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Network Working Group                    Noritoshi Demizu (SonyCSL Inc.)
Internet Draft                           Ken-ichi Nagami (Toshiba Corp.)
Expiration Date: April 1998             Paul Doolan (Cisco Systems Inc.)
                                           Hiroshi Esaki (Toshiba Corp.)
                                                            October 1997


                                VC Pool
                   <draft-demizu-mpls-vcpool-00.txt>


Status of this memo

     This document is an Internet-Draft.  Internet-Drafts are working
     documents of the Internet Engineering Task Force (IETF), its
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Abstract

   Several label switching schemes have been proposed to fuse and
   integrate Layer 2 and Layer 3.  They can be applied to various
   datalinks including intermittent links such as ATM SVC.

   Intermittent links require signaling to establish VCs before
   employing them and to release VCs after utilizing them.  Because
   signaling often introduces delays and costs, some kind of
   optimization is necessary.

   This document proposes to introduce a VC pool to reduce the delays
   and the costs of signaling.

1. Introduction

   Several label switching schemes[ARIS][RFC2098][RFC1953][RFC2105] have



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   been proposed to fuse and integrate the cost-performance and QoS
   assurance of Layer 2 devices and the flexibility and functionality of
   Layer 3 protocols.

   These label switching schemes can be applied to various datalinks
   including intermittent links such as ATM SVC.  Intermittent links
   require signaling to establish Virtual Connections (VCs) before
   employing them and to release VCs after utilizing them.  Because
   signaling often takes long time and carriers may charge each VC
   establishment, connection time and/or the amount of traffic, some
   kind of optimization is necessary to reduce the delays and the costs
   of signaling.

   This document proposes to introduce a VC pool to reduce them.


2. Proposal of VC pool

   A VC pool is where a number of established VCs is prepared a priori.
   VCs can be picked immediately from the VC pool on BIND procedures and
   will be put back to the VC pool on UNBIND procedures.  So, VCs can be
   recycled without unnecessary signaling.  If there are too many VCs in
   a VC pool, some of them may be released to reduce the costs to
   maintain these VCs.

   Each established VC in a VC pool should be associated with a VCID,
   because it is sometimes impossible to use datalink specific
   information as an identifier for a VC in a VC pool due to its small
   range.  For example, the BLLI field of ATM Forum Signaling cannot be
   used to distinguish more than 128 VCs.  However, the association
   between a VC and a VCID can be postponed until the VC will be used if
   protocol optimization is necessary.

   A Label Switching Router (LSR) may have multiple VC pools for each VC
   class.  Examples of VC classes are UBR VCs, CBR VCs, point-to-
   multipoint VCs, etc.

   The advantages of VC pool are:

     - It is possible to reduce delays and costs of signaling.
     - It hides the details of signaling procedures of each datalink from
       Label Distribution Protocols (LDPs).
     - It becomes easy to use both directions of bi-directional VCs such
       as ATM SVC with a VC pool, because each direction of a VC can be
       used independently.

   Note that the idea of VC pool does not conflict with current
   implementations that do not have a VC pool, because they can be



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   considered to have a special case of VC pool, where all VCs are
   prepared a priori and there is no need to establish VCs nor to
   release VCs.  Also note that VC pool can be applied to intermittent
   datalinks other than ATM.


3. Parameters of VC Pool

   A VC pool might have the following parameters:

      Low water mark:
        - At least this number of VCs should be prepared in the VC pool.
      High water mark:
        - If the number of VCs in the pool exceeds this number, excess
          VCs should be released under the constraint of the hold time
          parameter.
      Hold time:
        - It is required to wait for at least hold time seconds before
          releasing VCs after its use.  Releasing can be postponed
          until just before next charging time.
      Limit:
        - The total number of established VCs, including both those in
          the VC pool and those in use, must not exceed this number.
      Arrary consisting of Min and Max VCID pairs:
        - Each Min and Max VCID pair specifies a usable VCID range.
          Thus, the union of the members given in this array specifies
          the entire range of usable VCIDs.


4. Examples of Parameters

   Parameters of a VC pool should be carefully chosen to reduce delays
   and costs case by case, by considering various characteristics of
   datalinks, binding schemes, tariff, etc.  Bellow are some example
   cases.

      Case 1: ATM SVC with a traffic-driven scheme:
        - All VCs are UBR
        - Low_water = 5, High_water = 20, Hold_time = several seconds
        - Min, Max, Limit are given
        (Effective if signaling takes long time or signaling is expensive)

      Case 2: ATM SVC with a topology-driven scheme:
        - All VCs are UBR
        - Low_water = 0, High_water = 0,  Hold_time = several seconds
        - Min, Max, Limit are given.
        (Effective if signaling takes long time or signaling is
         expensive, especially when topology changes)



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      Case 3: When it is difficult to recycle VCs, for instance, VCs with
           reserved resources or point-to-multipoint VCs:
        - Low_water = 0, High_water = 0,  Hold_time = several seconds
        - Min, Max, Limit are given

      Case 4: ATM VP or PVC:
        - Low_water = High_water = Limit = the number of available VCs
        - Hold_time = 0
        - Min, Max are given.
        (VC pool need not be implemented for this case.)

   Note that case 4 is the same as current implementations that do not
   incorporate a VC pool.


Security Considerations

   Security issues are not discussed in this document.


Intellectual Property Considerations

   Toshiba Corporation may seek patent or other intellectual property
   protection for some of the aspects of the technology discussed in
   this document.  If any standards arising from this document are or
   become protected by one or more patents assigned to Toshiba
   Corporation, Toshiba intends to license them on reasonable and non-
   discriminatory terms.


Acknowledgments

   The authors would like to acknowledge valuable technical comments
   from members of LAST-WG of WIDE Project.


References

[ARIS]    A. Viswanathan, et al.,
     "ARIS: Aggregate Route-Based IP Switching",
     draft-viswanathan-aris-overview-00.txt, Mar 1997
[RFC2098] Y. Katsube, et al.,
     "Toshiba's Router Architecture Extensions for ATM : Overview",
     RFC2098, Feb 1997
[RFC1953] P. W. Edwards, et al.,
     "Ipsilon Flow Management Protocol Specification for IPv4 Version 1.0",
     RFC1953, May 1996
[RFC2105] Y. Rekhter, et al.,



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Internet Draft       draft-demizu-mpls-vcpool-00.txt        October 1997


     "Cisco Systems' Tag Switching Architecture Overview",
     RFC2105, Feb 1997
[VCID]    N. Demizu, et al.,
     "VCID: Virtual Connection Identifier",
     draft-demizu-mpls-vcid-01.txt, Oct 1997


Authors Information

   Noritoshi Demizu
   Sony Computer Science Laboratory, Inc.
   Takanawa Muse Bldg.
   3-14-13, Higashigotanda,
   Shinagawa-ku, Tokyo, 141 Japan
   Phone: +81-3-5448-4380
   E-mail: demizu@csl.sony.co.jp
   E-mail: nori-d@is.aist-nara.ac.jp

   Ken-ichi Nagami
   R&D Center, Toshiba Corporation,
   1 Komukai-Toshiba-cho, Saiwai-ku,
   Kawasaki, 210, Japan
   Email: nagami@isl.rdc.toshiba.co.jp

   Paul Doolan
   cisco Systems, Inc.
   250 Apollo Drive.
   Chelmsford, MA 01824, USA
   Phone: +1-508-244-8917
   email: pdoolan@cisco.com

   Hiroshi Esaki
   Computer and Network Division,
   Toshiba Corporation,
   1-1-1 Shibaura,
   Minato-ku, 105-01, Japan
   Email: hiroshi@isl.rdc.toshiba.co.jp














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