rfc2340.txt

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   From any point in a logical network, there may be multiple paths to
   reach a specific egress node. If VNS routing determines that more
   than one of these paths are of equal cost, VNS packets will be load
   spread between two of them.

   Equal cost multipath forwarding is supported not only on ingress
   nodes but on tandem nodes as well. Each packet on an ingress node is
   tagged with an equal cost multipath key. This key is acted upon at
   the ingress node and stored in the VNS header to be used on tandem
   nodes.

   The equal cost multipath key is calculated by running an algorithm
   over the source and destination network layer addresses. This means
   that, in a stable network, any given stream will always take the same
   path through a Logical Network avoiding the problems that misordering
   would otherwise cause.

8.2 Trunk Load Spreading Between Neighbors

   VNS allows multiple trunks to be configured between neighboring VNS
   nodes. VNS routing considers the aggregate bandwidth of those trunks
   to determine the metric between the nodes. Also, VNS load spreads its
   traffic amongst those trunks.

   As is the case with equal cost multipaths, the trunk load spreading
   key is calculated on the ingress node from an algorithm run over the
   source and destination network layer addresses. The key is then
   stored in the VNS header to be used on all tandem nodes through the
   Logical Network.






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RFC 2340        Nortel's Virtual Network Switching (VNS)        May 1998


9. Class of Service

   At the ingress to a VNS Network, packets are classified according to
   the Class of Service (Cos) policy settings. The CoS differentiation
   is achieved through different  Emission and Discard priorities. The
   semantics of the classification is carried in the VNS label (DP and
   COS Fields described in Section 3) to be used at the ingress node as
   well as all tandem points in the VNS network to affect queuing and
   scheduling decisions.

10. VNS Migration Strategies

   VNS supports several upper layer protocols such as IP, IPX, and
   Bridging. Therefore, it is a multiprotocol label switching
   architecture. In addition, VNS  is not tied to a particular L2
   technology. It runs on cell (e.g., ATM) trunks, frame trunks, or a
   mixture of both.

   VNS can be gradually introduced in a network. It can be implemented
   between switching elements interconnected by point to point links.
   Each of the switching nodes can run layer 3 routing simultaneously
   with packet switching. VNS also allows for the interconnection of VNS
   clouds through an ATM VC.

   Since VNS can run on a mixture of Frame and Cell trunks, it allows
   for the graceful migration of the frame links to ATM without
   requiring a complete immediate overhaul.

11. Summary

   VNS addresses scalability problems in several ways:

      1. By a generally distributed design which doesn't
         require a Label Distribution Protocol, or servers of any kind.
      2. By providing an efficient, distributed multicast mechanism.
      3. By allowing administrators to control the size of a
         Logical Network, limiting traffic to a subset of the physical
         topology.
      4. By reducing layer 3 address space/subnet requirements in the
         WAN which reduces the routing table size.

   VNS provides redundancy transparent to the network layer protocol by
   managing the network of trunks independently of the network layer.
   VNS will automatically discover any topology changes and re-route
   traffic accordingly.






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RFC 2340        Nortel's Virtual Network Switching (VNS)        May 1998


   VNS eases network administration by dynamically keeping track of
   which trunks are available for each LNN.  Network administrators
   don't have to configure VNS or network layer addresses on a per link
   basis.  Network layer addresses only have to be assigned on a per
   Logical Network basis.  For nodes which will only be tandem VNS
   nodes, network layer addresses aren't required at all.

   Since VNS traffic is constrained within an LNN, administrators have
   control of where VNS traffic is allowed to flow.

   Finally, VNS supports switching of several Upper Layer Protocols and
   supports  several media (cell and Frame) or a mixture thereof.
   Switching in the core of the WAN removes the need for routers and
   improves the performance due to a reduction in the  number of fields
   that need to processed.

12. Security Considerations

   Logical networks provide a means of restricting traffic flow for
   security purposes. VNS also relies on the inherent security of the L2
   media such as an ATM Virtual Circuit.

13. Acknowledgments

   The authors would like to acknowledge the valuable comments of Terry
   Boland, Pierre Cousineau, Robert Eros, Robert Tomkins, and John
   Whatman.
























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RFC 2340        Nortel's Virtual Network Switching (VNS)        May 1998


14. Authors' Addresses

   Bilel Jamoussi
   Nortel (Northern Telecom), Ltd.
   PO Box 3511 Station C
   Ottawa ON K1Y 4H7
   Canada

   EMail: [e-mail]


   Dwight Jamieson
   Nortel (Northern Telecom), Ltd.
   PO Box 3511 Station C
   Ottawa ON K1Y 4H7
   Canada

   EMail: [e-mail]


   Dan Williston
   Nortel (Northern Telecom), Ltd.
   PO Box 3511 Station C
   Ottawa ON K1Y 4H7
   Canada

   EMail: [e-mail]


   Stephen Gabe
   Nortel (Northern Telecom), Ltd.
   PO Box 3511 Station C
   Ottawa ON K1Y 4H7
   Canada

   EMail: [e-mail]















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RFC 2340        Nortel's Virtual Network Switching (VNS)        May 1998


15.  Full Copyright Statement

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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