Specifically, is there still a large number of circuits dedicated to only voice traffic? Or have most of them been combined with IP traffic?
Note: I’m not talking about the last mile (i.e. POTS lines); I know many people still have their analog lines. I’m talking about the routing between offices/cities/states/etc.
In order to make ADSL services available Telcos had to replace analog exchanges with digital ones that combine voice and data. So no there would be very few if any dedicated voice circuits left anywhere.
NO !. Not much got replaced. ADSL was typically added on.
Sure there are small boxes for replacing a voice only box with a voice and ADSL box, so that it can live in a basement of an apartment block,
like one of these ,
But most phone lines run to the exchange, and most of the exchanges had plenty of room from where the electromechanical (pure analog) exchange equipment was removed after the change to digital..
If the question was whether exchanges are VOIP between them, the answer is NO.
If the question was whether voice can use the same bandwidth as data, I doubt it. The fibre optics equipment that connects to the voice exchange, is just so specialised to voice, its just going to have to have its own fibres allocated to it.
So you’re saying those analog exchanges are still hooked up to the actual last mile copper? This page seems to show pretty clearly that the MDF where the copper terminates runs directly into an ADSL line card.
Analog dedicated voice equipment might still be inside exchanges where it was too expensive to remove but its not hooked up to anything.
Analog phones still work fine on the phone networks. I have an old push button desk phone from 1990 and a rotary Wall phone from the 1960’s hooked up at my house.
At work our lines are digital. I’m pretty sure all the analog lines are turned off. We have PBX digital type phones at work.
My boss was keeping a analog phone line in our server room because I had a 56k dial up modem connected. It was my emergency remote backdoor into the server. But that became a security issue and I unhooked the modem several years ago. Then my boss saved some money by switching off the analog line.
In Australia we have fibre connections between all exchanges so in effect once it hits the exchange it’s IP until it hits the last mile of copper again.
There is a difference between naked IP run over the fibres and carrying IP along with other protocols on a layered protocol on the fibre.
Prior to the Internet taking off telcos were already installing digital exchanges. And typically exchanges were connected with fibres. The protocol run over these networks is/was typically ATM - Asynchonous Transfer Mode. This protocol was designed with voice and very high quality of service guarantees as its main drivers. For instance the packet rate is 8kHz, which is a nice fit to digitally encoded voice. ATM networks are switched (which is a big difference to IP which is routed) and provides virtual circuits end to end. ATM networks span the globe. It is easy enough to tunnel IP traffic over ATM, and there are adaptation layers specifically designed to support data over ATM. A huge amount of Internet traffic is carried over telco networks over ATM. Indeed, a little known fact is that ADSL is basically ATM. Your internet connection using ADSL can run over ATM most of the way back to your ISP. More modern DSLAMs can reticulate the traffic over naked fibre using ethernet protocols to carry the IP traffic. But in general the digital phone infrastructure can carry IP traffic in the same systems as voice.
For a long time ADSL and baseband voice were served by different gear - the line would connect to your ISP’s DSLAM as well as your telco’s exchange frame. If you use the same provider for both voice and ADSL the same bit of gear can be used to provide both. But it will depend upon its age.
Once exchanges were connected by fibre it all became much easier - upgrades to bandwidth are accomplished with upgrades to the equipment at each end of the fibre. Before that the number of copper pairs was the limitation on the bandwidth. The move to digital voice started long before domestic internet became common, and that infrastructure co-exists in many places. But any new installation will likely be a combined baseband voice plus ADSL, or pure naked ADSL with VoIP as the only voice offering.
That’s not the question being asked - the OP specifically disallowed the last mile copper to the house - that’s all you need for a POTS phone to work. I’ve got fiber optic right into my house (FIOS), and my analog phone sets still work fine - the network termination in my basement handles the analog-digital conversion and puts the 48V on the internal phone lines.
What I find interesting is that the Internet is still mostly transmitted through wires and undersea cables and not satellites. It’s essentially just a modernized version of the telegraph system.
Satellites have too much latency, what with not being able to go faster than the speed of light and whatnot.
Yup- cables are faster and less prone to interference.
There’s too much delay going through a satellite path. While that may not matter for some purposes, it is critical for others. Satellite is (was?) a lot cheaper, and some of our international customers had both a satellite and undersea connection to us, and the equipment on each end would categorize traffic based on the delay it could tolerate and send it out the best path.
ummm, dsl was invented by the telcos FOR their trunk lines, so they could get more bandwidth out of their existing cable runs.
Once a phone call hits a telco’s central office (the provider end of the ‘last mile’) it becomes purely digital and is treated the same as any other data (except maybe with some priority handling to maintain the appearance of a real-time connection). That’s why modems couldn’t exceeed 56k until dsl came along; data was sampled at only 64k (of which 8k was reserved for emergency services), so anything over that would get lost in the conversion.
Not faster; shorter. A lot shorter: most communications satellites are in geosynchronous orbit, 44 000 km out, as opposed to your typical 4000- or 10 000- km cable hop across the oceans.
Say what? The S in DSL stands for Subscriber.
There was some later use of HDSL (T1 over 2, and later 1, pairs) to serve remote concentrators (not full central offices). However, the engineering constraints on the circuit (no load coils, special repeaters needed, and so on) meant that this did not get a lot of deployment by telcos to carry customer voice calls on the PSTN. By that time, the conversion to fiber was well under way and by the mid 90’s, telcos were often installing fiber even for customers who ordered T1 circuits.
Western Electric central office switches (non-tandem) before the 5ESS had analog trunks to the rest of the telephone network. There were external channel banks which converted those into digital transmission paths when going over digital circuits. A digital circuit was not guaranteed - for example, L carrier (you might have seen “Warning: Transcontinental coaxial cable” signs along railroad tracks) sends over 10,000 calls over an analog link.
The first big push for digital interoffice links was for SS7, which moved the call setup and routing out of the in-band channel. The phone company wanted this to get rid of the “phone phreaks”, and the fact that the US government had an interested in it and “strongly encouraged” its deployment helped move it along. But the calls were still on analog trunks.
These days, almost all trunks are indeed digital. But there is very little intermixing of digital telephone traffic with other data traffic, either for telco internal purposes or for circuits sold to customers. They may be in the same fiber bundle, but not on the same circuit. And that voice traffic doesn’t need “priority handling” as it is time-division-multiplexed into higher and higher levels of digital signalling - a voice channel has a “reserved seat”, whether it is being used or not.
Again, say what?
The 56k limit on a DS0 (a single voice channel in T carrier or higher) was due to a design decision made in 1958 due mostly to the technology available at the time, but partly for marketing reasons. The other 8k isn’t used for emergency services, instead it is used for housekeeping functions (primarily if the “phone” is off-hook or on-hook).
The 56k limit on analog modems is not exactly related to the DS0 limit. While the analog path will be capped at 56k due to the DS0 limit, other impairments may result in slower (often substantially slower) speeds. Look at the V.90 standard (Wikpedia 56k article) for more information.
The next step for customer circuits was ISDN, which was a near-total flop in the US for a number of reasons. Telcos eventually offered IDSL as the “last choice” for customers who were too far away (or had other loop impairments) for ADSL.
Isn’t that more or less the same thing though? I didn’t mean faster, like clock speed or bandwidth, but rather latency.