LTE being a packet based technology; there have been ongoing discussions about Voice implementation over LTE. This is going to be crucial as operators would want just one network to be maintained to reduce their CAPEX and OPEX. There have been quite a few solutions being pondered upon in the 3GPP community.
One way is the CS fallback mechanism to address this. By CS fallback they mean that for voice LTE will handover the call to 2G/3G networks. This is done by MME registering the device with the 2G/3G networks and acting as SGSN communicating with MSC for voice signaling. This will ensure that the voice quality is maintained as of today, but this would also mean that if an existing packet data call is in progress, then it might get suspended or handed over to 2G/3G networks. I am not sure is this will be good idea since earlier generation networks will not have the bandwidth and the capacity to support LTE multi-media applications.
I read a paper about CSoHS (Circuit Switched over HSPA+) . This explains about how HSPA+ radio bearers will be used to carry voice traffic but core used will be CS core.
This can be done via software upgrade on UE as well as RNC. This would add de-jitter and time warping mechanism to ensure smooth voice quality. I hope this can be further extended to LTE, which is approach pursued by VoLGA which stands for Voice over LTE via Generic Access (Thanks to Steve for clarifying this!!). The difference between 2 approaches is avoiding the fallback to legacy networks and also using high capacity radio bearers. Also user not be required to suspend/handoff his data call.
Though these above approaches sound good for now, they would still require different networks to be maintained. Going further, IMS will have an important role to play as it can support end-to-end voice over IP services with call signaling and switching functionality required for voice. It also supports Voice Call Continuity (VCC) that can enable gradual deployment of VoIP.
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Hello,
I write my own blog on the issues around voice over LTE and have an appreciation for the points you bring up. I want to make a couple clarifications.
VoLGA is *not* a CS fallback approach. CS Fallback is completely different from VoLGA. CSFB is something that was defined in 3GPP R8. I think many people in the industry are “not sure this is a good idea”. In fact, I think many would say it’s a quick and dirty stop-gap measure.
VoLGA is much similar to what you describe as CSoHS. VoLGA is transporting the voice and SMS over the IP-based LTE network back to the existing circuit core network. As you point out, the advantages are clear: it’s possible to maintain a data session with voice simultaneously. In general, it’s a much cleaner approach to voice over LTE than CS Fallback.
There is one other comment that was a bit confusing for me. You mention that both those solutions would “require different networks to be maintained”. I’m not sure if you’re talking about the 2G/3G network or perhaps specifically the CS core. But I think most mobile operators believe that for many years to come, the vast majority of users will be on the ‘existing’ networks.
There was an analysis the other dary by InStat which said that just 11% of mobile phones in the world were 3G capable. If that same metric were applied to LTE, it’s pretty clear that 90% of users will be making calls on the circuit network in 2020. Moving to IMS isn’t going to change that, IMS and SIP/VoIP really don’t work over 2G or 3G networks.
Anyhow, thanks for covering a topic near and dear to my heart.
Steve
thanks for clarifications. I was under the impression that VolGA has CS Fallback mechanism as one of the solutions.
Yes as you pointed you correctly, 2G/3G networks will be around for alteast another 5-7 years. I was just thinking about the cost benefits for an operator here.
I think IMS if used for voice (VoIP) would result in convergence of networks. VCC in IMS can be used for gradual deployment.
Rohit
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