds error-correcting code to data block
* Receiver calculates error-correcting code from incoming data bits
* If calculated code matches incoming code, no error occurred
* If error-correcting codes don’t match, receiver attempts to determine bits in error and correct
* Adaptive equalization
* Can be applied to transmissions that carry analog or digital information
* Used to combat inter-symbol interference
* Involves gathering dispersed symbol energy back into its original time interval
* Diversity techniques
* Diversity is based on the fact that individual channels experience independent fading events
* Space diversity – techniques involving physical transmission path
* Frequency diversity – techniques where the signal is spread out over a larger frequency bandwidth or carried on multiple frequency carriers
* Time diversity – techniques aimed at spreading the data out over time

## Week4
### Modulation and Encoding
* **Encoding** / **Decoding** uses a “**Codec**” to convert to **Digital signal** for transmission
* **Modulation** /**Demodulation** uses a “**modem**” to convert to **Analog signals** for transmission

## Week5
### Definition
#### Cellular Wireless Networks
##### Cellular Network Organization
* Use multiple low-power transmitters (<100W)
* Areas divided into cells
* Each served by its own antennas
* Served by base station consisting of transmitter, receiver, and control unit
* Band of frequencies allocated
* Cells set up such that antennas of all neighbors are equidistant (hexagonal pattern)
##### Approaches to Cope with Increasing Capacity
* Adding new channels
* Frequency borrowing – frequencies are taken from adjacent cells by congested cells
* Cell splitting – cells in areas of high usage can be split into smaller cells
* Cell sectoring – cells are divided into a number of wedge-shaped sectors, each with their own set of channels
* Microcells – antennas move to buildings, hills, and lamp posts
##### Cellular Systems Terms
* Base Station (BS) – includes an antenna, a controller, and a number of receivers
* Mobile telecommunications switching office (MTSO) – connects calls between mobile units
* Two types of channels available between mobile unit and BS
* Control channels – used to exchange information having to do with setting up and maintaining calls
* Traffic channels – carry voice or data connection between users

##### MTSO Controlled Call between Mobile Users
* 

##### Mobile Radio Propagation Effects
* Signal Strength
* Must be strong enough between base station and mobile unit to maintain signal quality at the receiver
* Must not be so strong as to create too much co-channel interference with channels in another cell using the same frequency band
* Fading
* Signal propagation effects may disrupt the signal and cause errors
##### Design of Cell Layout
* Propagation effects (many and highly dynamic)
* Maximum transmit power at BS and mobile unit
* Height of BS and Mobile unit antennas
* Size of individual cells
* Models have been developed to predict path loss…

##### Handoff Performance Metrics
* Cell blocking probability – probability of a new call being blocked
* Call dropping probability – probability that a call is terminated due to a handoff
* Call completion probability – probability that an admitted call is not dropped before it terminates
* Probability of unsuccessful handoff – probability that a handoff is executed while the reception conditions are inadequate
* Handoff blocking probability – probability that handoff cannot be successfully completed
* Handoff probability – probability that a handoff occurs before call termination
* Rate of handoff – number of handoffs per unit time
* Interruption duration – duration of time during a handoff in which a mobile is not connected to either base station
* Handoff delay – distance the mobile moves from the point at which the handoff should occur to the point at which it does occur

##### Handoff Strategies Used to Determine Instant of Handoff
* Relative signal strength
* Relative signal strength with threshold
* Relative signal strength with hysteresis
* Relative signal strength with hysteresis and threshold
* Prediction techniques
* May be affected by Power control features…

##### Types of Power Control
* Open-loop power control
* Depends solely on mobile unit
* No feedback from BS
* Not as accurate as closed-loop, but can react quicker to fluctuations in signal strength
* Closed-loop power control
* Adjusts signal strength in reverse channel based on metric of performance
* BS makes power adjustment decision and communicates to mobile on control channel
### Formula

## Week6
### Definition
#### Satellite-Related Terms
* Earth Stations - antenna systems on or near earth
* Uplink - transmission from an earth station to a satellite
* Downlink - transmission from a satellite to an earth station
* Transponder - electronics in the satellite that convert uplink signals to downlink signals

#### Ways to Categorize Communications Satellites
* Coverage area
* Global, regional, national
* Service type
* Fixed service satellite (FSS)
* Broadcast service satellite (BSS)
* Mobile service satellite (MSS)
* General usage
* Commercial, military, amateur, experimental

#### Satellite vs Terrestrial Wireless links
* Much larger reception area for satellite systems
* Spacecraft power and bandwidth - very limited
* Satellite to Satellite comms not as bad as terrestrial
* Broadcast, Multicast and Point-to-point applications
* Very high bandwidths/data-rates available
* Except for short-term outages, transmission quality is usually high
* Propagation delay to geo-stationary orbit is 0.25 sec
* Earth station transmissions often receives its own transmission as echo

#### Classification of Satellite Orbits
* Circular or elliptical orbit
* Circular with center at earth’s center
* Elliptical with one foci at earth’s center
* Orbit around earth in different planes
* Equatorial orbit above earth’s equator
* Polar orbit passes over both poles
* Other orbits referred to as inclined orbits
* Altitude of satellites
* Geostationary orbit (GEO)
* Medium earth orbit (MEO)
* Low earth orbit (LEO)

#### Geometry Terms
* Elevation angle
* the angle from the horizontal to the point on the center of the main beam of the antenna when the antenna is pointed directly at the satellite
* Minimum elevation angle
* To obtain maximum satellite coverage, we would like to use an elevation angle of 0°, which would enable the satellite's coverage to extend to the optical horizon from the satellite in all directions
* Reasons affecting minimum elevation angle of earth station’s antenna (>0o)
* Buildings, trees, and other terrestrial objects block the line of sight
* Atmospheric attenuation is greater at low elevation angles
* Electrical noise generated by the earth's heat near its surface adversely affects reception
* Coverage angle
* the measure of the portion of the earth's surface visible to the satellite

#### GEO Orbit
* Advantages of the GEO orbit
* No problem with frequency changes
* Tracking of the satellite is simplified
* High coverage area
* Disadvantages of the GEO orbit
* Weak signal after traveling over 35,000 km
* Polar regions are poorly served
* Signal sending delay is substantial. Satellite latency and time delay 240ms - 279ms
* Point to Point with large coverage wastes channels(use spot or steerable antenna to reduce coverage)

#### MEO Satellite Characteristics
* Circular orbit at altitude range of 5,000 to 12,000 km
* Orbit period of 6 hours
* Diameter of coverage is 10,000 to 15,000 km
* Round trip signal propagation delay less than 50ms
* Maximum satellite visible time is a few hours

#### LEO Satellite Characteristics
* Circular/slightly elliptical polar orbit under 2000 km
* Orbit period ranges from 1.5 to 2 hours
* Diameter of coverage is about 8000 km
* Round-trip signal propagation delay less than 20ms
* Maximum satellite visible time up to 20 min
* System must cope with large Doppler shifts
* Atmospheric drag results in orbital deterioration

#### LEO Categories
* Little LEOs
* Frequencies below 1 GHz
* 5MHz of bandwidth
* Data rates up to 10 kbps
* Aimed at paging, tracking, and low-rate messaging
* Big LEOs
* Frequencies above 1 GHz
* Support data rates up to a few megabits per sec
* Offer same services as little LEOs in addition to voice and positioning services

#### Orbital Comparisons
| Orbits | LEO | MEO | GEO |
| -------- | -------- | -------- | -------- |
| Orbital period | 1.5 to 2 hr | 5 to 10 hr | 24 hr |
| Altitude range | 500 to 1500 km | 8000 to 18,000 km | 35,863 km |
| **Visibility duration** | 15 to 20 min/pass | 2 to 8 hr/pass | Permanent |
| Elevation | Rapid variations; high and low angles | Slow variations; high angles | No variations; Low angles @ high latitudes |
| Round-trip propagation delay | few msec | 10’s of msec | ~250 msec |
| Ground coverage (diameter @10o) | ~6000 km | ~12,000 to 15,000 km | 16,000 km |
| Examples of Systems | Iridium, GlobalStar, Teledesic, Skybridge, Orbcomm | Odyssey, Inmarsat | Intelsat, Intersputnik, Inmarsat |

#### Frequency Bands Available for Satellite Comms
| Band | Frequency range | Total Bandwidth | General Application |
| -------- | -------- | -------- | -------- |
| L | 1 to 2 GHz | 1 GHz (15 MHz/channel) | Mobile satellite service (MSS) |
| S | 2 to 4 GHz | 2 GHz (70 MHz/channel) | MSS, NASA, deep space research |
| C | 4 to 8 GHz | 4 GHz(500 MHz/channel) | Fixed satellite service (FSS) |
| X | 8 to 12.5 GHz | 4.5 GHz(500 MHz/channel) | FSS military, terrestrial earth exploration and meteorological satellites |
| Ku | 12.5 to 18 GHz | 5.5 GHz(500 MHz/channel) | FSS, Broadcast satellite (BSS) |
| K | 18 to 26.5 GHz | 8.5 GHz | BSS, FSS |
| Ka | 26.5 to 40 GHz | 13.5 GHz(3500 MHz/channel) | FSS |

#### Satellite Link Performance Factors
* Distance between earth station antenna and satellite antenna
* For downlink, terrestrial distance between earth station antenna and “aim point” of satellite
* Displayed as a satellite footprint
* Atmospheric attenuation
* Affected by oxygen, water, angle of elevation, and higher frequencies

#### Capacity Allocation Strategies
* Frequency division multiple access (FDMA)
* Time division multiple access (TDMA)
* Code division multiple access (CDMA)

#### Frequency-Division Multiplexing
* Alternative uses of channels in point-to-point configuration
* 1200 voice-frequency (VF) voice channels
* One 50-Mbps data stream
* 16 channels of 1.544 Mbps each
* 400 channels of 64 kbps each
* 600 channels of 40 kbps each
* One analog video signal
* Six to nine digital video signals

#### Frequency-Division Multiple Access
* Factors which limit the number of sub-channels provided within a satellite channel via FDMA
* Thermal noise
* Intermodulation noise
* Crosstalk

#### Forms of FDMA
* Fixed-assignment multiple access (FAMA)
* The assignment of capacity is distributed in a fixed manner among multiple stations
* Demand may fluctuate
* Results in the significant underuse of capacity
* Demand-assignment multiple access (DAMA)
* Capacity assignment is changed as needed to respond optimally to demand changes among the multiple stations

#### FAMA-FDMA
* FAMA – logical links between stations are pre-assigned
* FAMA – multiple stations access the satellite by using different frequency bands
* Uses considerable bandwidth

#### DAMA-FDMA
* Single channel per carrier (SCPC) – bandwidth divided into individual VF channels
* Attractive for remote areas with few user stations near each site
* Suffers from inefficiency of fixed assignment
* DAMA – set of sub-channels in a channel is treated as a pool of available links
* For full-duplex between two earth stations, a pair of sub-channels is dynamically assigned on demand
* Demand assignment performed in a distributed fashion by earth station using CSC

#### Reasons for Increasing Use of TDM Techniques
* Cost of digital components continues to drop
* Advantages of digital components
* Use of error correction
* Increased efficiency of TDM
* Lack of intermodulation noise

#### FAMA-TDMA Operation
* Transmission in the form of repetitive sequence of frames
* Each frame is divided into a number of time slots
* Each slot is dedicated to a particular transmitter
* Earth stations take turns using uplink channel
* Sends data in assigned time slot
* Satellite repeats incoming transmissions
* Broadcast to all stations
* Stations must know which slot to use for transmission and which to use for reception

#### FAMA-TDMA Uplink

#### FAMA-TDMA Downlink

### Satellite and Wireless Quality of Service
* week6 p37-p68
### Formula

## Week7
### Disadvantages of a pair of wires
* EM fields spread for some distance around the wires. Pieces of metal or dielectric near the wires will be coupled onto these objects, and signal propagation behaviour altered by their presence.
* At high frequencies the wires will act like an antenna and radiate some of the power rather than guiding it to the intended destination…

### Co-Axial Cable
* Consists of two conductors, one surrounds the other
* Variation of wire-over-ground plane but with ground plane wrapped around the wire
* The power is carried by the EM fields ‘inside’ the cable
* Signal energy in the co-axial is not affected by objects outside of the cable.

### Transmission Lines
* Cables may be analysed as a form of Transmission Line
* The Electric fields between conductors ---> capacitance
* The capacitance relates the amount of energy stored in the electric field to the voltage between the conductors
* The Magnetic fields around conductors ---> inductance
* The inductance relates the amount of energy stored in the magnetic field around the cable to the current level
* The longer the cable, the larger the resulting values
* This is shown as capacitance and inductance ‘per unit length’

### Impedance
* Impedance of capacitors and inductors frequency dependent:
* Resistor: Impedance of a resistor is constant
* Capacitor: Impedance decreases with frequency
* Inductor: Impedance increases with frequency
* Depends upon the ratio of the capacitance/metre and inductance/metre.
* Impedance of cable is dynamic

### Type of transmission line cables
* Coaxial cable
* most of the RF energy is confined in the cable and not affected by external conductors
* Microstrip
* uses a thin flat conductor parallel to a ground plane. e.g. a strip of copper on one side of a printed circuit board while the other side is a continuous ground plane. The width of the strip(W), the thickness of the insulating layer(H) (PCB or ceramic) and the dielectric constant of the insulating layer determine the characteristic impedance.
* Stripline
* uses a flat strip of metal sandwiched between two parallel ground planes. The insulating material of the substrate forms a dielectric. The width of the strip, the thickness of the substrate and the relative permittivity of the substrate determine the characteristic impedance
* Balanced lines
* - a transmission line consisting of two conductors of the same type, and equal impedance to ground and other circuits. There are many formats of balanced lines, amongst the most common are twisted pair, star quad and twin-lead.
* Twisted pair - used for terrestrial telephone communications
* many pairs are grouped together in a single cable, from two to several thousand
* also used for data network distribution inside buildings
* Twin-lead - parallel-conductor transmission line mainly used to connect radio transmitters and receivers to their antennas.
* Advantages - losses are an order of magnitude smaller than coaxial cable
* – disadvantages - more **vulnerable to interference**, must be kept away from metal objects which can cause power losses

### Skin effect
* Where most of current is found near surface of a conductor
* Electric current flows mainly at "skin" of the conductor, between outer surface and a level called the skin depth(𝝏)
* This causes effective resistance of conductor to increase at higher frequencies where skin depth is smaller, thus reducing the effective cross-section of the conductor.

### Near-End and Far-End Crosstalk
* Near End Crosstalk (NEXT):
* is interference between two pairs of a cable measured at the same end of the cable as the transmitter
* Far end crosstalk (FEXT):
* is interference between two pairs of a cable measured at the other end of the cable from the transmitter

### Data Cabling
* Lecture 7 P25-44

## Week8
### Choosing a cable type
#### Topologies
* Hierarchical Star
* All computers are connected to a single, centrally located point; usually a hub of servers and switches located in the main equipment room and interconnected through the main cross-connection.
* Bus topology
* The **simplest** network topology. All computers are connected to a contiguous cable or a cable joined together to make it contiguous(連續的）.
* Ring topology
* A ring topology requires that all computers be connected in a contiguous circle. The ring has no ends or hub.
#### UTP, Optical Fiber, and Future-Proofing
* Advantages of using optical fiber:
* It has much **higher potential bandwidth**
* It’s **not susceptible** to **electromagnetic interference(EMI)**.
* It can transmit over **longer distances**. (40-70 km)
* Optical fiber also allows the use of telecomm’s enclosures which can provide savings of approximately 25 percent over the use of switches in TRs.
* Improved termination techniques and equipment make it easier to install and test.
* Cable, connectors, and patch panels are cheaper now.
* It offers better security (because the cable cannot be easily tapped or monitored).
* UTP cabling is still popular in traditional hierarchical topology where an intermediate switch is used in a TR; you may want to consider remaining with UTP cabling for the following reasons:
* The TIA estimates that the fiber installation and hardware costs are 30 percent more expensive than a Cat-5e or Cat-6 copper using a traditional hierarchical star topology.
* You don’t need Fiber if:
* higher bandwidth (>Gbit/s) requirements is not an issue
* security concerns are not critical
* EMI interference is not extreme.
#### Network Application
* Token Ring
* Developed by IBM, Token Ring uses a ring architecture to pass data from one computer to another. Token Ring employs a sophisticated scheme to control the flow of data.
* Fiber Distributed Data Interface(FDDI)
* a networking specification that was produced by the ANSI X3T9.5 committee in 1986. It defines a highspeed (100Mbps), token-passing network using fiber-optic cable.
* The FDDI protocol is **based on** the **token ring protocol**.
* The primary ring offers up to 100 Mbps capacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps.
* The single ring can extend the maximum distance; a dual ring can extend 100 km
* Asynchronous Transfer Mode (ATM)
* ATM was designed to be a high-speed communications protocol that does not depend on any specific LAN topology. It uses a high-speed cell-switching technology that can handle data as well as real-time voice and video.

## Week9
### Copper Cable Media
#### Why pick copper cabling?
* Copper cable (especially UTP cable) is as inexpensive as optical fiber and easy to install, the installation methods are well understood
* Components (patch panels, wall-plate outlets, connecting blocks, etc.) are inexpensive

#### Cable testing tools
* Wire-map testers
* Transmits signals through each wire in a copper twisted-pair cable to determine if it is connected to the correct pin at each end
* Continuity testers
* Checks a copper cable connection for basic problems, opens, shorts, and crossed pairs
* Tone generators
* Most often used to locate a specific connection in a punch-down block
* Time-domain reflectometers (TDR)
* Used to determine the length of a copper cable and to locate the impedance variations that are caused by opens, shorts, damaged cables, and interference with other systems
* Fiber-optic power meters
* Measures the intensity of the signal transmitted over a fiber-optic cable

### Fibre Optic Media
#### Introducing Fiber-Optic Transmission
* Fiber-optic technology is different in its operation than standard copper media because the transmissions are “digital” light pulses instead of electrical voltage transitions.
* Reflection of a light signal within a fiber-optic cable
#### Advantages of Fiber-Optic cabling
* Immunity to electromagnetic interference (EMI)
* Fiber-optic cabling is immune to crosstalk because optical fiber does not conduct electricity and uses light signals in a glass fiber, rather than electrical signals along a metallic conductor, to transmit data.
* Higher data rates
* Because light is immune to interference, can be modulated at very high frequencies, and travels almost instantaneously to its destination, much higher data rates are possible with fiber-optic cabling technologies than with traditional copper systems.
* Longer maximum distances
* Single-mode fiber optic cables can span distances up to 75 kilometers (about 46.6 miles) without using signal-boosting repeaters.
* Better security
* Because fiber-optic cabling uses light instead of electrical signals, it is immune to most types of eavesdropping.
#### Disadvantages of Fiber-Optic cabling
* Cost
* The cost of network electronics keeps the total system cost of fiber-based networks higher than UTP, and ultimately, it is preventing a mass stampede to fiber to the desk.
* Installation
* Fiber-optic cables can be much trickier to make connections for, mainly because of the nature of the glass or plastic core of the fiber cable.
* Polishing adds time to fiber-cable installation
#### Type of Fiber-Optic Cabling
* Fiber-optic cables come in many configurations.
* The fiber strands can be either:
* Single-mode
* Multimode
* Step Index
* Graded Index
* The cable jacketing can be either:
* Tight buffered
* Loose-tube buffered
* Composition of a Fiber-Optic Cable:
* Optical-fiber strand
* Buffer
* Strength members
* The strength member of a fiber-optic cable is the part that provides additional tensile (pull) strength.
* Optional shield materials for mechanical protection
* In fiber-optic cables designed for outdoor use, or for indoor environments with the potential for mechanical damage, metallic shields are often applied over the inner components but under the jacket.
* The shield is often referred to as armor.
* Outer jacket
* The cable jacket of a fiber-optic cable is the outer coating of the cable that protects all the inner components from the environment.

* Some rating of fiber-optic cabling (Lecture 9B P22-29)
* Core/cladding sizes
* Number of optical fibers
* LAN/WAN application

* Fiber Installation
* Remember the following:
* Match the rating of the fiber you are installing to the equipment.
* Use fiber-optic cable appropriate for the locale.
* Un-terminated fiber is dangerous.
* Components of a Typical Installation(Lecture 9B p32-34)
* Just like copper-based cabling systems, fiberoptic cabling systems have a few specialized components, including enclosures and connectors.
* Fiber-Optic Performance Factors (lecture 9B p36-40)
* Attenuation
* Acceptance angle
* Numerical aperture (NA)
* Modal dispersion
* Chromatic dispersion

## Week10
### Definition
#### Optical Fiber Components
* Core
* Carries light through the fiber
* The smallest part of the fiber
* Made of glass or plastic
* Higher refractive index than the cladding
* Dopants such as germania, phosphorous pentoxide, or alumina are used to raise the refractive index under controlled conditions.
* Manufactured in different diameters for different applications.
* Core sizes commonly used in telecommunications are:
* 9µm
* 50µm
* 62.5µm
* Cladding
* Surrounds the core
* Lower refractive index than the core
* Two most common diameters
* 125 µm and 140 µm
* 125µm typically supports core sizes of:
* 9µm
* 50µm
* 62.5µm
* 85µm
* 140µm typically has a 100µm core
* Coating
* The true protective layer
* Absorbs the shocks, nicks, scrapes, and even moisture that could damage the cladding.
* Solely for protection
* Does not contribute to the light-carrying ability of the optical fiber in any way.
* Most common type is acrylate
* Typically applied in two layers
* The primary coating is applied directly on the cladding.
* This coating is soft and provides a cushion for the optical fiber when it is bent.
* The secondary coating is harder then the primary coating and provides a hard outer surface.
* Silicone, carbon, and polyimide may be found on optical fibers used in harsh environments such as those associated with:
* Avionics
* Aerospace
* Space
* Mining
* Oil and gas drilling
* Standards:week10 p55-p56

#### Tensile Strength
* The amount of stress from pulling that the optical fiber can handlebefore it breaks.
* Optical fiber has a high tensile strength and resists stretching.
* Important for several reasons because if affects:
* The way fiber must be handled during installation
* The amount of curvature it can take
* The way it will perform throughout its lifespan
* The outer layer of the cladding provides much of the fiber’s tensile strength.
* Once the cladding is scratched or cracked the tensile strength is gone at that location.

#### Mode
* Characteristic used to distinguish types of fiber
* Potential path light it can take
* The number of modes possible in a length of fiber depends on:
* The diameter of the core
* The wavelength of the light
* The numerical aperture (NA)

#### Dispersion
* The types that affect optical fiber performance are:
* Modal dispersion
* Material dispersion
* Waveguide dispersion
* Chromatic dispersion
* Polarization-mode dispersion

#### Modal Dispersion
* Results from light taking different paths as it passes through the fiber
* The number of potential paths the light can take is determined by:
* Diameter of the optical fiber core
* Refractive indices of the fiber core and cladding
* Wavelength of the light
* Modal Dispersion
* A mode can be a straight line through the fiber, or the light can follow an angular path, resulting in reflections every time the light meets the interface between the core and the cladding.
* The more reflections, the longer the path through the fiber,and the longer the light takes to pass through it.
* Methods for overcoming modal dispersion include:
* Lower bit rate
* Graded index fiber
* Reducing the core size or increasing the wavelength
* Single-mode fiber

#### Material Dispersion
* Occurs when different wavelengths of light travel at different velocities in the optical fiber
* When the different wavelengths travel at different velocities, the slower wavelengths begin to lag behind as the light travels down the optical fiber core, causing the light to spread.
* Material dispersion in fiber causes some wavelengths to travel more slowly than others.

#### Waveguide Dispersion
* Occurs in single-mode fiber as the light passes through not only the core, but also part of the cladding
* By design, the core has a higher refractive index than the cladding, so the light will travel more slowly through the core than through the cladding.

#### Chromatic Dispersion
* Occurs in single-mode optical fiber, and results from the combination of effects from material dispersion and waveguide dispersion.
* Waveguide dispersion and material dispersion combine to create chromatic dispersion.
* One way to reduce chromatic dispersion is to take advantage of the fact that the relationship between wavelength, refractive index, and velocity is not linear.
* Dispersion profile of a typical optical fiber
* Refractive index profile of dispersion-shifted fibers
* Reduced Spectral Width
* Because material dispersion is caused by an overabundance of wavelengths in the optical signal, the simplest solution is to reduce the number of wavelengths by reducing the spectral width of the light source.

#### Polarisation-Mode Dispersion
* It is masked by other forms of dispersion until the bit rate exceeds 2.5Gbps.
* Polarized light shown in a cross section of optical fiber

#### How Dispersion Affects Bandwidth
* The product of **bandwidth** and **length** (MHz ⋅ km) expresses the information carrying capacity of a multimode optical fiber.
* Bandwidth is measured in megahertz (MHz) and the length is measured in kilometers

#### Attenuation
* The attenuation of a fiber-optic signal is the loss of optical power as the signal travels through the fiber.
* There are **two** types of **attenuation**:
* **Intrinsic**
* **Extrinsic**

#### Intrinsic Attenuation
* Intrinsic attenuation occurs because no manufacturing process can produce a perfectly pure fiber.
* Either by accident or by design, the fiber will always have some characteristics that attenuate the signal passing through it.
* Absorption
* The absorption of light is a form of intrinsic attenuation.
* It accounts for a very small percentage of attenuation in an optical fiber—typically between 3 and 5 percent.
* Absorption in optical fiber
* The absorption of light is a form of intrinsic attenuation. Absorption accounts for a very small percentage of attenuation in an optical fiber—typically between 3 and 5 percent.
* Sunglasses. Even on the brightest days, only a fraction of the light energy passes
* The wavelengths that do not pass through are mostly absorbed by impurities that have been placed in, or coated on, the lens material.

#### Extrinsic Attenuation
* Extrinsic attenuation is caused by external mechanisms that bend the optical fiber.
* These bends are broken into two categories:
* Microbends
* Macrobends

#### Attenuation
* Scattering
* The scattering of light is a form of intrinsic attenuation.
* Scattering accounts for the greatest percentage of attenuation in an optical fiber—typically between 95 to 97 percent.
* Scattering in optical fiber
* Total Attenuation
* It is the combination of the intrinsic effects of absorption and scattering in a fiber.
* An optical fiber’s attenuation curve

#### Numerical Aperture
* The numerical aperture (NA) expresses the light-gathering ability
* It is a dimensionless number, meaning that it is to be used as a variable in determining other characteristics of the fiber, or as a means of comparing two fibers.
* In order to maintain the critical angle, light must enter within a specified range defined by the cone of acceptance.
* This region is defined by a cone extending outside the optical fiber’s core.

#### Basic Cable
* Fiber-optic cables do not need to be large because the bandwidth of an optical fiber over a long distance is many times greater than the bandwidth of a wire.
* Greater bandwidth means fewer optical fibers are required to carry the same information the larger cable is carrying.
* This results in a small, low-cost fiber-optic cable that is much easier to handle and terminate than the large cable with wires.
* Optical fibers are used in many different configurations and environments; manufacturers have created a wide variety of cable types to meet the needs of almost any application.
* The type of signal being carried and the number of optical fibers required are just two of the many considerations when selecting the right cable for an application.
* Other important factors include:
* Tensile strength
* Temperature range
* Bend radius
* Flammability
* Buffer type
* Jacket type
* Weight
* Armor
* Crush resistance

#### Cable Components
* Whether a cable contains a single optical fiber, several optical fibers, or hundreds of optical fibers, it has a basic structure in common with other cables. A typical fiber-optic cable consists of:
* The optical fiber (made up of the core, cladding, and coating)
* A buffer
* A strength member
* An outer protective jacket or sheath
* Loose Buffer
* has diameter greater than the fiber diameter.
* ideal for direct burial and aerial installations.
* also very popular for indoor/outdoor applications.
* Loose buffer is also referred to as loose tube buffer or loose buffer tube
* Tight Buffer
* Tight-buffered cable is typically used in more controlled environments where the cable is not subjected to extreme temperatures or water.
* In short, tight-buffered cable is generally used for indoor applications rather than outdoor applications
* Tight-buffered cable uses a buffer attached to the fiber coating.
* Tight-buffered optical fibers extending out of the cable assembly
* Strength Members
* They may run through the center of a fiber-optic cable or they may surround the buffers just underneath the jacket.
* Combinations of strength members may also be used depending on the application and the stress the cable is designed to endure.
* Some of the most common strength member types are made of:
* Aramid yarns, usually Kevlar
* Fiberglass rods
* Steel
* Jacket
* It is the cable’s outer protective layer.
* It protects the internal components from the outside world.
* It may be subject to many factors such as:
* Sunlight
* Ice
* Animals
* Equipment accidents
* Rough treatment by installers !
* It must also provide protection from:
* Abrasion
* Oil
* Corrosives
* Solvents
* Other chemicals that could destroy the components in the cable
* Jacket materials vary depending on the application. Typical jacket materials include:
* Polyvinyl chloride (PVC) PVC is used primarily for indoor cable runs. It is fire retardant
* Polyethylene This material is typically used outdoors. It offers excellent weather and sun resistance.
* Polyvinyl difluoride (PVDF) This material is chosen for its lowsmoke and fire-retardant
* Polytetrafluoroethylene (PTFE) This material is primarily used in aerospace fiber-optic cables.
* Some cables contain multiple jackets and strength members.
* In such cables, the outermost jacket may be referred to as sheath, while the inner protective layers are stilled called jackets.
* - Ripcord
* The ripcord splitting the cable sheath
* it splits the jacket easily to allow the fiber’s to be separated for connectorization or splicing

#### Cable Types
* Cable configurations vary based on:
* The type of use
* The location
* Future expansion needs
* Cordage
* The simplest types of cables are actually called cordage, and are used in connections to equipment and patch panels.
* They are typically made into patch cords or jumpers.
* The two common types of cordage are simplex and duplex
* Duplex cordage
* Duplex cordage is a convenient way to combine two simplex cords to achieve duplex, or two-way, transmissions without individual cords getting tangled or switched around accidentally.
* Distribution cables
* These cable consists of multiple tight-buffered fibers bundled in a jacket with a strength member.
* They may also feature a dielectric central member to:
* Increase tensile strength
* Resist bending
* Prevent the cable from being kinked during installation
* Breakout cable
* Used to carry optical fibers that will have direct termination to the equipment, rather than being connected to a patch panel.
* They consist of two or more simplex cables bundled with a strength member and/or central member covered with an outer jacket.
* These cables are ideal for:
* Routing in exposed trays
* Any application requiring an extra rugged cable that can be directly connected to the equipment
* Armored cable
* They can be used for indoor applications and outdoor applications.
* They typically have two jackets.
* The inner jacket is surrounded by the armor.
* The outer jacket or sheath surrounds the armor.
* Messenger cable
* When a fiber-optic cable must be suspended between two poles or other structures, the strength members alone are typically not enough to support the weight of the cable and any additional forces that may be placed on the cable.
* For aerial installations a messenger wire is required.
* The messenger wire can be external to the fiber-optic cable or integrated into the cable.
* Ribbon cable
* It is a convenient solution for space and weight problems.
* Contains fiber ribbons, which are actually coated optical fibers placed side by side, encapsulated in Mylar tape similar to a miniature version of wire ribbons used in computer wiring.
* A single ribbon may contain 4, 8, or 12 optical fibers and can be stacked up to 22 high.
* Ribbon cables consist of parallel fibers held together with Mylar tape.
* Submarine cable
* This cable is specially designed for carrying optical fiber underwater
* Aerospace cable
* These cables are designed to be installed in aircraft and spacecraft.
* They are designed to operate in extreme temperature environments.
* Structure Type
* They are available in a variety of types to be used in different locations on the aircraft or spacecraft.
* These cables can typically be separated into two structure types: tight and loose.
* Structure types should not be confused with buffer types.
* ARINC Report 802, Fiber Optic Cables defines the construction requirements for loose and tight structure cables for aerospace and avionic applications.
* Applications
* The Boeing 787 Dreamliner has 110 fiber-optic links and over 1.7km of fiber-optic cable.
* Cables designed to be used inside avionics boxes or cabinets typically have a temperature range of –40° C to +85° C.
* Cables designed to be used between cabinets typically have a temperature range of –65° C to +125°
* Cables used by the engines have a temperature range of –65° C to +260° C.
* Hybrid Cable
* As applied to fiber optics, it combines multimode and single-mode optical fibers in one cable.
* Composite Cable
* As defined by the National Electrical Code (NEC), it is designed to carry both optical fiber and current-carrying electrical conductors in the same run.

#### Cable Duty Specifications
* The various combinations of strength members, jacket materials, and fiber arrangements are determined by the specific requirements of an installation.
* Among the factors considered are the amount of handling a cable will take, the amount of stress the cable must endure in normal use, and the locations where it will run.
* Light-duty cables - These are designed for basic protection of the fiber within and minimal handling.
* Heavy-duty cables - These are designed for more and rougher handling, with additional strength members and jacketing around the fiber.

#### Cable Termination Methods
* Some fibers, such as those found in simplex and duplex cords and breakout cable, are already set-up (crimped) to receive connectors and can be handled easily.
* Others, including loose-buffered cables, must be prepared for connectors and handling with special kits.
* These kits, are known as fanout kits and breakout kits.
* Fanout Kit
* It converts loose-buffered fibers into tight-buffered fibers ready for connectors.
* It typical contains an enclosure sometimes called a furcation unit.
* Breakout Kit
* The breakout kit, is similar to the fanout kit in that it spreads the fiber’s from the loose-buffer tube through a furcation kit and provides 900μm tight buffers to be applied over the optical fiber.
* The breakout kit, however, is designed to allow the optical fiber to be connected directly to equipment with standard connectors.

#### Blown Fiber
* Blown fiber installation starts with a hollow tube about 5mm in diameter.
* This tube is installed just like a cable and acts as a loose tube buffer for fibers that will run through it later.
* To run the fibers through the tube, you simply lead the fibers into one end of the tube and blow pressurized air through the tube.
* The air carries the fibers with it through the tube.
* The National Electrical Code (NEC) is published by the National Fire Protection Association (NFPA).
* It provides specific guidance for running fiber-optic cable within buildings.

#### NEC Standards for Fiber-Optic Cables and Raceways
* Listed and Nonlisted
* The outer surface of the cable or a marker tape should be clearly marked at intervals not to exceed 40″ (inches) with the following information:
* Cable type-letter designation such as OFN, OFC, OFNR, OFNP, etc.
* Manufacturer’s identification
* UL symbol or the letters “UL”
* Plenum Cable
* Whether conductive or nonconductive, are suitable for use in ducts, plenums, and other space used for environmental air.
* These cables will have fire resistance and low smoke-producing characteristics.
* Riser Cable
* Whether conductive or nonconductive, are suitable for a vertical run in a shaft or from floor to floor.
* These cables will have fire-resistance characteristics capable of preventing the carrying of a fire from floor to floor.
* Cable substitution guide

#### Cable Markings and Codes
* In addition to the NEC cable marking, optical fiber cables typically have a number of other markings and codes.
* Markings that appear on the jacket of the cable help identify what is inside the cable and where it originated.
* Date, Industry Standards, and Fiber type
* The date the cable was manufactured can be very helpful in determining the performance standards of the optical fiber within the cable.
* Color Codes
* TIA-598-C provides color-coding schemes for premises jackets and optical fibers within a fiber-optic cable.
* Cable Numbers
* The color-coding schemes for premises jackets and optical fibers within a fiber-optic cable described in TIA-598-C are not always used.
* External Markings
* Date, Industry Standards, and Fiber type
* Duplex cordage manufactured in example: June 2000
* Cable Numbers
* You can identify a specific simplex cable by locating the number that is printed on the jacket.
* The simplex cable number is printed every 6″ along the entire length of the cable.
* Example: Breakout cable with 12-simplex cables, each with printed cable numbers
* Sequential Markings
* They are numbers that appear every 2´ feet or 1 meter.
* These markings are useful in determining how much cable is left on a reel, measuring off large runs of cable, or simply determining the length of a piece of cable without pulling out a tape measure

#### Bend Radius Specifications
* To reduce the risk of excessive bending during installation, manufacturers specify a minimum installation and operational bend radius for their optical fiber cables.
* Following the manufacturer’s guidelines reduces the risk of damage to the cable and optical fiber during and after installation.

### Formula

## Week11
### 11A Fibre Networks
#### Why Splice?
* Splicing is one way to join two optical fibres together so the light energy from one optical fibre can be transferred into another optical fibre
* A splice is a permanent connection of two optical fibres and is typically employed for one of three reasons:
* To repair a damaged cable
* To extend the length of a cable
* To join two different cables types
* Splice Performance
* How well a splice performs depends on many variables. These variables can be broken into two groups:
* Intrinsic factors
* Extrinsic factors

#### Intrinsic factors
* Even when fibres are manufactured within specified tolerances, there are still slight variations from one optical fibre to another.
* These variations can affect the performance of the splice even though the optical fibres are perfectly aligned when mated.
* The variations between two optical fibres that affect splice performance are referred to as intrinsic factors.
* Splice performance – depends on these Intrinsic factors:
* Numerical Aperture mismatch
* When NA mismatch loss occurs, the receiving optical fibre cannot gather all of the light emitted by the transmitting fibre.
* Core Diameter mismatch
* This occurs when there is a difference in the core diameters of the two optical fibres
* Mode Field Diameter mismatch
* difference in the mode field diameters of two single-mode optical fibres
* Cladding Diameter mismatch
* differing cladding diameters
* Concentricity
* Off-center fibre cores cause concentricity loss
* Non-Circularity
* core and cladding may not be perfectly circular

#### Extrinsic factors
* These are factors related to the condition of the splice itself, external to the optical fibre
* In an ideal splice, the optical fibres are identical and they are aligned so that cores are perfectly centered on each other and the core axes are perpendicular to the endfaces being joined.
* Splice Performance depends on the following Extrinsic factors:
* Lateral misalignment
* This occurs when the two optical fibres are offset
* End Separation
* a gap between the transmitting and receiving optical fibres
* Angular misalignment
* when fibre ends are not perpendicular to each other. meet each other at an angle

#### Semiconductor Light Sources
* fibre optic light sources:
* Turn on and off millions to billions of times per second
* Project a near-microscopic beam of light into the optical fibre
* Light sources need to be:
* Reasonably priced
* Highly reliable
* Easy to use
* Available in a small package
* LED Sources
* The basic LED light source is a semiconductor diode with a p region and an n region..
* Current flows through the LED when it is forward biased.
* p|n junction emits random photons
* Photons emitted from the junction are:
* Not in phase
* Not launched in the same direction
* Called **incoherent light**
* Two types of LEDs commonly used in fibre-optic communication systems are:
* The surface-emitting LED (SLED)
* The edge-emitting LED
* Laser Sources
* Laser is an acronym that stands for light amplification by stimulated emission of radiation.
* Like the LED they are a semiconductor diode with a p region and an n region; Have an optical cavity that contains the emitted photons with reflecting mirrors on each end of the diode
* One of the mirrors is only partially reflective.
* This mirror allows some of the photons to escape the optical cavity
* Radiate photons in a fixed relationship that is referred to as **coherent light** or coherent radiation
* Every photon that escapes the optical cavity is a duplicate of the first photon to escape and has the same:
* Wavelength
* Phase relationship
* Direction
* Three families are used in fibre-optic communication systems:
* Fabry-Pérot (FP)
* Distributed feedback (DFB)
* Vertical-cavity surface-emitting laser (VCSEL)
* Light Source Performance Charateristics:(Details in Lecture11A p98-105)
* Output pattern
* Source Wavelength
* Spectral width
* Output power
* Modulation speed

#### Fibre-Optic Receiver(Lecture Week11A p107-123)

## Week12