SADIS FTP UTILISATION AND FUTURE BANDWIDTH …



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International Civil Aviation Organization

WORKING PAPER |SADISOPSG/14-WP/18

20/03/09

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SATELLITE DISTRIBUTION SYSTEM OPERATIONS GROUP (SADISOPSG)

FOURTEENTH MEETING

Bangkok, Thailand, 15 to 17 July 2009

|Agenda Item |6. |Development of the SADIS |

| |6.4 |SADIS Internet-based FTP Service |

SADIS FTP UTILISATION AND FUTURE BANDWIDTH CONSIDERATIONS

(Presented by the SADIS Provider State)

|SUMMARY |

|The working paper outlines the trends in SADIS FTP utilisation since 2007, and provides a projected trend |

|over the next 12 months. The paper also invites the group to consider whether the current SADIS FTP |

|bandwidth allocation is suitable to meet the future demands on the service. |

1. INTRODUCTION

This working paper presents statistics on the utilisation of the SADIS FTP service since SADISOPSG/12 (2007), and provides an indication on the likely utilisation by the time of SADISOPSG/15 (2010). Noting the development of products such as GRIB 2, which are to be placed on the SADIS FTP server by September 2009 (final report of WAFSOPSG/4 refers), this paper invites the group to consider whether the existing bandwidth arrangements of SADIS FTP is sufficient to meet future requirements.

2. discussion

The SADIS FTP service has been in operation for a number of years, and has consistently seen the number of users accessing the service grow year-on-year, as well as seen a growth in the number of products being accessed by those users.

Chart A below illustrates the number of products accessed (‘pulled’) and the number of users accessing the SADIS FTP service on a typical day. The statistics have been generated from weekly access logs that the Met Office produces for internal use. The trends are considered interesting and worthy of sharing with the group.

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Above: Chart A – SADIS FTP utilisation since SADISOPSG/12 (2007)

3. SADIS FTP usage

Since SADISOPSG/12, the SADIS FTP service has seen the number of users accessing the service on an typical day grow from around 55 in 2007 to around 68 in 2009 – an increase of around 25%. At the same time, the number of products accessed on a typical day has grown from around 13,000 in 2007 to around 22,000 in 2009 – an increase of around 70%. These percentage increases clearly illustrate that a typical SADIS FTP user is tending to download more products than they were doing, say, 18 months ago.

Chart A clearly shows a marked peak in the number of products accessed around October to December 2007, before settling back down to more ‘normal levels’ by January 2008. This peak is considered attributable to the data losses that the SADIS 2G service was encountering towards the latter half of 2007, as outlined to SADISOPSG/13 last year. Users of SADIS 2G were evidently accessing the SADIS FTP service as an alternative means of acquiring the full complement of (GRIB) data. This is entirely in keeping with reason SADIS FTP was first developed – i.e. as a backup to the satellite broadcast.

4. FUTURE TRENDS AND CONSIDERATIONS

If the current trend in usage was to continue, with no additional products placed on the server (other than low capacity OPMET), by SADISOPSG/15 in 2010 some 37,000 products may be accessed on a typical day. The number of regular users accessing the service may be around 80. These trends are illustrated by Chart B below. Note that these trends are purely projections based on current usage, and do not take into account additional products that may become available on the SADIS FTP server (such as GRIB 2 WAFS data). Additional products such as GRIB 2 will have the effect of encouraging more users to access SADIS FTP, and thus download a greater volume of data.

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Above: Chart B – Projected SADIS FTP utilisation to end of 2010

At present, the SADIS FTP service is implemented with 2Mbps (2 megabits per second) bursting to 4Mbps available between the server and Met Office internet service provider (ISP). Individual client connections are guaranteed a minimum speed of 38Kbps (38 kilobits per second) bursting to 256Kbps between server and ISP. The Met Office (SADIS FTP provider) has no control over client-end internet connection speeds, and therefore actual download speeds that a user experiences may be lower than 38kbps.

A GRIB 1 WAFS data set, containing just upper wind/temperature data, is around 10MB in size per issue (4 issues per day). 8 bits = 1 byte and 1MB = 1,024 KB (kilobytes). Therefore, 10MB = 10,240 KB. And, 1KB = 8192 bits. Therefore, 10MB = 10,240 KB = 83,886,080 bits = 81,920 kb (kilobits). Downloading a 10MB data file at 256kbps would therefore take 320 seconds (= 3 minutes). Similarly, downloading a 10MB data file at 38kbps would take 2156 seconds (= 36 minutes).

On a typical day, between 35 and 40 users retrieve the GRIB 1 WAFS data from SADIS FTP (although not necessarily simultaneously). This equates to over half the total number of regular users. The table below summarises the typical number of users that may be able to access the SADIS FTP service based on the existing bandwidth capabilities:

|Speed between Server and ISP |Individual client connection |Maximum number of users |Minimum time to download a (future) |

|(Mbps) |speed (kbps) | |30MB GRIB 2 WAFS data set |

|2 |38 |52 |108 minutes |

| |256 |7 |16 minutes |

|4 |38 |105 |64 minutes |

| |256 |15 |8 minutes |

Noting that the SADIS FTP service currently has between 60 and 70 regular users, the table above would suggest that many users are unlikely to realise an individual connection speed of 256kbps, and that the figure may be closer to 38kbps.

A complete GRIB 2 WAFS data set, when available, will be in the region of 60MB before compression. Compare this with a current GRIB 1 WAFS data set which is only around 10MB. The reason that the GRIB 2 data will be six-times greater in volume (before compression) is because the data contains higher temporal and spatial resolutions plus additional products such as icing/turbulence/CB. If the products are compressed, using an appropriate compression utility, the volume of GRIB 2 data is expected to reduce to around 30MB (i.e. 2:1 compression). This is still three-times the volume of existing GRIB 1 data. With a large number of users, and client connections most likely available at around 38kbps, it would take approximately 1 hour 48 minutes to download a 30MB GRIB 2 WAFS data volume, as indicated in the above table.

According to the WAFS GRIB 2 implementation plan, endorsed by the WAFSOPSG/4 meeting in February 2008, the WAFC Provider States are expected to place the GRIB 2 WAFS data on ISCS and SADIS FTP services in parallel with GRIB 1 by September 2009 (Appendix F of the WAFSOPSG/4 report refers). No decision has been taken for placement of these products on the ISCS and SADIS satellite broadcasts. Therefore, the sole means of accessing the GRIB 2 WAFS data for SADIS users may be SADIS FTP service, at least in the near-term. As noted in paragraph 4.1 above, this will likely lead to an increasing number of users of SADIS FTP, wishing to download ever increasing volumes of data. It is therefore imperative that the group considers whether the existing SADIS FTP bandwidth provisions are suitable as the service moves forwards. The SADIS Provider State believes that the current SADIS FTP bandwidth is not suitable to meet the future demands that will be placed on the service.

5. INCREASING SADIS FTP BANDWIDTH CAPABILITIES

The SADIS Provider State believes that a service running at 4Mbps bursting to 8Mbps is essential to meet future requirements. Simultaneously, it would be advantageous to consider increasing the guaranteed individual client connection speeds from ‘38kbps bursting to 256kbps’ to ‘64kbps bursting to 512kbps’. A budgetary estimate on these proposals will be presented to the group at SADISOPSG/14.

Noting that by SADISOPSG/15 (2010), the total number of regular users of SADIS FTP may have grown to 80 – or perhaps more owing to the fact that GRIB2 data will be available later this year – the capacity demonstrated by the table below would indicate that a SADIS FTP service provided at 4Mbps bursting to 8Mbps would be more than capable of handling the likely the increase in demand moving forwards.

|Speed between Server and ISP |Individual client connection |Maximum number of users |Minimum time to download a (future) 30MB |

|(Mbps) |speed (kbps) | |GRIB 2 WAFS data set |

|4 |38 |105 |108 minutes |

| |256 |15 |16 minutes |

| |64 |62 |64 minutes |

| |512 |7 |8 minutes |

|8 |38 |210 |108 minutes |

| |256 |31 |16 minutes |

| |64 |125 |64 minutes |

| |512 |15 |8 minutes |

An indication of the expected (minimum) time to download a 30MB GRIB 2 WAFS data set has also provided as information in the above table.

6. Conclusions

In view of the above discussion and the budgetary estimates to be presented to SADISOPSG/14, the group is invited to formulate the following draft conclusion:

Conclusion 14/.. – SADIS FTP internet bandwidth allocation

That,

a) the SADIS Provider State be invited to increase the SADIS FTP internet bandwidth allocation to 4Mbps bursting to 8Mbps between server and internet service provider (with individual client connections guaranteed at 64kbps bursting to 512 kbps) in time for the SADISOPSG/15 meeting; and

b) the Chairman of the SADISOPSG be invited to inform the Chairman of the SCRAG of the estimated costs of increasing the SADIS FTP internet bandwidth allocation.

7. ACTION BY THE SADISOPSG

The SADISOPSG is invited to:

a) note the information contained in this paper; and

b) decide on the draft conclusion proposed for the group’s consideration.

— END —

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