The outage affected many people and businesses, and also impacted the emergency services number, Triple Zero.

The Senate committee wants to know what caused the outage and how Telstra plans to prevent it from happening again.

Telstra has said that the outage was not due to a lack of backup systems, but rather a problem with one of its timing servers.

The server, which is used to keep the network's clocks in sync, was being repaired when it malfunctioned and caused the outage.

The committee is also asking questions about Telstra's preparedness for such an event and its communication with customers during the outage.

The hearing is ongoing, and the committee will likely ask many more questions before it is finished.

This is a developing story, and we will provide updates as more information becomes available.