Question : CISCO - ACCESS - DISTRIBUTION - CORE - DO I NEED THEM ALL

ive never quite grasped if when working on networks if all of the below are needed:

core - backbone router
distribution - border router at ISP/BT etc
access - users site

can anyone help
Id rather gets someone elses understanding first of all instead of adding what i think and confusing things?

Answer : CISCO - ACCESS - DISTRIBUTION - CORE - DO I NEED THEM ALL

No you do not have to have all there, you can collapse the core to the distribution layer:

http://conft.com/warp/public/cc/so/neso/lnso/cpso/gcnd_wp.pdf

Small and medium campus networks usually have a two-tier design, with an Ethernet access layer and a core/distribution layer that is consolidated to form a collapsed backbone. Large campus networks usually have a three-tier design with an Ethernet access layer, a distribution layer and core layer.  

Billy