Synchronizing asynchronous bounded delay networks

Abstract

An efficient way to synchronize an asynchronous network with a bounded delay message delivery is presented. Two types of synchronlzaiioo algorithms are presented. Both types require an initializing phase that costs IEl messages (where IEl is the number of links). The first requires an additional hit in every message and increases the time complexily by a factor of 2. The second does not require any additional hits but increases the time complexity by a factor of 3. We also explain how to overcome differences in nodal timer raies.

Formalization and Correctness of the PALS Architectural Pattern for Distributed Real-Time Systems

“…2. As a consequence of (1), in systems using the synchronizers in [6,33], the nodes are not closely synchronized in physical time, so that, at the same global physical time, one node could be in its nth round while another node is in its kth round, for any n, k ∈ N. There may therefore be no global physical time at which all nodes are in the same round. The fact that a state s in the synchronous system may not have a corresponding "stable" state s in the asynchronous execution makes it impossible to relate the temporal logic properties of the synchronous system and its asynchronous counterpart in physical time, as we have done for PALS, although it would still be possible to relate them with a notion of logical timeà la Lamport.…”

“…The ABD Network model used by the synchronizers in [6,33] and by PALS is a very useful abstraction. However, this abstraction places stringent demands on an actual network design that must guarantee such bounded time delivery of messages in the physical world under some stringent model of possible failures.…”

“…PALS can then be understood as a synchronizer that also assumes the ABD model (plus clock synchronization) as its infrastructure and furthermore provides real-time guarantees needed for embedded systems applications. The main differences between the synchronizers in [6,33] and PALS can be summarized as follows:…”

“…Very general synchronizers such as those in [3] place no a priori bounds in message delays, so that physical time in the original synchronous system is simulated by logical time 10 in its asynchronous counterpart. More recent work has developed synchronizers for the Asynchronous Bounded Delay (ABD) Network model [6,33], in which a bound can be given for the delay of any message transmission from any process to any other process. PALS can then be understood as a synchronizer that also assumes the ABD model (plus clock synchronization) as its infrastructure and furthermore provides real-time guarantees needed for embedded systems applications.…”

“…PALS therefore assumes that a clock synchronization algorithm with a skew bound is running in the underlying infrastructure. Instead, the synchronizers in [6,33,32] provide a clock synchronization algorithm as part of the synchronizer itself. 2.…”