*Whole block [#k30061e1]
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.

-[[B2BUA Layer>architecture#gf94fd32]]
-[[UA Layer>architecture#nde67d6f]]
-[[Stack Layer>architecture#fb15ebe6]]
-[[Transport Layer>architecture#ec301860]]

***design [#rc287cc3]
-[[detail design>development/design]]

*B2BUA Layer [#gf94fd32]
This layer defines a sequence required as operation of UA.~
and it has responsibility about two or more transactions and dialogs.

*UA Layer [#nde67d6f]
This layer implements the function in the single functional unit.~
It exists as a module (API) for B2BUA Layer to use it.

*UA Layer [#nde67d6f]
*Stack Layer [#fb15ebe6]
This layer has responsibility to processing of a transaction level. 

*Transport Layer [#ec301860]
This layer treats processing of the Socket level which adopted [[MINA:http://mina.apache.org/]].