Hi,

I have reviewed this document (draft-ietf-opsec-v6-26) as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review.  Document editors and WG chairs should treat these comments just like any other last call comments.

This draft proposes an extension to the ALTO protocol to allow the definition of Abstract Network Elements (ANEs) on a path between two endpoints that can be considered when orchestrating connectivity between those endpoints, rather than just computing based on the abstract cost of a path.  A Path Vector allows a set of such ANEs to be defined for a path.  

Caveat:

I am generally familiar with the work of the ALTO group.  My work at Jisc, a national research and education network, includes assisting universities and research organisations optimise large scale data transfers (up to petabytes of data).

Overall:

I believe the document is generally well written, and the problem space it is addressing is one for which there is value in defining a solution, but I feel the document suffers from being too abstract and vague about what it is defining, and its consideration of practical use cases could be improved.  Thus I feel at this stage it is Not Ready for publication.

General comments:

The use cases defined are quite varied - large scale analytics, mobile and CDNs.  SENSE and LHC are not specifically data analytics use cases in the usual sense of the word, rather SENSE is a model for orchestrating network links (and capacity) between sites, and the LHC provides large scale data sets for four major experiments that are distributed and computed upon via the WLCG (worldwide large hadron collider computing grid).

For LHC, QoE is not so much about time to complete; the important point is not to have data backlogging if performance drops.

For the WLCG, two networks have evolved over many years to carry the traffic from the four main experiments; LHCOPN, the optical network, and LHCONE, the overlay network, both of which are ‘manually’ configured, and with enough capacity for the traffic thanks to regular network forward look exercises.  While a little complex to administer, other emerging disciplines have expressed interest in using LHCONE to move data, and some have established agreements (e.g. SKA, I believe).  While a means to provision capacity on demand would be attractive, the R&E networks typically have capacity, LHCOPN/LHCONE carry the LHC traffic, and bottlenecks are in the end sites (hence the evolution of the Science DMZ principles).

Some specific examples of ANEs would be very helpful.  While the document does contain examples, they are not grounded around a use case I can readily relate to, such as the orchestration of a large data flow between two sites in different R&E networks.  Can the doc show some real examples?

Section 3 talks of definitions of ANEs being “similar to” Network Elements in RFC2216, but this is vague.  The topology in Figure 5 is quite simple, as an example; something more realistic would be interesting. Ultimately, if ALTO clients have the full network topology even then they may not know about the routing that occurs by default, so implicitly there's an assumption of a capability to steer traffic to meet a request.  What is the “request” referred to in 5.1.2, for example?

It seems that the document argues that ‘bottlenecks’ are typically capacity based; do ANEs include specific links, rather than routers, firewalls, etc?   A stateful firewall can be a significant bottleneck on throughput, for example.  

In 4.2.1 it talks of ALTO client identifying bottlenecks; a little more discussion and examples of that would be useful, for practical use cases such as an international R&E data transfer.

The discussion on p.9 about multiple flows is a little odd; in practice in R&E networks large transfers use tools like GridFTP which uses multiple parallel TCP flows, such that loss on individual flows does not severely impact throughput.  Of course, BBR also reduces this concern.

Is the use of ALTO designed for single domain, or can it span multiple domains?  It seems the latter, given the definition of ANE domains, but for the latter there is no specific model for the common definition of ANEs.

Given the definition of ANEs and PVs, how is traffic then orchestrated or optimised?  Some pointers here would be useful.  SENSE may be one example.  From my own discussion with people involved with SENSE (and AutoGOLE which uses it) there is as yet no use of ALTO (rather SENSE uses its own methods to orchestrate based on intent-based descriptors), but it is something that may be considered in the future.

What of non-ALTO traffic on the same links; is the approach to reserve x% capacity of a link for ALTO orchestrated traffic (the SENSE approach, I believe)?

Tim