[SIPForum-discussion] REFER in a call transfer ...

Sun Aug 29 04:29:07 UTC 2010

*SIP Call Transfer & Refer--Healthcare Model*

The functionality that is mentioned for SIP Refer & SIP Transfer Call has
got an inherent Healthcare Model.

I worked on such a Healthcare Model in GE Healthcare.

The Model works like this:

Consider a Patient P having diagnosed with a critical disease D goes to
Consultant C having speciality 100SUR (Surgery). C has not that speciality
to rectify disease D. So he refers to GP G having speciality 100MIN with a
commission of 5%. But, GP G is having busy schedule and he cannot keep
patient P in waitlist W for treatment, so he refers back the patient P to GP
G`. Also a patient P` having admitted in hospital occupying a bed B can be
tranferred to different bed B` having lesser Cost under some different or
same facility. P` can be transferred to a lesser cost bed B`` after some
more days.

So the Healthcare Model for SIP works like this. It is so easy to
practically write code for SIP Phones in this manner.

Regards
Rohan Sarker
IBM Kolkata & IBM Bangalore
Tel:+919903051236
Home:+913324288069
=.=.=.=.=.=.=.=.=.=.=.=.=.=.=.=.=

On 8/26/10, Vivek Batra <Vivek.Batra at matrixcomsec.com> wrote:
>
>  Murli;
>
>
>
> *Murali – Got your point. Need a small clarification further. B calls C, C
> is in some other call and B goes on hook immediately.  Would A be getting
> busy tone ?? And as B has already gone on hook there is no point of
> retrieving the call back. A can terminate the dialog with C. Pls. clarify
> me.*
>
> * *
>
> *Vivek – I think, its just mistype, B does not call C, in you case B is
> calling A and A calls C.*
>
> * *
>
> *Anyway yes, if transferor (B) goes onhook immediately after performing
> transfer activity and dialog between A & B has been terminated, A should
> honor the provisional and final responses received from C, and hence tones
> should be played by A accordingly.*
>
> * *
>
> *There is no point to terminate the dialog between A and C since this
> dialog would never have been existed due to receipt of final error response
> (486 Busy). So A should play Busy Tone in that case.*
>
> * *
>
> * *
>
> *Murali – As far as I know  B receives a NOTIFY only after the transfer is
> completed(i.e, after the speech path is established b/n A and C). I don’t
> see any NOTIFY being sent for alerting. Either it would be Notify with 100
> trying or Notify with 200OK. My only concern here is how come B gets Ring
> back without receiving the alert messages.*
>
> * *
>
> *Vivek – I couldn’t point any RFC which can give you better idea for
> NOTIFY with 180 Ringing or other messages, but what I can surely say that
> the protocols just provide the frame-work and it is upto us to innovate
> ensuring they are still compliant with the recommendations of protocol.*
>
> * *
>
> *In our implementation and mapped with your example, B receives NOTIFY
> with 180 Ringing and hence play RBT. I think this is the best practice and
> implemented by other vendors too.*
>
> * *
>
> * *
>
> *Murali : I guess there are a few phones that are connected trough PAP2
> which still doesn’t support REFER.*
>
> * *
>
> *Vivek –  Are you referring Linksys PAP2 ATA? If yes, I have worked a lot
> on this device and it also support REFER method. You need to check the
> settings again.*
>
> * *
>
> * *
>
> *Best Regards,*
>
> Vivek Batra
>
>
>
>
>  ------------------------------
>
> *From:* Murali Vuppandla [mailto:mvuppand at cisco.com]
> *Sent:* Thursday, August 26, 2010 5:23 PM
>
> *To:* 'Vivek Batra'; discussion at sipforum.org
> *Subject:* RE: [SIPForum-discussion] REFER in a call transfer ...
>
>
>
> Hi Vivek,
>
> For further analysis, here we go:
>
>
>
>
>
> Ø     Murli]: *There was a typo**J. I do agree with you that it’s the
> transferor that should be getting the busy tone. But if we observe the
> standard call flows, it’s transferee( A in our case) that receives 486 busy
> response. I’m stuck exactly here... I don’t have any manual setup to test
> the scenario .. I’m totally relying on automated scripts .. that’s the
> reason why I’m so concerned about this .. what does 486 busy sent to
> Transferee convey (If we go by call flows defined in docs) ?*
>
> * *
>
> *[Vivek] – Yes, its correct that A receives 486 Busy, but A does not need
> to play Busy Tone for this. A should only send NOTIFY (with 486 Busy) to B
> and B should immediately retrieve the call back on              receipt of
> NOTIFY (with 486 Busy).*
>
> * *
>
> *            As I mentioned earlier, Playing bust tone to A would lead to
> hangup the call by A and B would never be able to retrieve the call back.*
>
> * *
>
> *Murali – Got your point. Need a small clarification further. B calls C, C
> is in some other call and B goes on hook immediately.  Would A be getting
> busy tone ?? And as B has already gone on hook there is no point of
> retrieving the call back. A can terminate the dialog with C. Pls. clarify
> me.*
>
> * *
>
> * *
>
> * *
>
> * *
>
> Ø     *[Murli]: But if you see the message flow, it’s only A that would be
> receiving all the alerting messages though you hear the ring back tone at
> B(obviously B has to be receiving alerting messages to get a ringback) …I’m
> stuck here again. Just need to confirm whether or not B receives any
> alerting messages.*
>
> * *
>
> *             [Vivek]: Yes, again only A receives all provisional/final
> response from C, but at the same time A will send each alert in NOTIFY
> message to B and hence, B will play tones locally if required.*
>
> * *
>
> *Murali – As far as I know  B receives a NOTIFY only after the transfer is
> completed(i.e, after the speech path is established b/n A and C). I don’t
> see any NOTIFY being sent for alerting. Either it would be
>                Notify with 100 trying or Notify with 200OK. My only concern
> here is how come B gets Ring back without receiving the alert messages.*
>
> * *
>
> * *
>
> * *
>
> Ø     *[Murli]: I was referring to the SIP  phones that don’t support
> REFER method.*
>
> * *
>
> *             [Vivek]: Without support of REFER method, how they support
> Call Transfer?*
>
> * *
>
> *             Murali : I guess there are a few phones that are connected
> trough PAP2 which still doesn’t support REFER.*
>
>
>
>
>
> Regards,
>
> Murali.
>
>
>
> *From:* Vivek Batra [mailto:Vivek.Batra at Matrixcomsec.com]
> *Sent:* Thursday, August 26, 2010 12:38 PM
> *To:* 'Murali Vuppandla'; discussion at sipforum.org
> *Subject:* RE: [SIPForum-discussion] REFER in a call transfer ...
>
>
>
> Murli;
>
>
>
> [Murli]: *There was a typo**J. I do agree with you that it’s the
> transferor that should be getting the busy tone. But if we observe the
> standard call flows, it’s transferee( A in our case) that receives 486 busy
> response. I’m stuck exactly here... I don’t have any manual setup to test
> the scenario .. I’m totally relying on automated scripts .. that’s the
> reason why I’m so concerned about this .. what does 486 busy sent to
> Transferee convey (If we go by call flows defined in docs) ?*
>
> * *
>
> *[Vivek] – Yes, its correct that A receives 486 Busy, but A does not need
> to play Busy Tone for this. A should only send NOTIFY (with 486 Busy) to B
> and B should immediately retrieve the call back on receipt of NOTIFY (with
> 486 Busy).*
>
> * *
>
> *As I mentioned earlier, Playing bust tone to A would lead to hangup the
> call by A and B would never be able to retrieve the call back.*
>
> * *
>
> * *
>
> * *
>
> *[Murli]: But if you see the message flow, it’s only A that would be
> receiving all the alerting messages though you hear the ring back tone at
> B(obviously B has to be receiving alerting messages to get a ringback) …I’m
> stuck here again. Just need to confirm whether or not B receives any
> alerting messages.*
>
> * *
>
> *[Vivek]: Yes, again only A receives all provisional/final response from
> C, but at the same time A will send each alert in NOTIFY message to B and
> hence, B will play tones locally if required.*
>
> * *
>
> * *
>
> *[Murli]: Again a typo here. My questions here is if B goes onhook and say
> C is not reachable … Does A hear any REORDER tone or any announcement.*
>
> * *
>
> *[Vivek]: You haven’t any choice other than to play reorder tone. You can
> not play blank anytime.*
>
> * *
>
> * *
>
> *[Murli]: I was referring to the SIP  phones that don’t support REFER
> method.*
>
> * *
>
> *[Vivek]: Without support of REFER method, how they support Call Transfer?
> *
>
> * *
>
> * *
>
> *Best Regards,*
>
> *Vivek Batra** *
>
>
>
>
>  ------------------------------
>
> *From:* Murali Vuppandla [mailto:mvuppand at cisco.com]
> *Sent:* Thursday, August 26, 2010 11:24 AM
> *To:* 'Vivek Batra'; discussion at sipforum.org
> *Subject:* RE: [SIPForum-discussion] REFER in a call transfer ...
>
>
>
> Vivek,
>
> Thanks for your points. Pls. check below my comments in blue.
>
>
>
> Regards,
>
> Murali.
>
>
>
> *From:* Vivek Batra [mailto:Vivek.Batra at Matrixcomsec.com]
> *Sent:* Thursday, August 26, 2010 10:28 AM
> *To:* 'Murali Vuppandla'; discussion at sipforum.org
> *Subject:* RE: [SIPForum-discussion] REFER in a call transfer ...
>
>
>
> Murli,
>
>
>
> Comments inline in RED.
>
>
>
> Best Regards,
>
> Vivek Batra
>
>
>  ------------------------------
>
> *From:* discussion-bounces at sipforum.org [mailto:
> discussion-bounces at sipforum.org] *On Behalf Of *Murali Vuppandla
> *Sent:* Wednesday, August 25, 2010 11:55 AM
> *To:* discussion at sipforum.org
> *Subject:* [SIPForum-discussion] REFER in a call transfer ...
>
>
>
> Hi All,
>
>
>
> Just need some basic clarifications on SIP REFER in a transfer scenario.
>
>
>
> Say there are three SIP phones that support REFER method.
>
>
>
> A calls B and B answers the call. B hook flashes and blind transfers the
> call to C. Ideally B would  be supplied with the ring back tone, but at the
> same time some docs say that when C is in ringing state, A would be hearing
> ring back tone.
>
>
>
> What is wrong in it?
>
>
>
>  I’m in a state of confusion here if it’s  A or B that is supplied with
> Ring Back tone since that practical implementation of Transfer seems to be a
> bit different from the one described there in docs.
>
>
>
> If you are talking about traditional PBX, then its more complex. In
> traditional legacy PBX, only transferor gets RBT as long as transferor is
> off-hook, and transferee gets MoH. As soon as transferor goes on-hook before
> transfer target answers the call, transferee now starts getting RBT instead
> of MoH.
>
> That is what most of the legacy PBX does.
>
>
>
>
>
> To add on this, Say when B blind transfers the call to  C and C is busy …
> who should be hearing the busy tone(A or B) … if you go by the practical
> scenario .. when B blind transfers the call it hears the busy tone … but if
> we go by the standards it’s A that should be getting busy tone ..
>
>
>
> Nops, If u give busy tone to A, A would probably hangup the call. Only B
> should get Busy Tone as a part of transfer notification and after short busy
> tone, A and B should be connected again.
>
>
>
> To summarize the above points …
>
>
>
> 1)       A calls B.. B blind transfers the call to C … If C is busy with
> another call .. who should be getting the busy tone(A or C).
>
>
>
> Neither A nor C J its B who should get Busy Tone else the Transferor (in
> this case its B) will never become to know that Transfer Target was Busy.
> You can play Busy Tone for short period of time and then again connects the
> call between A & B.
>
>
>
> *There was a typo**J. I do agree with you that it’s the transferor that
> should be getting the busy tone. But if we observe the standard call flows,
> it’s transferee( A in our case) that receives 486 busy response. I’m stuck
> exactly here... I don’t have any manual setup to test the scenario .. I’m
> totally relying on automated scripts .. that’s the reason why I’m so
> concerned about this .. what does 486 busy sent to Transferee convey (If we
> go by call flows defined in docs) ?*
>
>
>
> 2)       A calls B .. B blind transfers the call to C … if C is ringing
> who should be getting the ring back tone …
>
>
>
> A and B, both should get Ringing Tone. In result, B will become to know
> that the transfer activity performed by him is in ringing state. For A, that
> will be indication that he has been transferred to some other phone and that
> phone is ringing now.
>
>
>
> *But if you see the message flow, it’s only A that would be receiving all
> the alerting messages though you hear the ring back tone at B(obviously B
> has to be receiving alerting messages to get a ringback) …I’m stuck here
> again. Just need to confirm whether or not B receives any alerting messages.
> *
>
>
>
> 3)       A calls B .. B blind transfers the call to C ..A goes on hook
> immediately and If REFER fails .. what has to be the ideal behavior…
>
>
>
> If A goes on-hook and has been triggered BYE, dialog at both side viz A and
> B should be terminated.
>
>
>
> *Again a typo here. My questions here is if B goes onhook and say C is not
> reachable … Does A hear any REORDER tone or any announcement.*
>
>
>
> 4)       And does the call transfer in case of Normal phones differ from
> the ones that supports REFER .
>
>
>
> What you are referring as normal phones?
>
>
>
> *I was referring to the SIP  phones that don’t support REFER method.*
>
>
>
>
>
> Awaiting your responses on this.
>
>
>
> Regards,
>
> Murali.
>
>
>
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