Virtual Networks at the IRIS DMC
A virtual network is a group of stations representing an affiliation that goes beyond the traditional bounds of networks to represent an umbrella organization or initiative. A virtual network definition allows the arbitrary grouping of stations each with independent time ranges. Virtual networks are identified by a virtual network code. To differentiate virtual network codes from traditional FDSN/SEED network codes virtual network codes are prefixed with an underscore '_' character. Most of the IRIS DMC's public access tools allow users to query for and access data based on virtual network codes.
A good example of virtual network utility is the Global Seismographic Network (GSN) which is a collection of more than 220 stations from over 10 different networks. Data and information about these stations as a group is accessible using the _GSN virtual network code.
For further discussion of virtual networks at the IRIS DMC refer to the following DMS Electronic Newsletter articles:
- Virtual Networks - Volume 6, Number 2 (June 2004)
- Virtual Networks becoming a reality at the DMC - Volume 6, Number 3 (December 2004)
- Virtual Networks at the IRIS DMC - Volume 8 Number 4 (December 2006)
Virtual Network Discovery and Browsing:
MetaData Aggregator (MDA) » Includes a list of public virtual networks (below the traditional networks) in expanded form and combined with station metadata.
Vnets interface » Shows the current virtual network descriptions (VNDs) loaded in the DMC's database. This interface also allows downloading of VNDs in either MS-Excel (.xls) format or command-separated value format.
SeismiQuery Virtual Network Query Form » Allows for flexible searching of virtual networks when needed.
Virtual Network Description (VND)
A virtual network is defined using a Virtual Network Description (VND) which contains a list of network-station pairs each with independent start and end times. The Vnets interface presents VNDs including all fields except the virtual network code. Description of fields
Virtual network :: Virtual network codeEach unique primary and secondary data center affiliation code must be included in a VND and indicate a URL to the given data center.
Network :: FDSN/SEED network code
Station :: FDSN/SEED station code, may be '*' for entire network
Install date :: Station installation date, optional
Certification date :: Station certification date, optional
Start date & time :: Start of station in this VND, two fields for date and time
End date & time :: End of station in this VND, two fields for date and time
Primary DC :: Primary data center affiliation code
Secondary DC :: Secondary data center affiliation code
As an example the VND for the GSN is easy obtained in comma-separated value format using the vnets interface: _GSN VND in comma-separated value format
Virtual Network Description Maintenance
The recommended way to update (or create) a VND is to download a current VND from the Vnets interface, edit as needed and return, usually by email, to the DMC. Note: the DMC will only load pre-approved VNDs.
Important points regarding maintenance:
- A VND completely defines a virtual network, there are no partial updates.
- The required fields are: virtual network, network, station, start date, start time, end date and end time, all other fields are optional.
- The station field may be '*' to indicate all stations from the network.
- The date fields are in YYYY/MM/DD format and the time fields are in hh:mm:ss format.
- Any primary or secondary codes must be accompanied by matching "DCC:" lines indicating a URL for the data center.
- Only lines starting with a virtual network code or "DCC:" are parsed from the VND, all other lines are ignored. The Vnets interface includes more lines for informational purposes only.
VNDs can be submitted to the DMC in either MS-Excel (.xls) format or comma-separated value (.csv) format. XML-based MS-Excel formats, i.e. with a .xlsx extension, are not supported.