12.3.1 Evaluating Protocol Performa

12.3.1 Evaluating Protocol Performance
The evaluation of protocol performance is performed by brute force experimentation.
During protocol specification, a configuration file is used to identify microprotocol
resources and default protocol configurations. Using this file it is possible for the APSL
parser to automatically generate client and server applications that evaluate the performance
characteristics of all valid protocol configurations.
Evaluating every protocol configuration in a static environment, where connection
characteristics remain fixed, does not account for the protocols performance over real world
connections in which connection characteristics are potentially variable. To function
correctly in such circumstances an adaptation policy requires knowledge of how different
configurations perform under different conditions. To simulate precisely defined network
characteristics, a traffic shaper is introduced. This intercepts packets traversing a host’sNeural Networks for the Optimization of Runtime Adaptable Communication Protocols 209
network interface, incurs bit and block errors, introduces variations in delay, loses packets
and restricts throughput. The shaper is contained within a microprotocol module that may be
dynamically loaded into the runtime framework. In concept this module lies on the
connection between the client and server evaluation applications. In fact it is located in the
runtime framework at the server side node. A basic overhead of 0.0438 microseconds is
incurred for each invocation (measured on a Pentium II 300MHz based machine) with
additional undefined overheads for the shaping code. The use of a modular structure permits
protocol designers to add their own code for the shaping of network characteristics. Each
microprotocol posses a control interface allowing instructions to be passed from the runtime
framework. This permits an application to simulate numerous network conditions by scaling
parameters, such as residual error rate, used by the shaper mechanisms.