In a GSM network, often one way speech/mute calls/no audio is observed.In this condition if two persons calls each other,their call is established ,both persons keeps on saying Hello...Hello...but they can not listen voice of each other hence can not communicate.this condition is called "way speech/mute calls/no audio " in telecom terminology.
This problem can be due to transmission media mismatch.In this case describing the situation when E1,s are added between two Swicthes/MSC,s to carry Inter-MSC/Switch voice traffic and Mute calls are observed due to E1 cables mismatch at Site#2(Please see the attached diagram).For simplicity E1 addition of two E1 is taken,E1#1 is of black colour and E1#2 is of red colour.
A caller obeserve one way speech/mute calls/no audio when call is established.This condition can be checked by a Measuement instrument called "Audio Tester".
Audio tester is attched with each E1 interface and Live call is heared for testing,to confirm that No audio is obeserved on that particular E1 or not.
Fault Location can be analysed by Loop/break techniques.Step by step technique can be addopted.
1-Break one E1(black cables) at Site#1 for MSC1 and observed the status of E1,s at MSC2.Tranmsission path break of both E1,s is observed at MSC2.Hence it is confirmed the two E1,s are swpped between MSC1 and MSC2,exact Location of Fault can be located by next steps.remove this break and make this E1 connect.
2-Break both the E1,s at MSC2 side and Starting from MSC1 side,Make a loop/break from MSC1 DDF towards MSC1 and check the status of these E1,s at MSC1.Cable b/w MSC1 and MSC1 DDF is confirmed to be OK.
3-Make a Loop/Break at OSN1 DDF,if OK,then Jumper Cables are also verifed.
4-Make a Outloop from OSN1 system,if OK.transmission path from MSC1 to OSN1 is OK.
5-Make a Inloop at OSN2,if OK, transmission path from MSC1 to OSN2 is OK.Cross connections are also verifed as well.
6-Make a Loop/Break from OSN2 DDF towards MSC1,If OK,then transmission path from MSC1 to OSN2 DDF is OK.
7-Make a Loop/Break from MSC2 DDF towards MSC1,It is found to be Not OK,hence problem Lies between OSN2 DDF and MSC2 DDF.
Hence correcting the Jumper Cable sequence/connectivity between OSN2 DDF and MSC2 DDF solves the problem.Same approach can be applied from opposite direction of path.
BERT meter can also be used for troubleshooting of this kind of mismatch between E1,s.
As descirbed in attached figure.two E1,s are added bewteen MSC1 and MSC2(Located at Site#1&2 respectively). Transmission Path will be as follows:
MSC1--->MSC1 DDF-->Single pair Jumper Cable --->OSN1 DDF --->OSN1 --->Fiber Cable --->OSN2 --->OSN2 DDF --->Single pair Jumper Cable --->MSC2 DDF ---> MSC2.
As described in attached figure Jumper cables for TX (transmit) signal of two E1,s are inter changed with each other at Site#2. (TX and RX of E1#1=Black , E1#2 =Red).Hence caused the No Audio/Mute calls on thes two E1,s all the voice traffic on these two E1,s will observe No Adio/Mute Calls.
The same can be happend in following cases as well:
1- RX cable jumper is interchanged instaed of TX jumper.
2- Whole of the E1 is interchaned at a site.Means E1#1 of MSC1 is attached with position of E1#2 at MSC2 and vice versa.
This situation often happen with multiple E1,s when E1,s are added between two switches,if jumper cables are swapped between E1,s.
1-Newly added E1,s sholud be tested on BERT by connecting the BERT at last point and take loop/break from far end last point to confirm the tramsmission path is OK.
2-No audio testing should be performed after each E1 addition/Inter MSC capacity addition.
3-If some problem is obserevd,it sholud be rectified prior to commercial traffic loading on these E1,s.