This document specifies a mechanism enabling enterprise SIP networks to request a set of operational parameters from a SIP provider. The resulting list of parameters can be used to automate the configuration of the SIP peering interface between the enterprise and the SIP provider networks.

This document is notably clear and easy to understand, even for those less familiar with SIP.  I would specifically commend the authors for clearly explaining the terminology and providing corresponding references.

The proposed mechanism seems to be rather useful for operating SIP networks, especially as it promotes automation and reduces chances of human errors.

I believe the document is ready for publication. I do not really have any comments, except for two minor questions (more for my own curiousity) and a few nits:

Questions, both related to Section 5:

1. is it intentional that "recommended" is a lower-case?

2. With my limited SIP background, I apologize if this is an obvious question, but..

Could a SIP operator ever make a change to the capability set that would demand an update to enterprise networks faster than the current predefined interval allows, or is that scenario highly improbable?  If such scenario is possible, was the possibility of including the recommended polling frequency within the capability set itself considered?

Nits:

Section 2.1
"Call Control within a telephony networks refers to software that is responsible for delivering its core functionality. "

Does "its" in "its core functionality" refers to "telephony network"? I guess so, but I found that phrase a  bit hard to parse, so maybe "for delivering the core telephony functions" or smth like that?

Section 2.3

"The capability set document is constructed according the guidelines of the YANG model described in this draft." 

I think it should be 'according to the guidelines':
"The capability set document is constructed according to the guidelines of the YANG model described in this draft."