Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/ietf/mpls/mpls-minutes-97aug.txt

Text File | 1997-10-10 | 10KB | 247 lines

Draft MPLS Minutes

Framework Document - Ross Callon

  <draft-ietf-mpls-framework-01.txt>

Ross made a brief presentation on the framework document.  Another
draft was submitted.  In it, several sections of the former draft were
fleshed out.  The framework document is also being used to capture
architecture discussions which have lead to particular decisions in the
architecture document.  The hierarchy and multicast sections were
pointed out as in need of further work.


MPLS Architecture - Callon, Rosen, Viswanathan

   <draft-rosen-mpls-arch-00.txt>

Eric Rosen presented the draft.  An extensive number of architectural
issues have been agreed and settled.  These include the semantics of
labels, the concept of equivalence classes, the need for hierarchy and
thus the label stack, the need for explicit routes, a preference for
topology based (actually control) label distribution vs traffic (data)
based setup.

Several important issues remain to be resolved.  These were discussed
extensively during the meeting, but with no resolution.  The
discussion did have the effect of getting a large number of people
informed on the issues.  The most prominent issues are:

  1.  Distributed vs Egress control

  The debate here is one of both versus egress only.  The observation
  was made that the two modes can interoperate in a natural way.  Arun
  on the other hand argues that egress control offers all the
  capabilities of distributed control and more, so why have two.
  In particular, egress control allows the level of aggregation to be
  consistent across the network.  Eric Rosen pointed out that this
  only holds when you want to explicitly configure granularities other
  than coarse or fine.  Those in favor of the distributed
  method point to the issues of scalability and convergence time as
  weaknesses of egress control.


  2.  Loop Prevention

  Rick Bovie presented the loop prevention scheme that is in the current
  architecture draft.  The scheme is based on the diffusion algorithm.
  It pins down routes until it can verify that a change will not result
  in a loop.  The effects of this are that for traffic moving from a
  good path to a better path will continue to use the good path.
  Traffic which is being black-holed may be black-holed longer.

  The architecture team believes that this is a workable approach with
  acceptable trade-offs.  The point of contention is whether the
  algorithm is mandatory or optional.  It was pointed out that in all
  cases except ATM with VC merge, there are other mechanisms to deal
  with looping packets.  Also, Jeremy Lawrence made a presentation
  showing that some classes of ATM switches have the capability of using
  fair queuing or fair buffering schemes to contain the effects of loops
  in the VC merge case.


  3.  LDP Transport

  It is agreed that LDP transactions need to be reliable, but there is
  no agreement on how that reliability should be achieved.


The architecture draft was accepted as the baseline text for the
working group.


LAN Encapsulation  (Ghanwani)

   <draft-srinivasan-mpls-lans-label-00.txt>

IBM presented an update of the LAN proposal to carry labels in the
destination MAC address field.  The most significant changes are:

1) switches are now required to swap labels

2) labels are placed in the source address of label update messages to
   allow bridges to learn them

The authors will continue to refine their draft.


MPLS encapsulation format  (Rosen)

   <draft-rosen-tag-stack-02.txt>

Eric presented the changes to his encaps draft, namely that the label
is now 20 bits, the tos 3 bits and the TTL 8 bits.

It was proposed that the document be accepted as baseline text.  Vijay
objected to the presence of a LAN encapsulation in that document given
that the above LAN encaps has also been proposed.  Rosen agreed to
drop the LAN section from his document (for now).  It was then agreed
that rough consensus existed to promote the draft to a working group
document.


Soft State Switching (Blake)

    <draft-viswanathan-mpls-rsvp-00.txt>

IBM presented an update of their draft and then moved that it be
accepted as baseline text.  This was objected to on the grounds that
a) there was already another existing draft on the subject and b)
their draft was a late submission.  After some discussion it was
agreed that the authors of the two drafts would work together to
create a combined document.  The two drafts appear to be quite
reconcilable.


MPLS in VC environments   (Doolan/Esaki/Demizu)

The soon-to-be-published draft addresses problems related running MPLS
in ATM networks where the LSR's are not directly connected.  In this
situation, the label (VPI/VCI) will not be preserved between the
logically adjacent LSR's.

The document points out that there are two functions of a label.
These are 1) to provide the value upon which something is switched and
2) to provide the binding between the switching operation and the
associated equivalence class.  When LSRs are directly connected the
same value is easily used for both functions.  But when ATM switches
are not directly connected, the VPI/VCI cannot be used as a binding as
the intermediate switch may not preserve the VPI/VCI from the incoming
to the outgoing link.

The authors plan to continue developing their draft.


VC pool (Noritoshi)

    <draft-demizu-vcpool-00.txt>

Setting up ATM SVCs require signaling and this will introduce delay is
setting up LSPs.  The proposal is to pre-create a pool of VCs.  When a
tag is allocated, the VC is then picked in the LDP BIND procedure.


Two modes of Explicit Label Distribution Protocol (Katsube)

    <draft-katsube-mpls-two-ldp-00.txt>

There are two modes of assigning labels, edge initiated and
distributed.  The TDP specification could be classed in both
categories where the conservative mode over ATM represents a edge
initiated approach and the liberal mode the distributed.  The
distribute approach are more light-weight as it only is link by link,
while the edge initiated approach implies end to end signaling.  Edge
initiated is desirable for controlling LSPs with arbitrary
granularity, while distributed is adequate for multicast, RSVP driven
or unicast with limited granularity.


Double Identification Label Switching  - DILS (Droz)

    <draft-droz-dils-arch-00.txt>

The goal of this draft is to have a scalable solution for n
endpoints, avoid the n**2 cross connect problem, preserve ATM traffic
characteristics, and not require hardware changes.  The DILS concept
involves the use of flow merging and connection setup as proposed by
ARIS and the use of VP merging.

Two cases are supported a symmetric and an asymmetric. The proposal is
considered complementary to ARIS, it is possible to extend with QoS
support.  It was claimed that this could be achieved with no ATM
hardware changes.

The presentation generated quite a bit of discussion.  It was pointed
out that most ATM hardware does not allow the VCI replacement function
to be independent of the VPI replacement, since these operations are
coupled in normal ATM.  This means that in a worst case, the number of
cross connects required is still n**2.


Performance Issues in VC merge MPLS Switches  (Widjaja)

     <draft-widjaja-mpls-vc-merge-00.txt>

VC merging requires that all the cells of a packet be buffered before
the first cell can be transmitted.  This changes the queueing behavior
of ATM systems.  To investigate the effects of VC merge a series of
comparative simulations was run across various utilizations and
traffic models.

The simulations showed that within normal operational limits that the
additional buffering for VC merging is minimal and that best effort
traffic would benefit from VC merging.  As utilization increases, the
additional drops due to VC merge decreases.


Multi-Protocol Labels Switching: Performance and QoS Issues (Crosby)

The requirements on improved forwarding performance has to be better
defined.  What is the metrics?  The intention is to explicitly
describe the performance requirements and include them in the Framework
document.


CSR Experimental Operation (Esaki)

The WIDE project is an experimental network in Japan using legacy routers
and CSRs all based on ATM.  Hiroshi gave an update of their progress,
pointing out the various service offerings and pointing out that the
project incorporates hardware and software from different vendors.


Scalability Issues in MPLS over ATM (Wang)

      <draft-wang-mpls-scaling-atm-00.txt>

Scalability is a major concern for MPLS over ATM.  While VC merging
address this issue, it may not be available on all platforms.  This ID
analyzes the scalability of MPLS without VC merge in terms of the size
of the VPI/VCI space.  If all 28 bits in the VPI/VCI field are
available for label switching, then the number of end to end LSPs that
can be supported is equivalent to 32k endpoints.  Given that LSPs will
end on routers rather than hosts, this is quite sufficient to support
most real networks.

Support of different services between the same end points will consume
additional VPI/VCI space.  However, the conclusion is that the
combined VPI/VCI space in ATM should still be able to support networks
of sufficient size.

In the ensuing discussion, it was pointed out that in most cases the
size of the cross connect tables of the ATM switch would be the
limiting factor.





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