Latency tuning Step 4: Optimize the network and transport layers
Digi Connect Family and ConnectPort TS Family
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Command Option Description
set network garp=30-3600
(seconds)
Frequency of Gratuitous ARP (GARP) announcements, which are a
broadcast announcement to the network of a device’s MAC
address and the IP address. These allow the network to update its
ARP cache tables without performing an ARP request on the
network. Gratuitous ARP announcements can affect latency in a
limited way, because some systems stall or dispose of data that is
transmitted during an ARP cache refresh. If this happens, setting
the GratuitousARP frequency to be more often than the problem
system’s time-to-live variable can cause it to refresh the cache
without needing to perform a request.
set network rto_min=30-
1000
The TCP maximum retransmission time out (RTO) in seconds. TCP
uses progressively larger retransmit values, starting at a
minimum value calculated from a sliding window of ACK response
round-trip times bounded at the bottom by rto_min. Essentially,
rto_min is not necessarily the timeout that will be used as the
starting retransmit timeout, but the smallest such value that
could be used. This affects latency, because lowering rto_min can
ensures that retransmits, if they occur, take place in less time. By
occurring sooner, the network can recover lost data in less time at
the expense of possibly retransmitting data still in-flight or
successfully received by the other side, but unacknowledged due
to a “delayed ACK” mechanism or something similar.
set service range=range The index number associated with the service.
set service nodelay={on|off} Allows unacknowledged or smaller-than-maximum-segment-sized
data to be sent for the specified range of network services.
nodelay=off disables Nagle’s algorithm, which is on by default, for
some TCP services. Nagle's algorithm reduces the number of
small packets sent. It establishes not sending outgoing data when
there is unacknowledged sent data, or is less-than-maximum
segment size (typically around 1500 bytes for Ethernet) worth of
data to be sent. While Nagle's algorithm allows efficient data
transmission, there are times where it is desirable to disable it.
set service delayed_ack=0-
1000
Time, in milliseconds, to delay sending ACK packets in response to
received data for the specified range of network services. Default
is 200 milliseconds. Setting this option to 0 (zero) sends an ACK
packet back acknowledge the received data immediately. Setting
this option to any other value than 0 means that the ACK packet
will be sent after the specified time. If the network services
generate new data during that time, the ACK packet is sent along
with the data packet. You can use this setting to avoid congestion
and reduce network traffic, However, do not change this option
from its default setting unless you have a solid understanding of
network services and data transmission, or have been instructed
to the change.
Considerations for using latency-related command options
There are several considerations for using these latency-related command options:
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