User`s guide

Latency Tuning
163
Latency Tuning
CHAPTER 6
What is Latency?
This section discusses latency and a recommended process for defining and addressing latency
issues in your network and application.
Latency is the amount of time a packet takes to travel from source to destination. Together, latency
and bandwidth define the speed and capacity of a network. Several factors influence latency,
including the traffic pattern and traffic generated by an application, the physical wiring for the
network, the use of various TCP/IP timers, and the amount of additional traffic on the network
besides that generated by the application.
Recommended Process for Deterministic Ethernet/IP Performance
Following is a process recommended to achieve deterministic Ethernet/IP networking behavior. It
uses Digi commercial off-the-shelf firmware and hardware, and not any specialized products
specifically designed to reduce latency. By following this process, you should be able to define and
address latency issues at multiple levels in your network and application. The process involves
these steps:
1 Determine the characteristics of your application, in terms of traffic pattern and amount of
traffic generated.
2 Determine the latency budget and the type of latency in which you are interested.
3 Depending on the results produced in steps 1 and 2 and if applicable, optimize the physical
layer.
4 Depending on the results produced in steps 1, 2, and 3 and if applicable, optimize the
network and transport layer.
5 Depending on the results produced in steps 1, 2, 3, and 4 and if applicable, optimize the
application layer.
Best-case scenario for achieving deterministic Ethernet/IP networking behavior
The best-case scenario for achieving deterministic Ethernet/IP networking behavior with Digi
firmware and hardware is a unidirectional master-slave application running over an isolated
Ethernet network that is built around Ethernet switches instead of Ethernet hubs. In other words, a
network that eliminates unnecessary traffic and minimizes Ethernet collisions.