Hi,

> While transmitting the classmark or any message from mobile on
> SDCCH during a call, does it transmit on the frequency we get
> after converting the ARFCN or is there a slight variation ?

I don't get this, what do you mean by 'converting the ARFCN'?

There are two (as I know) possible types of call assignment:

  - Early Assignment, when the network allocates TCH/F or TCH/H
    right after getting RACH-request from a mobile phone. The
    frequency (or a set of them) is indicated in the Immediate
    Assignment message.

  - Late Assignment, when the network allocates an SDCCH channel
    first, where a mobile phone indicates a connection reason
    (Paging Response or Service Request) and also indicates the
    classmark. Then the network eventually sends the Assignment
    Command message, where just like in Immediate Assignment a
    new channel data (both FDMA and TDMA) are described.