Despite the long list of threats to which a telecommunications network is exposed in practice, there are many mitigation measures that can be taken to reduce the risk that these threats can pose. Although no network can ever be totally ‘non-stop’, the performance of telecommunications networks, especially the public telephone networks, are very high.
Here is a list of potential threats to telecommunications and how to mitigate them.
Exchange buildings are fitted with smoke, gas and flood detectors. Some buildings will be physically hardened and be fitted with CCTV monitoring. Building access is controlled by door entry systems which can record who have entered the building. Internal cellular security, as well as perimeter security may be used.
Radio masts are designed to cope with high wind and ice-loading.
Loss of key inputs
Equipment mitigation measures secure against loss of electricity both by having a battery backup (which might support service for about an hour) plus a diesel generator designed to cut in when the public mains supply fails.
Because the large majority of home telephones are powered by the telephone line itself, service can be provided even when the domestic electricity is cut off. (Some domestic phones, such as cordless phones and answering machines do need local mains power, however).
Generator back-up is not practical to secure most mobile network base stations or street cabinets in cable networks. This means that in an extended electrical power outage, the mobile phone networks may become subject to failure. Equally, the phones themselves rely on battery recharging from the mains supply.
Telecommunications operators are vulnerable to loss of fuel. However, mitigation measures include priority provision of fuel, alongside other essential services should ensure continuation of critical business functions.
Many telecommunications companies hold as little stock of material as they can, according to modern ‘just-in-time’ provisioning principles. Many telecommunication companies make arrangements with their suppliers to hold emergency stocks on their behalf.
This is an issue that has to be designed-in from the start. For example each concentrator can have diverse routings to its host local exchange. Each local exchange is then typically connected to 3 tandem/trunk exchanges.
Each trunk exchange is connected to every other. The result of this is that any two local exchanges have a multitude of possible paths over which calls can be set up, so the resulting network is extremely resilient to the loss of either individual trunk exchanges or the transmission systems connecting them.
But any given customer will still be vulnerable to the loss of his concentrator or local exchange. For this reason, telecommunication companies strategically position trailer-mounted exchanges which can be deployed where necessary for fast restoration.
Similarly, replacement power equipment and generators can be deployed. All telephone exchanges also use duplicated computers and switch paths internally.
The Internet has not been planned as a single logical entity, which is both a strength and a weakness. The Internet can often reconfigure itself in times of outage. On the other hand, many parts of the Internet rely on just a few buildings where different Internet providers both site their equipment and make connections with one another.
Mobile networks are highly reliant on the fixed network operators to connect their base stations and exchanges together. Hence, the mobile network cannot be seen as a separate and alternative network to the regular public fixed network.
A similar situation arises with the Internet, where the many smaller Internet Service Providers are dependent on others for their transmission. The telecommunications infrastructure has significant elements of mutual dependency.
Software failures mitigation measures
Exchange equipment is designed to detect software which is not working properly, contain the problem and restart the offending sub-system. If all else fails, the entire exchange will automatically restart. So unlike personal computers, they never stop entirely.
To avoid ‘common mode’ failures, some companies will deliberately use two types of equipment in their network from different suppliers, to avoid any ‘domino failures’.
It has to be realized that no network has enough spare capacity to cope with the increased demand for calls which occur during major incidents. Traffic overloads in telephone networks can cause major problems which can be avoided by invoking traffic management techniques, such as ‘call gapping’ which reduces the load on the system to one that can be safely managed.
In some circumstances, priority access to the networks can be provided to ensure that appropriate public authorities can continue to function.
Telecommunications operators will invest in resilience commensurate with the risk to their commercial interests, including their reputations. In a competitive environment, where prices are constantly falling, companies will often switch from competing on price to competing on quality.
Good resilience therefore becomes a competitive imperative and many of the desirable resilience features that government will wish to see are often delivered by the operation of the market itself.
But not always. In particular, the mobile and Internet industries have arisen from a quite different commercial culture than the telephony providers. The Internet is commonly described as a ‘best efforts’ network.
There are particular risks as telephone companies move towards the adoption of Next Generation Network IP technologies. The diversity of the present network may be reduced and switching will be concentrated in fewer nodes than at present.
The telephone network could start to suffer some of the weaknesses described above relating to the wider Internet. Added to that, the introduction of any new software driven technology is likely to cause some instability before the inevitable software bugs are driven out. Hence mitigation measures will become even more critical.