Welcome to TPG Community!
Is the Sagemcom F@ST5355 modem/router locked with Telstra or not?
If it is, then it is not possible to be configured on our TPG NBN service.
If not, then you can check this community link with discussions on some router that was used for NBN HFC successfully. Click here.
You may check the settings if it can fit your Sagemcom modem.
The TPG NBN HFC router is still in progress and a follow up was already sent to our logistics team. Further updates will be given via SMS/Call or E-mail once available.
Let us know should you require further assistance.