UK Resilience
Last updated: 25 November 2008
Public cellular mobile telephony has played an important role in responding to recent emergencies. However, both society and the responder community has embraced the convenience of mobile telecommunications often without pausing to appreciate the inherent resilience issues.
Geographic coverage is a widely appreciated limitation of public cellular mobile telephony. Selection of a service provider is frequently made on geographical coverage relevant to customer needs. Selection can be informed using interactive maps available on service providers' websites. In use, handsets provide immediate and visual indication of signal strength. Network coverage is closely mapped to population density - in rural areas coverage can be non-existent or very patchy where a dominant supplier may not exist.
Having multiple SIMs available for a handset might cause problems. Many organisation's business continuity plans seek to mitigate shortfalls with coverage and congestion by issuing responders with SIMs obtained from several different UK network operators. Handsets can be locked to a particular service provider preventing SIMs from other operators from working in the handset.
SIMs issued by international operators have their own drawbacks. International SIMs can allow roaming onto available UK networks, thereby taking advantage of available coverage and network capacity. However, UK network operators only allocate limited capacity for roaming users and permission for a handset to roam is sought by the handset from the operator issuing the SIM. This may require access to international telephone circuits. Following the bombs in London on July 7th, 2005 one technique used by network operators to manage the huge increase of inward calls to the UK was to request constraints to be applied on international circuits. In addition, out-bound calls from the handset to UK numbers will have to be prefixed with the UK international access code and in-bound calls to the handset will have to be prefixed with the international code applicable to the SIM. Both activities could result in confusion, particularly in times of stress.
The capacity of public mobile telecommunications networks is finite and they are not sized for an abnormally high level of demand. Networks can become overwhelmed when presented with a high concentration of calls such as those that occur immediately after a major incident and capacity constraints are often an issue at other times such as at one minute past midnight on New Year's morning. Here, the difficulty in 'getting through' is often incorrectly attributed to the called party already receiving a call.
Mobile networks are highly dependent on the availability of grid distributed electricity. In the event of local power failure, network infrastructure is designed to revert to back-up batteries. After around an hour on battery supply services become increasingly degraded.
While 'Pay as you Go' services may appear attractive, telephone numbers can be reallocated if the handset has not been used for a period of time. While this may not present any difficulty for out-going calls if contact lists are not regularly maintained the handset may be inaccessible to incoming calls.
Enhanced access to mobile networks. When a major incident has been declared, access to a cellular mobile network may be enhanced through a special SIM installed in a mobile handset. The SIMs were issued under a scheme called ACCOLC further details about the scheme can be found here. The scheme is being refreshed and will be relaunched as the Mobile Telecommunications Privileged Access Scheme, or MTPAS. SIMs issued under the legacy scheme will continue to confer privileged access. Privileged access may not work with SIMs issued by overseas service providers that require in international access code (00 44) from the UK for out-going calls to UK numbers. However, international SIMs compatible with the UK national numbering system do respond to MTPAS activation.
Keep calls as short as possible. In the event of an emergency, capacity on mobile networks is greatly enhanced by keeping calls as short as is possible - particularly in the hours immediately following the event. For example, following the bombs in London on 7 July 2005 at 08:50, by 10:00 voice traffic on both fixed and mobile networks and SMS traffic on mobile networks had started to increase rapidly, reaching a peak at around 11:00. Typically fixed telecommunications service providers were offering ten times as many calls as normal to mobile network operators. The picture was very different on the fixed infrastructure, typically the number of attempted calls increased by 75% compared to the previous week. On mobile networks, the pattern of use changed - the average call duration rose by a factor of four from 2.5 to 10 minutes. The number of SMS sessions typically increased by a factor of three and at peak demand, the delivery delay was typically between 90 – 150 minutes. By 14:00 fixed line traffic had reduced to 20% above a typical day, tailing off by mid-evening. On mobile networks traffic back to normal by early evening.
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