|
Hi Adrian,
First of all, highly appreciate your all great comments. See my comment below.
Regards, Lucy
-----Original Message-----
Hi Lucy,
> The draft layouts the basic PCE
architecture and expresses the motivation
Thanks.
I think it is true that PCE supports this model, but I don't think it is the case that the assumptions you state are universal.
1. The user-network model and the client-server model are examples of how one might use a control plane-based switching network, but they are not the only examples. Accept this comment.
2. To say that all connection paths are based on instant requests from end users slightly misses the point of PCE. PCE performs computations based on requests from an external entity (the PCC), and PCE operates on a TED. There is nothing that says that the TED must be a representation of the network at only one instant of time, and there is nothing that says that the computation request must demand a computation "now". OK PCE does specify an instant request from end-user or NMS. TED defined in the draft contains the topology and resource information of the domain. It is very unclear if it can sever bandwidth reservation purpose or not. In addition, TED is not excluded to reside within network, which is hard to use this purpose.
Hmmm. This may be why I disagreed with your assumptions! :-)
Maybe my words here are not clear to you. I means that it is hard to see that transport service will be only offered in the way that an end user sends a signal request at ingress point at the time that a bandwidth needed.
> Typically, carrier has a
service order reservation
Yes, this is another valid model. But it is also not the only valid model and many transport networks are operated today on a much more flexible approach. I agree. Does the architecture need to enable other approaches?
> A path computer engine has
a
I am unsure whether what you say matches reality perfectly.
That is, when a pending future order is entered into the system, the reservation is made. This means that the TED reflects the results of the order/computation/fulfilment cycle, and that computations are still prefomred on demand (i.e. "now"). The difference is that the provisioning (fulfilment) is some time in the future.
In this case, it seems unlikely that you would feed your TED from the routing protocols, but rather from inventory discovery and from the service ordering/fulfilment process. Figure 5 in the architecture shows this model.
That is the goal to feed TED from the routing protocols and let PCE use TED information and SORD information to compute the path. I think resource inventory should come from network instead of human entering. Figure 5 show NMS initiating the service request, but does not show the reservation capability.
You mention that the architecture does not prohibit time-based reservation. But it does not explicitly support that either. It is hard to see through it. If this is a valid function, could we explicitly specify it instead of “imply it”? Maybe insert section 5.6 to illustrate this model. That is my suggestion to expand the architecture including this scenario. This adds value for the PCE.
> The architecture is pretty
close to the PCE-based
There is nothing (IMHO) in the current architecture that prohibits either the management plane use of PCE, or the inclusion of a time dimension in the TED and the computaiton requests.
It seems that current TED definition does not serve this function.
> Here is the recommendation for
the PCE-based architecture: > Here, SORD is the service order
reservation database, it contains all
This would be hugely inefficient, wouldn't it? Since PCE cannot guess which resources might be blocked out for future requests, it would have to make this query for every computation. Further, if PCE only made the query for resources that satisfied the computation, it might have to make repeated recomputations, so it would be more efficient for it to retrieve information about every future blocking. So, in fact, it makes more sense for SORD to feed the information into the TED and allow PCE to operate on the full database.
But consider: How does SORD know which resources will be reserved and when? Presumably, it has consulted PCE as well.
> It is clarified that not all
pending orders in SORD need to reserve the If you wanted to work on some issue like "Applicability of PCE to time-scoped service requests" this might be of interest to people. It was raised in the early days of PCE and of L1VPN, but did not attract significant interest. I think that the feeling at the time was that it was out of scope for PCE, but formed part of a management system. However, it might be that there would be value in enhancing the PCE protocol to carry time delimiters for computation requests.
Note that the PCE working group is interested in applications of PCE and the protocols involved, but is not so interested in abstract functional components that are beyond the scope of the working group.
Regards, Adrian |
_______________________________________________ Pce mailing list [email protected] https://www1.ietf.org/mailman/listinfo/pce
