(Submitted on behalf of Stephen Shew)
I would like to raise an issue with draft-ietf-ccamp-rfc5787bis-05.txt. The
issue does not affect the proposed sub-TLVs or their semantics, so it would not
affect an implementation. I believe some statements in the document should be
edited to avoid confusion over ASON terminology as defined in ITU-T
Recommendation G.8080, for which I am editor.
It concerns the definition of "ASON reachability" which changed during the
course of the document from being a transport plane address, the SubNetwork
Point Pool (SNPP) space, to the Signalling Control Network (SCN) address space.
I think the root of the issue is that the visibility of the three address
spaces described in ASON (G.8080) is not always made clear when discussing
using OSPF for ASON Routing. Section 3 of G.8080 states that:
There are three categories of identifiers used for ASON routing
(G7715.1): transport plane names, control plane identifiers for
components, and Signaling Communications Network (SCN) addresses.
In -03 of the document, the term SNPP was used. This is the SubNetwork Point
Pool space that describes the data plane and is defined in G.8080 Section 10.
It names the subnetwork (and/or containing subnetworks) to which Subnetwork
Points (SNPs) are scoped. From G.8081: "The SNP is an abstraction that
represents an actual or potential underlying connection point (CP) (or
connection termination point (CTP)) or an actual or potential termination
connection point (TCP) or trail termination point (TTP). Several SNPs (in
different subnetwork partitions) may represent the same TCP or CP."
In concrete terms, an SNPP would name an OTN switch, and an SNP would be a
label identifying an ODU0. For the topology of the transport plane, SNPP and
SNPP link names are used. Path computation is performed over such a topology.
If a path can be computed between two SNPPs, they are reachable in ASON terms.
For example, and ingress OTN switch for an ODU1 connection that terminates on
an egress OTN switch.
The Signalling Control Network (SCN) is a separate network over which control
messages are sent. It has a topology independent of the transport plane. Path
computation on the SCN address space is used to connect SCN address. SDH/OTN
networks often have a separate IP network as the SCN network and the topology
of the SCN network does not have to follow the topology of the transport
network.
ASON Control Plane Component identifiers are the third name space and identify
routing and signalling instances. It is expected that they form adjacencies
over the SCN. The topology of the adjacencies is independent of the SCN and
transport plane topologies. "Reachability" between two control plane
components would be some sequence of adjacencies. It is entirely possible to
have two separate control planes running over the same SCN network, or one
control plane that uses several SCNs. For example, imagine some OSPF instances
whose adjacencies were all targeted and each adjacency traversed a separate
private IP network. The OSPF instances would need to identified by a common
address space so that they are distinguished from each other, but the TE
interfaces could have overlapping IPv4 values because they would be in
different private IP network spaces.
What makes the discussion of "TE router ID" confusing is that as applied to a
transport network, every node gets a "TE router ID" and so it can be used in
the transport topology for path computation. In that sense it is "reachable"
in the dataplane. However, it is also (I think) an address that is implicitly
in the SCN space in some implementations and so it takes on a dual meaning of
"reachability" at the IP layer as in the sentence from the I-D "This TLV
specifies a stable OSPF TE node IP address, i.e., the IP address is always
reachable when there is IP connectivity to the associated OSPF TE node.". If a
router were instantiated without any routing protocols, as in one form of
Software Defined Networks (SDNs), an identifier would be needed for the node
itself so that path computation in a centralized controller could form the
router data plane topology.
Suggested changes to the draft are:
In section 3, third paragraph: "In the context of OSPF Traffic Engineering
(TE), an ASON transport node corresponds to a unique OSPF TE node. An OSPF TE
node is uniquely identified by the TE Router Address TLV [RFC3630]. In this
document, this TE Router Address is referred to as the TE Router ID, which is
in the ASON SCN name space." However, G.8080 distinguishes between the
transport node and its associated control plane components, esp. the Routing
Controller. It is the control plane component that is accessed through the SCN
rather than the transport node itself.
I propose changing the statement to say: "In this document, this TE Router
Address is referred to as the TE Router ID, which is in the ASON SNPP name
space."
Alternatively, we could just delete the sentence "In this document, this TE
Router Address is referred to as the TE Router ID, which is in the ASON SNPP
name space.".
In section 4, first paragraph, reachability of endpoints in the transport plane
is described as follows:
"In ASON, reachability refers to the set of endpoints reachable in the
transport plane by an associated ASON transport node. Reachable entities are
identified in the ASON SCN name space." As discussed above, only the control
plane components are accessed through the SCN, not the transport nodes
themselves. Entities that are reachable in the transport plane are identified
through ASON SNPPs rather than ASON SCN addresses. Therefore I suggest
removing the second sentence completely so that it reads simply "In ASON,
reachability refers to the set of endpoints reachable in the transport plane by
an associated ASON transport node. "
Finally, in section 6.2, first paragraph following the format diagram, it is
stated: "If it is not included in a Node Attribute TLV or a value of 0 is
specified for the Local TE Router Identifier, the Note Attribute TLV will not
be used for determining ASON SCN reachability."
Again, the text should be edited to make the distinction between transport
plane and SCN clearer, I suggest modifying the statement to refer to "ASON
reachability" rather than "ASON SCN reachability". The statement would read as
follows (also correcting the spelling of the TLV):
"If it is not included in a Node Attribute TLV or a value of 0 is specified for
the Local TE Router Identifier, the Node Attribute TLV will not be used for
determining ASON reachability."
Stephen Shew
-----Original Message-----
From:
ietf-announce-bounces(_at_)ietf(_dot_)org<mailto:ietf-announce-bounces(_at_)ietf(_dot_)org>
[mailto:ietf-announce-bounces(_at_)ietf(_dot_)org] On Behalf Of The IESG
Sent: Friday, July 20, 2012 11:19 AM
To: IETF-Announce
Cc: ccamp(_at_)ietf(_dot_)org<mailto:ccamp(_at_)ietf(_dot_)org>
Subject: Last Call: <draft-ietf-ccamp-rfc5787bis-05.txt> (ASON Routing for
OSPFv2 Protocols) to Proposed Standard
The IESG has received a request from the Common Control and Measurement Plane
WG (ccamp) to consider the following document:
- 'ASON Routing for OSPFv2 Protocols'
<draft-ietf-ccamp-rfc5787bis-05.txt> as Proposed Standard
The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
ietf(_at_)ietf(_dot_)org<mailto:ietf(_at_)ietf(_dot_)org> mailing lists by
2012-08-17. Exceptionally, comments may be sent to
iesg(_at_)ietf(_dot_)org<mailto:iesg(_at_)ietf(_dot_)org> instead. In either
case, please retain the beginning of the Subject line to allow automated
sorting. This is a four- week last call period because it spans the IETF-84
meeting.
Abstract
The ITU-T has defined an architecture and requirements for operating
an Automatically Switched Optical Network (ASON).
The Generalized Multiprotocol Label Switching (GMPLS) protocol suite
is designed to provide a control plane for a range of network
technologies including optical networks such as time division
multiplexing (TDM) networks including SONET/SDH and Optical Transport
Networks (OTNs), and lambda switching optical networks.
The requirements for GMPLS routing to satisfy the requirements of
ASON routing, and an evaluation of existing GMPLS routing protocols
are provided in other documents. This document defines extensions to
the OSPFv2 Link State Routing Protocol to meet the requirements for
routing in an ASON.
Note that this work is scoped to the requirements and evaluation
expressed in RFC 4258 and RFC 4652 and the ITU-T Recommendations
current when those documents were written. Future extensions of
revisions of this work may be necessary if the ITU-T Recommendations
are revised or if new requirements are introduced into a revision of
RFC 4258. This document obsoletes RFC 5787 and updates RFC 5786.
The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-ccamp-rfc5787bis/
IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-ccamp-rfc5787bis/ballot/
No IPR declarations have been submitted directly on this I-D.
Stephen Shew | Director, Standards
sshew(_at_)ciena(_dot_)com<mailto:jdoe(_at_)ciena(_dot_)com> | 3500 Carling
Ave. | Ottawa CANADA K2H 8E9
Direct +1.613.670.3211