"There is currently no congestion in the Chorus UFB network. Every UFB user can expect to receive the service and speed as per the plan they have purchased," he said.
"If an individual consumer or business is using their full connection speed then they can expect each individual service to be less fast as the connection is shared between all the applications they are using on their computer.
"For example, downloading Windows 10 on a 30Mbps connection will have an impact on other applications sharing this connection, while downloading it on a 1Gbps business connection will have little impact."
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Digital Island chief executive, Blair Stewart said earlier this week that UFB speeds in some areas were dipping as low as 2mbps, "a far cry from the advertised 'up to 100mbps' touted by many telcos".
He said the slow speeds caused by the download had the potential to significantly disrupt businesses which were reliant on fast internet connections.
"As businesses rapidly build their reliance around UFB for their audio and video communications it becomes increasingly important for our broadband infrastructure to offer stability.
"Video conferencing and VoIP call capacity and quality are the first things to be affected when there is a high number of users all downloading and streaming at the same time," Stewart said. "An inability to provide top quality video conferencing or VoiP calls can reflect negatively, and could ultimately cost them business."
Stewart said the problem would continue as hundreds of thousands of computers throughout the country downloaded the new operating system.
"Although it's not known how many computers in New Zealand are eligible for the free operating system update, we can estimate that for every million computers, 4000 terabytes of data will be transferred," he said.
"We believe this issue is only going to get worse as the uptake of UFB accelerates.
Currently just 14 per cent of the country is connected, but the congestion is set to increase and affect performance more as this number grows."
In addition to the Windows 10 upgrade, the company identified a number of events which could impact on the consistency of UFB speeds. These includes a virus outbreak, widespread hacking events and the ongoing increase in popularity of video on demand services.