Transcript A.5 Current operational procedures of data exchange on the

Lecture Note No.3
TRAINING SEMINAR ON INFORMATION
AND COMMUNICATION TECHNOLOGY
ON THE GTS
( Current Operational procedures of data exchange on the GTS and future outlook )
T.K.RAY
RTH NEW DELHI , INDIA
Email: [email protected]
Lecture note.3
Current Operational procedures of data exchange on the GTS and future outlook
T.K. Ray, RTH, New Delhi
The Global Telecomunication System (GTS) is organized in such a way
as to accommodate the volumes of meteorological data and
information and their transmission within the required time limits to
meet the needs of WMCs, RSMCs and NMCs, resulting from the
implementation of the WWW.
The GTS is organized on a three level basis, Viz.:
(a) The Main Telecommunication Network (MTN), linking together the
WMCs as well as designated RTHs.
(b) The Regional Meteorological Telecommunication Network (RMTN);
and
(c) The National Meteorological Telecommunication Network (NMTN).
WWW
General responsibilities of the Meteorological Telecommunication Centres
Collecting the observational data originating from their associated NMCs and transmitting such
data in the appropriate form on the Main Telecommunication Network, either directly or
through the appropriate WMC/RTH;
(a) Relaying selectively on the circuits of the Main Telecommunication Network,as
internationally agreed and in the appropriate form, the meteorological and related
information which they receive from these circuits and/or from RTHs not situated on the
Main Telecommunication Network;
(b) Transmitting over the Main Telecommunication Network, either directly or through a
designated RTH, as internationally agreed and in the appropriate form, the processed
meteorological information produced by the WMC or RSMC associated with them;
(c) Ensuring the selective distribution, in the appropriate form and at the appropriate speed, of
meteorological and related information to the associated NMCs and to the RTHs not situated
on the Main Telecommunication Network which they serve;
(d) Checking and making corrections in order to maintain standard telecommunication
procedures;
(e) Establishing data dissemination system (terrestrial and/or via satellite) as required in
accordance with regional plans;
(f)
Carrying out the monitoring of the operation of the GTS of the WWW.
Design principles of the GTS
(a)
Collecting the observational data originating from their associated NMCs
and transmitting such data on the MTN either directly or through appropriate
WMC/RTH.
(b)
Relaying selectively on the circuits of the MTN as internationally agreed
and in appropriate form.
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Transmitting over the MTN either directly or through a designated RTH
as internationally agreed in appropriate form.
(d)
Ensuring selective distribution in appropriate form and speed, of
meteorological and related information to the associated NMCs and to the RTHs
not situated on the MTN.
(e)
Checking, correcting and monitoring for efficient WWW operations
(f)
Establishing data dissemination system (terrestrial and/or via satellite) as
required in accordance with regional plans.
Responsibilities for the GTS
General responsibilities of regional associations
(a) Each regional association shall assume responsibility for the establishment and maintenance
of an effective telecommunication system which shall include the optimal and appropriate
use of terrestrial and/or satellite telecommunication means. The system shall be adequate to
meet the developing requirements stipulated by the Commission for basic Systems for the
interchange of meteorological and related information within the Region and with adjacent
Regions.
(b) To ensure rapid and reliable collection of meteorological data from all observing stations,
each regional association shall, when adopting its telecommunication plan, comply with the
design and operational principles given in this Manual. These principles apply to those
centres and circuits within its Region which are situated on the Main Telecommunication
Network.
(c) Each regional association shall decide on the implementation within its Region of the
regional options provided for in the global specifications and procedures.
(d) For data dissemination systems (either or via satellite), each regional association shall
establish, after consultation with known or probable recipients inside and outside the Region
and the Members responsible for the operation of such systems, the content, schedule, and
other co-ordinated aspects of operations.
General responsibilities of Members
In addition to the responsibilities stated explicitly in
Technical Regulation, the following principles shall apply:
(a) Members shall ensure that their national collecting system
for observational reports allows both national and
international needs to be met.
(b) When adopting international and regional
telecommunication plans, Members shall ensure that
technical characteristics and operational methods are
compatible with the regional telecommunication networks.
Deficiencies of the present GTS
• The present GTS has been predominantly used to support message switching
application using WMO message format over a limited OSI transport service
based on point-to-point (X.25) circuits.
• It is not capable of meeting new requirements of the WWW like DDBs
(Distributed Data Base).
• It does not support FTP (File Transfer Protocol), web browsing, electronic mail
and future applications like multi-media communications.
• It also does not support direct communication between members not adjacent to
each other.
• It is not cost effective following the emergence of technologies based on
predominantly used internet protocols and, as such, it is more expensive in terms
of financial and human resources cost since industries standard software is more
internet oriented in the present days.
•
X.25 Protocol
The use of ISO/ITU standard X.25 was adopted by WMO in the early 1980s to facilitate
exchange of data and products encoded in WMO binary code forms (GRIB, BUFR etc.)
and to act as a waste for higher level OSI applications. Since then X.25 at OSI layer
2&3 has been implemented on much of the GTS and virtually all of the MTN. The
facilities offered by the X.25 protocol was overshadowed by the advance features
offered by TCP/IP protocols subsequent to the emergence of the internet. Due to
adoption of TCP/IP protocols by predominant internet based industry and the inherent
deficiencies of the X.25 protocol made it less cost effective.
X.25 operates at OSI level 2 & 3 and as such is not capable of supporting higher level
protocols viz. FTP, email, web browsing etc.
CBS expert team on Data Communication System and Techniques (DCST)
recommended members to implement TCP/IP based systems rather than further
expansion of X.25 based systems.
What is TCP/IP ?
The ARPANet, internet’s earlier incarnation, does not follow OSI Model at all. It predates OSI by
more than a decade. The ARPANet, however, does follow protocols which roughly cover same
territory as the OSI “network” and “Transport” protocols. The network protocol named IP
(Internet Protocol) is connectionless and was designed to handle interconnection of vast number
of WAN & LAN comprising ARPA internet. The ARPANet transport protocol is a connection
oriented protocol called TCP (Transmission Control Protocol). It resembles the OSI transport
protocol in its general style, but it differs in all the formats and details.
Why TCP/IP ?
TCP/IP addresses to the deficiencies of the store and forward GTS. The transition to
TCP/IP is necessary because the vendor support for X.25 is declining and becoming
more and more expensive due to industry’s concentration on TCP/IP. Besides, TCP/IP
supports numerous application utilities available off the shelf, such as FTP, email, web
browsers and future applications such as multi-media communications.Finally, TCP/IP
provides instant connectivity amongst members in a more flexible and versatile manner.
These benefits equate to direct savings in financial and human resources cost to
members in terms of reduced cost for equipment, maintenance and software
development through the use of industry standard software available off the shelf.
Status of implementation of GTS circuits and future development
A large number of MTN ccts. are 64kpbs(digital) links and one link (Bracknell-Toulouse) is
operating at 128 kbps. The X.25 procedures are extensively used, and TCP-IP is already
operating on some circuits.
Implementation of X.25 circuits
All but one of the MTN circuits currently use X.25, with few centres supporting
passage of non-adjacent traffic via PVCs or VCs through their packet switches. This
practice, while efficient, has been relatively cumbersome to establish and manage and for
this reason should not be extended on the MTN generally. The general policy of MTN
centres is to migrate to IP-based techniques for GTS links, which would provide more
efficient network services.
Implementation of TCP/IP
The TCP/IP protocol suite provides the potential to use the full range of TCP/IP
applications on the GTS. Some applications, such as file transfer and the World Wide Web,
have potential to place heavy loads on the limited bandwidth circuits that comprise the GTS
Limits need to be applied to ensure that the GTS carries only important traffic such as the
real-time data and products currently exchanged on the GTS plus data to be carried to fulfil
new requirements such as DDBs,and routinely exchanged large data files such as Satellite
imagery.Less important traffic such as ad hoc file exchange ,e-mail,general WW Web and
similar files should be carried on the internet.To protect the GTS, the full capabilities of
TCP/IP connectivity and information exchange must be retained.
Main Telecommunication
NetworkNetwork (MTN)
Main Telecommunication
Region VI
Moskau
Region II
Offenbach
Bracknell
Region IV
Prag
Toulouse
Washington
Peking
Sofia
Algier
Tokio
Kairo
Jeddah
Neu Delhi
Dakar
Region I
Brasilia
Region III
Buenos
Aires
Nairobi
Region V
Melbourne
= World Meteorological Centre (WMC)
= Regional Telecommunication Hub (RTH)
last update: 12.04.2001
The present MTN and the GTS, in general, suffers from the following
deficiencies:
a)
The GTS is not really in a network formation and, infact, it is more of a
bi-lateral links joined in a loose network formation;
b)
The links belong to the old concept of telecommunication and so are not
in many cases, cost effective;
c)
Various protocols are followed by various links depending on the availability
and, thus, no uniformity is available throughout the network.
d)
Latest telecommunication techniques and protocols are missing is most of the
cases resulting in inefficiency of the data exchange procedures
e)
There is no mechanism to exchange information between non-adjacent
MTN/RMTN Centres, without involving neighbouring centres.This is
one of the most serious deficiencies of the GTS and the MTN which
attracted the attention of the whole GTS community.
Improved
Main Telecommunication Network(IMTN)
IMTN
XII – RAII (Seol, 19-27 September, 2000) endorsed the concept of
Improved RMTN using modern cost-effective data communication
network services. In view of the geographical extent of RAII, it agreed
that the design of the IRMTN could be based on the implementation of
several networks grouping RTHs and NMCs as appropriate.
Considering that cost-effective data network services such as Frame
Relay and IP-VPN services were available in parts of the Region and
that the administrative mechanisms for implementation would not be
developed shortly.