Files are transferred via a dedicated communications line from EUMETSAT to the uplink facility. These files are encoded and transmitted to a geostationary communications satellite for broadcast to user receiving stations. Each receiving station decodes the signal and recreates the data/products according to a defined directory and file name structure.

A single reception station can receive any combination of the services provided on EUMETCast. Data, for which access is restricted in accordance with EUMETSAT Data Policy, is made secure by the USB decryption scheme. 

System Overview

The system uses a DVB/MPEG-2 based transport for carrying IP datagrams. It uses a set of broadcast satellite forward channels, but does not use the return channel. The forward links are provided by a set of geostationary, digital telecommunications satellites. The components involved include:

• Data providers (DP)
• Service management (SM)
• Uplink service provider (USP)
• Turn around service provider (TSP)
• Satellites
• Reception stations

Uplink, Turnaround and Data Providers

The Uplink service provider performs the following tasks:

1. Receives all the data to be disseminated from all the data providers
2. Co-ordinates all the transmissions according to the service configuration
3. Encrypts the data according to the user dissemination configuration
4. Applies Forward Error Correction (FEC) to multicast data (FEC techniques transmit additional redundant information to enable the receivers to correct a certain amount of lost data, without requiring retransmission)
5. Converts the files into Digital Video Broadcast (DVB)
6. Broadcasts the signal using a commercial satellite
7. Receives the multicast data into a local reference reception station for service monitoring.

Steps 3 to 6 are done "on the fly", i.e. without delaying the transmissions.

For EUMETCast, the multicast system provided by T-Systems GmbH is based on a client/server system developed by Tellitec with the server side implemented at the EUMETCast uplink site Usingen, Germany, and the client side installed on all the EUMETCast reception stations.

There are a number of data providers, including EUMETSAT, who deliver files to the uplink site via FTP over various communication lines.

The turn around service provider receives the DVB signal from one satellite and retransmits it, without unpacking the DVB packets, to another satellite. Telespazio S.p.a. provides the C-band turnaround service for EUMETCast Africa from its uplink site in Fucino, Italy and Globecast provides the C-band turnaround service for EUMETCast South America from its uplink facility in Paris, France.

Data File Encryption/Decryption

The EUMETCast system allows files to be independently targeted towards a single user, or group of users, thus enabling the secure control of access to the data at individual file and individual user level. The encryption of the data is performed by the EUMETCast uplink and decryption by the EUMETCast Client Software installed on the reception station. The data encryption keys are typically valid for just one transmission and encrypted with the user key (password) of the target user.

Those data controlled in accordance with EUMETSAT Data Policy are only accessible by users who have been given the necessary decryption keys for the EUMETSAT service/s they have been licensed to receive. To access these services in addition to the decryption keys users will need to operate a station equipped with a EUMETCast Key Unit (EKU).

The EKU decryption device is connected, via USB, to the reception station. The decryption device is used by the EUMETCast Client Software to decrypt the data key of the next transmission. EUMETSAT manages the distribution of the decryption devices to registered users.

Service Management and Service Directories

The service configuration management is done by EUMETSAT, who provides the service configuration (bandwidth, users, dissemination parameters, etc.) to the DVB uplink provider. Management of the satellite transponder bandwidth capacity available to EUMETCast is achieved with channels and by the use of a priority scheme. The DVB multicast management software adapts the uplink stream according to the relative priorities of the data waiting to be transmitted on a particular channel.

The EUMETCast interface is based on a concept called 'Service Directories' into which the data to be multicast are transferred from the EUMETSAT ground segment. These service directories are part of the multicast system normally resident at the service provider's uplink site. Associated with each service directory is a distribution list, which identifies all the EUMETCast users entitled to receive the data transferred to the directory.

The service directory structure is also used to allocate bandwidth characteristics to a particular set of products or directories.

Channel Allocation

Each service delivered via EUMETCast is assigned to a specific channel at the uplink provider site. A typical channel allocation resembles the following:

• Announcement Channel - includes the user keys required for decryption of the DVB
• EUMETSAT Data Channel 1 - a set of data files provided by EUMETSAT
• EUMETSAT Data Channel 2 - a further set of data files provided by EUMETSAT
• External Data Provider Channel - a dedicated channel allocated to those data provided by an external data provider

Each channel, which has its own multicast address, is itself assigned to a Packet Identifier (PID), for example:

TSL Announcement Channel - PID 100 - multicast address 224.223.222.223:4711

Several channels can be combined under one PID, for example:

EUMETSAT Data Channel 1 - multicast address 224.223.222.1:4811 - PID 500
BMD-RA-VI - multicast address 224.223.222.22:2911 - PID 500

The individual channels supply the data files at a different data rate depending upon the channel settings.

One of the advantages in using PIDs is that they can be filtered at the DVB receiver (DVB Card) thus allowing the user of a reception station to deselect the PID and its contents before it reaches their reception station Central Processing Unit (CPU).

For a list of current channels and PIDs, click here.

Telecommunication Satellites

The satellites used by the uplink providers to relay the EUMETCast multicast form part of the Eutelsat and New Skies satellite fleet.

EUROBIRD™ 9 delivers 20 fully operational Ku-band transponders supplying coverage across Europe, North Africa and the Middle East. Under the current arrangements provided by the uplink provider, EUMETCast is available via one of the Ku-band transponders.

ATLANTIC BIRD™ 3 carries a Ku/C-band payload of 45 transponders (35 Ku-band, 10 C-band) with European African and western Asia coverage. Under the current arrangements provided by the Africa turnaround provider, EUMETCast is available via one of the C-band transponders.

For more information on these two satellites see: http://www.eutelsat.com

Eutelsat Satellite (copyright EUTELSAT)

NSS-806 is located at 319.5º East, giving it an optimum view of South America while also reaching the Iberian peninsula, the Canary Islands, Western Europe and much of Eastern Europe. Its tailored, high-powered hemispheric beam provides simultaneous coverage of both Europe and the Americas, with virtually complete coverage of North, Central and South America. EUMETCast is available via one of the C-band transponders.

For more information on the satellite see: http://www.newskies.com

To view the current transponders in use for EUMETCast reception, click here.

Service Monitoring

Reference reception stations are used to monitor the status of the system. There are reference reception stations at each data provider, the uplink service provider and on every turnaround service provider. Each data provider is responsible for the end-to-end monitoring of its own data. EUMETSAT monitors the end-to-end service relative to the data provided by EUMETSAT.