Singtel has been fined $150,000 for a fixed-lined telephone service disruption that left some 7,400 subscribers in Ang Mo Kio unable to make and receive calls for about five hours in 2015.
This brings the total fines imposed on Singtel this year for fixed-line telephone service breakdowns to $350,000.
Investigations concluded recently by local regulator, the Infocomm Media Development Authority (IMDA), showed that the incident in 2015 was triggered during a planned upgrade of Singtel's digital network.
The upgrade had been done in batches since October 2015. But on Nov 17 that year, Singtel more than doubled the number of equipment upgraded without adjusting the limit on the calls customers could make. Thus, extra traffic from customers could not be processed due to the limit set on its network switch, resulting in the service disruption.
Referring to the recent fine, IMDA told The Straits Times that telcos providing key services to a large number of end users should adopt proactive measures to invest in and improve the resilience of their telecommunication networks to prevent widespread service disruptions.
"Singtel had not established to the satisfaction of IMDA that the incident was not within Singtel's control," said the regulator.
For a disruption of 500 or more subscribers' local fixed-line telephone service, a telco can be fined between $15,000 and $270,000 for every 30 minutes of outage. This is spelt out in IMDA's Telecom Service Resiliency Code, which sets out minimum service standards.
The maximum fine that IMDA can impose is $1 million, or 10 per cent of the annual turnover of a licensee, whichever is higher.
Nevertheless, IMDA noted that Singtel has since taken measures to prevent a similar recurrence.
A Singtel spokesman said the telco regrets the "localised disruption". She added: "We have reviewed and revised our processes so that planned upgrades are managed more carefully to ensure minimal impact to customers."
The telco was hit with a $200,000 fine in April this year for cutting off the fixed-line telephone services of up to 3,800 customers in each of the seven disruptions that happened two years ago. The seven disruptions were all due to failed, ageing equipment.
IMDA said there was "a clear pattern" in the cause of the disruptions, which could have been avoided.
Since then, Singtel has accelerated the replacement of the ageing equipment with plans for a complete change-out by early 2019.
Network upgrade is expected of all telcos.
Singtel will be shutting down its ageing copper-based digital network in April next year. It will also cease copper installations in commercial buildings that obtain Temporary Occupation Permit status from April next year, and will instead install fibre networks. Singtel ceased copper deployment to new residential buildings in 2013.