tailieunhanh - Data Communication Principles P2

In this switching mechanism, a circuit is allocated to every piece of complete information (called a call). This circuit allocation is all the way from the sending to the receiving computer or terminal. It stays in place throughout the duration of the call until the sending (or receiving) side signals that it is not needed any more. In more formal terms, we say that a fixed bandwidth is guaranteed throughout the communication session. | 11 Large File - Language format comparison with recipient - Break up into manageable slices - Sequencing and information integrity embedded in each chunk Routing Combat channel Link problem physical transmission In this example instead of emphasizing on signal type we care more about readability of the transmitted document. There is no need of format comparison breaking up in manageable chunks sequencing etc. in voice communication. Even functions common to both voice and file communications such as routing could have different implementations and following paragraph explains how. For speech communication the gaps in talk spurts occur naturally and form an essential part of information. It is necessary that these gaps be maintained at the receiving point. However such is not the case for a file that is stored in a directory at the sending end and would be stored at the receiving end in another directory. In other words if we use a different path for each data block of the file with a sequence number stamped on it we will not lose any information by having each chunk using different route. We can always look at the sequence numbers of the received data blocks and put them back in order. Not only that if we make quite small manageable chunks of file we can process them individually as if each one is from a separate user. So if one of the chunks is in error it can be requested again from the sending computer. In essence even though both voice and file transfer need routing the most suitable mechanism can be substantially different for the two. The most favorable way for routing voice data is what is called circuit switching. File like data on the other hand can best use chunk-based-switching called packet switching. Here s a brief account of each a detailed discussion will follow in Chapter 2 . . Circuit Switching In this switching mechanism a circuit is allocated to every piece of complete information called a call . This circuit allocation is all the way from