A woman using a mobile phone walks behind a Singtel signage at their head office in Singapore Feb 11, 2016. (Photo: REUTERS/Edgar Su)

CNA Explains: Are landlines still relevant?

They're more reliable than calls made over the internet, says an expert in the wake of a Singtel landline disruption.

11 Oct 2024, 04:35 by Abigail Ng · CNA · Join

SINGAPORE: For up to four hours on Tuesday (Oct 8), calls to emergency services, hospitals and businesses were disrupted because of a Singtel landline outage.

Members of the public were asked to SMS the Singapore Police Force and the Singapore Civil Defence Force instead of calling 999 and 995.

SingHealth, which operates hospitals and clinics in the east, said its telephone appointment lines were temporarily unavailable because of a Singtel ISDN outage.

What's an ISDN?

That's Integrated Services Digital Network, a system that digitally transmits voice and data content.

Landline calls run on this system.

At the back-end, they rely on legacy analogue lines known as the Public Switched Telephone Network.

ISDN is also used for point-of-sale systems, which is why some card transactions were affected by Singtel's landline outage.

Why do we still need landlines?

ISDN is more reliable, according to Assistant Professor Purnima Murali Mohan of the Singapore Institute of Technology’s infocomm technology cluster.

Newer, more hi-tech alternatives like Voice over Internet Protocol (VoIP) can be found in the digital phone line services offered by local telcos.

Here, calls are made over broadband internet connections, and rely on IP-based infrastructure.

This infrastructure uses packet switching, said Asst Prof Purnima. It means data is broken down into smaller packets and transmitted through the network.

If one packet is lost, the whole message has to be sent again.

When there is high congestion on the network - such as at a concert where many people in the same area might be trying to send messages at the same time - there'll be a lag in the transmission of data. That’s not ideal for emergency situations.

With ISDN, there is a dedicated channel for each ongoing call. When one person dials 999 and Channel One is in use, no one else can use it or share the bandwidth, said Asst Prof Purnima.

Other callers will be using separate channels until Channel One is released by the first person, she explained.

She likened ISDN to railway infrastructure where tracks are built for one train to travel on. The internet, on the other hand, is more of an expressway shared - and with the potential to be clogged up - by different vehicles.

Mr Oo Gin Lee, managing director of a tech-focused public relations company, added that landlines are always connected whereas mobile phones depend on last-mile wireless connectivity.

“During power outages, landlines should still work,” he said. Digital lines however will be cut off if internet connectivity is affected.

“It’s rare for the reverse to happen - landlines going down instead of the internet."

Is Singtel the only option?

In Singapore, Singtel owns most of the core infrastructure, said Asst Prof Purnima.

If other telcos want to use it, they would have to build services on it, she said, likening it to an apartment owned by Singtel with other telcos like StarHub and M1 leasing.

This way of doing things is cost-efficient because infrastructure is expensive, she said.

She estimated the ISDN infrastructure to be at least 17 years old, based on an old Singtel report from 2007.

Mr Oo pointed to an incident in 2013 when a fire at a SingTel facility took down critical services across the island, including for customers of other telcos.

There seemed to be a lack of contingencies in that case, he said, and similarly so in this week's disruption.

For critical services and infrastructure, there should be redundancy, he said, referring to the practice of intentionally having duplicates so a system is more reliable.

"If you have redundancy, you should not go down for three hours, right? You should be able to immediately switch over," he said. "Redundancy means that you're always on."

The Infocomm Media Development Authority (IMDA) has started investigations into the disruption. It can impose a financial penalty of up to S$1 million (US$766,000) or 10 per cent of the annual turnover of Singtel, whichever is higher.

What's the future for landlines?

Asst Prof Purnima also pointed to a June report by IMDA, which stated requirements to connect ISDN infrastructure to “next generation networks”.

Once in place, IP infrastructure will serve as an automatic backup in the event of disruptions to ISDN.

CNA has asked IMDA when this will kick in.

On contingencies, the authority said in a statement also sent to other media that Singapore's networks provide connectivity across voice, mobile, broadband, Wi-Fi and messaging through different service providers. "This diversity is a key part of our infrastructure resilience," a spokesperson said.

StarHub meanwhile has noted in a section on its website that both Public Switched Telephone Network and ISDN services "will be turned off in 2025".

CNA has also contacted IMDA for confirmation of this.