Why the behavior of the Default CSS NONE on CUCM and the behavior of the Default Incoming Corlist on CME are different?

[Meddane]

In CME the calling privileges are configured through the incoming corlist and outgoing corlist, following the same logic of calling privileges on Cisco Unified Communication Manager through the CSS and Partitions. Where the Incoming corlist is similar to the CSS and the Outgoing Corlist is similar to partition.

When no CSS and no Partition are configured, there are the CSS NONE and Partition NONE.

By definition, on CUCM, the Default CSS NONE has access only to the Partition None.

While In CME, When no incoming corlist command is configured on dial peer, the default incoming COR list is used. the default Incoming COR List has the highest possible priority and it therefore allows this dial peer to access all other dial peers, regardless of their outgoing COR list.

My question is "Why the behavior of the Default CSS NONE on CUCM and the behavior of the Default Incoming Corlist on CME are different?"

[Nithin Eluvathingal]

Simple answer , both are different platform.

[Meddane]

Of course, there is a reason.

[Jaime Valencia]

Because they're different products, built by completely separate teams, on different platforms, with completely separate agendas.

CUCM was not even originally developed by Cisco, it was developed by Selsius which was then acquired by Cisco.