I am from India and we do not have fast internet service so we must need to combine two or more different internet providers and get one speed kindly reply do you know any router/modem/switch which can do this for us.. we will be very thankful to you
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There are no elegant and simple ways to have two internet connections to increase speed. There are ways to setup a dual internet connection, but it won't help one file transfer. It will help if you have two computers downloading two files, but the fastest one transfer is going is the speed of one link.
Monowall and PFsense are operating systems designed to run on a PC with two (or more) network cards that have these capabilities. There may be more hardware that can do this, but I don't know of any to recommend.
Typically a second net connection would be used to provide a backup, and not a speed increase.