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In a synchronous connection, a receiver employs a clock that has been synchronized to a transmitter clock, while the situation is different with an asynchronous connection. In the case of the asynchronous connection, both the receiver clock and the transmitter are all independent, and these two elements are unsynchronized. Moreover, in the case of the asynchronous connection, data are often transmitted in character series, which is fixed in both format and size, thus making it unnecessary to time successive characters, but in the synchronous connection, the timing relationship must be enhanced. However, in the case of isochronous connection, there is no error checking, since the data is transmitted in real time, and this is contrary to the synchronous and asynchronous connections that perform error checking.
Asynchronous communication is advantageous, because it is a faster method of transmitting data. Besides, it facilitates error checking, which makes it possible to deliver information that is free of error to the receiver. Moreover, this communication makes use of a transmitting device, receiving equipment and, possibly, a connecting wire, which do not require the coordination on the timing of the transmitter. However, asynchronous communication is disadvantageous, because it appears to be a complicated process, which requires both the sender and the receiver to make use of the same encoding method or decoding procedure when data transmission has been encoded into someone’s signal. In addition, both the sender and the receiver must be well-equipped with the necessary knowledge on searching the required data in the signal and in case of failure, the transmission and communication process cannot be finalized.
A part from its error detection capability, the synchronous communication system is advantageous, because it is capable of negotiating the data link connection before the commencement of the communication process. In this regard, it synchronizes two timing clocks prior to the transmission process, and then resetting these clocks numerical counters to facilitate error detection. Moreover, both sides of this system can easily exchange status information and communication parameters due to the fact the connection can be synchronized simultaneously. Besides, the synchronous system of communication is even more efficient in cases, whereby the transmission media used radio signal, electric wire and laser beam prove to be unreliable. Even though, this is a more efficient system of communication, it suffers certain limitations since it takes a lot of time, especially on the lower error rate lines.
A half-duplex system allows communication to take place consecutively, but the transmission occurs simultaneously in the full-duplex system of communication. In the half-duplex communication, information transfer is only possible with only one individual doing it at a time, and then the other party does it later. This is due to the fact that both the individuals carry out the transmission process in one frequency. However, the full-duplex system allows the transmission to be done simultaneously. This makes it possible to communicate in both directions, which is not possible with the half-duplex system. For example, mobile telephony communication systems employ full-duplex, because both the speakers can speak and be heard concurrently.
Frequency Division Multiplexing (FDM) includes cable televisions, broadcast televisions and radios.
The sampling is done according to the assigned channel frequencies, and bytes from faster device are transmitted first to the recipient, and this sequence follows the same way the bytes are input.
T-1 and SONNET are similar, because both of them provide optical transmission services, which are capable of delivering a number of data channels from various data sources.
A.) Frequency Division Multiplexing (FDM) is advantageous, because it makes it possible to add another user to the system, and this can be done through incorporating an additional pair of the receiver demodulators as well as the transmitter modulator. Besides, it is important, because it supports the flow of full-duplex information that is often necessary in many applications. However, the FDM suffers several limitations: high initial costs involved for cabling, and every user of this system must have specific carrier frequency for it to operate.
B.) Synchronous Time Division Multiplexing (STDM) is advantageous, because it makes it possible for several users to share a dedicated high speed line. It is also important, because it functions as the best technique for digital data transmission. However, limitations are experienced since it is a costly system to install. In addition, wastage of this resource is experienced, especially when a client fails to make use of the time slot, thus making this resource to be idle at that time.
C.) Statistical time division multiplexing is advantageous because it is capable of allocating time slots/slices dynamically according to the usage demands. In addition, this system does not allocate channel capacities to the lower speed lines, which are not active. However, the system is disadvantageous, because it demands more guard time. In addition, this method requires synchronization for it to work effectively.
D.) The advantages of Wavelength Division Multiplexing (WDM) are: fewer channels, wires and required for data transmission and data reception. Only one optic can be used sufficiently in handling several channels. Moreover, it is usually cheaper, especially when a smaller space of the electromagnetic spectrum is used. However, these are some disadvantages associated with the WDM since it requires some complicated transmitters and complex receivers. In addition, wide band transmitters and receivers are needed for this process, and this translates to higher costs and little reliability.