Subject: [Pce] Liaison Statement received from ITU-T SG15

From: "Adrian Farrel" <[email-masked]>
Date: Sun, 2 Mar 2008 10:33:29 -0000

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-masked]>
To: IETF PCE WG([email-masked],[email-masked])
Cc: [email-masked], [email-masked], [email-masked]
    [email-masked], [email-masked], [email-masked]
Reponse Contact: [email-masked]
Technical Contact: [email-masked], [email-masked]

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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