[PANRG] 回复: Feedback on draft-zheng-panrg-path-properties-istn-00

Dear Theresa,

Thanks for your questions and comments,

For Q1, to my understanding, ISTN can be regarded as a use case of path selection, and protocol selection, because the protocol stacks currently used in this heterogeneous network are different. Or you can take ISTN as a specific scenario.

For Q2, 3, 4 about the path and path elements, I also confused a lot about the definition of the path, so I refereed to the RFC 5137. What in my mind is that,due to the time various topology of Space networks, it is possible that there is no entire path which is available  (and that is why the DTN store the data first).

Since periodicity of space can be used to derive the future link, therefore, I agree with the idea to stretch the path to "the path exists even though a packet cannot be transmitted over it right now, but it will become available again soon". Then, for a large scale networks, a more abstract path elements which is easier to implement is needed.

But providing a fine granular path elements/properties also has pros. A fine granular path elements can provide a more flexible networking and is helpful to do the failure location and recovery.  It is a great idea to have sub-path, and would it be possible that each sub-path is able to have different path elements and path properties?  Is it possible to provide an abstract path element while ensuring the flexibility of the network by allowing each sub-path to have different path elements and path attributes?

looking forward to hearing from you!

Zheng Shaowen

发件人: Theresa Enghardt<mailto:ietf@tenghardt.net>
发送时间: 2021年3月12日 01:12
收件人: chendanyang@chinamobile.com<mailto:chendanyang@chinamobile.com>; liupengyjy@chinamobile.com<mailto:liupengyjy@chinamobile.com>; zhengshaowen@chinamobile.com<mailto:zhengshaowen@chinamobile.com>
抄送: panrg@irtf.org<mailto:panrg@irtf.org>
主题: [PANRG] Feedback on draft-zheng-panrg-path-properties-istn-00

(Sending this again because the recipients' mailbox rejected my mail to
the draft authors alias... Apologies if you get this twice.)

Dear draft authors,

Thank you for posting draft-zheng-panrg-path-properties-istn-00 and for
presenting it at the IETF 110 PANRG session!

I've read the draft and I agree that ISTN is an interesting field for
path awareness.

A few questions and comments:

1. The abstract says that the use case is "integrated space-terrestrial
networks". I think it should be more specific: Is the use case path
selection? Is it (also) something else? For path selection, does the
definition in Section 3.1 of the Path Properties draft fit your use
case, or are you missing anything from that
section? -> https://tools.ietf.org/html/draft-irtf-panrg-path-properties-02#section-3.1

2. In the introduction, the draft defines a path as a series of links
that connect a series of nodes from the source node to destination,
referring to RFC 5136. In Section 2, the draft lists path elements
corresponding to individual nodes and links. I think that's a good
starting point, but I'm wondering if a more generic definition would
work better. Then, path elements could be more abstract: Not just a
single node or link, but also an entire network, for example. This would
be useful, as the endpoint may not have insight into all path elements,
and it may be difficult to make every endpoint aware of every single
path element. So, would it be better to consider more abstract path
elements here, e.g., consider an entire network as a path element with
its own properties?

3. The draft considers properties of the entire path and properties of
each individual path element (node or link). I think it could be helpful
to consider subpaths as well, for example, the "space part" of a path or
the "terrestrial part" of a path, or the subpath traversing a specific
network. Then, a network provider could expose information about this
subpath, instead of exposing information about every individual path
element. What do you think?

4. The draft defines availability as a path property, which makes a lot
of sense to me. In contrast, the Path Properties draft defines a path as
a "sequence of adjacent path elements over which a packet can be
transmitted". Does this part of the path definition work for you? I
think the definition could be stretched to say "the path exists even
though a packet cannot be transmitted over it right now, but it will
become available again soon". Do you agree?

Thank you for the draft, and I'm looking forward to hearing more!

Best,
Theresa

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