Team-mates: I've been grappling with mobility affects upon routing systems for much of this decade. I am not optimistic that this group will be able to directly address mobility in a manner that will result in an RRG consensus. I also do not believe that this group is likely to be able to qualify mobility attributes such as "granularity and churn" in a satisfying manner. Rather, the following is the view from my knothole:
1) The semantics of mobility differs in different contexts. In my own research, I have found it helpful to distinguish between geographical mobility (i.e., the affects of one node moving relative to another, which can also include the signal intermittence affects caused by attenuation (distance) or signal blockages due to landforms, foliage, buildings, particulate matter (dust storms), the weather, or the pitch, roll, or yaw of the moving node impacting its own antenna's signal propagation or reception) and organizational mobility (i.e., moving a computer from one vehicle to another, moving part of an organization into another part of an organization). 2) Different systems interpret geographical movement as being "mobility" very differently. For example, for certain satellite systems, an entity can move hundreds of miles and not leave the satellite's beam. From the perspective of that satellite, that entity has not moved (i.e., no mobility has occurred). By contrast, stationary nodes may exhibit "mobility" given certain weather or particulate matter environments (e.g., as a function of frequency ranges). 3) Routing protocols confuse underlying signal intermittence with mobility. The impact of signal intermittence varies in terms of which part of the protocol stack is being focused on. The higher one goes up the protocol stack, the longer the duration the signal intermittence event can be before the protocol must address it. One can take steps to dampen these affects, but ultimately signal intermittence events will be noted if their duration is long enough. 4) Mobility affects are a partial function of the network architecture. Architectures similar to 3GPP, for example, naturally view mobility from a mobile IP (MIP) perspective. By contrast, I have primarily been working in MANET environments and those environments view similar mobility events quite differently. It is my personal belief that adherents of those two perspectives naturally interpret the same facts differently -- and certainly various mobility attributes have very different routing implications to each orientation. 5) Ran Atkinson's posting on February 21st focused on a technical report that for entities moving every few minutes or less, the protocol system works better if mobility is handled at L2 than L3. Because I largely agree with this conclusion, I mention Ran's posting here as another datapoint suggesting that this group can't (fully) consider mobility because L2 issues are out of RRG's scope. 6) A great deal of published research has been addressing various cross-layer protocol integration mechanisms for wireless systems over the past many years. I believe that the technical literature is concluding that cross-layer protocol integration techniques can significantly dampen mobility affects upon IP routing protocols. However, even if you agree with this conclusion, can RRG presume that such techniques will be implemented in a consistent manner? I think not (for the foreseeable future) ... thereby making the creation of a consensus position for this group all the more difficult because we will be talking apples and oranges -- and to what purpose? 7) I believe that the research community has already formed a consensus that in wireless environments network performance and scaling is enhanced if the network's topology is hierarchical. Of all of my observations, I believe that this is the only useful observation that is suitable for the RRG to use in order to create a consensus position. Therefore, I believe that if RRG is to address mobility, it is because the selected RRG approach is so clean that it incidentally also enhances mobility (i.e., mobility is a secondary affect for RRG and not a gating requirement). --Eric -----Original Message----- From: William Herrin [mailto:[EMAIL PROTECTED] On Thu, Mar 13, 2008 at 6:18 PM, Tony Li <[EMAIL PROTECTED]> wrote: > Or, in other words, we should drop the mobility discussion for now, > deal with the granularity and churn issues, and then see if we are > happy with the bounds that that imposes on mobility. Hi Tony, Do we have a consensus on what target numbers for granularity and churn could support mobility directly in the routing system? If not, I submit that we should continue our tangent long enough to get them. While we might or might not want to support mobility directly in the routing architecture, it would be very informative if we could say: yes, this proposal meets the target criteria for mobility in the routing architecture and no, that proposal does not. Regards, Bill Herrin -- to unsubscribe send a message to [EMAIL PROTECTED] with the word 'unsubscribe' in a single line as the message text body. archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg
