Re: [irs-discuss] Comments on Topology API use case document

"Sadler, Jonathan B." <> Wed, 03 October 2012 12:49 UTC

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From: "Sadler, Jonathan B." <>
To: Shane Amante <>, Joel M.Halpern <>
Date: Wed, 3 Oct 2012 07:49:21 -0500
Thread-Topic: [irs-discuss] Comments on Topology API use case document
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Subject: Re: [irs-discuss] Comments on Topology API use case document
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Shane, Joel, et al -

You may be interested in modeling work that was done at ITU-T discussing multi-layer topology relationships.  The specific document to look at is G.800 (2012): Unified Functional Architecture of Transport Networks. (

The specific component in this approach to describing networks that describes multi-layer topology relationships is the Transitional Link.  See Section 6.2.1.

There was a liaison sent from ITU-T SG 15 to CCAMP that described how this topological component can be used in multi-layer ODU networks.  Please see SG15 LS221 - Examples of the use of Transitional Links (ITU-T G.709) (

>From this, work has been started on how a transitional link can be represented in link-state routing protocols thereby providing detail of the hierarchical relationships to path computation entities.

I see strong value in including this in IRS style applications as it enables the entity interested in topology to be able to understand all of the details where the service provider wishes it to be known (i.e. subject to policy controls).

Jonathan Sadler

-----Original Message-----
From: [] On Behalf Of Shane Amante
Sent: Tuesday, October 02, 2012 11:57 PM
To: Joel M.Halpern
Subject: Re: [irs-discuss] Comments on Topology API use case document

Hi Joel,

Thanks for your review.  Please see below.

On Oct 2, 2012, at 8:38 PM, Joel M. Halpern <> wrote:
> Overall, this looks very helpful.
> In the terminology section, two things struck me:
> First, we probably need to consistently qualify the term "Policy Manager".  What is described in this document as the "Policy Manager" is a very interesting and powerful function.  it is a policy function.  But it is no more the entire policy manager than a security policy manager is the entire policy manager.  It seems to me that this is a discipline we need to acquire early, or we will forever find ourselves arguing about the meaning of terms when we actually agree.  (The later description of the Policy Manager edges into the broader perspective, but isn't really the same.)

We'll look at making the text in terminology section better align with the broader definition of a Policy Manager in Section 3.3.

Indeed, a "Policy Management" function is indeed critical.  Arguably, it's in the top two most critical elements of this work, IMO.  And, you're right that we need to align on definitions for what it is for fear or forever qualifying it.  The reason we chose "Policy Manager" is that it seemed the closest match to what are (likely) considered routine functions in networking today, namely, "routing policies" (cf: BGP), "security policies" (cf: ACL preventing/allowing packets through), etc.  Is that part clear?  Note, at this stage, we're depicting this as a single "Policy Manager" function; however, if this work evolves it's likely this will get broken down into sub-components (security, routing, etc.) to more precisely define their domain-specific attributes.

> I have to disagree with the definition of Multi-Layer Topology.  I agree that topologies are layered.  However, the OSI topology abstraction is absolutely wrong.  As was pointed out to me many years ago, and has become more prevalent ever sine, w run L2 VPN services on MPLS infrastructure on IP infrastructure, which is in term supported by Ethernet, some which may actually be emulated Ethernet on MPLS on ...

Hrm.  Ultimately, what I think you're describe is a perfect example of building a specific hierarchical network.  The problem is, today, we *DO NOT* have any (standards-based) way to represent the reality of those hierarchical relationships /outside of/ the data-plane and control-plane[1].  Over the years, we've clearly engineered such hierarchy directly into the routing (and, forwarding) planes of network equipment.  In addition, we've barely enumerated some attributes of *individual* protocols or network components, (cf: SNMP MIB's), but they are entirely /standalone/.  Instead, we need to take the next step.  Specifically, we need to fully enumerate attributes and, more importantly, metadata of individual control & data-plane protocols (and, related network components) using a common, standards-based *vocabulary*.  Only once we do that will it be possible to:
a) Define hierarchical relationships between network components (protocols, services, etc.), using the aforementioned attributes/metadata as filtering/selection criteria, as appropriate; and,
b) Summarize all of this vocabulary into schemas/data-models that can then be exchanged between systems that *DO NOT* (cannot *and* will not) directly participate in routing & forwarding.
Ultimately, this is the core essence of SDN/IRS.

[1] BGP recursing to an IGP for next-hop; LDP relying on IGP to determine shortest-path, etc.

> While I appreciate the importance of the Inventory function in evaluating SRLGs, I think the document should probably point out that this often depends upon physical realities not visible to any automated system.  (The number of stories of operators failing to meet diversity guarantees are legion.)

Really!?!?  ;-)

More seriously, I thought this was made clear in the first two paragraphs of Section 4.1.1, "Capacity Planning and Traffic Engineering":
   [...] Due to this inefficiency, the
   underlying physical network inventory information, (containing SRLG
   and corresponding critical network asset information), used by the
   IP/MPLS Capacity Planning and TE applications is not updated
   frequently, thus exposing the network to, at minimum, inefficient
   utilization and, at worst, critical impairments.

> I find it strange that this draft describes change application using a different paradigm than the other IRS drafts.  Is this deliberate, indicating that these use cases need a different mechanism than is elsewhere described?  (I wold have simply indicated that the Topology manager will need to apply changes, and left it there as far as this document is concerned.

I'm not sure I understand the above comment.  Can you elaborate?

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