> I appreciate the observations related to cost and believe > some discussion is warranted but some observations: > > - Lower is better is mostly what you get in routers. For > example, OSPF has a well defined metric but you can import > BGP routes into OSPF (and > vice-versa) with default or different metrics. You can add > static routes, changes preferences, etc. > > An ALTO Server is no different. It needs to take inputs from > different sources and come up with a cost metric.
Yes. One can indeed use different input sources... > If we need > to define what cost means I suggest we take the definition > from routing folks (for example, ref PCE/BGP). Do they have > one? For example, if I dump the forwarding table of a router > and it shows that for a certain destination the cost is "50" > through a certain interface, what can I infer from it given > the mash of different inputs a router can take to calculate that? ... and there may be input metrics other than BGP/OSPF/... routing cost. > - Different ALTO Servers might be a problem if they are in > different domains. ALTO servers within a single domain that > need to exchange cost maps need to use the same algorithms. > > - Different ALTO servers in different domains in another > issue. This was an issue we worked on: > > https://tools.ietf.org/html/draft-penno-alto-cdn-03#page-17 > > I believe implementations just use BGP cost. While BGP cost is certainly a very relevant input parameter, we've shown an implementation that can also calculate the ALTO cost e.g. from delay (Section IV.C): http://dx.doi.org/10.1109/ICIN.2012.6376038 How to calculate the cost value really depends on the requirements and policies of the ALTO server operator. Michael _______________________________________________ alto mailing list [email protected] https://www.ietf.org/mailman/listinfo/alto
