What are we talking about?

There is a growing differentiation amonst router classes as to the roles they play within a network, beginning first with utilization and now emerging into implentation First, consider the following diagram:

                                     Core
                                    Routers
                                    -------         
                  Edge          |--------------|         Edge
                 Routers      --|              |---     Routers
                 -------     /  |--------------|   \    -------
 Customer      |---------|  /       |      |        \ |---------|
 Traffic --->  |         | <    |--------------|     >|         | Customer
               |---------|  \___|              |____/ |---------| Traffic --->
                            /   |--------------|   \
 Customer      |---------| /        |      |        \ |---------|
 Traffic --->  |         |<     |--------------|     >|         | Customer
               |---------| \____|              |____/ |---------| Traffic --->
                                |--------------|
                             ^                   ^
                             |___________________|
                                 Communications
                                     Links

So what are the differences?

Edge routers:

• Edge routers accept customer traffic (any traffic from any source outside the network) into the network.
• Edge routers characterize, police, and/or mark customer traffic between other edge or core routers.
• Edge routers provide security to the core and function as admission controllers to external traffic.

Core routers:

• Core routers provide transit packet forwarding service between other core and edge routers.
• Core routers only manage traffic to avoid and cope with transient congestion within the core.
• The core may often make use of statistical multiplexing to maximize the efficiency of core networking resources.

In Summary:

• Edge routers inject classified traffic from the customer into the core, and forward from the core to the customer.
• Core routers forward stuff between the edges as bloody fast as possible.