Analogue and digital telephony
Contents
- Analogue telephony
- Cordless telephone
- PSTN (SxS, Crossbar and Digital Exchanges)
- Community Telephone Plan for Australia 1960
- Transmission networks
- Digital telephony
- Digital PABX networks
- VoIP
- NBN
Analogue telephony
In an analogue (also spelt analog) telephone, the user’s voice sounds are converted by the telephone's transmission circuitry into electrical signals and transmitted to line. The electrical signals’ variations in frequency and amplitude closely copy the speech signals. At the receiving end these varying electrical frequencies and amplitudes are converted back to sound signals.
In an analogue (also spelt analog) telephone, the user’s voice sounds are converted by the telephone's transmission circuitry into electrical signals and transmitted to line. The electrical signals’ variations in frequency and amplitude closely copy the speech signals. At the receiving end these varying electrical frequencies and amplitudes are converted back to sound signals.
A delightful 1920s movie on how analogue telephones work can be seen at:
https://www.youtube.com/watch?v=YoOogesHB-Q
The irony is that it is a "silent" movie describing sound transmission!
The operation of a traditional analogue telephone is described here.
https://www.youtube.com/watch?v=YoOogesHB-Q
The irony is that it is a "silent" movie describing sound transmission!
The operation of a traditional analogue telephone is described here.
Cordless telephones
Cordless telephones consist of a handset and base station. Although modern versions have various enhancements, in general, they behave in a similar fashion to a traditional analogue "corded" telephone except the handset communicates with the base station via radio signals. The base station has two main functions; to interconnect to the telephone service and act as a (mains electricity) battery charger for the internal battery in the handset. Further information at: https://en.wikipedia.org/wiki/Cordless_telephone
Cordless telephones consist of a handset and base station. Although modern versions have various enhancements, in general, they behave in a similar fashion to a traditional analogue "corded" telephone except the handset communicates with the base station via radio signals. The base station has two main functions; to interconnect to the telephone service and act as a (mains electricity) battery charger for the internal battery in the handset. Further information at: https://en.wikipedia.org/wiki/Cordless_telephone
PSTN
The PSTN will mostly be closed by 2022 - superseded by NBN/internet. After that time this information will be of historical interest only.
Some background information on the genesis of the public switched telephone network (PSTN) can be found here and here. Early telephone networks were wholly analogue. Examples include manual exchange networks and the early PSTN, electro-mechanical, automatic exchanges. The analogue telephone signals were transmitted from the telephone and proceeded, unaltered, right through the switching equipment connections to the received end.
According to contributors on the Whirlpool site http://forums.whirlpool.net.au/archive/2241618 the last Australian SxS exchange closed in 1996 and the last crossbar exchange closed in about 1998.
In the modern Australian PSTN, the switching equipment in the exchange used digital techniques similar to those employed in typical computers. For “backward compatibility” the Australian PSTN still uses analogue telephones but employs analogue-to-digital conversion at the exchange interface. The exchange uses wholly digital switching processes.
There are numerous manufacturers of telephone switching equipment worldwide. An interesting list appears at:
https://en.wikipedia.org/wiki/List_of_telephone_switches
Information on early 21st c. telephone exchanges can be seen here.
The PSTN will mostly be closed by 2022 - superseded by NBN/internet. After that time this information will be of historical interest only.
Some background information on the genesis of the public switched telephone network (PSTN) can be found here and here. Early telephone networks were wholly analogue. Examples include manual exchange networks and the early PSTN, electro-mechanical, automatic exchanges. The analogue telephone signals were transmitted from the telephone and proceeded, unaltered, right through the switching equipment connections to the received end.
According to contributors on the Whirlpool site http://forums.whirlpool.net.au/archive/2241618 the last Australian SxS exchange closed in 1996 and the last crossbar exchange closed in about 1998.
In the modern Australian PSTN, the switching equipment in the exchange used digital techniques similar to those employed in typical computers. For “backward compatibility” the Australian PSTN still uses analogue telephones but employs analogue-to-digital conversion at the exchange interface. The exchange uses wholly digital switching processes.
There are numerous manufacturers of telephone switching equipment worldwide. An interesting list appears at:
https://en.wikipedia.org/wiki/List_of_telephone_switches
Information on early 21st c. telephone exchanges can be seen here.
Step by Step Switching (SxS)
SxS was the first significant automatic switching technology developed from the end of the 19th c. and first introduced into Australia in 1911. Below are extracts from PMG publication ETP018 (1971) showing the SxS concept. The full document can be obtained from the STAA website (members only). Details on how to join an affiliated STAA club at: https://telecommunicationsandsound.com/memberselect.html
An image of very early Strowger SxS switches (of the type used in Australia from 1912) can be seen at:
https://ethw.org/File:Step-by-Step_--_Dallas_Telephone_Co._1919.jpg
A video showing the operation and concept of an early SxS telephone exchange can be seen at:
https://www.youtube.com/watch?v=xZePwin92cI
And an Australian SxS training video can be seen at:
https://www.youtube.com/watch?v=HcvA5q8yOTo
SxS was the first significant automatic switching technology developed from the end of the 19th c. and first introduced into Australia in 1911. Below are extracts from PMG publication ETP018 (1971) showing the SxS concept. The full document can be obtained from the STAA website (members only). Details on how to join an affiliated STAA club at: https://telecommunicationsandsound.com/memberselect.html
An image of very early Strowger SxS switches (of the type used in Australia from 1912) can be seen at:
https://ethw.org/File:Step-by-Step_--_Dallas_Telephone_Co._1919.jpg
A video showing the operation and concept of an early SxS telephone exchange can be seen at:
https://www.youtube.com/watch?v=xZePwin92cI
And an Australian SxS training video can be seen at:
https://www.youtube.com/watch?v=HcvA5q8yOTo
In Australia, "Step by step" was superseded by "Crossbar" technology (but still employing analogue, electromechanical switching devices) in the 1960s. An article on the transition to crossbar can be viewed at:
http://schoolpa.com.au/sxs/crossbar%20switching%20oct%201961.pdf
Crossbar Exchanges
Crossbar Exchanges employing common control principles were Introduced into Australia from around 1960. Many companies produced this type of equipment but Australia settled on the Ericsson type.
The exchange types were primarily:
ARF: Metropolitan and larger country town switching centres.
ARK: Small country towns or areas. The exchange was "slaved" off a larger exchange (usually ARF) and relied on it for part of the call setup process.
ARM: Trunk line switching exchange serving metropolitan or large country areas.
ARB: Telex switching exchange here
Below an extract from PMG publication ETP015 (1971) introducing the common control concept. The full document can be obtained from the STAA website (members only). Details on how to join an affiliated STAA club at: https://telecommunicationsandsound.com/memberselect.html
http://schoolpa.com.au/sxs/crossbar%20switching%20oct%201961.pdf
Crossbar Exchanges
Crossbar Exchanges employing common control principles were Introduced into Australia from around 1960. Many companies produced this type of equipment but Australia settled on the Ericsson type.
The exchange types were primarily:
ARF: Metropolitan and larger country town switching centres.
ARK: Small country towns or areas. The exchange was "slaved" off a larger exchange (usually ARF) and relied on it for part of the call setup process.
ARM: Trunk line switching exchange serving metropolitan or large country areas.
ARB: Telex switching exchange here
Below an extract from PMG publication ETP015 (1971) introducing the common control concept. The full document can be obtained from the STAA website (members only). Details on how to join an affiliated STAA club at: https://telecommunicationsandsound.com/memberselect.html
A video of the main elements of a crossbar exchange (1971) can be viewed at the link following. It is in the Hungarian language but shows clear images of typical equipment and layout. It is interesting that the majority of technical staff were female. Europeans were much more progressive than their Australian counterparts. Women were (and still are) rare in our technical ranks.
https://www.youtube.com/watch?v=dA8-lG2Dpg0
https://www.youtube.com/watch?v=dA8-lG2Dpg0
Digital Exchanges
Telecom Australia introduced digital switching exchanges progressively from the mid 1970s through to the early 2000s. These included ARE, AXE and Alcatel S12.
As mentioned elsewhere on this site, although the exchanges used digital switching technology, the telephones continued to be analogue devices. A-D conversion taking place at the exchange interface. There were many millions of telephones in circulation and presumably the cost of upgrading would have been both huge and unnecessary. Even today with the rise of internet VoIP telephony over NBN, the domestic NBN telephone service still uses analogue telephones.
Publicly available information is scarce but a brief description of AXE (first appeared in Australia ca. 1982) appears at https://en.wikipedia.org/wiki/AXE_telephone_exchange and an image of typical AXE equipment
at: https://www.gettyimages.ie/detail/news-photo/telephone-switches-being-installed-by-ericsson-at-a-news-photo/453007074
And an interesting summary of Australian switching technologies by Paul Matthews (2014) http://schoolpa.com.au/sxs/introductiontoaussieexchanges.pdf
Telecom Australia introduced digital switching exchanges progressively from the mid 1970s through to the early 2000s. These included ARE, AXE and Alcatel S12.
As mentioned elsewhere on this site, although the exchanges used digital switching technology, the telephones continued to be analogue devices. A-D conversion taking place at the exchange interface. There were many millions of telephones in circulation and presumably the cost of upgrading would have been both huge and unnecessary. Even today with the rise of internet VoIP telephony over NBN, the domestic NBN telephone service still uses analogue telephones.
Publicly available information is scarce but a brief description of AXE (first appeared in Australia ca. 1982) appears at https://en.wikipedia.org/wiki/AXE_telephone_exchange and an image of typical AXE equipment
at: https://www.gettyimages.ie/detail/news-photo/telephone-switches-being-installed-by-ericsson-at-a-news-photo/453007074
And an interesting summary of Australian switching technologies by Paul Matthews (2014) http://schoolpa.com.au/sxs/introductiontoaussieexchanges.pdf
Community Telephone Plan for Australia 1960
This Commonwealth Gov't publication outlined the new telephone policy and described the plans for the future telephone network. The policy and plan represented a milestone in the history of Australia’s telecommunication services and a dramatic shift away from the system and methodology that had been in place for nearly five decades.
Click on download file below.
This Commonwealth Gov't publication outlined the new telephone policy and described the plans for the future telephone network. The policy and plan represented a milestone in the history of Australia’s telecommunication services and a dramatic shift away from the system and methodology that had been in place for nearly five decades.
Click on download file below.
communitytelephoneplan1960-1.pdf | |
File Size: | 5347 kb |
File Type: |
Transmission networks
An overview of the historical development of Australian transmission networks between about 1930 and 2000 can be seen here
An overview of the historical development of Australian transmission networks between about 1930 and 2000 can be seen here
Digital telephony
Digital telephony developed alongside computer systems. In a digital telephone, the sounds are first converted by the circuitry into electrical signals, as described above, but additional stages of electronic processing are applied. The variations in the signal's frequency and amplitude are digitally encoded in the phone (codec), transmitted as strings of digital information (0s and 1s) and processed digitally through the compatible digital switching exchange. At the receive end telephone, this digital data is decoded (codec) and converted back to the varying electrical signals and then to sound signals.
Digital telephony developed alongside computer systems. In a digital telephone, the sounds are first converted by the circuitry into electrical signals, as described above, but additional stages of electronic processing are applied. The variations in the signal's frequency and amplitude are digitally encoded in the phone (codec), transmitted as strings of digital information (0s and 1s) and processed digitally through the compatible digital switching exchange. At the receive end telephone, this digital data is decoded (codec) and converted back to the varying electrical signals and then to sound signals.
Digital PABX networks
PABX (PBX) concepts are described here. Various digital protocols appear in different systems. The Intel 286 microprocessor of the early 1980s not only revolutionised personal computing but was the heart of many early digital PABXs (private automatic telephone exchanges). Typically found in business and administrative organisations, digital PABXs use digital telephones that directly encode/decode the speech signals and these signals are processed and switched digitally by the central unit. In earlier times, PABX manufacturers often employed proprietary digital encoding and their telephone instruments were incompatible with other manufacturers but now they generally follow internationally agreed digital internetworking protocols. The image below shows an early 2 Line Ericsson "Dialog 2501" digital telephone handset used on their MD110 PABX System. introduced in the late 1980s, its external appearance is similar to an analogue phone of the same era.
PABX (PBX) concepts are described here. Various digital protocols appear in different systems. The Intel 286 microprocessor of the early 1980s not only revolutionised personal computing but was the heart of many early digital PABXs (private automatic telephone exchanges). Typically found in business and administrative organisations, digital PABXs use digital telephones that directly encode/decode the speech signals and these signals are processed and switched digitally by the central unit. In earlier times, PABX manufacturers often employed proprietary digital encoding and their telephone instruments were incompatible with other manufacturers but now they generally follow internationally agreed digital internetworking protocols. The image below shows an early 2 Line Ericsson "Dialog 2501" digital telephone handset used on their MD110 PABX System. introduced in the late 1980s, its external appearance is similar to an analogue phone of the same era.
Alternatives include PABX systems with analogue telephone instruments and digital switching and “hybrid” systems which contain a mix of technologies. In recent years "hosted" or "virtual" PBX have appeared in the market. These do away with discrete equipment at the customers' premises and provide the equivalent service using public infrastructure (PSTN or the internet). An overview appears at this site:
https://www.3cx.com/pbx/what-is-a-hosted-pbx/
https://www.3cx.com/pbx/what-is-a-hosted-pbx/
VoIP (voice over internetworking protocol)
VoIP is where the telephone service is again wholly digital and connections are made via the internet using internationally accepted digital protocols. “Skype” telephony is a type of VoIP. To access a VoIP line you need a compatible digital telephone instrument. Should you wish to use an analogue phone you will need to interface it with an an ATA (analogue telephone adapter). In the NBN (described below) an ATA is usually incorporated in the terminal equipment .
A simple introduction of how VoIP technology differs from the PSTN can be seen here:
https://voipstudio.com/how-is-voip-different-from-regular-telephone-service/
An unusual but informative video introducing VoIP and also the concept of ATA can be seen at:
https://www.youtube.com/watch?v=6Q_BrQpZfFE
SIP (Session Initiated Protocol) is a signalling protocol associated with VOIP etc. It is beyond the scope of this discussion but is described at: https://en.wikipedia.org/wiki/Session_Initiation_Protocol
VoIP is where the telephone service is again wholly digital and connections are made via the internet using internationally accepted digital protocols. “Skype” telephony is a type of VoIP. To access a VoIP line you need a compatible digital telephone instrument. Should you wish to use an analogue phone you will need to interface it with an an ATA (analogue telephone adapter). In the NBN (described below) an ATA is usually incorporated in the terminal equipment .
A simple introduction of how VoIP technology differs from the PSTN can be seen here:
https://voipstudio.com/how-is-voip-different-from-regular-telephone-service/
An unusual but informative video introducing VoIP and also the concept of ATA can be seen at:
https://www.youtube.com/watch?v=6Q_BrQpZfFE
SIP (Session Initiated Protocol) is a signalling protocol associated with VOIP etc. It is beyond the scope of this discussion but is described at: https://en.wikipedia.org/wiki/Session_Initiation_Protocol
NBN
The National Broadband Network is an integrated high speed digital data communications network that will ultimately connect all Australian premises to the internet via a mixture of transmission technologies. In addition to internet access, customers will generally have the choice of a digital VoIP telephone service transmitted over the broadband. If they wish to retain their familiar analogue telephone they may be able to choose a service connected via an analogue port provided on the NBN customer device.
Go to the NBN page for further information
The National Broadband Network is an integrated high speed digital data communications network that will ultimately connect all Australian premises to the internet via a mixture of transmission technologies. In addition to internet access, customers will generally have the choice of a digital VoIP telephone service transmitted over the broadband. If they wish to retain their familiar analogue telephone they may be able to choose a service connected via an analogue port provided on the NBN customer device.
Go to the NBN page for further information