Is it possible to perform many SIP transactions in parallel, for a UA with two other UAs? Fpor example, if UA1 is in the middle of an INVITE, can UA1 respond to an incoming INVITE from UA3? What about standalone transactions?
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Is it possible to perform many SIP transactions in parallel, for a UA with two other UAs? Fpor example, if UA1 is in the middle of an INVITE, can UA1 respond to an incoming INVITE from UA3? What about standalone transactions?
There’s nothing in the standard that prevents a SIP device from handling multiple concurrent transactions and in fact SIP servers need to do so in order to be able to handle any kind of load.
As to how a SIP user agent should handle concurrent SIP transactions that’s a separate consideration. IF UA1 is already on a call and a new INVITE request comes in from UA3 the typical way to handle it is with some kind of call waiting indication. With a softphone that indication can be visual whereas with an ATA that indication is often on the audio channel by injecting some tones into the UA’s audio stream.
For non-INVITE transactions it will generally be a lot simpler since most don’t require any user action. For example the UA could maintain half a dozen different registrations with different SIP servers and the various register and/or subscribe transactions (in this case the transaction is simply the combination of the request and response) could be running concurrently.