LAN

I have a small lan network for two buildings.I ma using high speed lan line of 2gb down load speed.I have cisco asdl router and 4 D link switches of 24 port each.I am connecting tow buildings computer using these harwares.The problem which i am facing is when i try to access the network the speed is very low.When i a pinging using -t method thhe result shows time out .Ther is no continuity in data sending and recieving