SeedLink Service

 

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, the transmission is started where it ended. Requested data streams may be limited to specific stations, locations and/or channels. All data packets are 512-byte Mini-SEED records. The most common implementation, and the one used at the DMC, is the seedlink server within the SeisComP package developed by GEOFON.

 

Real-time Data from the IRIS DMC

The DMC runs a publicly accessible SeedLink server on the following host and port:

host: bud.iris.washington.edu
port: 18000 (default SeedLink port)

All open data that the DMC receives in real-time is available via this SeedLink server.

 

Available Software

The following software is available from the DMC ( SeedLink downloads )

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.

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).

Other SeedLink related software is available (or referenced by) the GEOFON SeisComP website

 

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 bud.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

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 dependant 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.