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What can cause cross call in GSM, I have some complains from customers say during the call we hear the voice of somebody else talking while the original call stops.
If this had occurred on an analogue system – like TACS 900MHz – it would have been suggested a case of frequencies separation between mobiles being very close, thus poor radio planning. Of course TACS did use localised encryption is voice transmission.
In GSM Key Ciphering (Kc) along with allocation of TMSI is expected to eliminate cross-talk problems like you mention.
I am not sure though… but sounds like an internal network issue.
Yes, this kind of issues was already mentionned in the past. It is probably a misconfig of your MSC links, or MSC/PLMN links. From the transcoder to the MS, the call is entirely ciphered. Therefore it cant’ be heard on the radio by anyone else by mistake.
Hackers can, though…Most of the crosstalk problem comes from the A-interface and ater. It can be an cross-connected E1 or a faulty transcoding board. If I receive cross talk complain from customers I used to test every E1 between the MSC and BSC, one test call is enough for the whole E1 because if one timeslot is effected the others are also effected. It may take sometime to test 200 or 300 E1 but it is worthy and sure you will find the faulty E1 and then you can check the physical connection, and also the PCM number is very important both the MSC and BSC side must be the same. or you can replace the transcoding board and then make a test on the faulty E1 you find.
This problem happens to me dozens of times and every time I solved in that way. and it ussually arises after E1 expansions or new installations, so it is better to test every A interface E1 before you release the service to your customers.
Thank you gusy from the quick answers, I think there’s no any problem with my A-interface E1s because no body did touch them although they can be faulted but also i see no alarm on them, so i thought the problem arrising from my radio side or Abis interface because all complains come from 1 area so what do you think guys.
Majid,
Are you receiving a lot of complaints from many subscribers, or just one complaing from one subscriber ?
Have you experienced the problem yourself, during drivetest ?
how narrow is the area where this problem occur ? Can’t it be linked to one specific BSC ?
As Abdel said, if it’s not an E1, it might be a faulty transcoder board.
Actually i didn’t experience the problem by my self but the customer complains come from only 2 areas with same BSC served by 2 BTSs, but i found that this 2 BTSs share the same Abis Interface Board i mean their E1s share the same board, so how can i make sure.
Replace the suspected board with fault with another board in the same shelf and see if the cross talk moves to another area.
Majid,
Thanks for the details. Anyway, I am sure that between transcoder and mobile, it is impossible for another mobile to hear another conversation. You have ciphering activated, right ?
If the signal was hard by another mobile, that would probably sound like noise.
Therefore, the Abis or the BSC are probably not responsible for the problem.
Hi pix,
“Anyway, I am sure that between transcoder and mobile, it is impossible for another mobile to hear another conversation. You have ciphering activated, right ?”.
I am not sure but what about if no encryption is used by a5/0 in the network,is it able to listen to that frequency channel. One day one guy told us that he had heard several times telephone calls on his Shortwave (SW2) radio so I wonder if this is possible and at that time our network was using A5/0(encryptionless), after several months we received an email from GSMworld saying to move out from A5/2 and to move either to A5/1 or a5/0 encryptionless. Because some hackers have demonstrated in very short time that they are able to crack that alograthim for the voice traffic.
Anyway I didnt understand your last paragraph?”Therefore, the Abis or the BSC are probably not responsible for the problem.” Do you mean the problem is not related to the BSC? or do you mean the problem is within the BSC?Hi guys, i’ve experienced the problem by myself while there was a problem with the transmission of the site i was served by i saw it practically,
“Replace the suspected board with fault with another board in the same shelf and see if the cross talk moves to another area.”
i did it actually but yet didn’t recieve complains from those areas.Abdel,
GSM calls can’t be heard at SW radio even there is no encryption because it is an analogue device and can’t decode digital signals of GSM. We used to listen AMPS analogue calls on radio anyways 🙂
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