i’ve no idea at this time but it’s very interesting. which bss and nss vendors are you using? which ciphering algorithms are you using (sorted by order if several used)?
When you say that it reduced sd_drop can you give figures or percentage?
dear Jack!
I am thinking that it is because when network does not provide A5/1 ciphering algorithm, then it is mandatory to insert RR_Classmark_enquiry transaction in Location_Updating procedure (In MM_LU_request there is Classmark_1 information element which contains only A5/1 support indication). Hence SDCCH load is increased.
When A5/1 ciphering algorithm is provided in your network then it is not needs for Classmark_2 information element which contains A5/2 support indication also.
dear Jack!
CLASSMARK ENQUIRY message (gsm 04.008) is used in Classmark interrogation procedure (if the information initially sent by the mobile station is not sufficient for network decision (e.g. when A5/1 ciphering not active in network): network want to know A5/2 is supported in MS or not)
On receipt of the CLASSMARK ENQUIRY message the mobile station sends a CLASSMARK CHANGE message to the network on the main DCCH. This message contains the mobile station classmark 2 information element.
Oh, Jack!
my assumtion was that before activation A5/1 algorithm there is A5/2 algorithm provided in your network only. But really your network does not provided any algorithm before A5/1 activation, doesn’t it?