Chinese telecommunications company Huawei hit the spotlight in Australia last year after it was banned from taking part in the rollout of 5G mobile infrastructure due to national security fears.

Now, residents of a Sydney suburb are concerned about the company's involvement in the use of small cell boxes outside their homes, without the need for council approval.

The devices — roughly the size of two shoe boxes — are transmitters for 4G and mobile services that attach to power poles to help fill signal in areas where signal strength from big base stations is weak.

But why is a company that was disqualified from the 5G rollout involved in the installation of telecommunication boxes?

What are small cell boxes?

Robin Braun, professor of telecommunications and engineering at the University of Technology Sydney, said all of the big telcos had been using these small cell boxes in people's homes for years.

For example, in some parts of Coogee, which have very poor mobile signal due to being in a valley, Vodafone installed small cell boxes in people's homes to improve signal.

The boxes capture mobile signals and pass them on to the networks so that customers can communicate with each other.

"At the same time, it's recording what those connections are and could quite possibly be recording the content of these conversations," Professor Braun said.

How is 5G different?

A key factor here is the difference between what is known as core part of the network and the "edge" of the network.

Tom Uren from the Australian Strategic Policy Institute (ASPI) said the core deals with billing and subscriber details, including the duration of calls and identity of numbers, so telcos can bill for the service.

This is more information than what's exchanged during the role of the small cell boxes on the so-called "edge" of the network, which only set up connections between handsets and the core.

Mike Burgess, the Director-General of the Australian Signals Directorate — a Federal Government body concerned with national and cyber security — spoke about that the distinction in a speech last year.

Speaking at ASPI in October he said historically, sensitive information at the core of telecommunications networks was protected by confining high-risk vendors to the edge.

"But the distinction between core and edge collapses in 5G networks," Mr Burgess said.

"That means that a potential threat anywhere in the network will be a threat to the whole network."

Mr Uren said 5G technology was so complicated that it was difficult to isolate Huawei to a particular part of it.

What can I do to protect my security?

Professor Braun suggested those concerned about third parties potentially accessing their information through these small cell boxes should communicate through apps that use encryption.

"That's the only thing that you should be concerned about from a personal point of view," he said.

"If you do want to make sure that the content of your call is not understood, well then use an encrypted service of some form."

He did warn, however that there was no way of hiding the fact a call had been made in the first place.

"That information is necessary in order for the call to happen, so there's no way that can be hidden," he said.

In a statement to the ABC, Huawei's corporate affairs manager Brent Hooley said: "Huawei is the largest provider of mobile network infrastructure in Australia and has been supplying local telecommunications companies, private businesses and government customers without incident for 15 years".