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Reliability and dependability of information networks – Taiwan’s earthquake – are we redundancy compliant?

January 23rd, 2007 · No Comments ·

Our story about the damage done to eight submarine cables by the Dec. 26, 2006 – magnitude 6.7 – earthquake near Taiwan, raised some people’s interest:

Reliability and dependability of information networks – lessons from the Taiwan earthquake – with nice charts and much more

Despite optimistic estimates that it would take only three weeks to repair the massive damage, reports on January 17 indicated that not one of the cables is back in service. Although capacity was such that all services have been restored by now.

A critical issue is how close different cable-heads are to a port and neighbouring cables. The same still happens with much land-based sonet, where diverse paths still share the same entrance to a given facility.

Most transatlantic cables are in the same backhaul conduit systems. For instance,

– 3 systems landing in New Jersey use the same conduit to backhaul traffic to New York City (NYC),
– 3 cables landing in Long Island use the same conduct system to reach NYC,
– most in the UK are in the same conduit system

Accordingly, very few of those systems can avoid New York, which is a diversity requirement of many banks and one which the IP backbones should probably also adopt.

When of the:

– 7 TransAtlantic cables,
– 5 of them terminate at the same end points,

it is hard to achieve ‘redundant, diverse paths to redundant facility entrances into redundant wire centers.’

At least Apollo and Hibernia have diversity in that they offer different landing points to clients by:

– Apollo’s southern cable lands in France and
– Hibernia lands in Canada and Northern England.

The above shows that despite all the preaching about physical diversity, it is nearly impossible to secure redundant and diverse paths to redundant facility entrances into redundant wire centers. Indeed, undersea cables very often use the same conduits for terrestrial backhaul. In part one can understand this fact due to the pressure to save money. However, while this might be cost efficient it surely does not represent best practice for safeguarding system dependency and reliability demands.

Even if one purchases access via different undersea cables how much physical diversity will this buy one if if the same conduits are used on land?

How difficult it is managing these challenges according to best practice, while guarding your costs is outlined here:

– ‘End-to-end multi-carrier circuit diversity assurance currently cannot be conducted in a scalable manner.’ (2006-03-15 – Alliance for Telecommunication Industry Solutions – ATIS)

– ‘National Diversity Assurance Initiative 2006-03-15 Final report. Washington DC.: Alliance for Telecommunication Industry Solutions – ATIS

By the way, some insiders suggest that the ship that sank off the coast of Pakistan and cut both, the SWM3 spur into Pakistan and the Flag link was probably able to do so simply, because the two cables wer laid next to each other and left the harbor in the same area to take advantage of the same overland conduit. Cost efficiency can sometimes mean that systematic risk is increased significantly.


Diversity assurance is expensive and requires commitment by the customer to work closely with carriers in performing due diligence. However, circuit route diversity is difficult to meet since undersea cables very often use the same conduits for terrestrial backhaul. Moreover, cable-heads are often close to a port and/or close to another cable-head, therefore, diversity assurance remains a pipedream. Promoting it as best practice may neither be realistic according to cost constraints nor reflect the realities of where physical infrastructure has been built and is delivering the goods – bandwidth and data traffic.

In conclusion, while the risk cannot be eliminated completely (some residual risk we have to live with), it can only be reduced to an acceptable level, if physical diversity of the telecommunication infrastructure can be assured (submarine cables and their conduit on land are far away from each other).

PS. While almost all services are restored, the cables are still being repaired:

how submarine cables get laid and repaired – flash animation from Alcatel


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