Hello Mario,
the roots of the flexwan module are in the VIP linecards for cisco C7500 the first Cisco router to deploy a CEF distributed model ( not totally).
in a distributed multi layer device the main route processor, the PFC component more exactly, builds the master copy of the CEF table that is sent to all the intelligent linecards that need memory to host a read only copy of the CEF table.
if all linecards are intelligent and have a copy of the whole CEF table, the main RSP is not consulted not even for the first packet of a flow but the linecards can use the CEF table to perform packet rewrite.
There is also another reason for cpu and memory on flexwan and on SIP linecards: they need to be smart enough to handle WAN interfaces of various types and this is not possible on the RSP 720 because the C7600 and the C6500 are multilayer switches.
Flexwan modules use port adapters that can be used in VIP linecards for C7500. SIP linecards host SPA that are the next generation of port adapters.
>> whats the difference between a gigabit spa (shared port adapter) and a gigabit linecard (besides the number of ports)?
the GE port on the SPA has much more feature like more complex QoS similar to ISR routers , support for features like VPLS or other.
a normal linecard provides low cost per port but far less features
Hope to help
Giuseppe
