On Fri, Apr 20, 2012 at 19:33, Alexander Chemeris alexander.chemeris@gmail.com wrote:
Max,
On Fri, Apr 20, 2012 at 19:09, Max Max.Suraev@fairwaves.ru wrote:
- what is CKSN IEI and how do I calculate\use it?
IEI is a Information Element Identifier, which is a part of TLV-coded (Type-Length-Value) Information Elements (IEs). In other words, IEI represents type (T) of the data payload which follows it. TLV is an encoding used in most of the classical GSM protocols. I don't recall where it is described in the Standard, but here is a nice paper which you easily find on Google which describes ciphering and described TLV structure as well (section 6.1.2): http://www.cs.ru.nl/~fabianbr/scriptie.pdf
But as Sylvain mentioned, in almost all cases CKSN is sent as "V" IE, so no IEI is needed. The only place where you seem to need CKSN IEI is in GPRS Mobility Management Messages "Authentication and ciphering request" (section 9.4.9), where it CKSN is sent as "TV" IE. And there in the table left column you see the IEI value "8-", meaning that it's "8-in-the-MSB".