I was thinking more of scenarios in which there is an edge element/administrative border which can perform header manipulations, particularly adding identifying headers, but can't mangle to the same extent that an SBC (with a B2BUA internally) can. As a company specialising largely in proxies for such applications, that's something that comes up in our radar a lot. We can debate the propriety of using a proxy for such an application, but regardless, it's commonly done, for reasons of throughput and cost. The problem, as you know, is that proxies are quite circumscribed in the aspects of a SIP message they can manipulate--at least, standards-compliant proxies. In a very real sense, UAs on two sides of a proxy are interoperating with each other, rather than with the proxy. This creates both philosophical questions ("what exactly is the CPE here?") and a orthogonal, sometimes turbulent approach in relation to Bellhead expectations about how trunking works. -- Alex Balashov - Principal Evariste Systems LLC 235 E Ponce de Leon Ave Suite 106 Decatur, GA 30030 Tel: +1-678-954-0670 Fax: +1-404-961-1892 Web: http://www.evaristesys.com/, http://www.alexbalashov.com/