Dial up server speed

I’ve set up one computer on my network to be a dial up server so I can dial into the network from another location. It works O.K. except that the connection is very slow. I can never connect faster than 28.8 Kbps even though both modems are rated at56 K. This makes for very slow browsing. Is this a builtin limitation of using dial up server or is there a way to get a faster connection? BTW, these are both Win98SE machines.