NSF SAGE:
SeedLink
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SeedLink
Overview
The
SeedLink
protocol is a robust data transmission intended for use on the Internet or private circuits that support
TCP
/IP. The protocol is robust in that clients may disconnect and reconnect without losing data, in other words transmissions may be resumed as long as the data still exist in the servers buffer. Requested data streams may be limited to specific networks, stations, locations and/or channels. All data packets are 512-byte Mini-
SEED
records. Enhancements to the SeedLink protocol supported by the
DMC
’s server allow network and station codes to be wildcarded in addition to the location and channel codes.
Real-time Data from the EarthScope
DMC
The
DMC
runs a publicly accessible SeedLink server on the following host and port:
host
port
rtserve.iris.washington.edu
18000 (default SeedLink port)
All open data that the
DMC
receives in real-time or through real-time collection channels is available via this SeedLink server.
Usage Restrictions
Please note the
Usage Guidelines
for the SeedLink service.
Users are welcome to any data available via the server as long as client actions do not inhibit our capability to deliver data to other users. Users should strive to minimize the number of connections to our server. With SeedLink it is possible to select a nearly arbitrary selection of channels using a single connection. The
DMC
reserves the right to enforce connection limits in order to ensure that the service is available to a broad range of users and to maintain a stable service. Keep alive (heartbeat) packets should not be sent at intervals less than 4 minutes. Please read our
Expectations
policy below regarding service uptime.
Available Software
The following software is available from the
DMC
at
. For details about each individual software package, please visit the
software
pages, or click the package name link below:
libslink
– A SeedLink client library written in C.
slink2orb
– SeedLink to
Antelope
ORB
client (licensed Antelope libraries are required).
slink2ew
– SeedLink to
Earthworm
client. Windows binaries available. The most recent release of slink2ew is in the Earthworm source code repository.
slarchive
– A SeedLink client that writes all received data to the local disk in user defined directory and file structures.
slinktool
– Command line SeedLink client useful for data stream inspection and server testing.
ewexport_plugin
– An Earthworm export process plugin (data source) for a seedlink server.
orbplugin
– An Antelope
ORB
plugin (data source) for a seedlink server (licensed Antelope libraries are required).
Example configurations
slink2orb – Antelope client configuration
Example command line that would go into the
Processes
table (Tbl) in your
rtexec.pf
slink2orb-DMC slink2orb -S state/slink2orb-DMC -pf slink2orb-DMC rtserve.iris.washington.edu $ORB
Do not forget to add
slink2orb-DMC
to the
Run
array (Arr) in your
rtexec.pf
too!
You need to define which channels you would like to receive in the parameter file of
slink2orb
. Example contents of
slink2orb-DMC.pf
parameter file for use with the above instance of
slink2orb
is below.
slink2orb-
DMC
.pf:
stations &Arr{
# NET_STA [selectors]
IU_ANMO BH?
II_ADK BH?
TA_D15A BH?
This example parameter file would select
BH*
channel data from the
IU
network station
ANMO
, the
II
network station
BFO
and the
TA
network station
D15A
For more details regarding channel selection and other
slink2orb
parameters consult the
slink2orb
man page and the default
slink2orb.pf
parameter file, both are distributed with Antelope.
Expectations Regarding Real Time Data from the EarthScope
DMC
The EarthScope
DMC
exists primarily to serve data needed for scientific studies. As such, there is generally a weak case for delivering data in real time. The
DMC
receives most data through real time methods. Since the data received in real time can easily be made available in real time, the
DMC
does so through a SeedLink server with minor latency added. Generally, the
DMC
advocates for real time data transport since it is less costly to receive data at the
DMC
in real time rather than by delayed methods.
We do not have a mandate, nor is the
DMC
funded, to provide 24/7 real time data services. Therefore, interruptions in data flow may occur. The
DMC
will attempt to remedy interruptions in its real time data feeds in a timely manner but we can guarantee neither the quality nor continuity in our real time data services. All mission-oriented agencies should be aware of this limitation of real time data services from the
DMC
and plan accordingly.
To maintain communication regarding real time data issues, the
DMC
manages a real time data users mailing list. When problems with real time data flow are observed, messages will be posted to this list as the problems are discovered. Solutions to the problems or information regarding resumption of real time data feeds will also be posted to this list.
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Protocol Details
The
SeedLink
protocol can be summarized as a simple,
ASCII
-based, data selection phase followed by the streaming of data packets from the server.
SeedLink
packets are composed of a small header followed by a 512-byte
mini-
SEED
record (data only
SEED
). The negotiation phase allows the client to request only specified data from the server for each selected data stream. A data stream is defined by a network and station code pair.
By utilizing sequence numbers for each packet in a data stream the
SeedLink
protocol allows for connections to be resumed, eliminating most data gaps. The ability to resume data streams is primarily dependent on how much data, time-wise, the remote
SeedLink
has in its buffer.
Special, out-of-band packets created by a seedlink server and recognized by
libslink
are used to communicate server details to clients and to implement keep-alive packet swapping. These special
INFO
packets are
XML
formatted data embedded in
mini-
SEED
comment records.
The protocol allows for two different modes of data transmission, uni-station and multi-station modes. Uni-station mode operates by transmitting a single data stream (data from a single station) through one network connection. In this mode the data stream does not need to be specified by the client as it is implied by the internet address and port. Multi-station mode operates by transmitting multiplexed data streams (data from multiple stations) through a single network connection. Almost all connections are negotiated as multi-station, even if only a single station is requested; uni-station mode, for most publicly accessible servers is deprecated.
SeedLink was originally created as the transport layer for the
SeisComP package
originally developed by
GEOFON
More protocol details are available from the
SeisComP SeedLink Wiki page
Tags
SEEDlink
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EarthScope Consortium operates the
NSF Geodetic Facility for the Advancement of Geoscience (GAGE)
and NSF Seismological Facility for the Advancement of Geoscience (SAGE).
Any opinions, findings and conclusions, or recommendations expressed
in this material do not necessarily reflect the views of the
U.S. National Science Foundation.
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