Midterm - Conceptual Knowlege Flashcards
What is a communication system?
A collection of elements that provide information exchange service
What is information exchange service? Provide Examples.
The transmission and reception of information between two or more elements. Examples of information include:
1. Voice
2. Music
3. Pictures, Videos
4. Data files, emails, texts, etc
What are elements? list the main elements of a communication system.
Entities or components of a communication system (network).
1) Information source: generates the message to be transmitted.
2) Transmitter: converts the message to a transmitted signal (i.e., information-bearing signal).
3) Channel: carries the message from the transmitter(s) to the receiver(s).
4) Receiver: determines an estimate of the transmitted message
5) Information sink: uses the message generated by the source.
What elements comprise the origination point?
Information Source, and Transmitter.
What elements comprise the destination point?
Receiver, and Information Sink.
A communication system can be classified based on the distance between the origination and destination points. What are the different classifications?
- local area communication system.
- metropolitan area communication system.
- wide area communication system.
- global communication system.
A communication system can be classified based on the type of information source supported. What are the types of information sources?
- Digital communication system transfers information from a digital source to the sink.
- Analog communication system transfers information from an analogue source to the sink.
What is a digital message?
A digital message π takes on a value from a finite set π, where π = π1, π2, β― , ππΎ and πΎ < β is the size
of π
What are examples of digital messages?
- binary source, π = 0, 1
- telephone touch pad, π = 0, 1, 2, β― , 9, #,*
What is an analog message?
An analog message π takes on a value from a continuous range, π β ππΏπΏ, πππΏ , i.e., π takes on a value
from an βinfiniteβ number of possible values within the range
** LL = lower limit, and UL = upper limit
What are examples of analog messages?
- microphone
- video camera
What are characteristics of an information source?
- Source rate = rate at which information is generated.
- Randomness of source output
- Message signal (output signal of the info source) is at base band frequency
What is base-band frequency?
Baseband frequency refers to frequencies close to zero Hz.
Baseband transmission works well only for some channels. Give examples.
wired links such as:
1. twisted pair wire
2. coaxial cable
what are the two types of transmitters?
base band, and band pass
what does a Baseband transmitter do?
Converts the message signal at baseband frequency to a transmitted signal also at baseband
frequency.
What signal processing operations are performed at baseband to prepare the message for efficient transmission?
- filtering
- modulation
- amplification
- source coding
- error control
What are base band transmission limitations?
Not suitable for some channels, e.g.:
1. wireless
2. optical fiber
whose properties are not consistent with baseband frequency
What is band-pass (or carrier) frequency?
Band-pass (or carrier) frequency refers to frequencies much higher than the baseband frequency of the message signal (MHz, GHz, THz)
What channels does band pass transmission work well for?
- wireless
- optical fiber
What does a band pass transmitter do?
Converts the message signal at baseband frequency to a transmitted signal at band-pass frequency.
What signal processing operations performed at baseband to prepare the message for efficient bandpass transmission?
- filtering
- amplification
- source coding
- error control
What do carrier circuits at the transmitter do?
Carrier circuits convert the baseband signal to information bearing (i.e., carrier) signal.
What do carrier circuitsβ operations at the transmitter include?
- modulation
- up-conversion
- amplification
- filtering
what is the difference between baseband and bandpass communication systems?
-baseband communication system does not use carrier circuits at the transmitter (Tx) and receiver (Rx)
- band-pass communication system incorporates carrier circuits at the Tx and Rx
A communication system can be classified based on the channel category used between the Tx and Rx. What are the two types of communication channels?
- wired communication system uses guided media between the Tx and Rx
- wireless communication system uses unguided media between the Tx and Rx
What are guided media channels? Provide examples.
Channels where the transmitted signal propagates in solid media. e.g.:
1. twisted-pair wire
2. coaxial cable
3. fiber-optic cable
What are unguided media channels? Provide examples.
Channels where transmitted signal propagates freely, e.g.:
1. radio, satellite
2. microwave,
3. Bluetooth
4. infra-red
What are the two types of channel imperfections?
natural and man made.
what are some natural channel imperfections?
- Loss - random
- fading - time varying
- interference - frequency varying
- noise - non linear
what are the two channel characteristics?
imperfections, and bandwidth
What is bandwidth?
frequency range available for message transmission
What are bandwidth requirements for proper transmission?
For proper transmission, channel bandwidth»_space; message signal bandwidth
What does channel bandwidth depend on?
Channel bandwidth depends on the channel category
What are the effects of the channel characteristics?
- Imperfections distort (i.e., corrupt and attenuate) the transmitted waveform
- Channel bandwidth limits the amount of information that can reach the receiver
what are the two types of receivers?
baseband and bandpass
What does a baseband receiver do?
Converts the received signal at baseband frequency to an output signal also at baseband
frequency.
what are signal processing operations performed at baseband on the received signal to determine the
output signal?
- filtering
- demodulation
- amplification
- synchronization
What is a received message?
A received message is an estimate of the transmitted message.
what does a bandpass receiver do?
Converts the received signal at band-pass frequency to an output signal at baseband frequency.
what do carrier circuits at the receiver do?
convert the received signal at band-pass frequency to an output signal at baseband frequency.
what do carrier circuitsβ operations at the receiver include?
- down-conversion
- demodulation
- amplification
- filtering
what are signal processing operations performed at bandpass to determine the output signal from which an estimate of the transmitted message can be extracted.
- filtering
- equalization
- error control
What is the information sink? Provide examples.
Destination of the information sent by the source.
1. Loudspeaker β converts the electric signal to audio signal
2. TV screen β converts the electric signal to video signal
What is the communication problem?
Reliable and quality information transfer from the origination point to the destination point
What are the communication problem constraints?
- Randomness of the transmitted signal
- Limited transmitted signal energy
- Limited channel bandwidth
- Channel impairments
- Non-idealities in the transmitter and 6. receiver
- Cost
What are the two solution approaches to the communication problem?
- Proactive techniques: implemented at the Transmitter.
- Reactive techniques: implemented at the Receiver.
What is a communication network?
a collection of nodes interconnected by transmission links (channels), providing information exchange service
Information exchange over the network is governed by a set of rules referred to as:
communication protocols
what is a node?
houses the source, transmitter, receiver, and/or sink
What are types of nodes?
- Origination node: houses the source and transmitter
- Destination node: contains the receiver and sink
- Transmitter node: houses the transmitter
- Receiver node: houses the receiver
- Transceiver node: houses the transmitter and receiver
- Router or relay node: an intermediate node between the origination and destination nodes
What are the two types of connections with transmission links (channels)?
- One channel shared by all the nodes in the network (e.g., wireless channel)
- Multiple channels, with one dedicated channel between a pair of nodes
Communication protocols are a set of rules for:
- Setting up a call/session and data transmission
- Accessing and sharing the channel
- Detecting and correcting errors
- Routing of calls and data
Why deploy Communication Systems and Networks?
- Information transfer: Provide information exchange amongst the nodes in the systems and networks
- Interconnectivity: Support a large number of nodes, e.g., point-to-point (2 nodes), point-to-multipoint (multiple
nodes)
-Cost-effectiveness: Facilitates the sharing of network resources to support multiple services/applications and features
what are wireline system and network examples
- Public switched telephone network (PSTN)βhome and office landline phone system
- Public switched data networkβInternet
- Local area networkβEthernet
- Optical Communication systemsβvery high speed (Gigabits/sec) networks using optical
fibers
what are wireless system and network examples
- Cellular system or wireless wide area network (WWAN)βOld systems: 1G, 2G, 3G, and 4G;
Current: 5G; Future: 6G - Wireless local area network (WLAN)βIEEE 802.11 (WiFi)
- Wireless personal area network (WPAN)βBluetooth, Zigbee
- Satellite system
- Microwave system
Note: Wireless system and network examples 1, 2, and 3 are called terrestrial wireless systems while
examples 4 and 5 are called non-terrestrial wireless systems.
What is data flow?
direction of data between two communicating nodes at a point in time.
what are the three types of data flow?
- Simplex: communication is unidirectionalβone node transmits and the other receives (e.g.,
communication between keyboard and monitor) - Half-duplex: communication is bi-directional but not simultaneouslyβeach node can both transmit and
receive data, but not at the same time (e.g., walkie-talkies, citizens band radios) - Full-duplex: communication is bi-directional simultaneouslyβboth nodes can transmit and receive data
simultaneously (e.g., PSTN, cellular system)
what are network criteria?
measures of a networkβs effectiveness in providing information exchange
what are the three types of network criteria?
- Performance
- Reliability
- Security
How is the, performance, network criteria measured?
- Delay: which is comprised of transmission time + Response time.
where response time is the time elapsed time between one node transmitting a message and receiving a response from the receiver.
- Throughput: rate of successful information transfer from one node to the other
note: A trade-off exists between throughput (x) and delay performance (y) going up exponentially
How is the, reliability, network criteria measured?
- Accuracy of deliveryβbit error rate, packet error rate
- Frequency of failure
- Network failure recovery time
- Network robustness to failureβhow tolerant is the network to failure using redundancy?
How is the, security, network criteria measured?
- Protection of the network from unauthorized access and attacks by invalid network users
- Protection of data from damage and tampering
- Error control (i.e., error detection and recovery)
what does Network topology describe?
describes how the nodes and links are connected both physically
and logically
what does **Logical topology **show?
the flow of data between the nodes in the network
what does Physical topology show?
actual physical interconnection of nodes in the network
what are the 4 basic network topologies?
bus, ring, star, and mesh
describe the bus topology with examples
Bus: all the nodes are connected together by a single transmission link (e.g., Ethernet LAN
IEEE802.3)
describe the ring topology with examples
all the nodes are connected in a loop, where each node has a dedicated point-to-point link to
each node on either side of it (e.g., IBM Token ring LAN)
describe the star topology with examples
each node has a dedicated point-to-point link to a central node (i.e., the hub node), and communication between any two nodes goes via the hub node (e.g., cellular system, Wi-Fi)
describe the mesh topology with examples
each node has a dedicated point-to-point link to every other node in the network (e.g., backbone network in PSTN, Internet)
what do Switching techniques describe?
how data is routed between the input and output ports of each intermediate node (switching node) along the communication path (route) of a
(source node, destination node) pair
what are the Two principal technologies of switching?
Circuit switching and packet switching
what is an example of Circuit switching?
PSTN
what characterizes circuit switching?
A dedicated communication path (route) exists between a (source node, destination node) pair.
* A route comprises a set of point-to-point links connecting the switching nodes between a (source
node, destination node) pair.
what are the Three phases in circuit switching?
- Circuit (path) establishment
- Information transfer
- Circuit disconnect
talk about the efficiency of circuit switching.
Circuit switching can be rather inefficient, especially for bursty traffic transfer
what is an example of packet switching?
internet
what characterizes packet switching?
No dedicated communication path (route) exists between a (source node, destination node) pair
what are the phases of packet switching?
- Source node transmits each packet to the switching node it attaches to
- Switching node stores the packet briefly, determines the next switching node of the route, and then
transmits the packet to the node when the link between the two nodes is available - Above step continues until the packet reaches the last switching node that attaches to the
destination node
talk about the efficiency of packet switching.
Packet switching is more efficient and flexible than circuit switching, but with more delay
what are Communication standards?
Policies, rules, and guidelines the communication equipment vendors must abide by during the design,
manufacture, and operation of communication equipment
what is the Need for communication standards?
- Allow interoperability: equipment from different vendors to interwork
- Speed the growth of the communication industry
- Low equipment cost (to system/network operators and end users)
what are some Important standard organizations?
- International Standards Organization (ISO)
- International Telecommunication Union (ITU)
- Institute of Electrical and Electronics Engineers (IEEE)
- Federal Communication Commission
- Industry Canada Radio, Spectrum and Telecommunications
what is the The Open System Interconnection (OSI) protocol architecture (model)?
7-layer architecture, developed by ISO (International Standards Organization)
where Network functions are organized in a layered architecture
what is the benefit of The Open System Interconnection (OSI) protocol architecture (model)?
Different layers can be designed independently, which greatly simplifies network design.
where are the media layers implements in the The Open System Interconnection (OSI) model?
at all nodes from the source node to the destination node
where are the host layers implements in the The Open System Interconnection (OSI) model?
implemented only at the source node and destination node
how many data layers does the The Open System Interconnection (OSI) model have?
3
how many host layers does the The Open System Interconnection (OSI) model have?
4 (3 data layers and 1 segment layer)
how many media layers does the The Open System Interconnection (OSI) model have?
3 (a packets layer, a bits layer, and a frames layer)
what does the application data layer do in The Open System Interconnection (OSI) model?
Implements commonly used communication services including file
transfer, directory services, virtual terminal
what does the presentation data layer do in The Open System Interconnection (OSI) model?
Performs data format conversion, encryption/decryption,
compression/decompression
what does the session data layer do in The Open System Interconnection (OSI) model?
Performs session management, dialog type selection and control
what does the transport segment layer do in The Open System Interconnection (OSI) model?
Performs end-to-end (i.e., source node to destination node) information delivery, including end-to-end error control, segmentation
and reassembly
what does the network packet layer do in The Open System Interconnection (OSI) model?
Performs routing and addressing
what does the datalink frames layer do in The Open System Interconnection (OSI) model?
Performs framing, link-level error control, and medium access control
what does the physical bits layer do in The Open System Interconnection (OSI) model?
Transmits individual bits over the physical medium connecting two nodes
how many layers does the Transmission Control Protocol/Internet Protocol (TCP/IP) have?
5 (application, transport, network, link, physical)
what does the application layer in Transmission Control Protocol/Internet Protocol (TCP/IP) do?
supports network applications, e.g.
FTP: File Transfer Protocol; SMTP: Simple Mail Transfer Protocol; HTTP: Hypertext Transfer Protocol
what does the transport layer in Transmission Control Protocol/Internet Protocol (TCP/IP) do?
processes data transfer e.g.
TCP, UDP: User Datagram Protocol
what does the network layer in Transmission Control Protocol/Internet Protocol (TCP/IP) do?
routs of packets from the source node to the destination node e.g.IP, routing protocols
what does the link layer in Transmission Control Protocol/Internet Protocol (TCP/IP) do?
performs data frame transfer between neighbouring nodes attached to the same physical medium e.g.
MAC: Medium Access Control; LLC: Logical Link Control
what does the physical layer in Transmission Control Protocol/Internet Protocol (TCP/IP) do?
is comprised of bits βon the wireβ (Ethernet), 802.11 (WiFi)
what aspect of a communication channel causes linear distortion of a transmitted signal?
when the channel is operating at baseband frequency. under this condition, the channel behaves like a LPF.
what aspect of a communication channel causes non-linear distortion of a transmitted signal?
two aspects: time selective channel, frequency selective channel.
- a time selective channel causes different attenuation to different time components of the transmitted signal, hence, the different time components of the received signal have different amplitudes.
- a frequency selective channel causes different attenuation to the different frequency components of the transmitted signal, hence, the different frequency components of the received signal have different amplitudes.
time response is same as
impulse response
frequency response is same as
transfer function
what is the main property of a linear system?
A linear system is a system that obeys the principle of superposition:
π
ππ ππππ π π‘π ππ’ππ‘ππππ ππππ’π‘π πππππππ π πππ’ππ‘πππππ’π ππ¦ =sum of πππ ππππ πs π€βππ πππβ ππππ’π‘ π ππ πππππππ πππππ£πππ’ππππ¦
what are the two basic concepts in signal transmission? (needed for characterizing filters)
- Condition for Distortion-less Transmission
- Causality
what is the Condition for Distortion-less Transmission?
Input signal shape is preserved at the output but can be scaled or delayed
what is causality?
Output signal does not appear before the input signal is applied
mathematically, what is the time domain condition for distortion-less transmission? how about the frequency response?
y(t) = k x(t-td)
by applying the Fourier transform we get:
Y(f) = k X(f) e^(-j 2 pi f td)
the frequency response should have the form H(f) = Y(f) / X(f)
= k e^(-j 2 pi f td)
thus |H(f)| = k, beta(f) = -2 pi f td
what are the two forms of distortion?
Amplitude distortion, Phase distortion
what does amplitude distortion imply?
|π»(π)| , the amplitude response of the system is not a constant, but
changing with frequency
what is the definition of causality?
A system is causal if it produces an output only when (i.e., output not
delayed) or after (i.e., output is delayed) an input is applied.
Only causal systems are physically realizable
(i.e., practical and measurable in the Lab)
Filter definition: What is a Filter?
A filter is a linear system (obeys the superposition property).
A filter is a time-invariant system (Impulse response remains fixed, not changing with time)
A filter is a frequency-selective system(Passes only the frequencies in its passband and rejects the frequencies in its stopband)
Passband:
range of frequencies passed with little or no distortion
Stopband:
range of frequencies stopped (i.e., rejected)
In the context of Communication systems, a filter is used as a:
Frequency-selective device
Shaping device (Modifies the shape of an input signal waveform for its optimum transmission)
Cleaning device (Removes unwanted signals from an input signal to produce a clean output)
filters can either deal with analog of digital inputs. what are the two types of implementation of filters?
analog (built using lumped elements)
digital (built using digital hardware)
