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Firmware Support for Reliable Communication and Dynamic System Configuration in System Area Networks

Report ID:
May 1998
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Research efforts to provide fast multicomputer interconnection
networks for clusters of workstations (SANs) at low cost has lead to
the design of network interfaces that support minimal standard
functionality in the network interface and use powerful basic blocks
that allow communication system designers to implement the
functionality needed by different paradigms and systems using these
basic blocks. These network interfaces usually encompass a general
purpose processor, use simple switches to route packets to their
destination, and allow for arbitrary network topologies. These
characteristics result in the absence of reliability in the network
interface hardware and the need to support routing for arbitrary,
dynamic topologies in the communication system.

There are many ways to deal with these problems. However, if
performance is not to be compromised, these problems are highly
non-trivial and many issues need to be considered. Data copies need to
be avoided, algorithms and protocols need to be simple and memory
requirements must be low, since the network interface has limitations
in both network processor speed and memory.

In this work we address these two issues by presenting the extensions
we did to our communication system, called Virtual Memory Mapped
Communication (VMMC), to support reliable communication in the network
interface and dynamic system configuration. We propose and implement
reliable communication in the firmware that runs on the network
interface processor with minimal cost; less than 2.5 microseconds for
latency and less than 10% for all different types of bandwidth
Moreover, we propose a new scheme for dynamically determining the
network topology. This mechanism relies on the retransmission
mechanism that is used to provide reliable communication. Since the
support for dynamic system configuration is not on the common path,
there is no effect on system performance when no changes in the system
topology occur.

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