From owner-nanog@merit.edu Tue Sep 18 10:57:15 2007 Date: Tue, 18 Sep 2007 08:55:19 -0700 From: "Xin Liu" <smilerliu@gmail.com> To: "Bora Akyol" <bora.akyol@aprius.com> Subject: Re: Question on Loosely Synchronized Router Clocks Cc: nanog@merit.edu

Ideally, yes, a protocol should not rely on clock synchronization at all. However, to ensure freshness of messages, we don't have many choices, and clock synchronization seems to be the least painful one. So we asked about router clocks on the current Internet. If normally router clocks are synchronized and we have a mechanism to detect and fix out-of-sync clocks, is it reasonable to assume clock synchronization in the rest of our design?

You are free to "assume" anything you feel like in the design of a new protocol. The greater the divergennce between your 'assumptions' and *UNIVERSALLY* IMPLEMENTED conditions in the real world, the more barriers there are to acceptance and deployment. Within a single administrative domain, routers are 'usually' -- but *NOT* "almost always" -- moderately closely synchronized. Across different administrative domainns, any such synchronization is 'happy accident', nothing more. As far as 'assuming clock synchronization' goes, one of the other subscribers to this list has a _very_ applicable remark: "I encourage my competitors to design like this." <grin>