I don’t recall saying that pjsip or supporting multiple contacts is new. Flowroute has been doing it since launch.
I didn’t say that this is “for PJSIP.” And your response suggests that you might not understand the relationship between pjsip, Chan_SIP, and SIP. Pjsip and Chan_SIP are the drivers used in Asterisk. SIP is the protocol that goes out over the internet.
Thus, the splitting effect is not “for PJSIP.” Rather, as I said in my post, “the SIP headers” will get split if they are too long and go out over the public internet. This could conceivably happen with Chan_SIP, but since Chan_SIP doesn’t support multiple contacts, nobody would ever try to use it that way.
My source for this tidbit was Flowroute technical support. Flowroute has supported multiple contacts since they launched. I’ve been using multiple FreePBX boxes to register to the same Flowroute trunks for years. I use Chan_SIP, since my boxes all only connect to one contact. But, Flowroute is using something else (probably FreeSWITCH) that supports multiple contacts. Flowroute did warn me that if you get above 3 contacts, you run the risk of having the packets split, and things breaking. I believe, but am not positive, that they told me that it has do with the SIP packets exceeding the MTU.
I think our OP can decide for himself whether my advice will work for him. And if you think otherwise, I think we would all appreciate it if you would tell us why.