Cisco defined router in to 3 layer

Access layer router
Router which are used by a small organization used for end user connectivity
Router series – cisco 800,1600,1700,2500,2600
Distributed layer router
Router are used by isp .used for policy based routing and access control
Router series – cisco 2600.3200,3600,3700
Core layer router
Router are used by global isp used for fastest switching across Internet
Router series – cisco 6400,7200,7300,7400,7500,7600.10000,12000

ROUTER

Router is a device which makes communication between two or more network present in geo graphical location

Router are data forwarding devices which works at layer 3 .router forward data based on logical address

Ip ,ipx,apple talk

Routers – cisco ,nortel,dlink,novell,linksys,juniper