User`s guide

Recommended Process for Latency Tuning
106 Chapter 12 Latency Tuning
Step 1: Determine the characteristics of your application
The first step in addressing latency is to consider the characteristics of your
application in terms of traffic pattern and amount of traffic generated.
• What is the main purpose of the application, and the primary activities?
• Traffic pattern: Is it peer-to-peer or master-slave application?
• Amount of traffic generated (x bytes every y minutes): How much data
is being transmitted from and received by the application, and over
what amount of time? For example, 200 bytes of data sent over 500
milliseconds.
Step 2: Determine latency budget and type of latency
Identifying the latency budget for your application involves defining what
latency means for your network and the application running on it. This
latency budget influences how much optimization you may need to perform
at the physical, data link/network, and application layers.
• Define how much latency is acceptable.
• Is the latency one-way or round-trip?
Step 3: Optimize the physical layer
Depending on the results produced in steps 1 and 2, optimize the physical
layer; that is, address the physical-layer characteristics that can affect
latency.
Optimizing the physical layer, may include, but is not limited to, these
recommendations:
• Use Ethernet switches instead of Ethernet hubs to minimize
unnecessary traffic and minimize collisions.
• Use industrial-strength cabling and make sure the wiring is sound. Bad
wiring can result in increased collisions.
• Eliminate impedance mismatches.
• Avoid running communications cabling on the same tracks with power
cabling or other cabling exhibiting fast voltage swings
• Use a smaller less noise-induced error-prone Ethernet, or data rate.
Lower Ethernet speeds have higher voltages, at which background
noise is less relevant and has less of an impact on latency. Voltages
associated with 10, 100, and 1000 mbps Ethernet speeds are:
• 10 mbps: 2.3V (CAT5)
• 100 mbps: 0.8V (CAT5)
• 1000 mbps: 0.5V (CAT5E/CAT6)
• Ground to earth all your networking equipment, including the Digi
device.
• Use only networking equipment that is certified or known to operate
well within the required ranges for vibrations, shock, operating
temperature, relative humidity, etc.