The authors give several examples of virtual path and virtual channel use for different types of communication, and then compare the two mechanisms. For most types of communication, both virtual path and virtual channel connections are more-or-less equally capable. However, for relatively high bandwidth communication involving more than five to ten participants, virtual path connections can more efficiently support some interconnection patterns. In general, the authors believe that both connection types are desirable and both should be extended to the client by network providers.>

The notion of encapsulations is introduced as the basic construct used to support optimistic make (a software tool). The authors describe the implementation of optimistic make in the V-System on a collection of SUN workstations. Statistics measured from this implementation are used to synthesize a workload for a discrete-event simulation, and to validate the simulation's results. The simulation shows a speedup distribution over pessimistic make with a median of 1.72 and a mean of 8.28. The speedup distribution is strongly dependent on the ratio between the target out-of-date times and the command execution times. With faster machines the median of the speedup distribution grows to 5.1, and then decreases again.>

A connection management access protocol (CMAP) for managing multipoint connections in high-speed packet switched networks is described. The protocol is targeted to broadband integrated services digital networks (BISDN) using the asynchronous transfer mode (ATM) communication standard. To establish a multipoint connection, a client first creates a call between itself and the network. The client creating a call is designated the owner of the call. Immediately after creation, the owner is the only endpoint participating in the call. Additional endpoints are added either by invitation from the owner, invitation from another client of the network, or by explicitly requesting to be added. These three modes are sufficient for supporting point-to-point communication (for example, a telephone call), many-to-many communication (for example, a conference call), one-to-many communication (for example, broadcast video), and many-to-one communication (for example, error logging).>

The derivation of a semantically equivalent optimistic computation from a pessimistic computation by application-independent transformations is discussed. Computations are modeled by program dependence graphs (PDGS). The semantics of a computation is defined by a mapping from an initial state to a final state and is realized by a graph rewriting system. Semantics-preserving transformations are applied to PDGS of the pessimistic computation to produce an optimistic version. The transformations result from guessing data values and control flow decisions in the computation. The transformations are used to derive an optimistic version of fault tolerance based on message logging and checkpointing. The transformations yield an optimistic version similar to optimistic fault-tolerance algorithms reported in the literature, although additional application-dependent transformations are necessary to produce a realistic optimistic implementation.>

Optimistic make is a version of make that executes the commands necessary to bring targets up-to-date prior to the time the user types a make request. Side effects of these optimistic computations (such as file or screen updates) are concealed until the make request is issued. If the inputs read by the optimistic computations are identical to the inputs the computation would read at the time the make request is issued, the results of the optimistic computations are used immediately, resulting in improved response time. Otherwise, the necessary computations are reexecuted.

The results of a simulation study undertaken to evaluate a high-performance packet-switching fabric supporting point-to-point and multipoint communications are presented. This switching fabric contains several components, each based on conventional binary routing networks. The most novel element is the copy network, which performs the packet replication needed for multipoint connections. Results characterizing the performance of the copy network are presented. Several architectural alternatives for conventional binary routing networks are also evaluated. For example, the performance gains obtainable by using cut-through switching in the context of binary routing networks with small buffers are quantified. One surprising result is that networks constructed from nodes with more then two input and output ports can perform less well than those constructed from binary nodes. This result is quantified and explained.>