Telco M1 is not being fined for a five-hour service outage last February, despite having been chided by a Cabinet minister for not handling the glitch well.
An investigation by the authorities completed last month found the company to be blameless as the culprit was an "unknown" call-processing software bug and was "not within M1's control".
The bug that surfaced on Feb 4 prevented customers from being authenticated on the telco's 2G, 3G and 4G networks.
This resulted in customers not being able to make calls, connect to the Internet, and send or receive text messages for up to five hours from 7am.
Communications and Information Minister Yaacob Ibrahim had criticised M1 a day after the incident, saying it could do better.
The telco's network was also jammed up, worsening the problem which took place at one of its critical operation centres.
"This would mean that more than half of M1's base stations were affected," said the Infocomm Development Authority (IDA) in a document seen by The Straits Times.
Based on IDA's requirement that an aggregate of 5 per cent or more base stations must be working at any time, the telco could have been fined. But the authority was satisfied with the way M1 restored services, saying it did so "in an expeditious manner".
Dr Yaacob, however, was less sanguine in a Facebook post in February.
"While no network service is foolproof, telcos can improve in the way they update and assist their customers when disruptions occur. We should expect better service," he said.
"It has been a frustrating experience for M1 customers, especially having just experienced other disruptions in very recent months."
An M1 spokesman said yesterday the telco will continue to invest in its network and take steps to ensure high service quality.
It had an earlier six-hour outage in October 2013, for which it was not fined as well. This investigation ended last month too.
The incident, which occurred after a scheduled network upgrade, could have affected about 23,000 subscribers in Ang Mo Kio, Choa Chu Kang, Jurong, Yishun and Woodlands, said IDA.
It added that M1 had taken reasonable measures to test the new equipment and restored services promptly.
Senior analyst Clement Teo of US-based market research firm Forrester agreed with IDA's judgment.
"It's hard to pin the blame on M1 when a software bug is the cause. And M1 did take proactive steps to resolve the issue," he said.