How to organize a network of an enterprise with geographically scattered branches?

Question

Computer networks

Good afternoon.
There is a construction organization headquartered in the city of M.
There are subdivisions at construction sites in other cities (currently there are 2 such subdivisions).
These subdivisions have geographically scattered departments. For example, in the Division (any) there is:
- An office within the city, where the departments of TVET, personnel, accounting, management are located.
- Departments located outside the city, on rented sites: "Dispatch Department", "Warehouse", "Department of Mechanization", which, in turn, are also located in different places.
There is a great desire to combine all this together - with a single authorization and policies, backup (Bacula / BareOS), a single teamwork system (openXChange for example), reducing anarchy to 0 in terms of software installation, controlling the entire computer / office equipment fleet, maintaining an inventory accounting (OCS Inventory NG with GLPI), possibly IP-telephony, etc.
In a good way, you need a domain in the central office, and connect via VPN / IPSec, but I doubt this:
- Internet quality - if the offices of the Divisions can still have ADSL (if they are within the city, but even here the speed of outgoing traffic is a problem) , then in departments located outside the city, at best - whistles, at worst - to trick satellite Internet (in case there is no 3G coverage by any of the operators)
- Upon completion of construction, the division is curtailed and waiting for the move / moves to a new place, where we learn about the quality of the Internet only upon arrival.
Question:
What about these Divisions and their scattered departments? What to use, BranchCache? RODs? Something else? What bundle of hardware / software solutions can you recommend?
Users should always have access to their work documents and stay in work even during the absence of the Internet.

Answer 1

It is safer to raise an IpSec tunnel between all offices.

Answer 2

everything is very simple:
create a vpn server, preferably 2 pieces for a backup channel with l2tp.
create a terminal server park for users.
openfire, asterisk - and local soft backgrounds and all

Answer 3

if the Internet is terrible, then working offline with periodic synchronizations, sending change packages, etc., is preferable.

Answer 4

Build vpn networks between offices, correctly plan the network space, and so on. if you want, you can talk in private, I'll tell you in general terms

Answer 5

Oleg Di
As already mentioned here, you raise the VPN (choose the type for yourself) to the central office.
Choose from the available connection types. You wrote about whistles with 3G, they should naturally be used with external antennas, so increase the speed and reduce the ping, and in general you will catch the signal where it seems to be absent.
As for PTOs, install a NAS (any file server) on the spot, they work on it and move with it. And at night you synchronize everything with the central office.
Iron choose the one with which you know how to work.

Answer 6

Have you thought about moving to the Cloud? The provider will do most of this for you or offer a better solution.