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.
Here are the topics previously discussed:
These are the topics I am hoping to cover. If there is a preference for what you would like to see first, let me know!
Sounds like a lot of great reading is to be done this weekend
I would like to have more info on point 4
*3G vs 4G vs LTE. What is the difference? What are the paths to 1 Gbps, and how are peak network speeds calculated?
This might lead to understanding the question before of:
*How can I achieve very fast speed test results?
Many thanks in advance
An in-depth look at exactly which frequencies/channels/bands are used for LTE by Public Mobile (TELUS), along with their performance limits and capacities?
@Jeremy_M we seem to have a very valuable asset in @sheytoon not sure if anything like this is possible or been done before but a section where all of sheytoon's posts and explanations could be put in one central location for everyone to view easily as it is great info.
Topic #1: How do voice calls work? What is CSFB and VoLTE? Why does SMS work on LTE, but not voice?
Voice calls on 2G and 3G networks are circuit-switched (CS). 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. Whether there is conversation or not, the voice channel uses a flat-rate amount of resources.
LTE is an all-IP network, which is also packet-switched (PS). There are no circuits and voice calls are handled by a technical standard known as Voice Over LTE (VoLTE - prounounced voltee). VoLTE is a type of Voice Over IP (VOIP). With PS voice calls, the voice data is converted to packets and sent to an IP address, similar to regular internet data. 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. Packets can also take different routes to reach the destination. To ensure voice calls have high quality, VoLTE packets are prioritized in the network. If the LTE channel becomes congested, VoLTE calls will not be impacted. 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.
VoLTE requires the implementation of an additional core network, known as IMS.
When LTE first launched, coverage was poor, operators did not have IMS networks deployed, and phones were not VoLTE-ready. As a result, a temporary mechanism was required to handle voice calls. This technique is known as Circuit-Switched Fallback (CSFB). 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. The LTE core network informs the 3G core network and the user is registered in both cores. For an incoming call, the 3G core informs the LTE core to instruct the phone to switch to 3G and receive the call. 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. During a phone call, the phone stays on 3G. It can only go back to LTE once the phone call has ended.
If you force your non-VoLTE phone to "LTE Only" mode, you will not be able to make or receive any phone calls.
What happens if you start a VoLTE call and move to an area with no LTE coverage? CSFB will not help in this scenario, because CSFB works by having the voice call use the 3G RAN for the entire duration of the call. It cannot transfer an existing VoLTE call from LTE to 3G. For this scenario, another mechanism is needed, and it's called SRVCC (Single Radio Voice Call Continuity). SRVCC is the mechanism that allows an existing PS session (VoLTE voice + LTE data) to be split into 2 separate CS (3G voice) and PS (3G data) sessions. Once SRVCC is triggered, the voice call remains on the 3G network until it ends. The user can then go back to LTE after the call has ended.
SMS is handled a bit differently. Even in "LTE Only" mode, SMS works in both directions and doesn't need the 3G RAN. SMS messages are sent to the MME (one of the nodes in LTE core), and the MME sends it to the MSC (one of the nodes in 3G core). This works in the reverse direction as well. The MME sends and receives SMS to/from the phone using the LTE control plane. For more details, refer to this note:
As the demand for mobile data increases, new ways of delivering more data are needed. The amount of available spectrum is limited, and buying new spectrum is extremely expensive for operators. Another way of boosting capacity is by deploying MIMO.
Other upper limits also exist. Maybe there's no limit to how many active antenna can get stuffed into each phone; maybe people won't mind hauling around ever-larger devices, maybe engineers will always invent ways to decrease component sizes and increase technological densities.
But (FCC) regulatory limits cannot be circumvented. Useable portions of the EM spectrum are limited, and allowable portions even moreso. Allowable transmission power is strictly limited, so mobile data can't just multiply and multiplex across more and more antenna elements without consequence. And every Watt (well, milliWatt) of transmitted power has to come from an electrical power source - mobile batteries impose fundamental limits on how much energy they can store and on how much energy they can (safely) discharge - batteries in today's "ultra-power-efficient" devices can already get surprisingly (almost dangerously) hot and run charges down "into the red" after short activity sessions.
Many people and many organizations already protest radio noise for a variety of health, safety, aesthetic, and technical reasons. It's increasingly difficult for a ham radio operator to erect a radio tower without being shut down by concerned neighbours. People already campaign (sometimes successfully!) to shut down cellphone towers/repeaters in their neighbourhoods, and I'm sure that more antenna arrays to service more frequencies would attract even more attention as "dangerous" "noisy" "eyesores".
Just saying that many "real" limits are not technical, they're entirely different arenas - legal, financial, social, political, etc.