I have a project , a company and 3 offices.A office connect to company by modem.The SQl server is in company.It's a client /server .But I have some question :

1.If use the modem,is disconnect suddenly and how to do ?
2.If 3 offices access server at the same time, How about the speed ? If the data is huge .How to ehance access speed ?
3.What's different between SQL and DBC(Database Container) ?

Who has experience in the client/server, Please give me some ideas ?

Thanks a lot !