User`s guide

Latency Tuning
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Step 1: Determine the characteristics of your application
Consider your application in terms of traffic pattern and amount of traffic generated.
 What is the main purpose of the application, and the primary activities?
 What is the 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 the latency budget and type of latency
Next, determine the latency budget and type of latency in which you are interested. Identifying the
latency budget for your application involves defining what latency means for your network and the
application running on it. Consider how much latency is acceptable and whether the latency is ne-
way or round-trip. This latency budget influences how much optimization you may need to
perform at the physical, data link/network, and application layers.
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, where background noise is less relevant and has less
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.