[alto] Here is a review of draft-ietf-alto-performance-metrics-01

[xin wang <[e-mail]>]

Dear authors of "ALTO Performance Cost Metrics”,


Your draft about extending cost metrics of ALTO looks very useful, especially for varieties of applications with different criteria to make decisions for traffic engineering. The following is a review of your draft:


a. Link Maximum Reservable Bandwidth and Link Residue Bandwidth


These three cost metrics look very similar but have different meanings according to your draft. In my understanding, based on the concept of bandwidth oversubscription, a reserved bandwidth could be larger than current remaining bandwidth (equals to max bandwidth subtract the sum of all reserved bandwidth). Then, Link Maximum Reservable Bandwidth should be slightly larger than Link Residue Bandwidth. Is this right?


b. Unitless performance scores


In section 2.1, the draft suggests providing unitless performance scores for privacy issues. In ALTO cost mode, it defines “ordinal” which indicates the ranking of the cost values instead of actual costs. Do you suggest to add more intelligent abstraction of cost values besides of ranking?


c. Packet Delay Variation


The draft uses the minimum delay observed as the definition of packet delay variation. I am not sure it is a good solution. There are some other approaches you may consider, such as standard deviation.


d. The unit of Periodic One Way Delay


The draft uses seconds as the unit of Periodic One Way Delay. I am not sure it is typos or not since the example shows the powdelay cost values are 10, 20, and 30.


Also there are some typos you may fix:


Abstraction: add space between "BGP-LS,OSPF-TE";

Page 2: “delay sensitive” -> “delay-sensitive”;

Page 2: “a set new” -> “a set of new”;

Page 2: “ explicitely” -> “ explicitly”

Page 4: “ invlove” -> “ involve"


Best,

Xin