Sounds absolutely like an MTU issue. Probably because broadsoft/polycom don't support PMTUD. Ouch!
So one of the modems/routers doesn't support the MTU the broadsoft/polycom keep trying to jam through it like a piehole at a hotdog eating contest and when it comes to polycom.. mums the word. #typical.
There's a hint this is a known issue from a broadsoft manual: "A UDP datagram of 65507 bytes will have to be fragmented into 45 packets ( Max UDP size of 65507 bytes / UDP size per packet of 1480 bytes ~ 45) to be transmitted across a network. With this many number of fragments, customer firewalls or NAT devices may prohibit the entire packet from being delivered to the endpoint."
So if you have BLF Issues, think MTU and fragments! Try other modems and networks!
I've seen this MTU issue manifest itself in all kinds of wacky ways. like you send subscribe and get notify but only for <state>terminated<\state> and not for full or whatever the BLF state change is.
Hello SIP Shaman,
welcome to the Polycom Community.
Thanks for commenting on these post's with a possible root cause but without any hard evidence brought up to our support team we are unable to verify this. I am not aware if users in this or the other post you replied to have ever done so.
I am personally aware of BLF issues and these, to my knowledge , have been addressed in the past when working with our customers.
I rather not speculate on the issues discussed within this or the other post you replied to so if you are currently having an BLF issue yourself please work with your reseller so they can raise a ticket with us.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services