10.25.2.5. Call Waiting (CW) 
- Several calls can be signaled using CW.
- The B party needs an individual COS in order to be able to use this feature.
- CFB is performed with NDUB without signaling the call using CW.
- CFB is performed with UDUB if all stations acknowledged the CW call negatively (the reason for release is stored in the DH. USER_BUSY overwrites all other release reasons but is not overwritten).