Hi,
We have received the following liaison statement from the ITU-T Study Group
15.
There is no request for action, but we should consider these comments when
revising the PCE inter-layer drafts.
Thanks,
Adrian
===
Title: Liaison Reply to IETF PCE WG on Application of PCE to Inter-Layer
Networks
Submission Date: 2008-02-29
From: Greg Jones(ITU-T SG 15) <[EMAIL PROTECTED]>
To: IETF PCE WG([EMAIL PROTECTED],[EMAIL PROTECTED])
Cc: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED]
[email protected], [EMAIL PROTECTED], [EMAIL PROTECTED]
Reponse Contact: [EMAIL PROTECTED]
Technical Contact: [EMAIL PROTECTED], [EMAIL PROTECTED]
Purpose: For information
Thank you for bring the PCE drafts to our attention. There has been recent
work in SG15 on layer architecture and control plane discussion on
interlayer aspects.
A recent Recommendation G.800 "Unified Functional Architecture of Transport
Networks" describes the architecture of transport networks that encompasses
G.805, which is applicable to connection-oriented technologies, and G.809,
which is applicable to connectionless technologies. All three
Recommendations use the term "layer" which refers to the generation,
transport and termination of a particular type of information (or
"characteristic information"). While the use of the term has identical
meaning in many cases between SG15 documents and the PCE drafts, reading the
I-Ds with the G.800 definition of layer suggests that clarification of the
terms "higher layer" and "lower layer" would be helpful. We assume that
this is the same as the client-server relationship in G.800. One
implication of this is that a lower (server) layer does not necessarily
imply that the characteristic information transferred is larger (more bits)
than the higher (client) layer. Examples of this would be an inverse mux
layer (e.g., a VCAT layer such as VC-3-3v) to its constituent layer, or a
packet in packet case. Another implication is that the technology of the
higher and lower layer could even be the same (packet in packet).
Regarding draft-ietf-pce-inter-layer-frwk-05.txt, Q12/15 has been discussing
topology representations for multi-layer networks and two models have
emerged. The first represents a layer network with resources strictly in
that layer. If server layers can be used to connect portions of the layer
network of interest, then this can be represented as a link or node,
sometime called pseudo links or pseudo nodes. This appears to be similar to
the representation of the dotted link in the various figures of the I-D.
PCEs can have visibility of individual layers with the potential
connectivity. Multiple layer visibility would be accomplished by putting
several layers into scope of one PCE.
Another representation of the topology is one in which links from all layers
are in the graph and adaptations supported at each link end are represented.
Path computations on this model would be allowed to follow pairs of
adaptations that exist on links such that the ingress and egress layers end
up being the same. Pruning of the graph prior to, or during, the path
calculation by removing links whose ingress/egress layers are not desired,
can improve the efficiency of the calculation.
Restricting PCE visibility to one or subset of the available layers of this
second model is needed for the multiple PCE inter-layer path computation of
section 3.2. It could be done with some type of VNT manager.
Comments by section on draft-ietf-pce-inter-layer-req-06.txt are:
1. Introduction. Current text (in paragraph 3) suggests that the
optimization is required. We suggest that the requirement be phrased as "It
is important to be able to optimize network resource utilization globally"
"since there may be non-technical reasons that prevent global optimization."
Similarly, it is suggested that some brief discussion of resource ownership
be included as administrative/ownership boundaries between layers can affect
the ability to optimize. For example, if a server layer only uses the
management plane for connection establishment (no control plane).
2. Section 3.1.2. It should be clarified that when a PCC makes a request, it
should specify the layer for which it is requesting a path. If there are
several "mono" layers that could satisfy a path request, what indication is
given to the PCE about which to select?
3. Section 3.1.3. It may be helpful to have a depth indicator in the
original PCC request that limits the maximum number of adaptations allowed
in the returned path. Similarly some indicator of how many administrative
boundaries to cross could be useful to contain the cost of a potential path.
An electronic copy of this liaison statement is available at:
ftp://ftp.itu.int/tsg15opticaltransport/COMMUNICATIONS/index.html
====
You can see this liaison statement in the IETF repository at URL of the IETF
Web page:
https://datatracker.ietf.org/public/liaison_detail.cgi?detail_id=426
body text in pdf
(https://datatracker.ietf.org/documents/LIAISON/file533.pdf)
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