| | | Telephony | |
There have been two advanced development projects in the area of telephony: a digital multiplexed telephone system undertaken with The Philippines and a study of telecommunications routing with Vietnam.
The system being developed is designed for particular circumstances common in The Philippines: dispersed small population centres with difficult intervening terrain. Hence the project contributes to the areas of both self reliance and infrastructural development.
Local population centres are served by small telephone switches. These remote switches are connected by means of microwave links to a central switch, which is further connected to the public telephone network. There is a single microwave band for the outgoing communications from the centre to the remote switches, and another band for incoming (remote to centre) communications. Outgoing communications use a TDM (time division multiplexing) protocol; incoming ones use a TDMA (time division multiple access) protocol.
There is limited capacity in the communication; there is a maximum of 64 channels or "trunks" available (represented by slots in the protocols). These trunks must be dynamically allocated to particular remotes to handle connections.
Documentation of the complete system was completed by the time the Fellow left UNU/IIST (UNU/IIST Report 67 [1]). The proof that the network system satisfies the basic specification of a telephone system was completed. The proof that the more detailed specification, including the communication channels, satisfies the important properties that trunks are never allocated to more than one remote at a time, and that trunks are never "lost", was not completed. Several lemmas were proved, but this proof seems to be at the limits of current technology.
This project looked at the routing of telephone calls and other communications within a generic hierarchic communications network and at the processing of connection and disconnection requests in such a system. One of the most important aspects of the approach taken in this project is that the communications network is considered as a collection of local networks, each of which operates essentially independently of all the other local networks in the system. Each local network thus processes only a part of a connection or disconnection request, namely that using its own local communications lines, then transfers the responsibility for the request to the appropriate neighbouring network.
Vietnam Post and Telecommunications Training Centre No. 1, Hatay, Vietnam
Nowadays electrical communications systems are being used more and more widely to provide global connections between very large numbers of people. In order for such systems to operate efficiently and effectively, control must be distributed to local sub-networks, with each sub-network being responsible only for a small part of the system and passing on the responsibility to some adjacent part of the system whenever it is unable to perform the whole of a requested task itself. The aim of this work is to describe a generic hierarchic communications system which is structured in this way and the message-passing mechanism by which responsibility for connection and disconnection is delegated.
One fellow from the Vietnam Post and Telecommunications Training Centre No. 1 worked on the project and produced both an informal description and a formal specification of a generic hierarchic communications network as a set of largely independent local networks and of the mechanism for connecting and disconnecting communications lines in such a network. These can be found in UNU/IIST Technical Report #106 [2].
The work was successfully completed during the time the fellow was at UNU/IIST and there are no immediate plans for further work.
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