Hello Suresh, Thanks for your review. We will update the draft in light of your comments, but please see inline a few responses.
[snip] * Section 2.1 -> Not sure if the word encoded is appropriate here. s/hardware-encoded/usually implemented in hardware/ [CJ] OK. -> These two sentences are hard to read and it is not clear what point they are trying to make. Please consider rewording. As such, the current state-of-the-art tends to confirm the said separation, which rather falls under a tautology. [CJ] What is meant by this sentence is that data and control planes have always been separated from an implementation standpoint, hence the tautology: commercial routers use a (S/W-based) routing engine for route computation purposes, while packet forwarding functions are usually H/W encoded. But a somewhat centralized, "controller-embedded", control plane for the sake of optimized route computation before FIB population is certainly another story. [CJ] One of the main arguments of SDN proponents is that (1) the control plane is separated from the data plane but, more importantly, (2) this separation assumes a (logically) centralized control plane, which allows the use of commodity H/W. From an implementation standpoint, this is different from current router technologies, although there has been some vendors in the past who tried to promote this kind of design (I remember Newbridge's Vivid technology at the end of the '90s, for example). I'm not too sure about how we can possibly re-word this, admittedly. * Section 3.1 Not sure what this sentence is trying to convey. Can you clarify? Some of these features have also been standardized (e.g., DNS-based routing [RFC1383] that can be seen as an illustration of separated control and forwarding planes or ForCES ([RFC5810][RFC5812])). [CJ] What is meant here is that so-called SDN features have been there for quite some time and some of them have been standardized, hence the couple of examples above. * Section 3.4 This direct access to some engines using a vendor-specific could be beneficial to performance but may increase configuration complexity (in opposition to the final goal in Section 4.1 of accommodating heterogeneous network technologies). It may be worthwhile to add some text to the following paragraph in this regard. [CJ] Fine by me, we'll add an extra sentence. Maintaining hard-coded performance optimization techniques is encouraged. So is the use of interfaces that allow the direct control of some engines (e.g., routing, forwarding) without requiring any in-between adaptation layer (generic objects to vendor-specific CLI commands for instance). * Section 3.5 This sentence is ambiguous OpenFlow is clearly not the "next big thing" Does this mean a) OpenFlow is certainly not the "next best thing" (or) b) It is not clear if OpenFlow will be the "next best thing" Can you please clarify? [CJ] option a is the right one. We'll reword accordingly. * Section 3.6 This sentence about non-goals is unclear. What are the "respective software limitations"? o Fully flexible software implementations, because the claimed flexibility will be limited by respective software and hardware limitations, anyway. CJ: The sentence means that there are S/W and H/W limitations respectively that will always restrict the scope of claimed flexibility - another tautology, if you will. * Section 4.5 This sentence is long and complex, and the exact point it is trying to make is not clear. Can you simplify/reword? For example: while the deployment of a network solely composed of OpenFlow switches within a data center environment is unlikely to raise FIB scalability issues given the current state-of-the-art, data center networking that relies upon complex, possibly IP-based, QoS- inferred, interconnect design schemes meant to dynamically manage the mobility of Virtual Machines between sites is certainly of another scale. CJ: Fair enough. We'll simplify the wording, e.g., "DC networks that may rely upon OpenFlow switches are unlikely to raise FIB scalability issues. Conversely, DC interconnect designs that aim at dynamically managing VM mobility possibly based upon the enforcement of specific QoS policies may raise scalability issues." * Section 4.6 Can you clarify what risk is being assessed here? o Assessing whether SDN-labeled solutions are likely to obsolete existing technologies because of hardware limitations. CJ: the risk is both technical and economical. From a technical standpoint, the ability to dynamically provision resources as a function of the services to be delivered may be incompatible with legacy routing systems because of H/W limitations. From an economical standpoint, this is about assessing the impact of deploying SND solutions for the sake of flexibility and automation on CapEx and OpEx budgets. Editorial ========= * Section 3.3 s/policiy/policy/ CJ: thanks. 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