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wiki:slink2ew
Last modified 17 months ago Last modified on 05/02/12 09:11:44

# Earthworm Module: slink2ew

Contributed by: Chad Trabant

## Function

SeedLink importer module (Windows and Solaris compat) (new in EW v7.0)

## Details

slink2ew is a SeedLink client module for Earthworm. SeedLink is the data server component of the Seismological Communication Processor, or ​SeisComP, originally developed at ​GEOFON.

The SeedLink protocol can be summarized as a simple negotiation scheme 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 types from the server for each 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 it's buffer.

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.

The maxium size of the TRACEBUF messages created by slink2ew is limited to the maximum number of samples (using Steim2 compression) that can fit into a 512-byte Mini-SEED record (721 samples = 2884 bytes) plus the size of the TRACEBUF header (64 bytes). So 2948 bytes is a good estimate of the maximum size of TRACEBUF messages created by slink2ew.

Version 1.1 and greater of slink2ew supports the creation of either TRACEBUF or TRACEBUF2 messages depending on which version of Earthworm the module was built for. By default the module will create TRACEBUF2 messages if the system supports them and TRACEBUF messages otherwise. Additionally there is an optional command !ForceTraceBuf1 that will force the use of TRACEBUF messages on systems that support TRACEBUF2.

SeisComP and SeedLink are actively supported by the ​GEOFON Project, ​ORFEUS Data Center and ​IRIS Data Management Center in addition to the user community.

## Configuration File Commands

On startup, slink2ew reads the configuration file named on the command line. Commands in this file set all the parameters used for configuring the Earthworm SeedLink client module (SeedLink is a component of the Seismological Communication Processor, or SeisComP, originally developed at GEOFON). In the control file, lines may begin with a valid slink2ew command (listed below) or with one of 2 special characters:

    #  marks the line as a comment (example: # This is a comment).

    @  allows control files to be nested; one control file can be
       accessed from another with the command "@" followed by
       a string representing the path name of the next control file
       (example: @model.d).

Command names must be typed in the control file exactly as shown in this document (commands are case sensative). Blank lines are also permitted in the control file.

### FUNCTIONAL COMMAND LISTING

Below are the commands recognized by slink2ew, grouped by the function they influence. Most of the commands are required; they may be specified in any order in the control file.

            Earthworm system setup:
                    MyModuleId              required
                    RingName                required
                    HeartBeatInterval       required
                    Verbosity		optional

            SeedLink server and connection parameters:
                    SLaddr                  required
                    SLport                  required
    		Selectors		optional
    		Stream			optional
    		NetworkTimeout		optional
    		NetworkDelay		optional
    		KeepAlive		optional
    		ForceTraceBuf1		optional  (slink2ew >= 1.1)

    	Output control:
    		LogFile			required
    		StateFile		optional
    		StateFileInt		optional

### ALPHABETIC COMMAND LISTING & DESCRIPTION

In the following section, all configuration file commands are listed in alphabetical order. Listed along with the command (bold-type) are its arguments (in red), the name of the subroutine that processes the command, and the function within the module that the command influences. A detailed description of the command and is also given. Default values and example commands are listed after each command description.

The following list is organized by:

command [argument here]

!ForceTraceBuf1 [switch]
Processed by: ReadConfig
Function: Earthworm setup

Sets the on-off switch to force the creation of TRACEBUF messages on systems that support TRACEBUF2 messages. By default, the module will create TRACEBUF2 messages on systems that support them otherwise it will create the older TRACEBUF messages. This switch has no effect on systems that do no support TRACEBUF2 messages. This switch could be useful in environments where a transition is occuring between TRACEBUF and TRACEBUF2 messages, otherwise most people will never use this.

    Default:  0 (disabled)
    Example:  ForceTraceBuf1 1

HeartBeatInterval [interval]
Processed by: ReadConfig
Function: Earthworm setup

Defines the interval in seconds at which the module will issue TYPE_HEARTBEAT messages.

    Default:  none
    Example:  HeartBeatInterval 30

LogFile [switch]
Processed by: ReadConfig
Function: Earthworm setup

Sets the on-off switch for writing a log file to disk. If switch is 0, no log file will be written. If switch is 1, coaxtoring will write a daily log file(s) called coaxtoringxx.log_yymmdd where xx is coaxtoring's module id (set with MyModuleId command) and yymmdd is the current UTC date (ex: 960123) on the system clock. The file(s) will be written in the EW_LOG directory (environment variable). If switch is 2 the log file is written but output to stdout and stderr is suppressed.

    Default:  none
    Example:  LogFile   1

KeepAlive [interval]
Processed by: ReadConfig
Function: Data Selection

Specifies the interval in seconds that the module will send keep alive (heartbeat) packets to the remote SeedLink server. A value of 0 disables the feature. This feature only works with versions of SeedLink 2.93 or greater. This is useful for keeping a network connection open that might be closed by itermediate firewalls/gateways when the data stream only flows at intervals.

    Default:  0 (disabled)
    Example:  KeepAlive   600

MyModuleId [mod_id]
Processed by: ReadConfig
Function: Earthworm setup

Sets the module id for labeling all outgoing trigger, heartbeat, and error messages. mod_id is a character string (valid strings are listed in earthworm.d) that relates to a unique single-byte number.

    Default:  none
    Example:  MyModuleId MOD_SLINK2EW_GE

NetworkDelay [delay]
Processed by: ReadConfig
Function: Earthworm setup

Sets the re-connection delay in seconds. After the connection to the remote SeedLink server has been broken (network timeout or any other connection problems) the module will wait this many seconds before attempting to re-connect.

    Default:  30
    Example:  NetworkDelay 10

NetworkTimeout [timeout]
Processed by: ReadConfig
Function: Earthworm setup

Sets the network timeout in seconds. If the module has not received any packets from the remote SeedLink server in this amount of time the connection will be closed and re-opened if possible. A value of 0 disables this feature.

    Default:  600
    Example:  NetworkTimeout 300

RingName [ring]
Processed by: ReadConfig
Function: Earthworm setup

Indicates which shared memory region to use for waveform output. ring is a character string (valid strings are listed in earthworm.d) that relates (in earthworm.d) to a unique number for the key to the shared memory region.

    Default:  none
    Example:  RingName WAVE_RING

Selectors [selectors]
Processed by: ReadConfig
Function: Data selection

Specify the SeedLink selectors for uni-station mode or default selectors for multi-station mode. Multiple selectors must be enclosed by quotes. If Stream commands are also specified in the command file, implying multi-station mode, any selectors specified with this command will be used as defaults when no data stream selectors are specified with a given Stream command.

    Default:  none
    Example:  Selectors  "BH?.D LH?.D"

SLaddr [address]
Processed by: ReadConfig
Function: SeedLink parameters

Specify the address of the SeedLink server. This can be either on IP address (four period-separated numbers) or the domain name of the server.

    Default:  none
    Example:  SLaddr      st27.gfz-postdam.de

SLport [port]
Processed by: ReadConfig
Function: SeedLink parameters

Specifies the IP port number for the SeedLink server. This is commonly 18000.

    Default:  none
    Example:  SLport  18000

StateFile
Processed by: ReadConfig
Function: Earthworm setup

If this flag is specified a file with a list of sequence numbers is written, during a clean module shutdown, to the parameter directory with the name "slink<mod id>.state". During module startup these sequence numbers are used to resume data streams from the last received data. In this way continuous data can be collected even through system restarts. If this flag is not set the module will always request the next available data. Using this functionality is highly recommended unless you know that it is not necessary.

    Default:  none
    Example:  StateFile

StateFileInt [interval]
Processed by: ReadConfig
Function: Earthworm setup

This option specifies the interval for saving the state file in number of packets received. In otherwords, using the default interval of 100, the statefile will be updated every 100 packets received. The purpose of this functionality is to minimize the amount of duplicate data collected if the module is ever killed without saving the current state information.

    Default:  100
    Example:  StateFileInt 500

Stream streamkey [selectors]
Processed by: ReadConfig
Function: Data selection

Specifies one stream of data to be requested from the remote SeedLink server. This command implies the use of multi-station mode and can be specified multiple times to requested multiple data streams. The streamkey is composed of a network and station code separated by an underscore. Optional SeedLink selectors may be specified after the stream key. Multiple selectors must be enclosed in quotes. Beware of collecting multiple data streams with the same station code and differing location codes as the rest of Earthworm does not know about location codes, so the two data streams would get mixed together with bad results.

    Default:  none
    Example:  Stream  GE_DSB  "BH?.D HH?.D"

Verbosity [level]
Processed by: ReadConfig
Function: Earthworm setu

Specifies the level of logging verbosity. Level 0 is rather quiet and mostly reports errors, level 1 shows negotiation details and every received packet and level 2 shows a lot of details.

    Default:  0
    Example:  Verbosity 0

### Sample Configuration File

    #
    #                     Configuration File for slink2ew
    #
    MyModuleId       MOD_SLINK2EW
    RingName         WAVE_RING       # Transport ring to write output to.

    HeartBeatInterval     30         # Heartbeat interval, in seconds.
    LogFile               1          # 1 -> Keep log, 0 -> no log file
                                     # 2 -> write to module log but not stderr/stdout
    #Verbosity      0                # Set level of verbosity.

    SLhost     st27.gfz-potsdam.de   # Host address of the SeedLink server
    SLport         18000             # Port number of the SeedLink server

    StateFile      slink2ew.GE       # File with a list of sequence numbers which
                                     # is read during module startup to resume
                                     # data streams.  This file is written on a
                                     # clean module shutdown.  If this is not
                                     # specified as an absolute path the value of
                                     # the environment variable EW_PARAMS will
                                     # be pre-pended to this value.  Using this
                                     # functionality is highly recommended.

    #NetworkTimeout 600              # Network timeout, after this many idle
                                     # seconds the connection will be reset.
                                     # Default is 600 seconds, 0 to disable.

    #NetworkDelay   30               # Network re-connect delay in seconds.

    #KeepAlive      0                # Send keepalive packets (when idle) at this
                                     # interval in seconds.  Default is 0 (disabled).

    #ForceTraceBuf1 0                # On systems that support TRACEBUF2
                                     # messages this flag will force the module
                                     # to create TRACEBUF messages instead.
                                     # Most people will never need this.

    # Selectors and Stream's.  If any Stream lines are specified the connection
    # to the SeedLink server will be configured in multi-station mode using
    # Selectors, if any, as defaults.  If no Stream lines are specified the
    # connection will be configured in uni-station mode using Selectors, if any.

    Selectors      "BH?.D"           # SeedLink selectors.  These selectors are used
                                     # for a uni-station mode connection.  If one
                                     # or more 'Stream' entries are given these are
                                     # used as default selectors for multi-station
                                     # mode data streams.  See description of
                                     # SeedLink selectors below.  Multiple selectors
                                     # must be enclosed in quotes.

    # List each data stream (a network and station code pair) that you
    # wish to request from the server with a "Stream" command.  If one or
    # more Stream commands are given the connection will be configured in
    # multi-station mode (multiple station data streams over a single
    # network connection).  If no Stream commands are specified the
    # connection will be configured in uni-station mode, optionally using
    # any specified "Selectors".  A Stream command should be followed by a
    # stream key, a network code followed by a station code separated by
    # an underscore (i.e. IU_KONO).  SeedLink selectors for a specific
    # stream may optionally be specified after the stream key.  Multiple
    # selectors must be enclosed in quotes.  Any selectors specified with
    # the Selectors command above are used as defaults when no selectors
    # are specified for a given stream.

    # Combined with the above specified default selectors the BHx channels
    # will be requested for each of these stations except for DSB for which
    # we also want the LHx channels.

    Stream  GE_DSB   "BH?.D LH?.D"
    Stream  GE_ISP
    Stream  GE_APE
    Stream  GE_STU

## Advanced Description

### SeedLink data transfer, uni-station and multi-station mode

The SeedLink protocol allows two different modes of data transfer. Uni-station mode is the method used for transmitting a single data stream (station) over a single network connection. In this case the client does not specify a stream key (network and station code) as the data stream is implied by which address and port the client connects to (similar to LISS Protocol ver. 1). Multi-station mode is the method used for transmitting multiple data streams (stations) multiplexed together over a single network connection. Uni-station mode is supported by all current SeedLink versions. Multi-station mode is supported by SeedLink 2.5 or later (SeisComP-1.1.6 or later).

For slink2ew the presence of one or more Stream commands in the configuration file triggers multi-station mode. Otherwise the module defaults to uni-station mode.

### SeedLink selectors

SeedLink selectors are used to request specific types of data within a given data stream, in effect limiting the default action of sending all data types. A data packet is sent to the client if it matches any positive selector (without leading "!") and doesn't match any negative selectors (with a leading "!"). The general format of selectors is LLSSS.T, where LL is location, SSS is channel and T is type (one of [DECOTL] for Data, Event, Calibration, Blockette, Timing, and Log records). "LL", ".T", and "LLSSS." can be omitted, implying anything in that field. It is also possible to use "?" in place of L and S as a single character wildcard. Multiple selectors are separated by space(s).

Some examples:

    BH?          - BHZ, BHN, BHE (all record types)
    00BH?.D      - BHZ, BHN, BHE with location code '00' (data records)
    BH? !E       - BHZ, BHN, BHE (excluding detection records)
    BH? E        - BHZ, BHN, BHE & detection records of all channels
    !LCQ !LEP    - exclude LCQ and LEP channels
    !L !T        - exclude log and timing records

For slink2ew only data records will be written to the ring. In other words, requesting any records in addition to data records is a waste and you should always append ".D" to any specified selectors.

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