User`s guide

What is Latency?
Chapter 12 Latency Tuning 105
This chapter discusses latency and a recommended process for defining
and addressing latency issues in your network and application.
What is Latency?
Latency is the amount of time it takes a packet 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 Latency Tuning
Following is a process recommended to achieve deterministic Ethernet
networking behavior. It uses Digi commercial off-the-shelf (COTS) 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.
In summary, the process involves five 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. If applicable, depending on the results produced in steps 1 and 2,
optimize the physical layer.
4. If applicable, depending on the results produced in steps 1, 2, and 3,
optimize the network and transport layer.
5. If applicable, depending on the results produced in steps 1, 2, 3, and 4,
optimize the application layer.
Best-case scenario
The best-case scenario for achieving deterministic Ethernet networking
behavior with DIGI COTS 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,
the best-case scenario is a network that eliminates unnecessary traffic and
minimizes Ethernet collisions.
Chapter 12
Latency Tuning