Telephony on NBN This page follows on from NBN and Optical fibre
Contents
NBN Telephony
Contents
NBN Telephony
- NBN fixed line phone
- Power fail?
- 3/4G alarms
- Granny flats
- Business phones
- Old style analogue telephone equipment
- Dialling
- Rotary dial telephones
- Fax etc
- Telephony over a FTTP service (obsolescent)
- Telephony over FTTN/B, HFC and FTTC services
- FTTP
- FTTN/B modem
- FTTC modem
- HFC modem
- Telephone extensions
- SIP trunk lines
NBN Telephony
NBN fixed line phone
As previously mentioned, the NBN is an integrated high speed digital data communications network that replaces the existing, copper wire, street cabling between the telephone exchange and customer premises (i.e. customer access network - CAN). When NBN is fully implemented our familiar (PSTN) telephone network with be shut down and most general communications will be over the internet.
Should a customer require a fixed line "phone only" service s/he still needs to be connected to the internet via the NBN and requires a modem (or NTD) at the premises. The only cases where PSTN landlines will be retained are where they previously existed and the customers are too remote for cable access and provided with satellite or wireless NBN instead. An overview of how NBN telephony works appears later in this article.
There are many people in our society who have little or no interest in the internet and only wish to retain their existing telephone and its related services. Existing telephone services will be replaced by VoIP telephony. In my opinion the quality and reliability of NBN VoIP telephony is inferior to PSTN. I recommend you do your own research but as I see it:
Power fail?
A traditional (PSTN) telephone still works in a power fail (see Central Battery - CB here). The majority of the NBN will not have a backup power option (e.g. FTTN etc. using VDSL modems) so power fail means NBN telephone fail. This, in turn, means that medical alarms, security alarms, emergency services (e.g. 000) etc. are compromised if carried over NBN telephony.
3G/4G alarms
An alternative offered (2018) to customers requiring medical, security alarms etc. is a 3G or 4G (wireless) based system. This uses the standard mobile/cell-phone network. Permanently connected and with battery backup, these wireless alarms provide a reliable alternative to a PSTN. or now an NBN, based system. The two main negatives are that these wireless systems are more expensive than traditional PSTN systems were and require the customer to be in a reliable mobile phone reception area. In my opinion this shift to cell-phone technology will significantly affect the take up of NBN telephony.
NBN fixed line phone
As previously mentioned, the NBN is an integrated high speed digital data communications network that replaces the existing, copper wire, street cabling between the telephone exchange and customer premises (i.e. customer access network - CAN). When NBN is fully implemented our familiar (PSTN) telephone network with be shut down and most general communications will be over the internet.
Should a customer require a fixed line "phone only" service s/he still needs to be connected to the internet via the NBN and requires a modem (or NTD) at the premises. The only cases where PSTN landlines will be retained are where they previously existed and the customers are too remote for cable access and provided with satellite or wireless NBN instead. An overview of how NBN telephony works appears later in this article.
There are many people in our society who have little or no interest in the internet and only wish to retain their existing telephone and its related services. Existing telephone services will be replaced by VoIP telephony. In my opinion the quality and reliability of NBN VoIP telephony is inferior to PSTN. I recommend you do your own research but as I see it:
Power fail?
A traditional (PSTN) telephone still works in a power fail (see Central Battery - CB here). The majority of the NBN will not have a backup power option (e.g. FTTN etc. using VDSL modems) so power fail means NBN telephone fail. This, in turn, means that medical alarms, security alarms, emergency services (e.g. 000) etc. are compromised if carried over NBN telephony.
3G/4G alarms
An alternative offered (2018) to customers requiring medical, security alarms etc. is a 3G or 4G (wireless) based system. This uses the standard mobile/cell-phone network. Permanently connected and with battery backup, these wireless alarms provide a reliable alternative to a PSTN. or now an NBN, based system. The two main negatives are that these wireless systems are more expensive than traditional PSTN systems were and require the customer to be in a reliable mobile phone reception area. In my opinion this shift to cell-phone technology will significantly affect the take up of NBN telephony.
Granny flats
Another issue is that granny flats, and similar outbuildings are, as a general rule, excluded from having separate NBN services (including telephone). NBN will only provide one connection per property. A resident of a granny flat will need to negotiate with the property owner and retail service provider (RSP) for access to this connection and will become dependent on their cooperation/goodwill.
http://www.nbnco.com.au/connect-home/preparing-for-the-nbn/outbuildings-and-granny-flats.html
Business phones
Business phones and PBX with multiple exchange lines present their own issues. These are briefly discussed at the end of this article.
Remember; When the NBN is fully implemented (2021?), our familiar analogue Public switched telephone network (PSTN) will be completely shut down.
How NBN telephony works
Along with the high speed data options, NBN customers can have a digital VoIP telephone service connected through the internet. A fixed line "phone only" service is actually one of these VoIP links and needs to be connected to the internet via the NBN. Note: The customer needs to confirm that the chosen retail service provider actually provides telephony!
Old style analogue telephone equipment
The major service providers offer the option to connect an analogue telephone (i.e. your existing standard home phone) via the NBN terminal equipment. This is still the above-mentioned VoIP link over the internet but there is an "analogue telephone adaptor" (ATA) circuit built into the terminal equipment to emulate a traditional PSTN phone line. VoIP and ATA principles are described on this page under the heading "VoIP".
Dialling
To be able to dial out, the telephone needs to be a relatively modern (i.e. late 1980s onwards) push-button DTMF (tone dialling) version.
Rotary dial telephones
Old style decadic (AKA rotary dial) phones and related equipment will NOT DIAL OUT over NBN equipment.
For the enthusiasts - Old plastic and Bakelite dial phones can still receive calls very effectively, as do traditional answering machines. This Youtube video shows a couple of early analog telephones hooked up to an NBN modem phone port. Even with other phones in parallel they rang satisfactorily. The phones also transmitted and received speech effectively. https://www.youtube.com/watch?v=gdJOOv2hI9c&feature=youtu.be
Vintage telephone enthusiasts who enjoy using traditional decadic/rotary dial telephones, which still dialled out on most PSTN lines, will be thwarted by the NBN because it does not support rotary dialling. There are plug-in devices on the market (e.g. "Dialgizmo") that can convert decadic (rotary dial) pulses to modern DTMF dialling. I doubt these after-market devices are ACMA approved for our network so beware.
Fax etc.
Telstra stated in its publicity material that the majority of existing legacy analogue services such as EFTPOS, back to base alarms, fax and even extension corded telephones will not work on the NBN. This is an oversimplification and some of these legacy services can continue (after modifications) but, maybe, less effectively.
This NBNCo document of 2014 clearly states that services such as TTY (deaf/speech impaired communications) and fax are supported on FTTP but, unfortunately, FTTP is no longer the major NBN technology. Internet chatter suggests that performance of some devices (fax, TTY) may be degraded when sent over the analogue port of a FTTN service (this probably ties in with my comments below about traffic class - TC) but I have personally experimented with fax machines and they worked fine over an FTTN telephone service.
Some pundits suggest reducing the baud rate (i.e. transmission data speed) of the fax machine to cope better with distortion on above-mentioned VoIP lines. This website discusses the issue:
https://www.voipmechanic.com/voip-fax-settings-9600-baud.htm
Along with the high speed data options, NBN customers can have a digital VoIP telephone service connected through the internet. A fixed line "phone only" service is actually one of these VoIP links and needs to be connected to the internet via the NBN. Note: The customer needs to confirm that the chosen retail service provider actually provides telephony!
Old style analogue telephone equipment
The major service providers offer the option to connect an analogue telephone (i.e. your existing standard home phone) via the NBN terminal equipment. This is still the above-mentioned VoIP link over the internet but there is an "analogue telephone adaptor" (ATA) circuit built into the terminal equipment to emulate a traditional PSTN phone line. VoIP and ATA principles are described on this page under the heading "VoIP".
Dialling
To be able to dial out, the telephone needs to be a relatively modern (i.e. late 1980s onwards) push-button DTMF (tone dialling) version.
Rotary dial telephones
Old style decadic (AKA rotary dial) phones and related equipment will NOT DIAL OUT over NBN equipment.
For the enthusiasts - Old plastic and Bakelite dial phones can still receive calls very effectively, as do traditional answering machines. This Youtube video shows a couple of early analog telephones hooked up to an NBN modem phone port. Even with other phones in parallel they rang satisfactorily. The phones also transmitted and received speech effectively. https://www.youtube.com/watch?v=gdJOOv2hI9c&feature=youtu.be
Vintage telephone enthusiasts who enjoy using traditional decadic/rotary dial telephones, which still dialled out on most PSTN lines, will be thwarted by the NBN because it does not support rotary dialling. There are plug-in devices on the market (e.g. "Dialgizmo") that can convert decadic (rotary dial) pulses to modern DTMF dialling. I doubt these after-market devices are ACMA approved for our network so beware.
Fax etc.
Telstra stated in its publicity material that the majority of existing legacy analogue services such as EFTPOS, back to base alarms, fax and even extension corded telephones will not work on the NBN. This is an oversimplification and some of these legacy services can continue (after modifications) but, maybe, less effectively.
This NBNCo document of 2014 clearly states that services such as TTY (deaf/speech impaired communications) and fax are supported on FTTP but, unfortunately, FTTP is no longer the major NBN technology. Internet chatter suggests that performance of some devices (fax, TTY) may be degraded when sent over the analogue port of a FTTN service (this probably ties in with my comments below about traffic class - TC) but I have personally experimented with fax machines and they worked fine over an FTTN telephone service.
Some pundits suggest reducing the baud rate (i.e. transmission data speed) of the fax machine to cope better with distortion on above-mentioned VoIP lines. This website discusses the issue:
https://www.voipmechanic.com/voip-fax-settings-9600-baud.htm
FTTP telephony compared to others - FTTN etc
Telephony over a FTTP Service (obsolescent)
With NBN fibre to the premises (FTTP), the option existed for a traditional analogue telephone service to be plugged directly into the an analogue port (UNI-V) provided on the NTD at the customer's premises. This is still a VoIP service but ATA circuitry within the NTD will interface the analogue phone to digital VoIP, simulating (mostly) a PSTN/landline exchange service.
The early FTTP installations used this UNI-V option but it is falling out of favour. I suspect this is because of the relatively small penetration of FTTP compared to FTTN etc. and a move to standardise customer terminal equipment?
The service provider "iinet" promoted this option as a "Fibre phone service" but ceased to offer it to residential customers from August 2017. See their site https://iihelp.iinet.net.au/NBN_Fibre_Phone_Features.
Similarly, Optus chose to never use this UNI-V option. They employ a modem connected to a UNI-D (data) port and all telephone and data traffic goes through this port. See this comment at: https://yescrowd.optus.com.au/t5/NBN/NBN-uni-v-port/td-p/367268
I believe Telstra is moving down this path as well. Their published, standard setup employs a gateway modem connected via the UNI-D port similar to the Optus example above. I understand the Uni-V analogue telephone option is/was only by special order from Telstra?
Telephony quality over FTTN/B, HFC and FTTC services
These services require a VDSL modem in the customer premises. The modems supplied by Telstra etc. are usually fitted with an analogue telephone port (FXS), similar in concept to the above-mentioned UNI-V. Thus, on the face of it, similar functionality.
I suspect the quality of service of FTTN etc. telephony (and FTTP operating through a gateway modem on the UNI-D port) will be inferior to the FTTP UNI-V and the obsolete PSTN versions.There are two main reasons:
1. Battery backup is not offered so power fail = telephone fail.
2. The second reason is a bit more esoteric. There is a thing called "traffic class" (TC) which, in simple terms, is an allocated priority to data streams. Ideally, telephony data is assigned to TC1 (highest) to give best speech reproduction. FTTP UNI-V ports are usually configured TC1. Browser data is typically lower quality "best effort" TC4. With TC4, data may suffer (minuscule) delays - no problem with buffered downloads but introduces distortion into real-time transmissions such as speech and video.
Telephony over a FTTP Service (obsolescent)
With NBN fibre to the premises (FTTP), the option existed for a traditional analogue telephone service to be plugged directly into the an analogue port (UNI-V) provided on the NTD at the customer's premises. This is still a VoIP service but ATA circuitry within the NTD will interface the analogue phone to digital VoIP, simulating (mostly) a PSTN/landline exchange service.
The early FTTP installations used this UNI-V option but it is falling out of favour. I suspect this is because of the relatively small penetration of FTTP compared to FTTN etc. and a move to standardise customer terminal equipment?
The service provider "iinet" promoted this option as a "Fibre phone service" but ceased to offer it to residential customers from August 2017. See their site https://iihelp.iinet.net.au/NBN_Fibre_Phone_Features.
Similarly, Optus chose to never use this UNI-V option. They employ a modem connected to a UNI-D (data) port and all telephone and data traffic goes through this port. See this comment at: https://yescrowd.optus.com.au/t5/NBN/NBN-uni-v-port/td-p/367268
I believe Telstra is moving down this path as well. Their published, standard setup employs a gateway modem connected via the UNI-D port similar to the Optus example above. I understand the Uni-V analogue telephone option is/was only by special order from Telstra?
Telephony quality over FTTN/B, HFC and FTTC services
These services require a VDSL modem in the customer premises. The modems supplied by Telstra etc. are usually fitted with an analogue telephone port (FXS), similar in concept to the above-mentioned UNI-V. Thus, on the face of it, similar functionality.
I suspect the quality of service of FTTN etc. telephony (and FTTP operating through a gateway modem on the UNI-D port) will be inferior to the FTTP UNI-V and the obsolete PSTN versions.There are two main reasons:
1. Battery backup is not offered so power fail = telephone fail.
2. The second reason is a bit more esoteric. There is a thing called "traffic class" (TC) which, in simple terms, is an allocated priority to data streams. Ideally, telephony data is assigned to TC1 (highest) to give best speech reproduction. FTTP UNI-V ports are usually configured TC1. Browser data is typically lower quality "best effort" TC4. With TC4, data may suffer (minuscule) delays - no problem with buffered downloads but introduces distortion into real-time transmissions such as speech and video.
I only have a limited grasp of internet packet data transmission principles so this site may be useful in explaining quality of service (QoS) and TC: http://tektel.com.au/nbn-quality-of-service-qos/ . Unfortunately this document was written in 2014 and predates FTTN so I'm none the wiser regarding the traffic class on the FXS port of a FTTN service (or a gateway off a UNI-D port). I believe it is a lower TC unless specifically configured by the service provider? Voice transmitted over a lower traffic class may be distorted and comments on internet forums suggest that fax transmitted over TC4 may risk being corrupted.
This commentary on the Whirlpool forum has a technical description of TC on Uni-D worth reading.
http://forums.whirlpool.net.au/archive/2374881
This commentary on the Whirlpool forum has a technical description of TC on Uni-D worth reading.
http://forums.whirlpool.net.au/archive/2374881
Setting up NBN modems
FTTP
Fibre to the premises is an early and now uncommon technology compared to the other MTM technologies. Some information on setting up your equipment can be seen at:
https://www.barefoottelecom.com.au/app/uploads/Connection%20Guides/barefoot_guides_FTTP.pdf
FTTN/FTTB modem
Repeated from the NBN page; these Telstra videos explain the setup of their FTTN modem. They clearly state that a range of existing legacy services will no longer work but neglect to mention that some will work with subsequent modifications:
https://www.youtube.com/watch?v=QKfmwPxWfgo and https://youtu.be/-xthExADE18
FTTN/B is the simplest system to set up, requiring only one modem/router directly connected to the original incoming telephone line to work. Typical diagram below.
FTTC modem
Fibre to the Curb (AKA FTTdp) requires an NBN connection box in a similar fashion to HFC NBN.
Set up info here: https://www.nbnco.com.au/learn/network-technology/fibre-to-the-curb-explained-fttc
The FTTC NBN connection box is important as it is also part of the RPF for the DPU in the pit (described here).
Hybrid-fibre-coax (HFC) modem
Existing broadband coaxial cable (e.g. for Foxtel etc.) can be used to deliver NBN to the premises.
This NBNCo site explains the basics of Hybrid-Fibre-Coax NBN:
https://www.nbnco.com.au/learn/network-technology/hybrid-fibre-coaxial-explained-hfc-3
This Telstra site gives good information on setting up their HFC NBN equipment:
https://www.telstra.com.au/support/category/broadband/nbn/how-do-i-self-install-my-hybrid-fibre-coaxial-nbn-connection
Foxtel on HFC NBN. Some information at: https://www.foxtel.com.au/content/dam/foxtel/support/pdf/hfc-quick-install-guide.pdf
Beware: In early (pre-NBN) FOXTEL coax. cable systems, the return path for the interactive TV was provided via an Ethernet connection to the customer’s broadband service or, alternatively, via a standard telephone line. I recently came across a situation where this telephone line still appeared to be active and interfered with the new telephone service on NBN, via existing, common, telephone cabling. This reinforces the need to disconnect/reconfigure any unnecessary telephone cabling when installing NBN.
Telephone extensions
Note; this work must be done by a Registered Cabler.
Telephone extensions can be retained after an NBN telephone service has been installed but will require some re-cabling. It is a fairly straightforward process but requires an ACMA approved cabler to do the work. My thanks to LMB Industries (Qld) for their informative Youtube video on this process.
https://www.youtube.com/watch?v=M_4-JLwBK-I
These principles apply equally to FTTN and the other MTM technologies. In all cases, the extensions are isolated from the main incoming telephone line and reconnected to the analogue telephone port on the modem/router.
Below are some diagrams explaining the processes described in the above-mentioned video.
FTTP
Fibre to the premises is an early and now uncommon technology compared to the other MTM technologies. Some information on setting up your equipment can be seen at:
https://www.barefoottelecom.com.au/app/uploads/Connection%20Guides/barefoot_guides_FTTP.pdf
FTTN/FTTB modem
Repeated from the NBN page; these Telstra videos explain the setup of their FTTN modem. They clearly state that a range of existing legacy services will no longer work but neglect to mention that some will work with subsequent modifications:
https://www.youtube.com/watch?v=QKfmwPxWfgo and https://youtu.be/-xthExADE18
FTTN/B is the simplest system to set up, requiring only one modem/router directly connected to the original incoming telephone line to work. Typical diagram below.
FTTC modem
Fibre to the Curb (AKA FTTdp) requires an NBN connection box in a similar fashion to HFC NBN.
Set up info here: https://www.nbnco.com.au/learn/network-technology/fibre-to-the-curb-explained-fttc
The FTTC NBN connection box is important as it is also part of the RPF for the DPU in the pit (described here).
Hybrid-fibre-coax (HFC) modem
Existing broadband coaxial cable (e.g. for Foxtel etc.) can be used to deliver NBN to the premises.
This NBNCo site explains the basics of Hybrid-Fibre-Coax NBN:
https://www.nbnco.com.au/learn/network-technology/hybrid-fibre-coaxial-explained-hfc-3
This Telstra site gives good information on setting up their HFC NBN equipment:
https://www.telstra.com.au/support/category/broadband/nbn/how-do-i-self-install-my-hybrid-fibre-coaxial-nbn-connection
Foxtel on HFC NBN. Some information at: https://www.foxtel.com.au/content/dam/foxtel/support/pdf/hfc-quick-install-guide.pdf
Beware: In early (pre-NBN) FOXTEL coax. cable systems, the return path for the interactive TV was provided via an Ethernet connection to the customer’s broadband service or, alternatively, via a standard telephone line. I recently came across a situation where this telephone line still appeared to be active and interfered with the new telephone service on NBN, via existing, common, telephone cabling. This reinforces the need to disconnect/reconfigure any unnecessary telephone cabling when installing NBN.
Telephone extensions
Note; this work must be done by a Registered Cabler.
Telephone extensions can be retained after an NBN telephone service has been installed but will require some re-cabling. It is a fairly straightforward process but requires an ACMA approved cabler to do the work. My thanks to LMB Industries (Qld) for their informative Youtube video on this process.
https://www.youtube.com/watch?v=M_4-JLwBK-I
These principles apply equally to FTTN and the other MTM technologies. In all cases, the extensions are isolated from the main incoming telephone line and reconnected to the analogue telephone port on the modem/router.
Below are some diagrams explaining the processes described in the above-mentioned video.
In FTTN/B and FTTC the incoming telephone line into the premises is retained. It is discarded in FTTP and HFC NBN.
The FTTN modem's line side is typically connected to the first TO (i.e.socket). If the cabling is unaltered, as in the image below, the remaining extension sockets can no longer be used for telephony. If this extension wiring remains connected there is a possibility that the extra cabling may degrade the data quality so it is beneficial to disconnect it anyway.
The FTTN modem's line side is typically connected to the first TO (i.e.socket). If the cabling is unaltered, as in the image below, the remaining extension sockets can no longer be used for telephony. If this extension wiring remains connected there is a possibility that the extra cabling may degrade the data quality so it is beneficial to disconnect it anyway.
The second image shows the cabling modifications. The first TO (socket) is retained but extensions are reconnected to a new socket installed adjacent to the first socket. This new socket is connected by cord to the the phone (FXS) port on the modem. The extensions are isolated from the incoming line and now function correctly.
Note that the diagrams shown above are "bus-wired". Although electrically equivalent, "star wired" installations may confuse some cablers and require a bit more attention in rewiring. An example of star wiring appears here
In the case of FTTN or similar, the cabler will need to select a TO/socket as the first socket and isolate the remaining star wired sockets from it. A new socket is installed and connected to the, now isolated, extensions. The star configuration can be retained but electrically it will be similar to the example in the above image.
Further information can be obtained from the following technical document
https://www.commsalliance.com.au/__data/assets/pdf_file/0010/59446/G649-2_2017.pdf
In the case of FTTN or similar, the cabler will need to select a TO/socket as the first socket and isolate the remaining star wired sockets from it. A new socket is installed and connected to the, now isolated, extensions. The star configuration can be retained but electrically it will be similar to the example in the above image.
Further information can be obtained from the following technical document
https://www.commsalliance.com.au/__data/assets/pdf_file/0010/59446/G649-2_2017.pdf
What about business phones and PBX?
In general, a basic NBN service usually only allows one analogue phone connection. Customer equipment requiring multiple exchange lines, e.g an early analogue PBX, cannot be accommodated with this simple arrangement. Retail service providers - RSPs - are encouraging business customers to replace their existing business systems with modern hosted "NBN compliant systems" but what if you don't want to do this for such reasons as cost and disruption?
First of all, familiarise yourself with the term SIP trunking. There is plenty of information on the internet but, in very general terms, SIP (session initiation protocol) trunks are digital transmission pathways compatible with the internet and ideal for VoIP telephony. They replace the existing analogue PSTN exchange lines.
A couple of options exist;
Relatively modern PBXs generally have the option to upgrade the analogue exchange line electronic cards to SIP trunking cards. The old exchange lines are replaced by VoIP. The system becomes NBN compliant with minimal effort. Check with your system supplier regarding availability and cost.
Early analogue PBXs without SIP can be interfaced to SIP trunking with ATAs designed for the purpose to interface analogue exchange lines to SIP trunks.
Very old PBX/PABX systems with decadic (rotary) dialling will not be compatible with the above but I doubt that there are many of these still in the network?
These suppliers have spent some time describing SIP trunking and PBXs. Please note; I have no commercial interest in these sources listed but my thanks to them for publishing this information.
https://www.telstraglobal.com/insights/blogs/blog/key-differences-between-sip-voip
https://business.mynetfone.com.au/phone-systems/sip-trunking/how-it-works
https://www.icstechnologies.com.au/faq-phone-system-compatible-nbn/
It is also worth reading the following:
https://crowdsupport.telstra.com.au/t5/Home-Broadband/How-to-connect-multiple-phone-numbers-to-NBN/td-p/670271
https://www.accc.gov.au/business/business-rights-protections/moving-to-the-nbn-for-small-businesses
In general, a basic NBN service usually only allows one analogue phone connection. Customer equipment requiring multiple exchange lines, e.g an early analogue PBX, cannot be accommodated with this simple arrangement. Retail service providers - RSPs - are encouraging business customers to replace their existing business systems with modern hosted "NBN compliant systems" but what if you don't want to do this for such reasons as cost and disruption?
First of all, familiarise yourself with the term SIP trunking. There is plenty of information on the internet but, in very general terms, SIP (session initiation protocol) trunks are digital transmission pathways compatible with the internet and ideal for VoIP telephony. They replace the existing analogue PSTN exchange lines.
A couple of options exist;
Relatively modern PBXs generally have the option to upgrade the analogue exchange line electronic cards to SIP trunking cards. The old exchange lines are replaced by VoIP. The system becomes NBN compliant with minimal effort. Check with your system supplier regarding availability and cost.
Early analogue PBXs without SIP can be interfaced to SIP trunking with ATAs designed for the purpose to interface analogue exchange lines to SIP trunks.
Very old PBX/PABX systems with decadic (rotary) dialling will not be compatible with the above but I doubt that there are many of these still in the network?
These suppliers have spent some time describing SIP trunking and PBXs. Please note; I have no commercial interest in these sources listed but my thanks to them for publishing this information.
https://www.telstraglobal.com/insights/blogs/blog/key-differences-between-sip-voip
https://business.mynetfone.com.au/phone-systems/sip-trunking/how-it-works
https://www.icstechnologies.com.au/faq-phone-system-compatible-nbn/
It is also worth reading the following:
https://crowdsupport.telstra.com.au/t5/Home-Broadband/How-to-connect-multiple-phone-numbers-to-NBN/td-p/670271
https://www.accc.gov.au/business/business-rights-protections/moving-to-the-nbn-for-small-businesses