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SIP seems OK but no data transmission

Discussion in '3CX Phone System - General' started by stef, Mar 16, 2007.

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  1. stef

    Mar 13, 2007
    Likes Received:
    I have succesfully registered 2 IP FAX machines (t38 compliant) to a internal ip network.
    I tried to send a fax directly (from ip-fax to ip-fax) and it worked.
    I installed 3CX Phone System on a server in the same network.
    I succesfully registered the IP FAX machines to 3CX.
    Now i want to send a fax from IPFAX1 to IPFAX2 via 3CX.

    It seems that the SIP stuff is all OK, but no data is send. I've included the server status and ethereal sip comms at the bottom of this post.

    Can you please help?

    Stef Lauwers

    3CX Phone System v2.0.1618.0 - server status
    10:52:10.895 StratLink::eek:nHangUp: Call(C:22): got Hang-Up from Ext.633
    10:52:10.184 CallLegImpl::eek:nConnCfmd: ConnCfmd: 633@L:2@C:22
    10:52:10.174 StratInOut::eek:nConnected: Call from Ext.969 to Ext.633 is established
    10:52:10.174 CallLegImpl::eek:nConnected: Connected: 633@L:2@C:22
    10:52:10.174 CallLegImpl::eek:nConnected: Connected: 969@L:1@C:22
    10:52:09.853 CallConf::eek:nIncoming: Incoming call from Ext.969 to sip:633@

    ethereal capture (filter=sip)
    No. Time Source Destination Protocol Info
    69 23.468893 SIP/SDP Request: INVITE sip:;user=phone, with session description
    70 23.655310 SIP Status: 100 Trying
    71 23.656162 SIP/SDP Status: 180 Ringing, with session description
    73 23.722714 SIP/SDP Status: 200 OK, with session description
    74 24.074669 SIP Request: ACK sip:633@;user=phone
    78 24.231600 SIP/SDP Status: 200 OK, with session description
    79 24.273585 SIP/SDP Request: INVITE sip:969@;user=phone, with session description
    81 24.274462 SIP Request: ACK sip:633@;user=phone
    84 24.475305 SIP/SDP Status: 200 OK, with session description
    86 24.672693 SIP Request: ACK sip:969@;user=phone
    240 29.583829 SIP Request: BYE sip:633@
    241 29.673022 SIP Status: 200 OK
  2. Anonymous

    Anonymous Guest

    http://www.faqs.org/rfcs/rfc3362.html is some more info for ya,

    T38 does not ride on top of any voice codec. More often than not it kicks in as a result of a re-invite.


    1. Device A calls Device B.
    2. RTP media session is established using voice codec (g711, g729 etc).
    3. Device B detects the FAX pre-amble.
    4. Device B issues a re-invite back to Device A with T38 directives in the SDP message.
    5. T38 fax media session is establish and voice stream is muted.
    6. Device B detects end of fax and issues a re-invite back to A for voice.
    7. RTP media session is re-established using voice codec.

    In the above scenario if device A did not support T38 it would have returned a 606 after step 4, resulting in the fallback RTP media session (using g711, g729 etc) being used to send the fax payload.

    So having said that, i have to check but I am not sure if 3cx supports G711 if it does it should work, but I am not sure if they yet support fax.

    Another thing you might look at is the SIP ports, that you do not have a conflict.
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