Their have been a few threads asking if voip can replace your normal telkom line this is my 2c on the question (sorry its a bit long).
As a background let me say i am a bit of a voip junkie. It’s a technology that I use daily to keep in touch with some very special friends in New Zealand.
If we look at telkoms recent pricing adjustments it is clear the effect voip competition is having on bringing down international call prices. 3 yrs ago a telkom call to NZ cost close to R4.00 per minute, now R1,50 . We know our favorite telecom company does not reduce prices because it wants too, only because it has too!!
So can Voip be as effective for national calls as it has been for international?? Can one effectively ditch your telkom line for a voip service??
Unfortunately at the moment I don’t think so. Let me tell you why.
I recently acquired a linksys spa 3000 analogue telephone adapter(ATA). For those who don’t know this piece of hardware, it connects to a broadband router, a telephone and telkom phone line. It allows you to place Voip calls (sip based) on your broadband connection to any voip service you have subscribed too. It also allows you to place calls via the telkom line. You can set up “dial strings”, effectively dialing rules, so the ATA knows how to deal with each call.
Although as I said I use voip daily, I am no expert on how it actually works. I have done my share of googleing and this is what I understand.
When I dial a New Zealand number, my ATA knows that the call is international(because it is 12 digits), it then passes the number to my international voip provider (currently voipdiscount.com). Voipdiscount has set up, or has access to a POTS (plain old telephone service) gateway for each country you may want to call. The ATA and the gateway, under the direction of the voip provider’s sip server, connect too each other and my call is connected.
Simply drawn the connection is:
Telephone ----ATA-----------------------------------------Gateway-------------------NZ Phone
......................................./........................ \
....................................../........................... \
........................International bandwidth........Connection controlled by
...................................(SAT 3)...........................sip server
So far so good, but what about the quality of the call. For me the test of the quality of the call is if the person I am calling notices anything different about the call, then it’s not good enough.
Call quality is a combination of “clarity” and “latency”.
Clarity is determined by the codec used and whether any voice packets are lost. Even low bandwidth codecs can achieve quite acceptable levels of clarity eg the Gsm codec used by cell phones only uses 13kbps * 2.
Latency is the Voip killer in South Africa. Remember when making a voip to pots call the traffic is routed through the gateway. From what I can establish these gateways are usually situated in Europe or the USA. This means to call a South African landline your voice packets must travel from your ISP (saix) to the gateway and then return back to South Africa before the person you are calling can hear what you said. His reply must do the reverse.
Ideally the latency between you talking and your speech being heard should be less than 250ms (effective latency). This is never going to be achieved making a “local” call with a gateway situated in Europe or the USA, where simple ping times are 400ms or more.
When Mweb announced that they had a voip service I hoped this meant they would set up a local gateway, so that local calls would remain “local” and the latency issues would be resolved.
I somewhat reluctantly signed up – as the cost saving hardly seems worth it – and have been testing for the last few days. Initial results are not that promising, there is still noticeable latency.
I have devised a way to determine what the effective latency is. Essentially what I do is make a call from my Voip line to my home phone and record both. I make a sharp noise (actually I just hit a bic pen against my keyboard), the resulting noise is picked up as it is made and then again when it is heard in the telephones ear piece. I then open that wav file in a sound editing application and measure the time between the sound impulses, which then gives me the effective latency.
Take a look here for the results. http://img222.imageshack.us/img222/3590/new10uf.jpg
Voipdiscount has an effective latency of 780ms and 950ms using a unshaped / shaped account respectively. Despite decent “clarity” of speech this is clearly not good enough to replace your land line despite call charges of only R0.08 / minute.
Mweb voip has an effective latency of 620ms. This was on both a shaped and unshaped saix account. This confuses me (believe me it does not take much to do that) if the gateway is local I would expect lower latency, on the other hand if international I would expect a difference of about 100ms between shaped and unshaped accounts.
I have subsequently tested skypeout to South Africa, which returned a latency of 750ms on an unshaped account – so similar to Voipdiscount.
So in conclusion presently I have a “voip” phone connected to my ATA. I use it for all international calls – which thanks to a weird business model by voipdiscount are all free.I also use it for friends and family who will tolerate my attempts at giving telkom the finger and will put up with some latency, but if I have an important call I use Telkom.
As a background let me say i am a bit of a voip junkie. It’s a technology that I use daily to keep in touch with some very special friends in New Zealand.
If we look at telkoms recent pricing adjustments it is clear the effect voip competition is having on bringing down international call prices. 3 yrs ago a telkom call to NZ cost close to R4.00 per minute, now R1,50 . We know our favorite telecom company does not reduce prices because it wants too, only because it has too!!
So can Voip be as effective for national calls as it has been for international?? Can one effectively ditch your telkom line for a voip service??
Unfortunately at the moment I don’t think so. Let me tell you why.
I recently acquired a linksys spa 3000 analogue telephone adapter(ATA). For those who don’t know this piece of hardware, it connects to a broadband router, a telephone and telkom phone line. It allows you to place Voip calls (sip based) on your broadband connection to any voip service you have subscribed too. It also allows you to place calls via the telkom line. You can set up “dial strings”, effectively dialing rules, so the ATA knows how to deal with each call.
Although as I said I use voip daily, I am no expert on how it actually works. I have done my share of googleing and this is what I understand.
When I dial a New Zealand number, my ATA knows that the call is international(because it is 12 digits), it then passes the number to my international voip provider (currently voipdiscount.com). Voipdiscount has set up, or has access to a POTS (plain old telephone service) gateway for each country you may want to call. The ATA and the gateway, under the direction of the voip provider’s sip server, connect too each other and my call is connected.
Simply drawn the connection is:
Telephone ----ATA-----------------------------------------Gateway-------------------NZ Phone
......................................./........................ \
....................................../........................... \
........................International bandwidth........Connection controlled by
...................................(SAT 3)...........................sip server
So far so good, but what about the quality of the call. For me the test of the quality of the call is if the person I am calling notices anything different about the call, then it’s not good enough.
Call quality is a combination of “clarity” and “latency”.
Clarity is determined by the codec used and whether any voice packets are lost. Even low bandwidth codecs can achieve quite acceptable levels of clarity eg the Gsm codec used by cell phones only uses 13kbps * 2.
Latency is the Voip killer in South Africa. Remember when making a voip to pots call the traffic is routed through the gateway. From what I can establish these gateways are usually situated in Europe or the USA. This means to call a South African landline your voice packets must travel from your ISP (saix) to the gateway and then return back to South Africa before the person you are calling can hear what you said. His reply must do the reverse.
Ideally the latency between you talking and your speech being heard should be less than 250ms (effective latency). This is never going to be achieved making a “local” call with a gateway situated in Europe or the USA, where simple ping times are 400ms or more.
When Mweb announced that they had a voip service I hoped this meant they would set up a local gateway, so that local calls would remain “local” and the latency issues would be resolved.
I somewhat reluctantly signed up – as the cost saving hardly seems worth it – and have been testing for the last few days. Initial results are not that promising, there is still noticeable latency.
I have devised a way to determine what the effective latency is. Essentially what I do is make a call from my Voip line to my home phone and record both. I make a sharp noise (actually I just hit a bic pen against my keyboard), the resulting noise is picked up as it is made and then again when it is heard in the telephones ear piece. I then open that wav file in a sound editing application and measure the time between the sound impulses, which then gives me the effective latency.
Take a look here for the results. http://img222.imageshack.us/img222/3590/new10uf.jpg
Voipdiscount has an effective latency of 780ms and 950ms using a unshaped / shaped account respectively. Despite decent “clarity” of speech this is clearly not good enough to replace your land line despite call charges of only R0.08 / minute.
Mweb voip has an effective latency of 620ms. This was on both a shaped and unshaped saix account. This confuses me (believe me it does not take much to do that) if the gateway is local I would expect lower latency, on the other hand if international I would expect a difference of about 100ms between shaped and unshaped accounts.
I have subsequently tested skypeout to South Africa, which returned a latency of 750ms on an unshaped account – so similar to Voipdiscount.
So in conclusion presently I have a “voip” phone connected to my ATA. I use it for all international calls – which thanks to a weird business model by voipdiscount are all free.I also use it for friends and family who will tolerate my attempts at giving telkom the finger and will put up with some latency, but if I have an important call I use Telkom.
