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Mạng VSAT (P4)

NETWORKING ASPECTS NETWORK FUNCTIONS As mentioned in Chapter 1,VSAT networks usually offer communications service between user terminals. These terminals generate baseband signals that are analogue or digital,predominantly digital. For signals generated by asource terminal and to be delivered to adestination terminal, the VSAT network must provide the following functions: -establish a connection between the calling terminal and the called one; -route the signals from the calling terminal to the called one, although the physical resource offered the considered connection may be for shared by other signals on other connections; -deliver the information in a reliablemanner. . | VSAT Networks G.Maral Copyright 1995 John Wiley Sons Ltd ISBNs 0-471-95302-4 Hardback 0-470-84188-5 Electronic 4 NETWORKING ASPECTS 4.1 NETWORK FUNCTIONS As mentioned in Chapter 1 VSAT networks usually offer communications service between user terminals. These terminals generate baseband signals that are analogue or digital predominantly digital. For signals generated by a source terminal and to be delivered to a destination terminal the VSAT network must provide the following functions establish a connection between the calling terminal and the called one route the signals from the calling terminal to the called one although the physical resource offered for the considered connection may be shared by other signals on other connections deliver the information in a reliable manner. Reliable delivery of analogue signals implies delivering the signals within acceptable distortion limits and with a sufficiently high signal to noise power ratio S N. Reliable delivery of data means that data is accepted at one end of a connection in the same order as it was transmitted at the other end without loss and without duplicates. This implies four constraints FAI93 no loss at least one copy of each part of the information content is delivered no duplication no more than one copy is delivered first in first out FIFO delivery the different parts of the information content are delivered in the original order the information content is delivered within a reasonable time delay. It has been indicated in Chapter 1 section 1.3 that VSAT networks could be envisaged to support many different types of traffic. However the network cannot convey all such different types of traffic in a cost effective way. 102 Networking aspects Therefore VSAT networks are optimised for a given set of traffic types which reflect the dominant service demand from the user and may offer as an option other types of services but not as efficiently. Most VSAT networks are optimised for interactive exchange of data.