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David Boettger

This is a profoundly difficult question to answer and goes far beyond vocoder characteristics. Dimensions that have to be considered include the intrinsic efficiency of the radio technology, how well that efficiency is utilized by the control protocols (WCDMA, for example, is much less efficient than cdma2000 due to some poor physical- and upper-layer protocol choices), and phenomena that occur when lots of radios (cells) are in proximity, as when forming an actual network. Usually, computer simulations are required.

My presumption has always been that VoIP-over-cellular capacity can only be lower than "native" voice capacity, because native voice has no IP overhead and all modern cellular technologies already take advantage of statistical multiplexing of voice calls to improve capacity, just like VoIP.

That said, I think this probably misses the point. What VoIP buys you isn't increased radio capacity, but things like increased core/transport network capacity, lower core/transport hardware costs, and perhaps simpler integration with other internet applications.

canope

Hi,

You have to check your informations.
VoIP (in operator mode) over HSPA use RoHC (Robust Header Compression) for reducing the IP header overhead to 2 bytes.

The packet sizes are equivalent to CS ones.

Robert Syputa

Martin, I think David is right about this "What VoIP buys you isn't increased radio capacity, but things like increased core/transport network capacity, lower core/transport hardware costs, and perhaps simpler integration with other internet applications."

Network traffic, device sales, and profits, as you pointed out recently, are being increasingly driven by applications and diverse content including social networking. This shifts the priorities from efficiency of the network to streamlining and greater ability to work with the cloud of applications that proliferate.

In a gross analysis, it makes more sense to build upon VoIP and other IP protocols in order to simplify and leverage open development than it is to build greater efficiency into the RAN.

Martin

Hi canope,

Thanks for commenting. Yes, indeed when header compression is used you get rid of most of the overhead. In the post, I've mostly discussed over the top VoIP solutions that some people already use today and there's no header compression for them. Also, mostly plain PCM codec is used which wastes a lot of bandwidth, too.

So it will be interesting to see how network operators will adapt to this shift.

Kind regards,
Martin

S Perryman

VoIP over HSPA

1. HSPA MAC is not QoS-aware

At the Iub interface.

The Iu (23.107) service profile
cannot be conveyed in a
meaningful equivalent to allow a
MAC scheduler to define the
HSPA properties needed for VoIP.


2. Latency etc is an issue for
VoIP (C and U-plane) , especially in "mixed service" (ie real world) scenarios at the MAC layer (scheduling simulations etc) .

3. Degrading from a MOS of 4 for VoIP to something much less acceptable only needs low-ish average packet error rates (~ 2% ) on the radio link.

5. SIP message sizes (even when using Sigcomp) eats into the U-plane capacity (12 messages for service setup in IMS with
5 second call setup delay etc) .


All the above deduced from a
research study done 3 yrs ago
for a UMTS OEM looking to do
VoIP over HSPA.

Martin

Hi there!

Thanks for the input! Indeed, as I also mentioned in the post, the capacity impact of VoIP (including the SIP or other signalling) needs to be taken into account. Concerning the MOS, I use Skype over HSPA quite often and the quality is pretty much the same as over a fixed link, including video quality. That is, of course, while enough bandwidth is available and QoS priorization is not necessary...

Kind regards,
Martin

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