Data Communicatons Exam 1

Front 1

Circuit Configuration

Back 1

The basic physical layout of the circuit. There are two fundamental circuit configurations.
1. Point to Point
2. Multipoint

Front 2

Point to Point Circuit

Back 2

Goes from one point to another. Sometimes they are called dedicated circuits. Used when the computers generate enough data to fill the capacity of the communication circuit. Very expensive.

Front 3

Multipoint Circuit

Back 3

Many computers connected on the same circuit. Disadvantage is that only one computer can use the circuit at a time. When one comp is sending and receiving data, all others must wait. But, it's efficient and it uses less cable.

Front 4

Three ways to transmit data flow

Back 4

1. Simplex
2. Half-Duplex
3. Full-Duplex

Front 5

Simplex

Back 5

One way transmissions such as radio and TVs.

Front 6

Network Circuits

Back 6

Physical media [cables] and special purposes devices [routers and hubs]

Front 7

Three types of circuits

Back 7

1. physical circuits connect devices and include actual wires such as twisted pair wires.
2. logical circuits refer to the transmission characteristics of the circuit, such as a T-1 connection refers to 1.544 Mbps
3. Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits.

Front 8

Half-Duplex

Back 8

two-way transmission, but you can transmit in only one direction at a time. Similar to a walkie-talkie link. Computers use control signals to negotiate when to send and receive data.

Front 9

Turnaround time

Back 9

amount of time half-duplex communication takes to switch between sending and receiving.

Front 10

Full duplex transmission

Back 10

you can transmit in both directions simultaneously with no turn around time.

Front 11

Multiplexing

Back 11

To break one high-speed physical communication circuit into several lower-speed logical circuits so that many different devices can simultaneously use it but, still 'think' that they have their own separate circuits [the multiplexer is 'transparent'].
Enabled the huge growth in network capacity [otherwise the internet would have collapsed in 90s]. Benefit is to save money by lowering amount of cable used or the number of network circuits that must be installed. Inexpensive if you're close to server. Pricey if miles away.

Front 12

Analog Data

Back 12

Produced by telephones. Soundwaves which vary continuously over time analogous to voice. Can take on any value.

Front 13

Digital Data

Back 13

Produced by computers in binary form. On/Off.

Front 14

Frequency Division Multiplexing [FDM]

Back 14

Dividing the circuit 'horizontally' so that many signals can travel a single communication circuit simultaneously. Signals are on different frequencies so they do not interfere with each other. Disadvantage is that FDM needs guardbands. You have to allocate Kbps for the guardbands.

Front 15

Guardbands

Back 15

the unused portions of the circuit that separate these frequencies from each other. devices that are connected to FDM are unaware they are being multiplexed.

Front 16

Poling and Selecting

Back 16

There is a master [like a server] which asks the connected clients who wants to transmit something. The polling device hears message and let's the computer transmit.

Front 17

Time Division Multiplexing [TDM]

Back 17

shares a communication circuit among two or more terminals by having them take turns, dividing the circuit vertically so to speak. TDM is more efficient than FDM because it does not need guardbands.

Front 18

Statistical Time Division Multiplexing [STDM]

Back 18

STDM allows more terminals to be connected to a circuit than does FDM or TDM. It is called statistical because selection of transmission speed for the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be multiplexed. Don't need to proved 4 computers with 64Kbps 256Kbps because people pause to read etc.

Front 19

Two Complexities with STDM

Back 19

STDM needs internal memory to store incoming data that it cannot simultaneously transmit. You can have time delays if traffic is heavy.
Need to add address information to each packet so you can identify which logical circuit to which it belongs. Not very efficient.

Front 20

Wavelength Division Multiplexing [WDM]

Back 20

a version of FDM used in fiber-optic cables. Light has different frequencies [colors]. WDM uses lasers to transmit different frequencies of light through the same fiber-optic cable.

Front 21

Inverse Multiplexing

Back 21

Combines several low-speed circuits to make them appear as one high speed circuit to the user.

Front 22

BONDING [Bandwidth on Demand Interoperability Networking Group]

Back 22

Most common bonding is for room to room conferencing. Dunno what this is or if it's important...

Front 23

DSL [Digital Subscriber Line]

Back 23

Became popular as a way to increase data rates in the local loop. Uses full physical capacity of twisted pair [copper] phone lines instead of using the 0-4000KHz voice channel.

Front 24

Twisted Pair Cable

Back 24

Guided media. Most commonly used.

Front 25

Coaxial Cable

Back 25

Type of guided media that is quickly disappearing. Few additional benefits other than better shielding.

Front 26

Fiber Optic Cable

Back 26

LED [light emitting diodes] that carry information inside hair-thin strands of glass called optical fibers. Increases the effective distance to just under 1,000 meters.

Front 27

Radio Transmission

Back 27

When you connect your laptop into the network wirelessly you are using radio transmission.

Front 28

Infrared Transmission

Back 28

Needs a line of sight. [TV, sometimes building to building but if it rains you're fucked.]

Front 29

Satellite Communications

Back 29

Special form of microwave communications. Signals travel at speed of light yet long propagation delay due to great distance between ground and satellite.

Front 30

Factors when selecting media

Back 30

Type of network, cost, transmission distance, security, error rates, transmission speeds.

Front 31

Paralel transmission

Back 31

the way the internal transfer of binary data takes place inside a computer. The circuit is physically made up of eight separate wires wrapped in one outer coating.

Front 32

Serial transmission

Back 32

a stream of data is sent over a communication circuit sequentially in a bit by bit fashion. Serial transmission is considerably slower than parallel transmission.

Front 33

Digital transmission

Back 33

transmission of binary electrical or light pulses in that it only has two possible states. 1 or 0.

Front 34

Unipolar

Back 34

Signaling where the voltage is always positive or negative.

Front 35

Bipolar

Back 35

Signaling where the 1's and 0's vary from a plus voltage to a minus voltage. Experiences fewer errors than unipolar signaling because the symbols are more distinct.

Front 36

Manchester encoding

Back 36

a special type of bipolar signaling in which the signal is changed from high to low or from low to high in the middle of the signal. Less susceptible to having errors go undetected because if there is no transition in midsignal the receiver knows that an error must have occurred.

Front 37

POTS

Back 37

Plain old telephone service enables voice communication between any two telephones within a network.

Front 38

Analog transmission

Back 38

occurs when the signal sent over the transmission media continuously varies from one state to another in a wavelike pattern much like the human voice.

Front 39

Amplitude

Back 39

Measured in decibles.

Front 40

Frequency

Back 40

Expressed in hertz. Pitch of the sound.

Front 41

Phase

Back 41

The direction in which the wave begins. Measured in the number of degrees.