Hi everyone, I have noticed that there is some misunderstanding about the network sharing between Bell and Telus. Hopefully this will help with some of the confusion. I've worked as a network engineer for operators and vendors and this is an area I am familiar with.
To begin with, let's start with a simple LTE network diagram:
- UE is the phone.
- E-UTRAN is the LTE radio access network, also known as RAN. In LTE, the RAN is only comprised of 1 element, this is the base station, also known as eNodeB. This is basically the "tower" that your phone talks to. In 3G networks, the RAN is made up of NodeB (tower) and RNC (controller).
- EPC is the LTE core network (proper name is Evolved Packet Core), and this equipment is hosted in a few secure facilities across Canada. Data between RAN and core is carried via "backhaul" or transport network (not shown here).
Bell and Telus only share the RAN across Canada. They share 3G and LTE RANs. In some cities (Vancouver), Telus owns the RAN, and Bell users are allowed to use it. In other cities (Toronto), it's the other way around. This allows Bell and Telus to spend less money building out a network, while both benefiting from it. In a city like Toronto, there are only 3 RAN operators: Rogers, Bell, Shaw (Freedom Mobile/Wind). Any other company that sells service is really using the RAN of those 3 companies.
Bell and Telus have independent EPC and IMS networks (IMS is used for VoLTE among other things). The core network is what authenticates user SIM cards, tracks usage and billing, completes calls, delivers text messages, and connects data sessions to the internet. All Bell and Telus eNodeBs in Canada are connected to both Bell and Telus cores.
To make a phone call, or send/receive text, or use data, the whole network must be functional. The RAN cannot deliver any services on its own, and the core cannot directly talk to a phone. So if any of these parts go down, the user will not have service.
If there is ever an outage that only affects Telus subscribers, it's probably due to the core. If there is an outage that affect Bell and Telus subscribers simultaneously, it's probably due to the RAN.
Coverage is 100% due to eNodeB. Therefore, if you have good coverage with Bell or Virigin Mobile, you will have identical coverage with Telus, Koodo, or PM. It can be possible for coverage to be different if Bell and Telus didn't share all bands. However, they currently share all bands except Band 30 (2.3 GHz, which is high frequency and doesn't impact coverage). Band 30 is only for Telus at the moment.
UPDATE
As a result of Bell's 2017 acquisition of MTS, the situation in Manitoba is complicated. In Winnipeg and Brandon, Telus operates a new independent RAN, separate from the shared Bell/Rogers RAN. Coverage between Bell and Telus is different in these markets as a result.
/UPDATE
For a good map of NodeB (3G) and eNodeB (LTE) locations, refer to this link:
https://www.ertyu.org/steven_nikkel/cancellsites.html
After clicking on a site, refer to BW (bandwidth), this may give a clue to the technology being used.
1.25 MHz is CDMA (old 2G network that is not used by modern phones)As of mid-2019, there is no longer any CDMA networks in operation in Canada.- 4.15 MHz is Bell 3G
- 5 MHz can be 3G or LTE
- 10 MHz or higher is LTE
Here is a specific example of how it works in Quebec City:
If you have any questions, I'll do my best to help answer them!
Update: additional LTE topics explained here:
http://productioncommunity.publicmobile.ca/t5/Discussions/LTE-network-fundamentals/td-p/130581
Update 2: key information from this article was used in a 2020 post by Inside Towers, without crediting the original article here.
@McBryen Check this wiki: https://en.wikipedia.org/wiki/Telus_Mobility#LTE
Also, have look at the coverage maps: https://publicmobile.ca/en/on/coverage and http://www.telus.com/en/on/mobility/network/coverage-map.jsp
As a general rule, Bell & Telus share towers where they each lack coverage. We like to refer to them as Belus towers. 
@echf
Believe it or not, 5G (NR, or "New Radio") is not going to replace LTE, at least not for a very long time. LTE is already extremely efficient and doing a good job meeting traffic growth demand. Another important point to consider is that 5G specifications are only being finalized now, and commercial deployments won't be seen until 2020 or so.
From what I've seen so far, 5G spectrum will be very high frequency (3.5 GHz, 28 GHz, mmWave etc.) and have extremely large bandwidth (100+ MHz for one channel). Massive MIMO will be utilized as well (64T64R radios on the base station). This increases capacity tremendously, but the high frequency reduces coverage as I have explained before. For basic coverage, we will be living with LTE for a long time. For super fast speeds, 5G will overlap with existing LTE areas, but a lot more 5G sites will be needed as you have stated.
I'm sure Bell and Telus's partnership would help them against Rogers if they chose to continue with their arrangement.
Similar to LTE-A, which was a collection of new features, LTE-A Pro also refers to a collection of features (3GPP Release 13 or newer). The main focus is providing a smooth upgrade path to 5G, along with smart device connectivity (NB-IoT and eMTC). Yes, it's coming to Canada soon, all the operators are testing and conducting trials to see how well these features work in real life.
Good overview from Qualcomm here:
https://www.qualcomm.com/invention/technologies/lte/advanced-pro
In Quebec City, Telus is the RAN owner. Bell's sites are very old CDMA (2G network), which is incompatible with the modern 3G and LTE networks. Bell's CDMA network is to be decommissioned and shut down in the next year or two. There may be a handful of indoor 3G / LTE sites owned by Bell, and all of them would be shared with Telus users.
The arrangement that Bell and Telus have is technically known as Multiple Operator Core Network (MOCN). This means the Telus eNodeB (LTE tower) in Quebec City will broadcast/identify itself as Telus and Bell. Your phone has no idea who operates the site. It just sees the Bell (302-610) and Telus (302-220) network codes being broadcast, and since the Bell code matches the home network programmed in your SIM card, it tries to connect. The tower then connects you to the Bell core network for authentication. Once you're authenticated, you will receive service as allowed on your profile (phone calls, SMS, data, etc). If your phone scans all networks and doesn't find your home network, it will attempt to roam on a visited network. This can be domestic roaming (on Rogers for example), or international.
To answer your question, you will always attach to the strongest signal, regardless of who owns the site. If you move to an area where a Bell tower has a stronger signal, your phone will handover to that one. Again, your phone sees both Bell and Telus being broadcast, so it won't know or care who owns the site.
For question 2, the main advantage for this arrangement is cost savings for Bell and Telus. Generally speaking, Telus builds sites in BC, AB, Windsor, Ottawa, Montreal, Quebec, Gaspé. Bell builds the rest, except SK. They share all sites with each other's subscribers. In Saskatchewan, Sasktel owns the RAN, and they share it 3-way with Bell and Telus subscribers. Manitoba is a bit different and they don't share in Winnipeg and Brandon.
I have included links to all of my detailed posts here. Have a look for more info:
http://productioncommunity.publicmobile.ca/t5/Discussions/LTE-network-fundamentals/td-p/130581
Thanks @NDesai for tagging me.
