As there will be more devices there will be more traffic of information. We can include capacity to WAN by adding more links and packet switches. Packet switches use not have computers attached. There are two kinds of switch according to the attached devices.
The switch that has no attached devices is known an interior switch.
The switch that has device attached with it is known exterior switch. Both exterior and interior switches forward packets and they also have to routing tables. The routing table must have two basic things.