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TD Feed latency

The latency endpoints return the current feed latency, which is the difference in time from when the message was sent to when we received it.

This data is available at both the top level (i.e. for all messages) and for each individual describer. These are the endpoints which provide this data:

  • Top level
    • http://api.area51.onl/rail/1/td/latency
    • http://api.area51.onl/rail/1/td/latency/current
    • http://api.area51.onl/rail/1/td/latency/history
  • Train describer level where :area is the area ID:
    • http://api.area51.onl/rail/1/td/:area/latency
    • http://api.area51.onl/rail/1/td/:area/latency/current
    • http://api.area51.onl/rail/1/td/:area/latency/history

The output of each set of endpoints is the same, just the scope of the underlying data is different. Each set of endpoints returns the following:

latency
returns both the current and up to the last 6 hours of historical data
latency/current
Returns just the current latency
latency/history
Returns up to the last 6 hours of historical data

The latency object returns the following:

current
The current latency
history
Up to the last 6 hours of history
lastUpdate
The time the last message was received

The latency/current endpoint and the current object returned by the latency endpoint returns the following:

value
The latency in ms of the last message
max
The maximum latency in this sample period
min
The minimum latency in this sample period

The history endpoint and the history object returned by the latency endpoint returns the last 6 hours of history in 5 minute segments.

time
The time of the most recent history entry
history
Array of 0..72 history entries with the most recent first

Each history entry consists of:

time
The time of this entry in ISO format
timestamp
The time of this entry in milliseconds since the UNIX epoch
value
The latency in ms of the last message
max
The maximum latency in this sample period
min
The minimum latency in this sample period

What is latency?

This time is measured in milliseconds but is only an estimate as multiple factors can affect this so this is only a guide figure but it's being made available as other users of the source TD feeds often ask if anyone is seeing various delays in the data.