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VoIP Systems

VOIP vs PSTN

It’s no secret that carriers are looking to move from traditional, circuit-switched voice to voice-over-packet technologies. In a way, of course, they have already done this years ago with Asynchronous Transfer Mode (ATM), but ATM’s fixed-length micropackets (cells) and connection orientation were adopted specifically to be voice-friendly. What’s new is the wholesale move to the variable length and connectionless orientation of Internet Protocol (IP) packets, which are definitely not the obvious architecture of choice for voice.

IP was designed as a best-effort, data-networking system with the ability to recover (somewhat) from a nuclear holocaust. This is not a requirement high up on a voice engineer’s wish list. He or she is much more interested in almost total availability (pick up the phone and you hear dialtone always, even when the lights are out), high reliability (the line doesn’t go dead in mid conversation), and high voice quality (no annoying gaps or delays in the conversation that make human interaction difficult).

But the attractions of turning voice into yet another application running over IP are immense in terms of potential cost savings, network convergence, and service innovation. And everyone is pretty much agreed that the way to make this happen is to run VOIP over a converged IP/MPLS core, where Multiprotocol Label Switching (MPLS) provides the connection-oriented layer needed for low latency, traffic engineering, protection, and security, among other things.

Carriers are worried, though, that junking time-honored TDM cores for voice in favor of IP/MPLS cores for VOIP could get them into trouble. "If it isn’t broke, don’t fix it" is a good motto for network architectures that still support the bulk of carriers’ revenues. As anyone who has ever struggled with a Windows PC, a LAN, or a broadband connection knows, an IP application is great when it works and a complete pain to fix when it doesn’t. The carriers’ nightmare is that their shiny new IP/MPLS cores running VOIP to support millions of users could be less reliable than their existing networks, and much more difficult and expensive to fix and operate.

So what are the risks associated with the move to the new voice architectures? And, more pertinently, what can be done to reduce or even remove those risks? Read on to find out.

Here’s a hyperlinked contents list:

Webinar

This report was previewed in a Webinar moderated by Geoff Bennett, Chief Technologist, Heavy Reading, and sponsored by Avici Systems Inc. (Nasdaq: AVCI; Frankfurt: BVC7), Multiservice Switching Forum, Nortel Networks Ltd. (NYSE/Toronto: NT), and Riverstone Networks Inc. (OTC: RSTN.PK). It may be viewed free of charge in our Webinar archives by clicking here.

Background Reading

— Tim Hills, Freelance Telecommunications Writer and Journalist

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miladysiq 12/5/2012 | 3:15:36 PM
re: VOIP vs PSTN Can anyone tell me the proportion between the technologies VoIP and PSTN that are being used nowadays?

Thanx
mark8464 12/5/2012 | 3:47:38 AM
re: VOIP vs PSTN We started using a product called the EdgePRO by XRoads Networks and it has provided a very good solution for us in terms of VoIP Reliability. I would recommend it highly, as we have had several ISP outages and were concerned about our VoIP not working. PSTN is a good backup however for us at least it required a great deal of reconfiguration to get it working through our PBX in the event of an ISP failure.
HeavyDuty 12/5/2012 | 1:29:11 AM
re: VOIP vs PSTN PSDN: public switched digital network is where most TDM is these days...

Getting back to the topic: VOIP vs PSDN!

ROTFL!!!

Statistical multiplexing (IP,ATM, FR, etc...) was adopted so that sytems could be over-subscribed, 'cause folks weren't using all the bandwidth, that their contract tied up, all the time: "Let's share and resell that bandwidth..."

IP was chosen so that LECs could sell content (the internet), not just a commodity connection.

Once packet switching technology is built to NEBS standards it will be at least as expensive as TDM equipment that already qualifies.

Packet switching adds just a slew of QoE factors that will drive the carriers to drink (even more than they do already)!
rtfm 12/5/2012 | 1:29:08 AM
re: VOIP vs PSTN In terms of delay, isn't speed of light delay going to hit you almost 100 ms for a 20,000 km run (global traffic). [c{fiber OR copper} = 2/3 c{vacuum} ~200,000 km/sec]

TDM itself faces this, of course...but the lack of so many other delays may leave this tolerable, while this might be a bigger deal for VoIP.

Personally, I use skype to Asia and Europe (yes, I'm in the US), and I find the quality surprisingly good.

rtfm
HeavyDuty 12/5/2012 | 1:29:04 AM
re: VOIP vs PSTN "Personally, I use skype to Asia and Europe (yes, I'm in the US), and I find the quality surprisingly good."

Shouldn't be surprised, yet, because your probably going from metro to metro on very up-to-date (corporate purchased?) infrastructure. You're also an early adopter.

If you live an older neighborhood, and/or hit the internet via dial-up from the house (instead of the office) see if your results are the same.

When more people, and their employers, have migrated to VOIP and when more folks start swapping video via the internet things will start to tank. Unless, of course, all the vendors along all the routes do some serious (read: expensive) infrastructure upgrades.

May your VOIP experience continue to contradict my predictions.
jaynad 12/5/2012 | 1:25:56 AM
re: VOIP vs PSTN There are some people saying that VoIP will displace the Public Switched Telephone System (PSTN) in a few years. VoIP will continue to grow and be installed because it is absolutely "the future". BUT before we kill the PSTN...

IMHO VoIP has a few hurdles to overcome first:
1. Power fail operation. The PSTN is powered by central office battery and works without local power. IP phones (and terminal adaptors like the Cisco ATA) need local power.
2. Emergency 911 geographic location and callback. PSTN phone numbers define a geographic location - IP addresses do not. While one can "register" the location of an IP phone there is nothing to prevent the IP phone from moving to a new location. This isn't a problem until the ambulance shows up at the old location.
3. Hardware cost. You can buy a working PSTN telephone at the corner store, in a bubble pack, for $5 retail. Sure, it'll be a cheap plastic phone - but it works.
4. Standards. PSTN standards are 130 years old. If you take a 100 year old WOODEN phone and plug it in (ok, you'll have to change the connector ;-)...it WILL still work! You can even dial a number if you practice a bit with the flash hook. And you can do this anywhere on the planet that has copper pairs. By contrast your 5 year old PC is embarrassing garbage because it won't run current OS software or applications. (This is just an example of the difference between telecom standards and datacom standards. The analog phone system is a 100 year old global standard.)

VoIP certainly does have immediate and growing applications but it ain't gonna displace the PSTN, not anytime soon. If you were wondering how many analog phones there are out there - the answer is ALL OF THEM. The current PSTN is installed globally. We won't rip it out to use:
- expensive phone sets that
- require broadband access and
- don't sound as good and
- need local power to
- call a limited number of other parties.

Until you can plug your $5 VoIP set into any port on the planet and contact E911 services during a power failure - we will see the PSTN and VoIP co-existing. This period of co-existence may last 20-25 years.

Just my opinion
ironman 12/5/2012 | 1:25:38 AM
re: VOIP vs PSTN You've got some interesting comments, but I felt compelled to comment:

1. Power fail operation. The PSTN is powered by central office battery and works without local power. IP phones (and terminal adaptors like the Cisco ATA) need local power.

- Yes ATA requires AC power and runs on broadband service which isn't DC powered. That does mean it can't be UPC'd or DC powered.

2. Emergency 911 geographic location and callback. PSTN phone numbers define a geographic location - IP addresses do not. While one can "register" the location of an IP phone there is nothing to prevent the IP phone from moving to a new location. This isn't a problem until the ambulance shows up at the old location.

- IP addresses actually do define a geographical location - it's the E-14. While this is moveable and touted as IP flexability, it can be used as a permenant address; connecting or building the infrastructure to support E-911 can and will be as challenging as it was for PSTN. As for the flexability, I'm sure no one expects, that if you physically move the phone that the norm is to have the infrastructure automatically move the E-911 address too (no one expects their mail to be automatically routed).


3. Hardware cost. You can buy a working PSTN telephone at the corner store, in a bubble pack, for $5 retail. Sure, it'll be a cheap plastic phone - but it works.

- VOIP can use the same phone hardware (you even mention Cisco ATA modem). Some VOIP implementations have their unique and expensive phones, but there more for business applications then residential, which I took that your commenting on.

4. Standards. PSTN standards are 130 years old. If you take a 100 year old WOODEN phone and plug it in (ok, you'll have to change the connector ;-)...it WILL still work! You can even dial a number if you practice a bit with the flash hook. And you can do this anywhere on the planet that has copper pairs. By contrast your 5 year old PC is embarrassing garbage because it won't run current OS software or applications. (This is just an example of the difference between telecom standards and datacom standards. The analog phone system is a 100 year old global standard.)

- It takes more than changing out to an RJ-11 connector to make older phones work. Most, if no t all PSTN use digital and don't have analogue or digital/analogue line cards. Older phones did not use DTMF and/or ringing current, over voltage or switched pair technology...


Yes I plug the same PSTN phones, that I own in my VOIP service and yes I have E-911 so maybe the future isn't so far down the road.. I've learned technology and users of technology prevail everytime (I.e. VHS vs. Betacam, cellular phones, etc.)

I'd suggest the co-existance will be more based on regulation and capital not technology.

IM

jaynad 12/5/2012 | 1:25:29 AM
re: VOIP vs PSTN And some comments in return...

1. Yes ATA requires AC power and runs on broadband service which isn't DC powered. That does mean it can't be UPC'd or DC powered.

- You can certainly DC backup the local device but unfortantely you can't do the same for IP network outside of your premisis. The standards and expectations for power fail operation are very different for the PSTN and IP networks.

2. - IP addresses actually do define a geographical location - it's the E-14. While this is moveable and touted as IP flexability, it can be used as a permenant address; connecting or building the infrastructure to support E-911 can and will be as challenging as it was for PSTN. As for the flexability, I'm sure no one expects, that if you physically move the phone that the norm is to have the infrastructure automatically move the E-911 address too (no one expects their mail to be automatically routed).

- The expectation (in North America) is that when you pick up a phone and dial 911 that the 911 answering point knows where you are. An IP phone or ATA device can be moved and be connected behind a new router or even behind an ad-hoc network of wireless routers - and hence its geographic location will be unknown. I'm sure that in future there will be some mechanism to localize IP addresses but in the meantime VoIP emergency access will be different than PSTN. (And nobody uses the mail for emergency service requests.)

3. VOIP can use the same phone hardware (you even mention Cisco ATA modem). Some VOIP implementations have their unique and expensive phones, but there more for business applications then residential, which I took that your commenting on.

- I was talking about the cost of the IP phone or ATA device.

4. It takes more than changing out to an RJ-11 connector to make older phones work. Most, if not all PSTN use digital and don't have analogue or digital/analogue line cards. Older phones did not use DTMF and/or ringing current, over voltage or switched pair technology...

- You may be confusing the special sets that operate only behind proprietary line cards in PBX environments with standard PSTN sets. Standard analog sets all operate on a common 20mA, 48VDC central office copper loop. Same voltages and currents (loop start, ringing voltage, etc.) for over 100 years. DTMF signalling is new but pulse dialing still works. Even if you don't have a keypad or dial you can still pulse with the switch hook.

Bottom line is that if you simply change the connector on a 100 year old wooden phone you can call 911 during a power failure in every country on the planet. (Assuming that they have 911 service in that region, but you get my drift)

It's not so much the technology that prevails - it's the VALUE that the SERVICES deliver that will win in the end.

To use your examples: actually Beta is still very much with us - the Hi-8 handycam tape format is Beta technology. Sony learned their lesson and Hi-8 beat VHS-C in handycam applications. Of course it is now being replaced with fully digital tape/disc solutions. And cellular has been with us for ~20 years and while it is very popular it has not displaced the PSTN. They coexist.

VoIP will displace the PSTN when it can deliver similar services for a better price. Until that time I expect to see both solutions working together.

Just my opinion.
Ben Crosby 12/5/2012 | 1:25:24 AM
re: VOIP vs PSTN 1) Perhaps I was just lucky, but with a decent quality and size (2200VA) UPS at home, powering just my DSL modem and residential gateway, I stayed online throughout the power outage across most of the east of North America. This implies that my provider had adequate backup power for their IP network, as did many other locations. In fact, I'd welcome someone pointing me to a good study of the effects of that outage on the big-I Internet. I hunted on CAIDA, but nothing really interesting.

When I walk around BestBuy, Costco, Staples or Frys, I see a plethora of UPS systems at a reasonable price. Joe public is beginning to realise that even his/her cordless telephone doesn't work when the power is out.

2. I would never attempt to argue a link between geographic location and IP addresses. IP is too easily tunnelled or otherwise moved. However, I hear many people discuss ditching PSTN in favour of VoIP because they feel safe in the knowledge that 911 works from a cellphone. My own VoIP provider at home doesn't have 911. I knew that when I signed up, and it doesn't bother me.

3. The issue with VoIP phones is not so much one of cost as one of connectivity. Ultimately key-system like functionality will be available in home by way of SIP phones (room to room dialling, direct inward dial for multiple handsets for example) only when service providers figure out how to connect all these phones in a simple enough manner to the ethernet connection that comes from your broadband network termination point. (clue; the "answer" is not any one single incantation of wireless, cat3/5/5e/6, Coax, HPNA, Powerplug etc etc - due to the dramatic variation of all of the above from home to home across a SP's serving area). Again, there are VoIP phones available that are cheaper than some of the high-end multi-handset wireless systems that have become popular.

4. I agree with your correcting the original poster with respect to the exchange line types, but my understanding was that public phone lines used 48v *AC* not DC.

Cheers !
Ben
gbennett 12/5/2012 | 1:25:23 AM
re: VOIP vs PSTN Comrades,
I have been a VoIP sceptic for years, untill I installed Skype a couple of months ago. Right now I have ISDN in my home office, and Skype is the only free VoIP package that works over it.

In addition, unlike FWD, Skype is close to being a consumer grade product in terms of its ease of installation and use. FWD still needs far more technical knowledge and expertise than a typical home user would want to have.

I've been amazed by the voice quality of Skype (again, much better than FWD), and we can't argue with the price, but lately I've noticed two issues.

1. Dropped calls. Most of the calls I make now with Skype will drop at some time during the call. Maybe this is because I'm tending to make longer calls? I assume this is something to do with the overlay route that a Skype call takes (through supernodes)? Comments welcome.

2. Truly massive delays. As long as I call within the UK, or to the US, the delay is fine. But calls to France and Switzerland seem to involve much longer delays. Last time I did a TraceRoute to the other party and found that our respective ISPs do not seem to share a peering IXC. So the route of the call was inefficient, and we had ping delays of over 1 second reported.

I'm a definite VoIP convert, and I'll use the service whenever I can. But it's not appropriate to compare it to circuit voice just yet.

Cheers,
Geoff
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