FW: Comments on "Network Hierarchy and Multilayer Survivability" draft

[Dave McDysan <dave.mcdysan@wcom.com>]

Additional off-line comments received.

Dave

-----Original Message-----
From: Yong Xue [mailto:yong.xue@wcom.com]
Sent: Wednesday, September 12, 2001 12:46 AM
To: dave.mcdysan@wcom.com; wlai@att.com
Cc: Yong Xue
Subject: Comments on "Network Hierarchy and Multilayer Survivability"
draft



Hi, Dave and Wai,

Here are some of my comments on the draft. At least two of them I have
expressed at the last TE meeting in London.

1) I would suggest to change the word "Hierarchy to "Partition" in the
document. It's true that the vertical partition will generate hierarchy,
but horizontal partition based on technology, administration domain,
network architecture, usually generates domains/areas of sub-networks which
could either bear an implied hierarchical relationship (e.g.
metro-core-metro) or a peer relationship (e.g. two ISP networks)

I have attached a page of write-up on the network partition cut and pasted
from one of my writing before. Please feel free to use it if you think they
are useful.

2) In section 4.2, the document has described different "operation modes"
(detection, protection, etc.), but it did not give the description of the
order of sequence in terms of mode changes. This is needed to give reader a
sense of how the network failure will be monitored, detected and mitigated
and how to identify different phases for the failure handling, which will
impose the requirements on the signaling control.

3) The document has focused on the P&R requirement at the network layer,
but ignored the drop-side interface failure (e.g. between customer and
network border node, or a router to an OXC). This is a very important type
of network failure. This may be either inter-layer or inter-domain cases
depending on the actual network configuration.

4) In many places, the document has claim the difficulty of edge-to-edge
signaling under multi-domain (e.g. 6.2, 6.3). It's not clear to me if it is
the LSP path calculation problem due to topology information aggregation
across the domain boundary or actually the signaling problem. You need to
define exactly what the problem is with example.

5) In section 5.5, do you allow the lower layer to trigger the upper layer?
If the lower layer does not have rerouting capability (say unprotected
SONET circuit), then it should allow the SONET layer to trigger (LOS) the
IP layer and let IP to reroute immediately.

Hope these comment are useful.

I am very interested in the P&R, let me know if you need any help.

Thanks.

/Yong

Distinguished Engineer
Optical and Data Network Technology Development
WolrdCom, Inc.
email: yong.xue@wcom.com
Tel: 703-886-5358

network_partition.doc