Please consider the following comments on these drafts:
draft-ietf-ccamp-gmpls-routing-05.txt
draft-ietf-ccamp-ospf-gmpls-extensions-09.txt
Many of the comments are based on implementation experience. These comments are
marked with a (*).
Jonathan Sadler
==========
1. In section 4.4.2 of draft-ietf-ccamp-gmpls-routing-05.txt, the operations for
Packet Switch Capable (PSC) are defined. Reference is made to Minimum LSP
bandwidth
for SDH encoding. None of the examples in section 5 of
draft-ietf-ccamp-gmpls-routing-05.txt show how this field should filled.
2. The mechanism for showing relationships between server and client layers is
not
generalized*. Specifically:
- Relationships between SONET/SDH layers (ISC type: TDM) are
implicitly stated based on the Min and Max LSP bandwidth
advertised*. To quote draft-ietf-ccamp-gmpls-routing-05.txt:
"On an interface having Standard SDH multiplexing, an LSP
at priority p could reserve any bandwidth allowed by the
branch of the SDH hierarchy, with the leaf and the root
of the branch being defined by the Minimum LSP Bandwidth
and the Maximum LSP Bandwidth at priority p."
This requires node doing the route calculation to understand
the G.707 multiplexing hierarchy. Since LSP routing is source
routed, it could be the node doing the route calculation
doesn't understand G.707.
Furthermore, the G.707 multiplexing hierarchy is not a simple
tree. For example VC-11 and VC-12 can be supported over VC-3
as well as over VC-4. Consequently, the definition provided
does not allow a system to explicitly state which "branch" of
the G.707 hierarchy should be followed.
- Relationships between PSC-n (for IP switching) and SONET/SDH are
explicitly specified on the encoding type specified in the PSC-n
announcement*. However, SONET/SDH is not a single layer. It
must be possible to identify if the PSC-n layer can be carried
by a VC-11 trail, a VC-12 trail, a VC-3 trail, a VC-4 trail,
or a VC-4-nc trail.
Section 4.4.2 of draft-ietf-ccamp-gmpls-routing-05.txt tries
to deal with this in the following paragraph:
"On a PSC interface that supports Standard SDH encoding, an
LSP at priority p could reserve any bandwidth allowed by
the branch of the SDH hierarchy, with the leaf and the root
of the branch being defined by the Minimum LSP Bandwidth
and the Maximum LSP Bandwidth at priority p."
The problem is this contradicts the following paragraph:
"The Maximum LSP Bandwidth takes the place of the Maximum
Bandwidth ([ISIS-TE], [OSPF-TE]). However, while Maximum
Bandwidth is a single fixed value (usually simply the link
capacity), Maximum LSP Bandwidth is carried per priority,
and may vary as LSPs are set up and torn down."
Specifically, how does a completely available OC-48 interface
with VC-11 over VC-3, VC-3, and VC-4 get encoded? Based on
the first paragraph, the encoding would be MinLSPBW=1.5M, and
MaxLSPBW[p]=155M. Ignoring the issue that VC-11 over VC-4
ends up being shown as supported, the second paragraph states
that the MaxLSPBW[p] should be 2.5G.
Knowing the OC-48 is completely available is useful information,
as multiple VC-4s could be used in an LCAS group to support
connections that need data rates over 155M*.
- The mechanism does not support describing common muli-layer
relationships such as IP over DS1 over VC-11 or IP over DS3
over VC-3*.
- Sometimes layer relationships are described in an "inverted"
manner*. Section 5.1 of draft-ietf-ccamp-gmpls-routing-05.txt
states:
"STM-16 POS Interface on a LSR
Interface Switching Capability Descriptor:
Interface Switching Capability = PSC-1
Encoding = SDH
Max LSP Bandwidth[p] = 2.5 Gbps, for all p"
Where PSC-1 is the client of an SDH (sic) server.
Section 5.5 states:
"Interface of an opaque OXC (SDH framed) with support for
one lambda per port/interface"
" Interface Switching Capability Descriptor:
Interface Switching Capability = LSC
Encoding = SDH"
In this case, SDH is a client of a wavelength server (LSC).
However, unlike in section 5.1, the layer relationship is
inverted.
3. Layer specific attributes are not supported*. Specifically:
- It is not possible to have a link with different costs at
different layers (ex. VC-11, VC-4, VC4-4c). The link cost
is a tool used by network designers to bias traffic toward or
away from specific links.
Since different hardware platforms are optimized for different
layers, the network designer may wish to bias traffic in a layer
to use or avoid a platform that inefficiently supports a
particular layer. The announcement of a link in the layer may
still be desirable to allow for diverse routing.
- Many attributes discussed actually refer to a specific layer*.
For example SRLG can be an MS-layer attribute that is inherited
by all supported layers (VC-11, VC-12, VC-3, VC-4, VC-4-nc).
Likewise Protection mechanisms supported can be specified at
the MS-layer and the path layer.
Knowing the specific layer the attributes exist at allow for
higher quality routes to be developed*. It can also allow for
proper provisioning of upper layer functions, such as protection
hold off timers*.
- Combining layer specific attributes with layer relationships can
provide a more efficient encoding mechanism than requiring
separate link announcements per layer*.
4. The "TDM" Interface Switching Capability presumably includes
layers other than SONET/SDH, such as PDH* (DS1, DS3, E1, E3) and
G.709. The interaction with these layers needs to be defined.
5. In many cases, 8 levels of priority are not necessary*. A more
compact encoding that has a bitfield stating the priority levels
being announced would reduce the size of the announcement.
The IESG wrote:
The IESG has received a request from the Common Control and Measurement
Plane Working Group to consider publication of the following two
Internet-Drafts as Proposed Standards:
o Routing Extensions in Support of Generalized MPLS
<draft-ietf-ccamp-gmpls-routing-05.txt>
o OSPF Extensions in Support of Generalized MPLS
<draft-ietf-ccamp-ospf-gmpls-extensions-09.txt>
The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send any comments to the
iesg(_at_)ietf(_dot_)org or ietf(_at_)ietf(_dot_)org mailing lists by
2003-2-24.
Files can be obtained via
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-routing-05.txt
http://www.ietf.org/internet-drafts/draft-ietf-ccamp-ospf-gmpls-extensions-09.txt
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