On Tue, Oct 26, 2010 at 12:43 AM, <[email protected]> wrote: > >> I'm not sure where the term was coined, but stretch is a well-known > term >> in compact routing literature. > > Right.Compact routing discriminated hierarchical routing by asserting it > would induce routes of stretch 17,e.g.. What kind of hierarchical routing > was that? Obviously a bad concept. > Those statements hurted my feeling, because I also conceived TARA routing > (using several hierarchies of zooms) to be some sort of hierarchical > routing. For TARA shortest path still means shortest path. Period. And of > course, TARA would also enable detours.
Hi Heiner, I was also a little bit shocked - since I have proposed hIPv4 -when I noticed that hierarchical routing is a bad choice... But after studying a bunch of Compact Routing papers I discovered that when CR researchers are discussing hierarchical routing they are actually discussing CIDR, i.e. routing tables are kept under control by aggregating and summarizing prefixes - and a global flat address space is used. With this concept there will be stretch issues, the more compact RT the the more likely it is to have a high stretch value for a session. If I got it all wrong I ask kindly the CR researchers to correct me, thanks. Think this is not the hierarchical routing TARA is proposing, think TARA falls into Landmark Routing category -there are papers available on-line and I also found one draft http://tools.ietf.org/html/draft-ietf-manet-lanmar-05: The concept of landmark routing was first introduced in wired area networks [6]. The original scheme required predefined multi-level hierarchical addressing. The hierarchical address of each node reflects its position within the hierarchy and helps to find a route to it. Each node knows the routes to all the nodes within its hierarchical partition. Moreover, each node knows the routes to various landmarks at different hierarchical levels. Packet forwarding is consistent with the landmark hierarchy and the path is gradually refined from the top level hierarchy to lower levels as a packet approaches its destination. You might find the paper of Paul Francis Tsuchiya. "The Landmark hierarchy: a new hierarchy for routing in very large networks" interesting There is also a very nice explanation of the stretch issue in the paper, see section 2.1 Area Hierarchy I also think CR researchers are assuming that the session leverages a single path between the two endpoints - this is a fair assumption since the majority of the sessions are either TCP or UDP based. What if in the future (if it ever happens), most of the sessions are multipath enabled sessions and the endpoints can have several exit and entry points between the private network and Internet (multi-homing). E.g. the initiator have two attachment points to Internet, also the receiver has two attachment points to Internet. Then the endpoints can setup four subflows and the transport protocol will most likely found out which of the subflows have the best throughput, i.e. the lowest stretch (assuming no congestion occurs) . Thus the question is, to which degree should the stretch issued be/can be solved by the routing architecture, how much will/can be solved by a multipath enabled transport protocol? Patrick _______________________________________________ rrg mailing list [email protected] http://www.irtf.org/mailman/listinfo/rrg
