SDK 6.7.2 is the latest Brooktrout development kit providing feature rich capabilities to our partners. In addition to the normal assortment of bug fixes, 6.7.2 also has added some new features that will be quite useful. I’m going to focus on a few of them here, over several blog posts, to give more details on why they can help you.
The first I’d like to talk about has to do with using SIP Session Refreshes with a Cisco Call Manager. You may have noticed that when the Call Manager sends a SIP INVITE message, it does so with no SDP. SDP is what contains information about a call’s capabilities like what codecs are supported. Instead, the Call Manager sends the SDP in a later ACK message. That’s okay for the initial call establishment. However, if the Call Manager is set to send Session Refreshes it will do so by again sending an INVITE without an SDP. Prior to SDK 6.7.2, the SR140 would see the Session Refresh INVITE as changing call parameters from what had already been negotiated. The SR140 wouldn’t recognize this new INVITE as a session refresh and wouldn’t respond to it. Of course the Call Manager doesn’t like this and continues to send more INVITEs until it gives up and hangs up the call. So this isn’t really helpful when you want to use session refreshes. So we added a new feature in SDK 6.7.2 to allow these SDP-less INVITE messages so that session refreshes can be used with the Call Manager.
Below are some line diagrams showing the before and after behavior.