Call Setting中的Line Switch功能作用

该功能同CPHS规范中的ALS功能。具体内容为：ALS provides the MS with the capability of associating two alternate lines with one IMSI. A user will be able to make and receive calls on either line as desired and will be billed separately for calls on each line. Each line will be associated with a separate directory number (MSISDN) and separate subscription profile. Where ALS is available each directory number shall be treated separately from the point of view of basic and supplementary services, so that independent service sets may be assigned for each number. The exception is “Call Waiting”, which shall be treated as applying to both directory numbers if either or both numbers carry a subscription to this service. In such cases, the handset shall generate a call waiting indication if a call arrives whilst either line is engaged on another call. The user should be able to store and recover customised (alpha)numeric descriptions of the two lines. Where there is no user customised description, the handset shall display a default description of “Line 1” and “Line 2” for the two lines.The handset shall provide an indication of the line on which incoming and outgoing service is being requested by audible and/or visual differentiation. For outgoing calls, the handset shall enable the user to select the desired line via a single command interface.