Hi,

I am setting up openbsc with LCR and Asterisk to provide external connectivity for the GSM clients, and I encountered and interesting problem.

If the GSM phone initiates a voice call towards a SIP phone it works perfectly, the voice goes both ways, the quality is OK, everything is fine.

But when the SIP phones initiates a voice call towards the GSM phone, only the SIP phone can hear the voice of the GSM phone, and not the other way around (half sided call). The connection setup works both ways just fine.

The GSM and the SIP phone can also call the asterisk test numbers, and even can do echo test just fine. The two GSM phones can call each other too without any problem.

Does somebody has any idea what could go wrong?

Config:

E1 based Nokia BTS with DAHDI card and TCH/F FR codec. The SIP phone uses Alaw, LCR also set to use Alaw.

The LCR is bridged to Asterisk, interface.conf:

[GSM] gsm-bs tones yes earlyb no bridge ast

[ast] remote asterisk context from-lcr earlyb no tones yes bridge GSM

routing.conf is completely empty.

Astrisk SIP.conf:

[general] context=incoming disallow=all allow=alaw allow=ulaw allow=gsm transport=udp udpbindaddr=0.0.0.0 tcpenable=no tcpbindaddr=0.0.0.0 tlsenable=no tlsbindaddr=0.0.0.0

[5010] type=friend username=5010 secret=123456 dtmfmode=rfc2833 callerid="5010" <5010> host=dynamic canreinvite=no context=myphones

Asterisk extensions.conf

[general] static=yes writeprotect=no clearglobalvars=no

[globals] ; Global variables goes here

[incoming] ; Nothing should land here yet, but every context should end in ; a Hangup(), so we do that. exten => s,1,Hangup()

[myphones] ; When we dial something from the phones we just added in ; sip.conf, Asterisk will look for a matching extension here, ; in this context.

; SIP phone exten => 5010,1,Dial(SIP/5010) exten => 5010,n,Hangup()

; Another SIp phone ;exten => 1001,1,Dial(SIP/1001) ;exten => 1001,n,Hangup()

; GSM phone 1 exten => 12346,1,Dial(LCR/ast/${EXTEN:0},60) exten => 12346,n,Hangup()

; GSM phone 2 exten => 12345,1,Dial(LCR/ast/${EXTEN:0},60) exten => 12345,n,Hangup()

; Testing extension exten => 201,1,Answer() exten => 201,n,Playback(levan_polka.mp3) exten => 201,n,Hangup()

; Echo-test, it is good to test if we have sound in both directions. ; The call is answered exten => 202,1,Answer() ; Welcome message is played exten => 202,n,Playback(dir-welcome) ; Play information about the echo test exten => 202,n,Playback(demo-echotest) ; Do the echo test, end with the # key exten => 202,n,Echo() ; Plays information that the echo test is done exten => 202,n,Playback(demo-echodone) ; Goodbye message is played exten => 202,n,Playback(vm-goodbye) ; Hangup() ends the call, hangs up the line exten => 202,n,Hangup()

[from-lcr] include => myphones exten => _X.,1,Dial(LCR/ast/${EXTEN:0},60) exten => 5010,1,Dial(SIP/5010) exten => 5010,n,Hangup()

BR, Csaba