[ASN.1] BER encoding for Choice type

[Sriraman, Santhosh Kumar]

Hi:

I have a question regarding the  BER encoding of IMPLICIT tags for choice
type in MAP-GSM Phase 2+ Specifications.

Suppose the Choice type has two alternatives. One is a primitive type and
other is a constructor. 
It is possible to identify the choice alternatives even with implicit
encoding. 
Do i need to still encode them explicitly? 

Note: ASN.1 module says IMPLICIT TAGS.

Example from the MAP-GSM Phase 2+ specifications(IMPLICIT TAGS by Default):

        gprsSubscriptionDataWithdraw    [10] 
        GPRSSubscriptionDataWithdraw    OPTIONAL,

        ...
        GPRSSubscriptionDataWithdraw ::= CHOICE {
        allGPRSData     NULL,
        contextIdList   ContextIdList}
 
        ContextIdList ::= SEQUENCE SIZE (1..maxNumOfPDP-Contexts) OF
                                ContextId

Thanks!

Regards,
santhosh.