![]() ![]() My phone sends a re-INVITE to Session Manager. From my desk phone, I put the call on hold.Here is the complete flow from the point of me pressing hold.Īt a high level, you should see the following: To demonstrate this, I placed a call to my desk telephone, answered it, started up the Avaya traceSM utility, put the call on hold, stopped traceSM, and then took a few screen shots of the resultant call flow. That same party will take the call off hold by sending another re-INVITE with SDP indicating that media transmission will resume. The party putting the call on hold sends a re-INVITE with SDP indicating that media will no longer be sent. The most common use for re-INVITE is call hold. ![]() It can change every other header as well as the message body, but those two things tell the SIP stack that this is not a new INVITE. VOIP SIP DEFINITION UPDATEYou send an UPDATE message prior to session establishment, but that’s an article for another day.Ī re-INVITE will have the same Call-ID and From tag as the INVITE it is modifying. This means that it will apply to an existing INVITE after a final response has been received and an ACK has been sent. If you aren’t familiar with SIP tags, please see Let’s Play (SIP) Tag.Ī Re-INVITE, it comes after a session has been established. This clues you in that something is different. The one exception is that you will see a tag on the To header. You will see most of the same headers and a similar message body. In fact, if you saw a re-INVITE out of the context of its call flow, you might not be able to tell it from an INVITE used to create a new session. A re-INVITE looks just like any other INVITE. You need to know that re-INVITE is not a new message. To help alleviate any questions and doubts, I decided that a couple pages of explanation and traceSM screen shots would be worthwhile. They sort-of, kind-of get it, but are still unsure as to what they actually get. I’ve encountered that confusion in my SIP class and from emails and comments from my blog readers. One thing that often confuses people new to SIP is the concept of re-INVITE. I continue to have my own ah-ha moments as I wade through Wireshark traces or read RFCs. This is even true for someone like me who has worked with SIP since the late 1990s. Still, there are aspects that can be a bit confusing. ![]() In previous articles, I have shown how vendors like Avaya have implemented SIP solutions that make it more difficult to follow some call flows, but even they become manageable once you understand the basic piece parts and architectures. The messages are fairly easy to understand and the call flows are straightforward enough. For the most part, SIP isn’t all that complicated. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |