PDF of this tutorialIn view of the above, DTM was developed in an effort to combine the simple, nonblocking, real-time traffic-supporting properties of circuit-switching technology with the dynamic resource-handling properties of packet-switching technology. Combining the advantages of synchronous and asynchronous media-access schemes, DTM forms a transport-network architecture that enables high transfer capacity with dynamic allocation of resources.
As will be shown in the following sections, DTM is fundamentally a circuit-switched, time division multiplexing (TDM) scheme, and, like other such schemes, it guarantees each host a certain bandwidth and uses a large fraction of available bandwidth for effective payload data transfer. In common with asynchronous schemes such as ATM, DTM supports dynamic reallocation of bandwidth between hosts. This means that the network can adapt to variations in the traffic and divide its bandwidth between nodes according to demand.
DTM, like existing transport networks, uses a similar kind of framing structure—synchronous digital hierarchy (SDH)/synchronous optical network (SONET) (i.e., 8-kHz frame repetition frequency)—and is extended with dynamic reallocation of resources. DTM operates at layers one to three in the open systems interconnection (OSI) model and includes switching, control signal for setup, routing, and support functions for easy management. In contrast to SDH/SONET, multirate channels or circuits can be established on demand in DTM, and the capacity of a channel can be changed according to traffic characteristics during operation. Because the distribution of resources among nodes on a ring or bus can be changed, free resources are allocated to nodes with the highest demands, providing an autonomous and efficient dynamic infrastructure. Also, an important aspect of DTM is that it provides a multichannel interface similar to the one provided by ATM.
