It is the modularized layer structure which made the four following things one unit.
At present, it has only a module relevant to "SIP."
In the future, other things are due to be added.
This layer defines a sequence required as operation of UA.
and it has responsibility about two or more transactions and dialogs.
This layer implements the function in the single functional unit.
It exists as a module (API) for B2BUA Layer to use it.
This layer has responsibility to processing of a transaction level.
This layer treats processing of the Socket level which adopted MINA.