cs601 final term paper of fall 2010 on 14-02-2011

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What is the difference between a unicast, multicast, and broadcast address? [3]

T lines are designed for Digital data how they can be used for Analog Transmission ?
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Describe method of checksum briefly?

Explain Asynchronous Time Division Multiplexing in detail? Also discuss its advantages over synchronous TDM?

Ans:
Asynchronous time-division multiplexing (ATDM) is a method of sending information that resembles normal TDM, except that time slots are allocated as needed dynamically rather than pre-assigned to specific transmitters. ATDM is more intelligent and has better bandwidth efficiency than TDM.

Time-division multiplexing (TDM) is a type of digital or (rarely) analog multiplexing in which two or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. A sample byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of one timeslot per sub-channel. After the last sub-channel the cycle starts all over again with a new frame, starting with the second sample, byte or data block from sub-channel 1, etc.

asynchronous time-division multiplexing comprising receive circuits (CRl/i) supplying cells received via input links, transmit circuits (CTl/j) transmitting retransmitted cells on output links, a buffer memory (MT) storing the received cells and delivering the cells to be retransmitted and a buffer memory addressing device (SMT) including a write address source (SAE) and a read address source (fsl/j).
The switching unit further comprises a write disabling circuit (pi) conditioned by a signal (adl) derived from the content of at least one received cell or a signal (tle) derived from the absence of any received cell and supplying a disabling signal (spi) and the address source includes a disabling device (pac, pal) influenced by the disabling signal (spi) so that no memory location is then occupied in the buffer memory (MT).

Advantages asynchronous TDM:

In asynchronous TDM, the timeslots are not fixed. They are assigned dynamically as needed.
In order to reduce the communications costs in time-sharing systems and multicomputer communication systems, multiplexing techniques have been introduced to increase channel utilization. A commonly used technique is Synchronous Time Division Multiplexing (STDM). In Synchronous Time Division Multiplexing, for example, consider the transmission of messages from terminals to computer, each terminal is assigned a fixed time duration. After one user's time duration has elapsed, the channel is switched to another user. With synchronous operation, buffering is limited to one character per user line, and addressing is usually not required. The STDM technique, however, has certain disadvantages. As shown in Figure 1, it is inefficient in capacity and cost to permanently assign a segment of bandwidth that is utilized only for a portion of the time. A more flexible system that efficiently uses the transmission facility on an "instantaneous time-shared" basis could be used instead. The objective would be to switch from one user to another user whenever the one user is idle, and to asynchronously time multiplex the data. With such an arrangement, each user would be granted access to the channel only when he has a message to transmit. This is known as an Asynchronous Time Division Multiplexing System (ATDM). A segment of a typical ATDM data stream is shown in Figure 2. The crucial attributes of such a multiplexing technique are:
1. An address is required for each transmitted message, and
2. Buffering is required to handle the random message arrivals.

Question#1
What are the Asynchronous protocols in data communication layer? ………….Marks (10)

Asynchronous protocols in data communication layer employed mainly in Modems. They treat each character in a Bit stream independently.
Disadvantage:
Inherent slowness is its disadvantage. It requires addition of start and stop bits
and extended spaces between frames, so these are mainly replaced with High speed synchronous mechanisms.
Advantages:
1. Not Complex and Inexpensive to Implement.
2. Transmission does not require timing coordination; Timing is done by using extra bits.


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One new update with this helping subjective material please check it.
Question#1
What are the Asynchronous protocols in data communication layer? ………….Marks (10)

Question#2
What is Frequencly division multiplexing ?.......Marks (5)


Question#3
Find the binary equivalent Marks (5)


Question#4
What is stop and wait ARQ in error control ?....Marks (3)


Question#5
What is Interleaving ?........Marks (3)


Question#6
What is DSU in terms of digital services?.........Marks (3)


Question#7
Which architecture of Ethernet developed by ITU_T and
ANSI?........... Marks (2)


Question#8
What is a spike in noise term?.........Marks (2)

Question#9

What is even parity generator in VRC error detection mechanism?...........Marks (2)