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<p>Hi all,</p>
<p>Doing some testing recently with osmo-sip-connector, I noticed a
few things that seem to be important regarding the user experience
of a network with osmo-sip-connector. <br>
</p>
<p>* The osmo-sip-connector is an external MNCC handler interface
for one MSC. The MSC doesn't have any information about what is in
the HLR. <br>
</p>
<p>When the osmo-sip-connector sends a call towards the MSC, the msc
does a VLR lookup: vlr_subscr_find_by_msisdn() in gsm_04_08_cc.c
around line 1860.</p>
<p> if that returns false we are doing mncc_release_ind() with
GSM48_CC_CAUSE_UNASSIGNED_NR. That is getting translated into a
SIP 404, which informs the caller that the number was not found.
Logical but it's not correct if the subscriber does actually exist
in the HLR.</p>
<p>
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<p>Actually the same problem exists when using the internal MNCC, If
you call a subscriber that has just switched off their phone,
you'll get an Un Assigned Number error cause. That would be
incredibly confusing for the users. In rhizomatica's case, the
audio played back to the caller would be "The number you have
dialed does not exist, please verify it", while it should
obviously be "The number you have dialed is temporarily
unavailable, please try again later."</p>
<p>What we have done there is send the caller to go physically ask
ask the callee why they canceled their phone service, when all
they did was switch off the phone.</p>
<p>SO:</p>
<p>There was some discussion about this at the devcon, I want to
outline some points here, hopefully I understand it right.</p>
<p>* The osmo-sip-connector should ask the HLR if the number exists
before forwarding the call to MNCC.<br>
</p>
<p>* There may be more than one MSC, in which case the HLR would
inform osmo-sip-connector about which MSC to use.<br>
</p>
<p>* The osmo-sip-connector could either be SIP associated, or MSC
associated, that is to say:<br>
</p>
<p>a) one osmo-sip-connector per SIP UA, sip-connector talks to HLR,
and has multiple connections to MSCs (UDP then, not Unix Socket?)<br>
</p>
<p>or <br>
</p>
<p>b) one osmo-sip-connector per MSC, in which case the SIP UA would
have to somehow query the HLR to ask where to send the call. </p>
<p>Does that all sound correct?</p>
<p>and then.. still a doubt: <br>
</p>
<p>IIUC, in the traditional core network. When an MSC receives a MO
SETUP from a local MS, and it does not have this number in the
VLR, it should be querying HLR for routing info, (which may
subsequently query another HLR) no? why are we only doing VLR
lookup in the MSC? Is it simply "To be implemented" ?<br>
</p>
<p>thanks!</p>
<p>k/</p>
<p><br>
</p>
<p><br>
</p>
<p><br>
</p>
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