Stephen R. Besch wrote:

Olle E. Johansson wrote:

Going back to the subject, what does the grandstream really do, SIP-wise, when you press
the transfer button?



4.3.7 Call Transfer The user can transfer an active call to a third phone by using the “Transfer” button. The sequence is like this: The user presses the “Transfer” button and if the other voice channel is available (i.e., there is no other active conversation besides the current one), he/she will hear a dial tone. He/She can then dial the 3rd phone and then hangs up his own phone. 2 kinds of blind call transfers are supported: using REFER and using BYE/Also. The SIP message flow based on SIP REFER method looks something like this:


Call Flow Diagram For Blind Call Transfer:

From Transferee to Transferor

     INVITE ->
    <-100/180/200
     ACK ->
    <- RTP Media ->
    <- REFER
     202 ->
     NOTIFY ->
    <- 200
    <- BYE
     200 ->

From Transferee to Recipient

    INVITE ->
    <-  100/180/200
     ACK ->
    <- RTP Media ->


The SIP message flow based on BYE/Also method looks something like this:


From Transferee to Transferor

     INVITE ->
    <- 100/180/200
    ACK ->
    <- RTP Media ->
    <- REFER
    501 Not Implemented ->
    <- BYE with “Also:”
    200 ->

 From Transferee to Recipient
    INVITE ->
    <- 100/180/200
    ACK ->
    <- RTP Media ->

I have no idea if this is accurate, I just copied it and replaced the arrows indicating direction with "->" and "<-". You can download the manual itself from the GS web site.
I'll do that.

Does Asterisk work with this transfer button or not? We have implementation of both 
REFER
and BYE/also in the sip channel.

/O
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