APPENDIX 3 – E-DBA THROUGHPUT/LATENCY MEASUREMENTS METHODS
The contents of this appendix are also available in Technical Instruction Sheet 044 (TIS044), dated March 01, 2006.
Overview
The instructions in TIS044, intended for end-users, discuss the effectiveness of TCP/IP troubleshooting tools in E-
DBA networks. It shows how to assess network performance in the E-DBA environment. It is reproduced here to
complement the information given in section 5.4.
Performance Metrics
The following metrics are typically used to measure communication network performance:
♦
Latency
Also called “Response Time”. In this context, latency measures the amount of
time it takes for a response to return from a request. It takes into account the
delays accumulated at every step of the round trip.
Usually expressed in seconds or milliseconds.
♦
Throughput
The amount of information that can be transferred over a connection in a given
period of time.
Usually expressed in bits per second (bps), bytes per second (Bps) or packets per
seconds (pps)
E-DBA Primer
E-DBA is a
scheduled air-link protocol
whose algorithms were designed to favor throughput over latency. To
achieve that goal, the air-link uses adaptive timeslots called
cycles
to schedule traffic. These cycles dynamically
vary in length (typically, between 200 to 1500 milliseconds) based on various factors, including network load.
Each packet of data transiting through an E-DBA network must therefore be scheduled for transmission, which
introduces a
scheduling latency
of one or more cycles.
PING as a Performance Measuring Tool
Ping is a utility used to determine whether a particular IP address is reachable by sending out a packet and waiting
for a response. It is therefore a good tool to measure network latency.
Because of E-DBA’s cycle mechanism, a ping packet could take up to 3 cycles to make the round trip, producing an
unexpectedly large ping time even when the radio channel is lightly loaded. For this reason, CalAmp recommends
that ping should only be used to verify if a device is reachable, not as a measure of network performance.
On Ethernet-only networks, ping is normally set to timeout its request packets after 1 or 2 seconds. When using
ping over an E-DBA network, CalAmp recommends setting the ping timeout to 5000 milliseconds or more.
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