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Font Paragraph Styles e are ready to be installed, but first we need to close some apps. Update now Short Answer Questions 1. Describe how digital signals are transmitted over an analog circuit and analog signals over digital circuit. 2. Differentiate between the following multiplexing techniques in terms of mechanics, technology, and applications. (a) FDM; b) TDM: (c) STDM 3. What are the key shortcomings of TDM and how does STDM seek to overcome 4. (a) What is a signal? (b) What is propagation? (c) What are propagation these? effects? 5. Transmission Media: a. Conducted Media 1. Twisted Pair UTP. STP Characteristics Applications Advantages Disadvantages 2. Coaxial Characteristics ApplicationsExplanation / Answer
2)Answer:
FDM:
Frequency Division Multiplexing (FDM) is a networking technique in which multiple data signals are combined for simultaneous transmission via a shared communication medium. FDM uses a carrier signal at a discrete frequency for each data stream and then combines many modulated signals.
When FDM is used to allow multiple users to share a single physical communications medium (i.e. not broadcast through the air), the technology is called frequency-division multiple access (FDMA).
Frequency Division Multiplexing has many applications. Stereo FM transmissions use carrier signals referred to as subcarriers (a previously modulated signal modulated into another signal of higher frequency and bandwidth), which differentiates signals to left and right channels, one for each speaker and sometimes a third, forth and fifth signals for three, four or five speaker sound systems. Television channel signals are divided up into different subcarrier frequencies for video, audio and color. And DSL (digital subscriber line) transmissions use different subcarrier frequencies for voice, upstream and downstream data transmissions (frequency duplex,” i.e. simultaneous transmissions in both directions); these too are all multiplexed into the same communications medium.
Twentieth century telephone companies used FDM for long-distance connections to multiplex thousands of voice signals through co-axial cable systems. This was done in numbers of stages by utilizing channel banks (a device for multiplexing or demultiplexing groups of channels, i.e. physical transmission paths). Shorter distance connections used communications mediums (cables) with less bandwidth, some with only 12, and later 24, voice channels multiplexed using four wires – a pair for each direction; these were common in households and small businesses. These signals went through twisted pair telephone lines, i.e. copper wires with insulation twisted around each other to prevent signals from interfering with each other, known as crosstalk or more technically, electromagnetic induction. However, near the 21st century use of FDM became rare and instead it was replace with time-division multiplexing (TDM).
TDM:
Time division multiplexing (TDM) is a communications process that transmits two or more streaming digital signals over a common channel. In TDM, incoming signals are divided into equal fixed-length time slots. After multiplexing, these signals are transmitted over a shared medium and reassembled into their original format after de-multiplexing. Time slot selection is directly proportional to overall system efficiency.
Time division multiplexing (TDM) is also known as a digital circuit switched.
TDM was initially developed in 1870 for large system telegraphy implementation. Packet switching networks use TDM for telecommunication links, i.e., packets are divided into fixed lengths and assigned fixed time slots for transmission. Each divided signal and packet, which must be transmitted within assigned time slots, are reassembled into a complete signal at the destination.
TDM is comprised of two major categories: TDM and synchronous time division multiplexing (sync TDM). TDM is used for long-distance communication links and bears heavy data traffic loads from end users. Sync TDM is used for high-speed transmission.
During each time slot a TDM frame (or data packet) is created as a sample of the signal of a given sub-channel; the frame also consists of a synchronization channel and sometimes an error correction channel. After the first sample of the given sub-channel (along with its associated and newly created error correction and synchronization channels) are taken, the process is repeated for a second sample when a second frame is created, then repeated for a third frame, etc.; and the frames are interleaved one after the other. When the time slot has expired, the process is repeated for the next sub-channel.
Examples of utilizing TDM include digitally transmitting several telephone conversations over the same four-wire copper cable or fiber optical cable in a TDM telephone network; these systems may be pulse code modulation (PCM) or plesiochronous digital hierarchy (PDH) systems. Another example involves sampling left and right stereo signals using resource interchange file format (RIFF), also referred to as waveform audio file format (WAV), audio standard interleaves. Also synchronous Digital Hierarchy (SDH) and synchronous optical networking (SONET) network transmission standards have incorporated TDM; and these have surpassed PDH.
TDM can also be used within time division multiple access (TDMA) where stations sharing the same frequency channel can communicate with one another. GSM utilizes both TDM and TDMA.
STDM:
Statistical time-division multiplexing (STDM) is a form of communication link sharing, which is almost identical to dynamic bandwidth allocation (DBA).
In STDM, a communication channel is split into a random range of variable bit-rate data streams or digital channels. The link sharing is tailored for the instantaneous traffic requirements of the data streams which are transmitted over every channel.
This type of multiplexing is a replacement for creating a fixed link sharing, such as in standard time division multiplexing (TDM) and frequency division multiplexing (FDM). Upon precise execution, STDM can offer an improvement in link utilization, referred to as the statistical multiplexing gain. STDM is facilitated by means of packet-mode or packet-oriented communication.
STDM is more efficient than standard TDM. In standard TDM, time slots are allotted to channels even when there is no data to transmit. This leads to wasted bandwidth. STDM was originally developed to address this inefficiency, where the time allocation to lines happens only when it is actually required. This is attained through intelligent devices that are ideal for identifying an idle terminal.
STDM is same as TDM, with the exception that every signal is assigned a slot based on priority and demand. This indicates that STDM is an "on-demand" service as opposed to a fixed one. Standard TDM and various other circuit switchings are executed at the physical layer in the OSI and TCP/IP model, while STDM is executed at the data link layer and above.
Scenarios of statistical time-division multiplexing are:
Diffrences:
FDM:
(application) can interfere with any timing which might have been previously set-up between the remote device and the central processor. This is particularly important in manufacturing or process control operations
(application) can interfere with any timing which might have been previously set-up between the remote device and the central processor. This is particularly important in manufacturing or process control operations
3)Answer:
The key shortcoming of TDM is that it uses a fixed portion of time for each attached input device whether the device is active or not (efficiency is sacrificed for the sake of simplicity). STDM overcomes this by eliminating idle time allocations to inactive terminals and by eliminating padded blanks or null characters in the composite message blocks
4)Answer:
a)Signal:
A signal is an electrical or electromagnetic current that is used for carrying data from one device or network to another.
It is the key component behind virtually all:
A signal can be either analog or digital.
Typically, a signal is created when a command or data is sent to a device. It has implementation in electrical and electronic components as well, but it mainly refers to analog and digital communication technologies and devices. Each signal carries data in some form. The data is fed into the signal using analog or digital modulation techniques, depending upon the source and destination device and/or medium.
Besides communication devices that broadcast a signal externally to the host system, signals are also used to communicate and send instructions by:
Propagation:
Propagation literally means to reproduce or spread; in wireless networks, signal propagation refers to the radiation of an radio wave through the air and intervening objects. To learn some of the basics about radio signal propagation, check out these primers from Breezecom and SSS Online.