Before data arrive at the University of Athens Seismological Laboratory data center, they are transmitted from the stations over a variety of different SeedLink connection and nodes. These may include fast Internet connections as well as relatively slow dialup telephone lines. Therefore, the delay of a data sample from the moment it is recorded at the station until it is archived at the data canter varies greatly not only between different stations but also with time.
The data latency is the time elapsed since the last archived data sample was recorded at the station. The feed latency is the time elapsed since the last data packet was received at the data center. The difference between these two latencies thus reflects the data latency at the moment the last packet was archived.
Obviously, the aim is to keep all latencies as small as possible. Latencies can be as small as 2 seconds where data are transmitted through fast Internet links. They can exceed an hour where (possibly irregular) dialup connections are involved, without signifying any error.
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