We do it on our Class 5 softswitch ... and it works consistently. There may be a few seconds, once, where a new call can't be made, but most people will re-dial. It just works. It can be done, but the product has to be built with that in mind. Frank -----Original Message----- From: Kasper Adel [mailto:karim.adel@gmail.com] Sent: Thursday, November 08, 2012 5:23 PM To: NANOG list Subject: Whats so difficult about ISSU Hello, We've been hearing about ISSU for so many years and i didnt hear that any vendor was able to achieve it yet. What is the technical reason behind that? If i understand correctly, the way it will be done would be simply to have extra ASICs/HW to be able to build dual circuits accessing the same memory, and gracefully switch from one to another. Is that right? Thanks, Kim