It can only go back to LTE once the phone call has ended. During a phone call, the phone stays on 3G.
For an outgoing call, the phone informs the LTE RAN that it will be switching to the 3G RAN to initiate a call, and then it proceeds to do so. For an incoming call, the 3G core informs the LTE core to instruct the phone to switch to 3G and receive the call.
The LTE core network informs the 3G core network and the user is registered in both cores. When an LTE phone registers on the LTE RAN, it also informs the core network that it needs to be simultaneously registered with LTE and 3G core networks. This technique is known as Circuit-Switched Fallback (CSFB). As a result, a temporary mechanism was required to handle voice calls. When LTE first launched, coverage was poor, operators did not have IMS networks deployed, and phones were not VoLTE-ready. VoLTE requires the implementation of an additional core network, known as IMS. Advantages of VoLTE include: extremely fast call setup times, better call quality due to higher rate wideband codecs, LTE data speeds while on a call, more efficient use of network resources, and longer battery life for users who make lots of calls. If the LTE channel becomes congested, VoLTE calls will not be impacted. To ensure voice calls have high quality, VoLTE packets are prioritized in the network. Packets can also take different routes to reach the destination. If the phone call is silent, no voice packets need to be sent, and the utilization of the channel is dynamically reduced as a result. With PS voice calls, the voice data is converted to packets and sent to an IP address, similar to regular internet data. There are no circuits and voice calls are handled by a technical standard known as Voice Over LTE (VoLTE - prounounced voltee). LTE is an all-IP network, which is also packet-switched (PS). Whether there is conversation or not, the voice channel uses a flat-rate amount of resources. This means an end-to-end communications link is established between the two parties and the circuit for that cellular channel is reserved for the call. Voice calls on 2G and 3G networks are circuit-switched (CS). Topic #1: How do voice calls work? What is CSFB and VoLTE? Why does SMS work on LTE, but not voice? What frequencies does my phone need to work on Public Mobile?.Which frequencies/channels/bands are used for LTE by Public Mobile (TELUS).Who are the main players in providing network equipment for the cellular operators like Telus?.How is a SIM card used to help a phone attach to the network?.Basics of LTE roaming and why I don't need to change my APN (disclaimer: This is not a strong point for me).What does a cell site look like in real life?.What is the difference? What are the paths to 1 Gbps, and how are peak network speeds calculated? How can I achieve very fast speed test results?.How do voice calls work? What is CSFB and VoLTE? Why does SMS work on LTE, but not voice?.
If there is a preference for what you would like to see first, let me know! These are the topics I am hoping to cover. Here are the topics previously discussed: In response to the positive feedback on my first post about network sharing last weekend, I thought it would be a good idea to expand to other topics that people might be interested in learning about.
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