[Serusers] Query on the Back-Up Server

Hi all, Could any one help me to understand the back-up servers concept. In the RFC 3263, section 2 says the following " It is possible for elements to fail in the middle of a transaction. For example, after proxy 2 forwards the request to UA 2, proxy 1 fails. UA 2 sends its response to proxy 2, which tries to forward it to proxy 1, which is no longer available. The second aspect of the flow in the introduction for which DNS is needed, is for proxy 2 to identify a backup for proxy 1 that it can send the response to." This talks about the Proxy 2's work ,but how the backup server will collect the Details of the calls handled by the Proxy 1?. Thanks in advance John Miller -- ___________________________________________________________ Sign-up for Ads Free at Mail.com http://promo.mail.com/adsfreejump.htm