4. SYSTEM DESIGN

The GDPS data handling system can be subdivided into three main functional sub-systems:

The Application subsystem can, in turn, be divided into several modules, which can be independently implemented.

4.1     COMMUNICATION LINKS SUB-SYSTEM

The WMO GTS circuits use both terrestrial and satellite communication links to provide NMCs with different types of meteorological data and products; which can be in text, GRIB, BUFF, Satellite and Radar image format.

4.1.1 Satellite Communication Links

Presently, several satellite-based data distribution systems are available to Members of RA I , which include:

To be able to receive and display satellite data/products the NMCs and RTHs require ground equipment, which include receivers and computers. By the year 2003, all current MDD, DRS and DCP services and the HRI and WEFAX which are provided by METEOSAT will be replaced by fully digital LRIT and HRIT of the MSG receiving systems. This requires new ground receiving equipment.

4.1.2 Terrestrial Communication Links

At an NMC different types of data such as synoptic, upper air, etc., may be received through a variety of means.

Where national observing stations are spread over large areas and are at long distances to the NMC, it may be cost-effective, in a number of ways, to group them into zones and then establish a medium speed link to one station within a designated zone as "zone office". Resources permitting and where the technology exists, the zone offices could be networked using Frame Relay on the Public Telephone Network System to form a single "Cloud". The practical benefits of the cloud approach include:

The implementation of a cloud which extends beyond single NMC, while has benefits, has problems regarding:

Could the following political groupings in RA I be used to bring about the establishment of clouds?

4.1.3 The X.25 and IP Protocols

The strategic direction in the development of the GTS is based on the Open System Interconnections (OSI) as set out by the International Standards Organisation (ISO). In consideration of the hyper evolution of the Internet and the supporting technical standards, vis--vis, WMO is expanding functional needs of its various programs. The WMO has decided to replace X.25 with IP of the TCP/IP protocol suite for supporting GTS operational needs.

The OSI is a layered model consisting of seven layers. There are several protocols, which operate in the network layer (third layer) of this model including: IP, CLNP, IPX, etc. The WMO has chosen the IP protocol because:

These IP (TCP/IP ) characteristics ensure savings in both direct costs and in the cost of human resources development. However, a wide spread application of IP protocol on the GTS requires not only adoption of switching applications, naming convention and IP address convention but also a very serious security consideration. These are some of the things which stand as challenges to the WMO as the Organisation contemplates applying Internet technology to the process of building up an improved GTS.

4.1.4 The Role of Internet in the GTS

The Internet is a global network of PC networks. It is an open system as opposed to the likes of CompuServe, AOL, the WMO GTS, etc., which are basically closed systems. Several services are presently available on the Internet:

The commercial closed systems are collaborating with the Internet by making themselves gateways to these services, thus acting as ISPs, so too the WMO GTS. Using the above Internet services an NMCs could:

but considering:

There is a need to protect the WMO GTS operating in a mixed environment with Internet.

But from where, exactly, the GTS be protected? The GTS should be protected from the adverse results of the modalities of its interaction with the Internet and its technology. The nature of the mix in the application of GTS and Internet technology. The mix can be as outlined below.

4.1.4.1     Application of Internet Technology within GTS

In this scenario the GTS is viewed as a closed private network system - an INTRANET- in which:

4.1.4.2     The GTS completely turned over to Internet

Assuming that Internet security issues have been resolved satisfactorily and WMO, therefore, decides to replace the complete GTS with the Internet system. In this situation the following remarks are pertinent:

4.1.4.3     A Mix of GTS and Internet

In the countries where Internet put through is high and connection tariffs are cost-effective the less time-critical meteorological data and products can gradually be put on the Internet. The gradual approach is preferred not only to ensure non-interruption to data/products transmissions but also to protect the investment of the NMCs in RA I have made on GTS. Besides, the WMO itself requires time to prepare guidelines on Internet implementation, design Internet compatible data/products formats etc.