Comments on Applicability Statement

["Lai, Wai S (Waisum), ALSVC" <wlai@att.com>]

The "Applicability Statement for Traffic Engineering with MPLS" draft is an
excellent summary of MPLS TE issues.  To broaden its coverage, I propose
below some further points (A, B, C, D) for consideration.  Your feedback
would be appreciated.
Thanks, Wai Sum.

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(A) In Section 1, 2nd paragraph, add the following after the 2nd sentence:

Another signaling protocol that performs similar functions is CR-LDP, the
applicability of which is described in
G. Ash, M.K. Girish, E. Gray, B. Jamoussi, and G. Wright,
   "Applicability Statement for CR-LDP", work in progress, July 2000.

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(B) After Sub-section 3.3, add a new Sub-section:

3.4 Re-optimization after restoration
 
After a network failure, a new set of LSPs can be calculated that optimize
the performance of the new topology. This re-optimization is complementary
to the fast-reroute operation used to reduce packet losses during routing
transients under network restoration.  Traffic protection can also be
accomplished by associating a primary LSP with a set of secondary LSPs,
hot-standby LSPs, or a combination thereof.

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(C) After Sub-section 4.2, add two new Sub-sections:

4.3 Capacity Engineering Aspects

Traffic engineering has a goal of ensuring traffic performance objectives
for different services.  This requires that the different network elements
be dimensioned properly to handle the expected load.  More specifically, in
mapping given user demands onto network resources, network dimensioning
involves the sizing of the network elements, such as links, processors, and
buffers, so that performance objectives can be met at minimum cost.  Major
inputs to the dimensioning process are cost models, characterization of user
demands and specification of performance objectives.

In using MPLS, dimensioning involves the assignment of resources such as
bandwidth to a set of pre-selected LSPs for carrying traffic, and mapping
the logical network of LSPs onto a physical network of links with capacity
constraints.  The dimensioning process also determines the link capacity
parameters or thresholds associated with the use of some bandwidth
reservation scheme for service protection.  Service protection controls the
QoS for certain service types by restricting access to bandwidth, or by
giving priority access to one type of traffic over another.  Such methods
are essential, e.g., to guarantee a minimum amount of resources for flows
with expected short duration, to improve the acceptance probability for
flows with high bandwidth requirements, or to maintain network stability by
preventing performance degradation in case of a local overload.

4.4 Network Measurement Aspects

To ensure that the QoS objectives have been met, performance measurements
and performance monitoring are required so that real-time traffic control
actions, or policy-based actions, can be taken.  To characterize the traffic
demands, traffic measurements are used to estimate the offered loads from
different service classes and to provide forecasting of future demands for
capacity planning purposes.  Forecasting and planning may result in capacity
augmentation or may lead to the introduction of new technology and
architecture.

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(D) In Section 5, add the following paragraph to end of the 4th paragaph:

Connection-oriented mode of operation allows the use of admission control at
the connection or flow level to avoid QoS degradation at the packet level.
This is a form of preventive control to ensure that the QoS requirements of
different service classes can be met simultaneously, while maintaining
network efficiency at a high level.  However, it requires proper network
dimensioning to keep the probability for the refusal of connection/flow
requests sufficiently low.