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Requirements of the data communication networks:
  1. The network should be based on an agreed technology available to the participating centres
  2. The network should be capable of handling the data volumes
  3. The network should include satellite communication channels, terrestrial links and managed data network services, and use of Internet
  4. The network should handle the agreed transmission protocols
  5. The network should build on the Global Telecommunication System (GTS), including its satellite-based elements and the Improved Main Telecommunication Network (IMTN), for real-time data exchange.

Data communication networks that will be used:

  1. The Global Telecommunication System (GTS) in its entirety will be part of WIS, especially for meeting real-time exchange requirements. 
  2. Internet Virtual Private Network (VPN) - Will be an indispensable communication element for the WIS.
  3. Satellite communication channels such as those provided by the Integrated Global Data Dissemination Service (IGDDS) - for the exchange of data and products related to the WMO Space Programme, as well as terrestrial links or managed data network services.

The Improved Main Telecommunication Network (IMTN)

The IMTN which supports and interconnects the six Regional Meteorological Telecommunication Networks (RMTNs) of the GTS, has been performing a fundamental role of exchange between NMHSs of data and products globally on a real-time basis, mainly for the World Weather Watch (WWW) Programme. The WMO Commission for Basic Systems, at its 1998 extraordinary session, stressed that the MTN shall be reviewed fundamentally to meet evolving data exchange requirements of WMO Programmes other than the WWW.

The IMTN project has been promoting the reform of MTN structure and capability as a genuine network since its commencement in 1999. One of the major reform concepts is its evolution from bilateral links by individual suppliers to seamless network “cloud”. The shorthand word “cloud” is defined as the following summary: “Three or more centres use a common provider of network services within a contractual framework to implement the required connectivity among the centres concerned.”

The current IMTN is structured with two “clouds” of frame relay network services due to the pragmatic evolution process and risk management. One cloud is the actual multi-regional extension of the framework of the Regional Meteorological Data Communication Network (RMDCN) in WMO Region VI (Europe). The other cloud is based on a new contractual framework with practical coordination between centres. The implementation of the IMTN brings various benefits such as further reliability, better performance in throughput and quality, an efficient solution to unbalanced traffic condition, flexibility and scalability for evolving requirements, and cost-effectiveness. The remarkable progress in the implementation and operation validates that the IMTN would be the basis for the core network of WIS data communication structure.

The Global Meteorological Data Communication Network (GMDCN)

The fundamental concept for WIS real-time networks is on the precondition of the establishment of a single coordinated global network
Design principles of GMDCN are based on the following key ideas:
  1. The GMDCN should provide any-to-any connectivity in transport level for all participating centres by using a managed data network service (e.g. IP-VPN with MPLS could be most feasible);
  2. A well-organized framework with its control body is indispensable for overall technical and administrative management (e.g. traffic, security, monitoring, backup arrangement, competitive procurement and contract, funding coordination and so on);
  3. Required connections for new and traditional message switching applications between centres are mapped on the top of the any-to-any connectivity network (i.e. separation of application-level communication from transport-level capability);
  4. The GMDCN should keep scalability and flexibility to respond to new requirements from all WMO and related international programmes (e.g. improving the exchange of high priority data and products in support of a virtual all hazards network within the WIS-GTS, increasing participating centres, applications, data types and volume, and easy introduction of new technology);
  5. Gateway facilities/functions and guidelines should be provided to promote the migration to the GMDCN.

Internet VPN

There is no doubt that the Internet will be an indispensable communication element for the WIS. Its use, however, has advantages and disadvantages. Investment in security as a countermeasure against risks and its cost-effectiveness could be the major considerations. A Virtual Private Network (VPN) is commonly defined as a private communications network over a public network, such as the Internet, and is a promising technique. It provides a secure channel such as a leased line between a local site and a remote site. For security, it uses features such as encryption, encapsulation, authorization and tunnels. In particular, VPN based on Internet Protocol Security (IPsec) is coming into wide use because its technologies are well standardized and available off-the-shelf.

In this context, the VPN Pilot Project in Regions II (Asia) and V (South-West Pacific) was launched in December 2003 with the purpose of contributing to WIS development through practical feasibility tests involving a wide range of participating National Meteorological Centres. In addition, a European VPN project was coordinated to test VPN for the RMDCN back-up. The projects have evaluated well-known VPN techniques, i.e. IPsec, Point-to-Point Tunnelling Protocol (PPTP) for simplified VPN techniques available for mobile and PC users, and Secure Socket Layer (SSL) for Web and specific applications.

The outcome of the projects shows that Internet VPN is useful to establish WIS branch connections but it is worth keeping in mind that the Internet cannot provide guaranteed bandwidth and quality of service that is needed for operation critical communications, and is subject to various attacks, including DoS (Denial of Service) attacks.