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VoLTE is a relatively newer technology. I understand that calls made using VoLTE use internet data (The same data that we use to browse the internet, watch YouTube videos etc.) It kind of fascinates me. I tried getting more info about how it works and came to know that VoLTE is something like an "optimized" data network for Voice (Which makes it much better than VoIP). My question is:

Q. 1) If it is "optimised" data network, then how come we make VoLTE calls using the same general purpose internet. Q. 2) Is the optimization done on the client side. If YES for Q. 2), what are those optimizations and how to use them in an android app. Is there any library for it? (For Ex. This)

Q. 3) Also, does VoLTE means an end to VoIP and hence an end for Skype, Facetime etc.? Can Skype or Facetime port their mobile apps to use VoLTE over VoIP?

Ankit Mundada
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In a very general sense, yes VoLTE does use "internet data" like Youtube, etc, whereas traditional voice calls are circuit-switched.

However, LTE uses a QoS mechanism to prioritize VoLTE so that it is not treated the same as data coming from your web browser, etc. You can see from the standard QCI table below the properties of different bearers (logical connections): enter image description here

While your typical web browser will use QCI 8 or 9, a VoLTE call will use QCI 5 for control plane signaling and QCI 1 for the actual voice call. This ensures that a tighter packet delay budget is used and the bitrate is guaranteed. This is mainly a core network functionality, however the end user device (UE) must be able to support it. You cannot change the QCI of the device from the client side, it must be changed in the HSS (Home Subscriber Server, a core network component).

With regards to your last question, Skype and other similar applications are considered OTT (Over The Top) applications which are treated like normal QCI 8/9 applications and not given any special priority. So, what this means is that if you are in good coverage on a non-congested cell (and core, etc) you may not notice a difference between a Skype call and VoLTE call. However, if you are in a coverage- or capacity-challenged area, the VoLTE call will be superior. Finally, I do believe there are some operators that have built native apps that can take advantage of the various QCI profiles.

Jeff
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VoLTE is almost same as VOIP, only difference here is where the data flows(LTE or Ethernet/Wifi). You can say VoLTE is evolved from VOIP.It does not mean that it is an end to VOIP.

SIP signalling in VoLTE will be over dedicated bearer or PDN of QCI 5.

Since LTE IP based(Packet switch) network, your SIP signalling and Voice data(RTP) is transmitted as IP packets in different bearers. It is the NW/operator who decides the priority for this dedicated bearers. So Internet data will have different priority over the VoLTE data.

  1. If you have any SIP application , you can configure it to use the INTERNET PDN/Bearer for the SIP signalling and media. This will be treated as internet data.
  2. Optimization is with respect to codecs used in the client to for the media. You should have bandwidth efficient codecs to support.(LTE protocol(PDCP) takes care of optimizing your IP packet including UDP and RTP packet of the media.
  3. If your VoLTE call is using qci-5 and QCI-1, then data of VoLTE will given more prio. But VoLTE calls will be generally charged from the operator.But skype will not charged from the operator. SO you can guess whether it is an end to skype or not.
Lohith h s
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VoLTE technology is not just the device side , it includes Carrier's Infrastructure as well . Even if you use same signalling (SIP ) and media (RTP) protocol , Unless you use bearer specified by operator negotiated in NAS and RRC signalling , it will all be treated as just other internet traffic and will not be eligible to have dedicated bandwidth for the duration of call . You will also miss out on any Supplementary Services that your Carrier Provides. This all makes more sense if you are mobile and may have fluctuating network , In Ideal conditions , quality offered by VoIP applications may be same or even much better than VoLTE call quality.

Q. 1) If it is "optimised" data network, then how come we make VoLTE calls using the same general purpose internet.

we dont , there is a negotiation between network and handset for a channel with guaranteed quality of service , ie in bad network , this data will be dropped last.

Q. 2) Is the optimization done on the client side. If YES for Q. 2), what are those optimizations and how to use them in an android app. Is there any library for it? (For Ex. This)

This is done in ODM (phone makers) software after following specifications and certifications from Operator Body (GSMA like) . There is no lib for this , One can invoke android telephioy framework but that will essentially be same as using dialer

Q. 3) Also, does VoLTE means an end to VoIP and hence an end for Skype, Facetime etc.? Can Skype or Facetime port their mobile apps to use VoLTE over VoIP?

Facetime , skype etc are called OTT apps , whereas volte calls are native apps . You may consider Volte calls as something which violates net neutrality but as its in compliance with government rules , its considered to be ok.

Manik Mahajan
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