Network Communications Method 2 Flashcards
What makes a data transfer instantaneous
Data immediately converted into a network compatible format and transmitted without being stored either in main memory or on a disk
What is data transmission
The exchange of data among different devices through a network
Digital data transmission uses
Uses voltage difference to represent 1’s & 0’s in data. Not modulated over a carrier. Each bit takes a predefined time to transmit. the sender and receiver synchronize their clocks by transmitting a bit pattern or by monitoring for the reception of the first bit
On-keying or Manchester encoding converts
Converts data into a digital waveform
Describe on-keying
A digital data transmission encoding scheme in which a change in voltage from one state to another within a predetermined interval is symbolized by a 1. No voltage transmission is symbolized by 0. The receiver synchronizes its clock with the sender by watching for the 1’s
What problems can arise when using on-keying & off-keying data transmission
When long sequence of 1’s and 0’s must be sent problems can arise because the receiver is synchronizing its clocks to 1’s received. They may not be able to synchronize over long intervals. Making its clock out of sync and leading to data corruption. Used over serial ports. Low speed digital data transmission
Manchester encoding is
Used over the ethernet. high speed digital data connections. Transitions from positive to ground represents a binary 0
A negative to positive voltage transmission in the middle of the bit period is a binary 1
Unicode transmission is a method for
Data transfer from a source address to a destination address. Main mode of transportation on LANs and the Internet
List some unicast applications
HTTP hyper-text transfer protocol
SMTP simple mail transfer protocol
FTP file transfer protocol
Broadcast transmission is
A transmission method where data is sent from a source node to all other nodes on a network. Checks for the availability of a particular service on the network
Multi-cast transmission is
Give an example
Transmission method where data is sent from a server to specific nodes that are predefined as members of the group
Ex video server transmitting tv signals
With serial data transmission the transmission of bits occurs as
On clock cycle across a single transmission medium. Does not use DC pulses for transmission
List some devices that connect over a serial transmission port
Keyboard
Mice
Modems
The receiver of an analog signal delineates between bytes in a stream of data using either
Synchronous communication. A byte is sent after a standard time interval
Or
Asynchronous. A sender inserts special start stop bit patterns between each byte of data.
With parallel data transmission how does transmission take place
Transmission if multiple bits takes place by using g multiple lines many bits transferred per clock cycle. Commonly used in parallel port connecting printers and scanners
In baseband transmission
Digital signals are sent via DC direct current. Pulses over a single unmultiplexed signal channel. Cannot send and receive simultaneously
In broadband data transmission
Uses analog signal to send data over a transmission medium using the complete bandwidth of the medium. Signals travels unidirectionally.
Broadband over power lines (BPL)
Allows broadband data transmission over domestic power lines. Has potential to cause interference with other data signals. Raises security issues because easily detected and intercepted
The media access method determines
Determines whether or not a particular node can transmit data in the network at a given time.
Name the two media access methods two categories
Contention based on competitive media access. The nodes themselves negotiate for media access time
Controlled or deterministic media access. A central device controls when and for how long each node can transmit.
Compare the media access categories.
Deterministic or control based are beneficial when a network access is time critical. Ensures that a single node cannot saturate the media
Contention based media access systems are simpler to set up and administer. Timeliness not guaranteed
What is multiplexing.
A controlled media access method. A central device combined signals from multiple nodes and transmits the combined signal across a medium
Two ways signals can be multiplexed
Using TDM time division multiplexing. Or
FDM frequency division multiplexing.
Relies on a central device called a multiplexer or mux to manage multiplexing from the sending end.
At the receiving end a demultiplexer or demux separates the signals.
In TDM time division multiplexing a communication channel is
Divided into discrete time slots. Each node on a network is assigned a time slot.
Category of media access method
In FDM frequency division multiplexing
Data from multiple nodes is sent over multiple frequencies using a network medium. Multiple broadband signals can be combined and sent over a single medium
Category of media access method
Polling is a controlled media access method in which
Give an example
A central device contacts each node to check I’d it has data to transmit
Ex is demand priority. The technique in which nodes signal the state either ready to transmit or idle to an intelligent hub which grants permissions to transmit
What is CSMA/CD
Carrier Sense Multiple Access/Collision Detection
A contention based media access method used in Ethernet LANs to provide collision free data transfer
Ethernet formalized IEEE standard
802.3 standard
List the five steps involved in CSMA/CD process
Carrier Sense Multiple Access/Collision Detection
- A node has data to transmit
- Node checks network by polling
- Node transmits data waits for ACK
- Node checks packet size for any collisions
- Waits if collision occurs both transmitting devices wait for a random backoff period before retransmitting. Repeats until successful
PoE standard
Power over Ethernet. 802.3af
Specifies a method for supplying electrical power over Ethernet connections. Specifies two device types
PSE powered sourcing equipment. Provides the power
PD powered devices. Those that receive the power from the PSE
Requires cat 5 cabling or higher
What is CSMA/CA
Carrier Sense Multiple Access/Collision Avoidance
A contention based media access method primarily used in 802.11 wireless LANs
Nodes can transmit whenever they have data to send
List the six steps for CSMA/CA
Carrier Sense Multiple Access/ Collision Avoidance
- Node has data to send
- Node checks network by polling
- The node transmits a jam signal advertising its intent to transmit data
- Node waits until all nodes receive jam signal
- Node transmits data
- Node monitors media for jam signal from other nodes
Contention domain is
Also called a collision domain. Is a contention based network on which a group of nodes are allowed to compete with each other for media access. Results in collisions
Broadcast domain
A logical area in a computer network where any node connected to the network can directly transmit to any other node in the domain without having to go through a central routing device
A broadcast domain refers to
The set of devices that received a broadcast data frame originating from any device with A LAN subnet. A layer two switch config defines the boundaries of the domain while a layer three switch or router is required to connect them
Broadcast domain vs. collision domain
Main difference is size of the domains.
Multiple collision domains can make up a broadcast domain but a broadcast domain associates itself with only a single collision domain. Also differ in the way they affect performance on a network. Collision domain increase in traffic results on higher probability of collisions on the network
What is a signal
Data transmitted as electromagnetic pulses across a network medium
An analog signal carries
Info as continuous waves of electromagnetic or optical enemy
Electrical current commonly generates analog signals the intensity is measure in
Volts
An analog signal oscillates between
Maximum & minimum values overtime and can take any value between those limits
Analog signal characteristics
Amplitude. Is one half the overall distance from the peak to the trough of the wave
Cycle. One complete oscillation
Frequency. The number of complete cycles per second in a wave. Measured in hertz
Phase. Where a wave cycle begins in relation to a fixed point.
Wavelength. Distance between two successive crests or troughs in a waveform.
An oscilloscope is
A device that plots the amplitude of an analog signal as a function of time. Displays as sine waves
A digital signal can have
Combinations of only two values. 0 & 1 represents the presence and absence of s signal
Every pulse in a digital signal represents
One binary digit or bit
Eight bits constitutes
One byte
Digital data is represented as
Binary 1s & 0s or logical states
Units of digital data
Bit. Single 1 or 0
Nibble. Four bits
Byte. Eight bits
Word. 16 bit, 32 bit or 64 bit
Explain analog signal modulation demodulation
Analog signals transmit at low frequencies. To overcome info loss and interference the analog signal is superimposed over the high frequency signal called a carrier using a modulator. When this new modulated signal reaches its destination the receiver uses demodulation to remove the carrier signal from the data signal
A codec is
Software or hardware that encodes digital data to and from the analog format. Modem is a type.
DAC & ADC
Digital to analog codec. Specific chip that performs the digital to analog conversion
Analog to digital codec. Chip that performs analog to digital conversion
Digital signal modulation & demodulation
Digital data cannot be directly transmitted through a medium over a long distance. The digital data must be represented in the form of an analog signal for transmission of data between device ie modulation. For demodulation the receiving digital device compares the modulated analog signal with the preset frequency or amplitude of the signal and uses the comparison results to reconstruct the digital data
A modem is a device that
Modulates and demodulates data to an analog signal sent over telephone lines
Digital signal modulation techniques
ASK amplitude shift key. Changes the amplitude of the analog signal depending on the logical state of digital data.
FSK frequency shift key. Changes the frequency of the analog signal depending on the logical state of digital data.
BPSK binary phase shift key. Changes the phase of the analog signal depending on the logical state of digital data.
QPSK quadrature phase shift key. Changes the phase of the analog signal to represent two logical states at a time. 00,01,10,11
QAM quadrature amplitude modulation. Combines both amplitude and phase shift key modulation. This helps represent more than two logical states at a time
Digital signal reference methods
Need a reference method to determine the conditions of the signal. Demodulation using one of two methods
Differential. A modem compares modulated and demodulated digital signals. The difference in output is result.
Single ended. The modem compares the signal on one line to ground. Difference from ground is output.
