Why and how to solve Iphone, BB and some kinds of Nokia, Samsung, ext

Smart Phone can’t Inter RAT HO problem

This problems happened in our network. The phenomenon is that: When I made an drivingtest in 3G

network, the BB and Iphone can’t go to 2G when it go out the 3G coverage as other phone. I made an test

in our laboratory, the result is same. I traced the same IMSI with other kinds of mobile. And we found

this different between other mobile:

Group 1: The Mobile kinds can IRAT HO from 3G to 2G: The relocation procedure is success:

[03:39:07.888]0202 >>--->> (RANAP) RelocationRequired (UE:1868)

(cause:radioNetwork/ relocation-desirable-for-radio-reasons) (sourceSAI:452-04-41017-670)

(targCGI:452-04-11122-5220)

[03:39:08.228]0202 <<---<< (RANAP) RelocationCommand (UE:1868)

Group 2: The Mobile kinds can’t IRAT HO from 3G to 2G: The relocation procedure is fail:

[03:31:57.612]0202 >>--->> (RANAP) RelocationRequired (UE:10791)

(cause:radioNetwork/relocation-desirable-for-radio-reasons) (sourceSAI:452-04-41017-670)

(targCGI:452-04-11122-5220)

[03:31:57.632]0202 <<---<< (RANAP) RelocationPreparationFailure (UE:10791)

(cause:radioNetwork/relocation-failure-in-target-CN-RNC-or-target-system)

With this phenomenon, we made the IMSI trace at MSC interface between 3G MSC and 2G MSC. And

the reason of this problem is found. Both of 3G MSC and 2G MSC is E\\ equipment. The reason is that:

With some smart phone, the length of message they send is longer than 255 octet – the maximum length

that 1 UDT can transmit at 1 time and 3G MSC used UDT way to transmit the message. So that 2G MSC

can’t understand what information that 3G MSC send, the Irat HO 3G- 2G fail.

To solve this problems, we turn on the XUDT feature at 3G MSC, the result is that: All smart phone can

make the IratHO from 3G to 2G. With this feature, all long message we be divided at some parts with the

length of each part is 254 octets before transmitted. At 2G MSC, all of these parts will be stick again. Use

this feature, the maximum length of the message can rich to 3968 octets.