IPv6 Working Group                                        Rahul Banerjee
Internet Draft                                   Sumeshwar Paul Malhotra
                                                              Mahaveer M
                                                    BITS, Pilani (India)
                                                           February 2002



    A Modified Specification for use of the IPv6 Flow Label for providing
          An efficient Quality of Service using a hybrid approach.
                draft-banerjee-flowlabel-ipv6-qos-01.txt


Status of This Memo

    This document is an Internet Draft and is subject to all provisions
    of Section 10 of RFC 2026. Internet Drafts are working documents of
    the Internet Engineering Task Force (IETF), its areas, and its
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    Copyright(C) The Internet Society (2002).  All Rights Reserved.

Abstract

    This memo suggests a modified specification for defining the 20-bit
    Flow Label field using a hybrid approach that includes options to
    provide IntServ as well as DiffServ based support for Quality of
    Service. It also compares various suggested approaches for defining
    the 20-bit Flow Label field in IPv6 Base Header based on RFC 2460
    (December 1998) and draft-conta-ipv-flow-label-02.txt by Conta &
    Carpenter (July 2001). Addressing the IPv6-Multicast-QoS issues also
    Becomes possible as a consequence. The resultant mechanism is fully
    implementable and unambiguous as even the lower-level details have
    been worked out as may be required for real implementations.









Rahul Banerjee                                                 [Page 1]


Internet Draft   A Modified Specification for use of the  February 2002
                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


Table of Contents

   1. Introduction..................................................3
   2. IPv6 Flows and Flow Labels....................................3
   3. Integrated Services Flow......................................4
   4. Differentiated Services Flow..................................5
   5. Issues related with IPv6 Flow Label...........................6
      5.1 What should a router do with Flow Labels for which
          it has no state?..........................................6
      5.2 Flushing old Flow Labels..................................7
      5.3 Which datagrams should carry non-zero Flow Labels?........8
      5.4 Mutable/Non-mutable IPv6 Flow Label.......................9
      5.5 Using random numbers in setting the IPv6 Flow Label.......9
      5.6 Filtering using Flow Label...............................10
   6. Various approaches in defining IPv6 Flow Label format........10
      6.1 First approach...........................................10
      6.2 Second approach..........................................11
      6.3 Third approach...........................................12
      6.4 Fourth approach..........................................12
      6.5 Fifth approach...........................................13
   7. A modified specification for the IPv6 Flow Label and related
      implementation mechanism.....................................14
      7.1 Overview.................................................14
      7.2 Definition of first three bits of the Flow Label.........14
      7.3 Defining the remaining 17 bits of the IPv6 Flow Label....15
         7.3.1 Random Number.......................................15
         7.3.2 Using Hop-by-Hop extension header...................15
         7.3.3 Using Multi Field Classifier........................16
         7.3.4 Using the Port Number and the Protocol..............17
         7.3.5 A new structure and mechanism for the use
               of the Flow Label...................................17
   8. Possible data structures required for the implementation of
      the above design (at the router).............................22
   9. Overview of the whole design. ...............................23
      9.1 Function of the source...................................23
      9.2 Function of each relevant intermediate router............23
         9.2.1 Initial Processing..................................23
         9.2.2 Searching for the entry.............................24
         9.2.3 New Entry...........................................24
   10. Security Considerations.....................................25
   11. Conclusion..................................................25
   Acknowledgements................................................25
   References......................................................25
   Disclaimer......................................................26
   Author Information..............................................26
   Full Copyright Statement........................................26





Rahul Banerjee                                                 [Page 2]


Internet Draft   A Modified Specification for use of the  February 2002
                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


1. Introduction

    IntServ and DiffServ present two alternative solutions of resolving
    QoS problems in the Internet. This paper talks about the design of
    Quality of Service (QoS) in IPv6 that provides support for IntServ
    and DiffServ Quality of Service. Though the IPv6 Base Header has a
    20-bit Flow Label field for QoS implementation purposes, it has not
    yet been exploited. Few Internet drafts give various definitions of
    the 20-bit Flow Label in IPv6, each with its own advantages and
    disadvantages. This paper provides an analysis of these definitions
    and subsequently suggests a specification, which in view of the
    author can provide an efficient Quality of Service using a hybrid
    approach.


2. IPv6 Flows and Flow Label

    As defined in [draft-conta-ipv6-flow-label-02.txt], a flow is a
    sequence of packets sent from a particular source, and a particular
    application running on the source host, using a particular
    host-to-host protocol for the transmission of data over the
    Internet, to a particular (unicast or multicast) destination, and
    particular application running on the destination host, or hosts,
    within a certain set of traffic, and QoS requirements.

    The IPv6 Flow Label [RFC 2460] is defined as a 20-bit field in the
    IPv6 header which may be used by a source to label sequences of
    packets for which it requests special handling by the IPv6 routers,
    such as non-default quality of service or "real-time" service.
    According to RFC 2460, the nature of that special handling might be
    conveyed to the routers by a control protocol, such as RSVP, or by
    information within the flow's packets themselves, e.g., in a
    hop-by-hop option.

    The characteristics of IPv6 flows and Flow Labels given in [RFC
    2460] are rearranged as follows:

    (a) A flow is uniquely identified by the combination of a source
        address and a non-zero Flow Label.

    (b) Packets that do not belong to a flow carry a Flow Label of zero

    (c) A Flow Label is assigned to a flow by the Flow's source node.

    (d) New Flow Labels must be chosen (pseudo) randomly and uniformly
        from the range 1 to FFFFF hex. The purpose of the random
        allocation is to make any set of bits within the Flow Label




Rahul Banerjee                                                 [Page 3]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


        field suitable for use as a hash key by routers, for looking
        up the state associated with the flow.

    (e) All packets belonging to the same flow must be sent with the
        same source address, destination address, and Flow Label.

    (f) If packets of flow include a Hop-by-Hop options header, then
        they all must be originated with the same Hop-by-Hop options
        header contents.

    (g) If packets of a flow include a routing header, then they all
        must be originated with the same contents in all extension
        headers up to and including the routing header.

    (h) The maximum's lifetime of any flow-handling state established
        along a flow's path must be specified as part of the description
        of the state-establishment mechanism, e.g., the resource
        reservation protocol or the flow-setup hop-by-hop option.

(i) The source must not reuse a Flow Label for a new flow within the
        maximum lifetime of any flow-handling state that might have been
        established for the prior use of that Flow Label.


3. Integrated Services Flows

    The Integrated Services architecture [RFC 1633] defines a flow as an
    abstraction, which is a distinguishable stream of related datagrams
    that results from a single user activity and requires the same QoS.

    The IntServ architecture supports services on per flow basis. The
    IntServ model uses Resource Reservation Protocol (RSVP) as the
    standard signaling protocol to provide QoS to application flows in
    the network. It offers three classes of service:

    1. Best Effort Service (FCFS, meant for ordinary data: default).

    2. Guaranteed Service (meant for Hard Real time requirements)
       - Known upper bound on delay.
       - Reliable (lossless) delivery for IP packets that conform to
         specification.
       - Guaranteed Bandwidth support.

    3. Controlled Load service (meant for Soft Real time requirements)







Rahul Banerjee                                                 [Page 4]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    As specified in [RFC 1633], the IntServ architecture defines a
    classifier:

      For the purpose of traffic control (and accounting), each
      incoming packet must be mapped into some class; all packets in
      the same class get the same treatment from the packet scheduler.
      This mapping is performed by the classifier. Choice of a class
      may be based upon the contents of the existing packet header(s)
      and/or some additional classification number added to each packet.

      A class might correspond to a broad category of flows, e.g., all
      video flows or all flows attributed to a particular organization.
      On the other hand, a class might hold only a single flow.


4. Differentiated Services Flow

    The Differentiated Services architecture [RFC 2475] defines a flow
    or microflow as a single instance of an application-to-application
    flow of packets, which is identified by the source address, source
    port, destination address, destination port and protocol id (fields
    in the IP and host-to-host protocol headers).

    Unlike IntServ, which offers 'Per-Flow-based' QoS support, the
    DiffServ offers 'Aggregate-Flow-based' QoS support. It has the
    potential to complement the IntServ (rather than replacing it).

    As specified in [RFC 2475], the DiffServ architecture defines a
    classifier:

      as a mechanism that selects packets in a traffic stream based on
      the content of some portions of the packet header. The MF (Multi-
      Field) classifier selects packets based on the value of a
      combination of one or more header fields, such as source address,
      destination address, DS field, protocol ID, source port and
      destination port numbers, and other information.

    In order to support the Flow Label, a Differentiated services IPv6
    classifier definition should be added. This classifier would be a
    multi field classifier that would include at least the Flow Label
    and the source address as the IPv6 specification suggests.

    According to Differentiated Services architecture [RFC 2475], the
    classification fields have values according to the Service Level
    Agreements (SLA) and Traffic Conditioning Agreements (TCA),
    (Service Level Specifications - SLS and Traffic Conditioning





Rahul Banerjee                                                 [Page 5]


Internet Draft   A Modified Specification for use of the  February 2002
                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    Specification - TCS) which are contractual agreements between
    clients and the network service providers. The Flow Label based
    DiffServ MF classifier would allow the same model, and would rely
    on the Flow Label that is a field with a value or a range of values
    on which or service providers would have to agree on. These values
    will be reflected in SLAs, TCAs, SLSs and TCSs.

    The potential advantage of the DiffServ model is a substantial
    reduction in router state and a simplification in router design and
    implementation. The potential drawback to the DiffServ model is
    that all flows in the same service aggregate may receive the same
    level of service. This may force flows with very different QoS
    requirements into the same service class.


5. Issues related with IPv6 Flow Label

    According to RFC 1809, the IPv6 specification originally left open
    a number of questions, of which the following are important.

5.1 What should a router do with Flow Labels for which it has no state?

    What should be the default action of the router on receiving a
    datagram with a non-zero Flow Label for which it has no state
    information?

    Unknown Flow Labels may also occur if a router crashes and loses
    its state.

    The IPv6 specification gives the following possible solutions to
    the above-mentioned problem.

    1. The routers can ignore the Flow Label.

    2. IPv6 datagram may carry flow setup information in their options.

    In any case, it is clear that treating this situation as an error
    and, say dropping the datagram and sending an ICMP message, is
    inappropriate.  Indeed, it seems likely that in most cases, simply
    forwarding the datagram as one would forward a datagram with a zero
    Flow Label would give better service to the flow than dropping the
    datagram.

    There may be situation in which routing the datagram as if it's Flow
    Label were zero might cause the wrong result, but these situations
    can be treated as the exceptions rather than the rule. It is also
    reasonable to handle these situations using options that indicate




Rahul Banerjee                                                 [Page 6]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    that if the flow state is absent, the datagram needs special
    handling.  (The options may be Hop-by-Hop or only handled at some
    routers, depending on the flow's needs).

    Finally, [RFC 1809] and the author's view suggest that the default
    rule should be that if a router receives a datagram with an unknown
    Flow Label, it treats the datagram as if the Flow Label is zero.
    As part of forwarding, the router will examine any hop-by-hop
    options and learn if the datagram requires special handling.  The
    options could include simply the information that the datagram is
    to be dropped if the Flow Label is unknown or could contain the
    flow state the router should have.

5.2 Flushing old Flow Labels

    How does an internetwork flush old Flow Labels?

    The flow mechanism assumes that state associated with a given Flow
    Label is somehow deposited in routers, so they know how to handle
    datagrams that carry the Flow Label.  A serious problem is how to
    flush Flow Labels that are no longer being used (stale Flow Labels)
    from the routers.

    Stale Flow Labels can happen in a number of ways, even if we assume
    that the source always sends a message deleting a Flow Label when
    the source finishes using a Flow.

    1. The deletion message may be lost before reaching all routers.

    2. Furthermore, the source may crash before it can send out a Flow
       Label deletion message.

    The mechanism suggested by [RFC 1809] is to use a timer.  Routers
    should discard Flow Labels whose state has not been refreshed
    within some period of time. At the same time, a source that crashes
    must observe a quiet time, during which it creates no flows, until
    it knows that all Flow Labels from its previous life must have
    expired. (Sources can avoid quiet time restrictions by keeping
    information about active Flow Labels in stable storage that
    survives crashes). According to [RFC 1809], there are two options
    for refreshing the Flow Label and its state:

    1. The source could periodically send out a special refresh message
       to explicitly refresh the Flow Label and its state.

    2. The router could treat every datagram that carries the Flow
       Label as an implicit refresh or sources could send explicit
       refresh options.



Rahul Banerjee                                                 [Page 7]


Internet Draft   A Modified Specification for use of the  February 2002
                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    The choice is between periodically handling a special update
    message and doing an extra computation on each datagram (namely
    noting in the Flow Label's entry that the Flow Label has been
    refreshed).

    Based on the discussion mentioned above according to [RFC 1809],
    the authors of the document suggest the following approach as a
    solution to this problem:

    1. The MRU (Most Recently Used) algorithm should be used for
       maintaining the Flow Labels. At any point of time, the most
       recently used Labels alone will be kept and the remaining should
       be flushed.

    2. Before flushing a label, the router should send an ICMP message
       to the source saying that the particular label is going to be
       flushed. So the source should send a KEEPALIVE Message to the
       router saying not to flush the Flow Label in case the source
       requires the Flow Label to be used again. On the other hand, if
       the source agrees with the router to delete the Flow Label, it
       should send a GOAHEAD Message to the router. On receiving the
       GOAHEAD Message, the router immediately deletes the label for
       that particular source. These messages are also sent to all the
       intermediate routers, so that, those routers can as well flush
       the Flow Labels for that particular source.

    3. In case, the router does not receive any consent from the
       source, it will re-send the ICMP message for at most two or
       three times. If the router does not receive any reply from the
       source, it can flush the particular Label assuming that the
       Flow Label was not important for the source or any other
       intermediate router. The intermediate routers will also delete
       that Flow Label as they didn't receive any message from the
       source. The policy of sending the ICMP message to the source
       two or three times ensures the proper behavior of the method
       of flushing Flow Labels in case of packet loss. This method
       assumes that the ICMP message would not be lost all the three
       times. Hence, if the router doesn't receive any reply from the
       source even after sending the ICMP message three times, it
       deletes the label.


5.3 Which datagrams should carry non-zero Flow Labels?

    According to RFC 1809, following were some points of basic
    agreement.





Rahul Banerjee                                                 [Page 8]


Internet Draft   A Modified Specification for use of the  February 2002
                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    1. Small exchanges of data should have a zero Flow Label since it
       is not worth creating a flow for a few datagrams.

    2. Real-time flows must always have a Flow Label.

    One option specified in [RFC 1809] is to use Flow Labels for all
    long-term TCP connections. The option is not feasible in the view
    of the authors as it will force all the applications on that
    particular connection to use the Flow Labels which in turn will
    force routing vendors to deal with cache explosion issue.

5.4 Mutable/Non-mutable IPv6 Flow Label

    According to [draft-conta-ipv6-flow-label-02.txt], another issue is
    whether the Flow Label should be mutable or non-mutable, that is it
    should be read only for routers or not?

    Agreeing with the suggestions of [draft-conta-ipv6-flow-label-02.txt],
    the Flow Labels should be non-mutable because of the following
    reasons:

    1. Using mutable Flow Labels would require certain negotiation
    mechanism between neighboring routers, or a certain setup through
    router management or configuration, to make sure that the values or
    the changes made to the Flow Label are known to all the routers on
    the path of the packets, in which the Flow Label changes. On the
    other hand, the non-mutable Flow Labels certainly have the advantage
    of the simplicity implied by such a characteristic.

    2. A mutable Flow Label characteristic goes against the IPv6
    specification of the Flow Label explained in section 2 and the IPv6
    Flow Label characteristics explained in the coming sections.

5.5 Using random numbers in setting the IPv6 Flow Label

    The IPv6 specification specifies the requirement of pseudo-
    randomness in setting the value of a Flow Label as it can be used
    as hash key by routers for flow lookup.

    However, a random value in the header introduces unpredictability
    of the field. Since predictability is a necessary condition for a
    deterministic behavior, network operators may require that packets
    of a flow always have the same IPv6 content. Random values in the
    IPv6 Flow Label certainly breaks this requirement. So supporting the
    arguments given in [draft-conta-ipv6-flow-label-02.txt], the
    authors of this document suggest the IPv6 specification of having a
    random number in the Flow Label field to be relaxed.




Rahul Banerjee                                                 [Page 9]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.

5.6 Filtering using Flow Label

    If, at all, any filtering has to be done based on the Flow Label
    field in the IPv6 header, the expectation is that the IPv6 Flow
    Label field carries a predictable or well-determined value. This is
    not the case if the Flow Label has randomly chosen values.

    Again, supporting the arguments given in [draft-conta-ipv6-flow-
    label-02.txt], the authors of this document suggest that the
    problem of not being able to configure load-filtering rules, which
    are based or are including the Flow Label, can be resolved by
    relaxing IPv6 specification of having a random number in the Flow
    Label field.


6. Various approaches in defining IPv6 Flow Label format

    This section discusses the various already suggested approaches for
    defining the 20-bit Flow Label. It discusses the advantages and
    disadvantages of these approaches. Finally it tells about accepting
    or rejecting these approaches and includes the accepted approaches
    (with modifications wherever required) in the final definition of
    the Flow Label discussed in the next section.

6.1 First approach [draft-conta-ipv6-flow-label-02.txt]

    Following format can be used for the Flow Label:

        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        | 0 |   Pseudo - Random value               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        | 1 |   DiffServ IPv6 Flow Label            |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The DiffServ IPv6 Flow Label is a number that is constructed based
    on the Differentiated services "Per Hop Behavior Identification
    Code".

        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        | 1 |   Per Hop Behavior Ident. Code|  Res. |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The "Res" bits are reserved.

    The PHB ID is either directly derived from a standard differentiated
    services code point, or it is an "IANA Assigned Value".




Rahul Banerjee                                                [Page 10]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    Advantages:

    Preserves compatibility with the random number method of selecting
    a Flow Label value defined in IPv6 specification.

    Captures the differentiated services treatment intended to be
    applied to the packet.

    Unlike the value of the traffic class field, it is not locally
    mapped and hence suitable for use in an end-to-end header field.

    Disadvantages:

    It captures less information than the port number and protocol
    number normally used in multi field classifier.

6.2 Second Approach [draft-conta-ipv6-flow-label-02.txt]

    DiffServ with multi field classifier can be used in a more efficient
    and practical manner as an alternative to IntServ and RSVP. The Flow
    Label classifier is basically a 3-element tuple - source and
    destination address and IPv6 Flow Label.

    The classifier can be defined in any of the following two ways:

    C = (SA, SAPrefix, DA, DAPrefix, Flow Label).

    C` = (SA, SAPrefix, DA, DAPrefix, Flow Label min: Flow Label max).

    Incoming packet header (SA, DA, Flow Label) is matched with
    classification rules table entry C or C`.

    Advantages:

    Helps the IPv6 Flow Label to achieve, as it is supposed, in a more
    efficient processing of packets in QoS engines in IPv6 forwarding
    devices.

    Disadvantages:

    When packets are transmitted, the end nodes have to force the
    correct Flow Label in the IPv6 headers of outgoing packets or the
    first hop routers have to do this job. To accomplish these rules,
    these routers will be configured with MF classifiers. This puts
    extra computations to be done by the routers.






Rahul Banerjee                                                [Page 11]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


6.3 Third approach [draft-conta-ipv6-flow-label-02.txt]

    Includes the algorithmic mapping of the port numbers and protocol
    into the Flow Label. It reserves 12 bits for the port number and 8
    bits for the protocol.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        | Server port number   | H-to-H protocol|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Advantages:

    Classification rule is 5 or 6 element tuple format of a DiffServ MF
    classifier, containing the source and the destination address, the
    source and the destination ports, the host-to-host protocol. So no
    new classification rule format is needed.

    Disadvantages:

    It cannot differentiate among multiple instances of the same
    application running on the same two communication end nodes.

    The reduced number of bits (12 out of 16) limits the value of ports.
    12 bits can represent only the "IANA well-known ports", that is from
    1 to 1023 and a subset of "IANA registered ports", that is from 1024
    to 4095. Registered ports have values between 1024 and 65535.

6.4 Fourth approach [draft-conta-ipv6-Flow-label-02.txt]

    The field occupied by host-to-host protocol could be reduced to 1,
    as TCP and UDP are the only well known protocols.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |    TCP Server port number      |Res |0|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |    UDP Server port number      |Res |1|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The "Res" bits are reserved.

    The "TCP Server Port Number" or "UDP Server Port Number" is the 16-
    bit port number assigned to the server side of the client/server
    application.



Rahul Banerjee                                                [Page 12]


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                 Quality of Service using hybrid approach.


    Advantages:

    Again the classification field is a 5 or 6 element tuple. So no new
    classification rule is needed.

    This approach keeps 16 bits for the port number so that all the
    "IANA well-known ports" and "IANA registered ports" can be
    accommodated in these 16 bits.

    Disadvantages:

    This approach, too, cannot differentiate among multiple instances
    of the same application running on the same two communication end
    nodes.

    Reserving only 1 bit for the protocol field in the Flow Label
    restricts the use of any protocol other than TCP and UDP.

6.5 Fifth approach [draft-conta-ipv6-flow-label-02.txt]

    Header length format:

    Another possible solution is to store the length of IPv6 headers
    length that is the length of the IPv6 Base Headers and IPv6
    extension headers preceding the host-to-host or transport header.
    The length of IPv6 headers in the Flow Label value would provide
    the information, which a DiffServ QoS engine classifier could use
    to locate and fetch the source and destination ports and apply
    those along with the source and destination address and host-to-
    host protocol from the Flow Label, to match the source and
    destination address, the source and destination ports and the
    protocol identifier elements of a DiffServ MF classifier.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |Length of IPv6 headers| H-to-H protocol|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Advantages:

    "Length of IPv6 headers" allows skipping the IPv6 headers to access
    directly the host-by-host header for other purposes. This format is
    useful for classifying packets that are not TCP or UDP, and have no
    source and destination ports.

    Disadvantages:

    IPv6 header does not include "Total Headers Length" field. So
    introducing this new field in the Flow Label puts extra computation


Rahul Banerjee                                                [Page 13]


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                 Quality of Service using hybrid approach.


    to be done that may result in the processing delays.

    Including "Length of IPv6 headers" in the Flow Label does not carry
    any significance in case ESP is used for IP Security.

    This approach is discarded in this paper because of the reasons
    given above. Again, it does not carry any direct advantage in
    keeping the "Length of IPv6 headers" in the Flow Label.


7. A modified specification for the IPv6 Flow Label and related
   implementation mechanism: A hybrid approach suggested by this work

7.1 Overview

    This section specifies a modified Flow Label for IPv6 for providing
    efficient Quality of Service that utilizes the results of some of
    the works referred above, extends some of the suggested mechanisms
    and finally presents an integrated hybrid approach.

7.2 Definition of first three bits of the Flow Label

    The hybrid approach suggested in this document includes various
    approaches already mentioned in the previous section. The 20-bits
    of the Flow Label should be defined in an appropriate manner so
    that various approaches can be included to produce a more efficient
    hybrid solution. Hence, for this purpose, the first three bits of the
    IPv6 Flow Label are used to define the approach used and the next
    17 bits are used to define the format used in a particular approach.

    Following is the bit pattern for the first 3 bits of Flow Label
    that defines the type of the approach used:

    0 0 0       Default.

    0 0 1       A random number is used to define the Flow Label.

    0 1 0       The value given in the Hop-by-Hop extension header is
                used instead of the Flow Label.

    0 1 1       Multi Field Classifier is used.

    1 0 0       A format that includes the port number and the protocol
                in the Flow Label is used.

    1 0 1       A new definition explained later in this section is used.

    1 1 0       Reserved for future use.



Rahul Banerjee                                                [Page 14]


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    1 1 1       Reserved for future use.

    This definition of Flow Label includes IntServ and DiffServ and
    includes above mentioned approaches for defining the Flow Label. A
    further explanation of these options is provided in the remaining part
    of the document. The default value specifies that the datagram does
    not need any special Quality of Service.

7.3 Defining the remaining 17 bits of the IPv6 Flow Label

    The remaining 17 bits of the IPv6 Flow Label are defined based on
    the approach defined in the first three bits of the Flow Label as
    mentioned in the previous section.

7.3.1 Random Number

    As specified in IPv6 specification, a random number can be used to
    define the Flow Label. Here a 17-bit random number can be used. The
    random numbers can be generated in the range from 1 to 1FFFF. The
    advantages and disadvantages of using a random number are already
    discussed in the previous section. Keeping the IPv6 specifications
    in mind, the authors of this document believe that the random
    number can be used as one of the approaches. As other approaches
    are defined in the Flow Label, this random number approach may not
    be used whenever not feasible or efficient to do so.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |0 0 1|     Pseudo - Random value       |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7.3.2 Using Hop-by-Hop extension header

    As defined in [draft-banerjee-ipv6-quality-service-01.txt], Hop-by-
    Hop extension header can be used for defining the Flow Label in case
    IntServ is used. In this case the value in the 20-bit Flow Label is
    ignored. The modified Hop-by-Hop extension has been suggested and defined in
    the reference [draft-banerjee-ipv6-quality-service-01.txt]. In that
    document, the Hop-by-Hop extension header has been defined to be
    used with IntServ. This mechanism applies to define for DiffServ as well.


         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |0 1 0|         Don't care              |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





Rahul Banerjee                                                [Page 15]


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                 Quality of Service using hybrid approach.


7.3.3 Using Multi Field Classifier

    As mentioned in the previous section, DiffServ with MF classifier
    can be used. In that case the format of the Flow Label will be as
    shown below:

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |0 1 1|     DiffServ IPv6 Flow Label    |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    As suggested in [draft-conta-ipv6-flow-label-02.txt], this Flow Label
    can be a PHB ID (Per Hop Behavior Identification Code). In this case,
    16-bit PHB ID will be used and the remaining 1 bit is reserved for
    future use.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |0 1 1|  Per Hop Behavior Ident. Code |R|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    'R' is reserved.

    Packets coming into the provider network can be policed based on the
    Flow Label. The provider, based on the SLAs, SLSs, TCAs, TCSs agreed
    with the client, configures MF classifiers. This document specifies
    the classifier which is little different from the one suggested in the
    [draft-conta-ipv6-flow-label-02.txt]. The classifier looks like:

    C  = (SA/SAPrefix, DA/DAPrefix, Flow-Label).

    Or

    C` = (SA/SAPrefix, DA/DAPrefix, Flow-Label-Min: Range).

    The range here specifies the difference between the maximum and the
    minimum Flow Label. The significance of using the range instead of
    Maximum Flow Label is the reduced number of bits. Definitely the
    difference between the two values can be specified in a lesser number
    of bits as compared to the value itself.

    Flow-Label-Classifier:

    IPv6SourceAddressValue/Prefix:  10:11:12:13:14:15:16:17:18::1/128
    IPv6DestAddressValue/Prefix:    1:2:3:4:5:6:7:8::2/128
    IPv6 Flow Label:                50

    Or



Rahul Banerjee                                                [Page 16]


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    IPv6SourceAddressValue/Prefix:  10:11:12:13:14:15:16:17:18::1/128
    IPv6DestAddressValue/Prefix:    1:2:3:4:5:6:7:8::2/128
    IPv6 Flow Label:Range:          10:20

    Incoming Packet header (SA, DA, Flow Label) is matched against
    classification rules table entry (C or C`).

7.3.4 Using the Port Number and the Protocol

    This approach already discussed in this document in the previous
    section defines Flow Label by including the server port number and
    the host-to-host protocol. The "Server Port Number" is the port number
    assigned to the server side of the client/server applications. As
    specified in [draft-conta-ipv6-flow-label-02.txt], this approach
    reserves 16 bits for the port number and 1 bit for the protocol with
    the remaining bits reserved for the future use.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |1 0 0|    TCP Server port number     |0|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |1 0 0|     UDP Server port number    |1|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    But this approach puts the restriction on the protocol to be used
    by any application.

    As most of the application seeking Real-time service use TCP or UDP
    as the transport layer protocol, this approach would work fine in most
    of the cases. In case the application requires to use any other host-
    to-host protocol, the other methods for specifying the Flow Label,
    discussed in this section can be used. Anyhow, this method for
    specifying the port number and the protocol can be exploited further
    in the future to remove any limitations.

7.3.5 A new structure and mechanism for the use of the Flow Label

    This section describes an innovative approach to define the 20-bit
    Flow Label field in IPv6 header. By the optimal use of the bits in
    the Flow Label, this approach includes various Quality of Service
    parameters in the IPv6 Flow Label that may be requested by any
    application. The various Quality of Service parameters are:

    1. Bandwidth
    2. Delay or Latency
    3. Jitter


Rahul Banerjee                                                [Page 17]


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                 Quality of Service using hybrid approach.


    4. Packet Loss
    5. Buffer Requirements

    As packet loss and the jitter are often desired to be of minimum value
    by any application, these two parameters may not be defined in
    the Flow Label field itself. Instead, if needed, the Hop-by-Hop EH space can
    be effectively used to specify these parameters. Bits thus saved in the FL
    can be effectively used for more demanding purposes.The Quality of Service
    parameters that are to be included in the Flow Label are:

    1. Bandwidth (to be expressed in multiples of kbps).
    2. Delay (to be expressed in nanoseconds).
    3. Buffer requirements (to be expressed in bytes).

    As there are only 17 bits left, the optimal use of the bits is very
    important so as to obtain the maximum information out of those 17 bits.
    The first bit out of these 17 bits is used to differentiate between the
    hard real time and soft real time applications. This bit is set to 0 for
    soft real time applications and it is set to 1 for hard real time
    applications.

    Soft Real time applications:

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |1 0 1|0|      Flow Label               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    This service is meant for RTT (Real Time Tolerant) or soft real time
    applications, which have an average bandwidth requirement and an
    intermediate end-to-end delay for an arbitrary packet. Even if the
    minimum or maximum values specified in the Flow Label are not exactly
    met, the application can afford to manage with the QoS provided.
    These RTI applications demand weak bounds on the maximum delay over
    the network.

    Hard Real time applications:

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |1 0 1|1|      Flow Label               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    This service is meant for RTI (Real Time Intolerant) or hard Real
    Time applications, which demand minimal latency and jitter. For
    example, a multicast real time application (videoconferencing).
    Delay is unacceptable and ends should be brought as close as possible.




Rahul Banerjee                                                [Page 18]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    For this videoconference (DTVC) case, the required resource reservations
    are

      a. Constant bandwidth for the application traffic.
      b. Deterministic Minimum delay that can be tolerated.

    These types of applications can decrease delay by increasing demands
    for bandwidth. The minimum or maximum values specified in the Flow
    Label have to be exactly met for these kind of applications.

    After keeping one bit for Hard/Soft real time applications, we are
    left with 16 bits for defining the Flow Label. The remaining part
    of this section discusses how to represent the values of bandwidth,
    delay and buffer requirements.

    1. Bandwidth

    This definition specifies 6 bits out of the 16 bits to be used for
    specifying the bandwidth value. The application can demand for a
    minimum or a maximum value of bandwidth. So one bit out of these 6
    bits is used for specifying whether the application is asking for a
    minimum value of bandwidth or a maximum.

    0 - minimum expected value is specified.
    1 - maximum expected value is specified.

        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |1 0 1|0|      Flow Label               |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    In the above bit sequence, the application uses this new definition
    for defining the Flow Label, as described by the first 3 bits. The
    application is a hard real time, as evident by the 4th bit. It asks
    for a minimum bandwidth of  value that will be described in the next
    few bits.

    The 5 bits for the bandwidth can be exploited in two ways as shown
    below:

    Approach 1:

    This approach uses a simple formula to calculate the bandwidth from
    the five bits. The following values of bandwidths can be obtained for
    various bit-sequences.






Rahul Banerjee                                                [Page 19]


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                 IPv6 Flow Label for providing efficient
                 Quality of Service using hybrid approach.


    00000 - 32 kbps
    00001 - 64 kbps
    .
    .
    .
    00111 - 4 mbps
    .
    .
    .
    01111 - 1 gbps
    .
    .
    .
    11111 - 64 tbps

    The formula used here to calculate the bandwidth in decimal from
    the bit pattern is:

    Bandwidth (in decimal) = 2^B * 32.

    Where B is the decimal equivalent of the bandwidth specified in 5
    bits.

    Approach 2:

    This approach uses a hashed lookup table that maps the value mentioned in
    the bandwidth field of the Flow Label to the value already defined
    in the lookup table. These values have to be universally accepted
    and uniformly defined in all the routers and end-nodes.

    In the opinion of the authors, using first approach will result in
    saving the time for lookup in providing the quality of service. In
    event of the requirement of certain intermediate values, the second
    approach could be used. However whichever be the case, it is to be
    recommended  explicitly in this specification-field. This option may be
    indicated by an all-zero bit-string that in turn might indicate that the
    Look-up Table is embedded in the Hop-by-Hop EH Payload area as appended to
    the standard defined payload. [draft-banerjee-ipv6-quality-service-01.txt]

    2. Buffer Requirements

    This definition specifies 6 bits out of the 16 bits to be used for
    specifying the buffer value.

    00000 - 512 bytes
    00001 - 1 kbytes
    .
    .
    .


Rahul Banerjee                                                [Page 20]


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                 Quality of Service using hybrid approach.


    00111 - 64 kbytes
    .
    .
    .
    01111 - 16 mbytes
    .
    .
    .
    11111 - 1 tbytes

    The formula used here to calculate the buffer in decimal from the
    bit pattern is:

    Buffer (in decimal) = 2^B * 512.

    Where B is the decimal equivalent of the buffer specified in 5 bits.

    3. Delay

    This definition specifies 5 bits out of the 16 bits to be used for
    specifying the delay value. The application can tolerate a specified
    value of delay. So the five bits left for the delay value can be
    used in the following manner:

    00000 - 4 nanoseconds
    00001 - 8 nanoseconds
    .
    .
    .
    01000 - 1 microseconds
    .
    .
    .
    11111 - 8 seconds

    The formula used here to calculate the buffer in decimal from the
    bit pattern is:

    Delay (in decimal) = 2^B * 4 nanoseconds.

    Where B is the decimal equivalent of the delay specified in 5 bits.

         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        |1 0 1|1|0|0 0 0 0 1|0 0 0 0 1|0 0 0 0 1|
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





Rahul Banerjee                                                [Page 21]


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                 Quality of Service using hybrid approach.


    The above bit pattern tells that the application is a hard real time
    application. It asks for a minimum bandwidth of 64 Kbps at any time,
    a buffer requirement of 1 kilobyte and can tolerate a minimum delay
    of 8 nanoseconds.

8.  Possible data structures required for the implementation of the
    above design (at the router).

    Any router that tries to implement QoS maintains a QoS routing table
    and keeps track of the QoS available to each destination through the
    required number of hops. [RFC 2676]. Apart from this table, the
    router needs to keep track of the allotted QoS to each and every flow.
    This table is the ALLOTTED_QOS_TABLE.

    1. Defining the different approaches.

       enum MODEL_ID {
         RANDNUM=1,       // the random number method
         HOPTBYHOP=2,     // the hop-by-hop extension header method
         MFCLASS=3,       // the multi-field classifier
         PORT_PROT=4,     // port/protocol method
         HYBRID=5         // the hybrid approach
       };

    2. Defining the different Resource Identifiers.

       enum RES_ID {
         BANDWIDTH=0,     // bandwidth requirement
         DELAY=1,         // delay requirement
         BUFFER=2,        // buffer requirement
       };

    3. Defining the value of the resource.

       typedef unsigned int RES_VAL;

       struct RESOURCE {
         RES_ID res_identifier; //the identifier of the resource
         RES_VAL res_value;     //the 32 bit value of the resource
       };

    4. Defining the Quality of Service.

       struct QOS_INFO {
         MODEL model_id;
         RESOURCE resource;
       };




Rahul Banerjee                                                [Page 22]


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                 Quality of Service using hybrid approach.


    5. Defining the port/protocol and the flow label.

       struct port_protocol {
         unsigned port;
         unsigned protocol;
       };

       union format {
           unsigned flowlabel;
           struct port_protocol port_prot;
       };

    6.  Defining the packet information.

        struct PACKET_INFO {
           struct sockaddr_in6 src_addr;
           struct sockaddr_in6 dest_addr;
           union format format_value;
         };

    7. Defining the Alloted QoS table.

       struct ALLOTED_QOS_TABLE {
         struct PACKET_INFO packet;
         struct QOS_INFO qos;
       };

9. Overview of the whole design.

    This section describes the whole process by taking an example.
    Consider any application (like Videoconferencing or Video/Audio on
    Demand) that needs some specified QoS.

9.1 Function of the Source

    The application specifies the desired QoS and the Flow Label
    Field in the IPv6 header is filled based on the QoS asked by the
    application. The application has the flexibility of specifying
    which format it wants to use for getting the desired QoS. It can
    specify any of the formats described earlier in this document.
    The packet is then put on the network and it reaches the intermed-
    -iate routers.

9.2 Function of each relevant intermediate router

9.2.1 Initial Processing (Checks for default service)

    It gets the format used by the packet by reading the first three
    bits of the Flow Label. In case the first three bits are 000 or 110


Rahul Banerjee                                                [Page 23]


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                 Quality of Service using hybrid approach.


    or 111, it represents the default service. No specific treatment
    required for this particular packet. In this case no further processing
    of the packet is required and the default QoS is provided to the packet.
    If the value given in the first three bits is 010, no further processing
    is done and the router knows that the required QoS is specified in the
    hop-by-hop extension header.

9.2.2 Searching for the entry (In case of non-default service)

    1. The ALLOTTED_QOS table is searched based on the source address.
    2. If an entry is found, then for that particular source, a search
       is made based on the PACKET_INFO structure defined above. If all
       the information stored exactly matches with the information contained
       in the incoming packet, the IPv6 packet is processed so that the
       reserved QoS is met.

9.2.3 New Entry

1.      If an entry is not found, a new entry is made in the ALLOTTED_QOS
   table for the source and further processing of this new entry is
   done as follows.
    2. All the relevant structures defined above are filled based on the
       information contained in the packet. Information about the packet
       is stored in the PACKET_INFO structure.
    3. It reads the desired QoS from the packet's header. If the format
       specifies that a random number is used in the Flow Label field, it
       reads the RANDOM_NUMBER table and searches for the given random
       number in the packet. It reads the specified QoS from the table
       and maintains that in the QOS_INFO structure after updating the
       RESOURCE structure. It then moves onto step 6.
    4. If the format specifies that PHB ID is used in the Flow Label field,
       it reads the PHB_ID_TABLE and searches for the given ID. It reads the
       specified QoS from the table and maintains that in the QOS_INFO
       structure after updating the RESOURCE structure. It then moves onto
       step 6.
    5. If the value in the Flow Label field specifies that the PORT/PROTOCOL
       field is used in defining the QoS required by the packet, it fills the
       RESOURCE structure and the QOS_INFO structure and moves onto step 6.
    6. It then checks with the QoS Routing table, to find out if the desired
       QoS is possible to be provided to the packet. If yes, it updates the
       new entry in the ALLOTTED_QOS table in the memory or else this entry
       is removed.
    7. If any relevant router en-route is not able to guarantee the
       requested QoS, an ICMPv6 message is sent to the source and the
       other routers (that had guaranteed the QoS) are also notified of
       the same so that they delete the corresponding entry from their
       QoS tables.




Rahul Banerjee                                                [Page 24]


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                 Quality of Service using hybrid approach.


    This process happens at all the intermediate routers between the
    source and the destination.

10. Security Considerations

    The specifications of this draft don't raise any new security issues
    as the Flow Label field in the IPv6 header cannot be encrypted because
    of the known reasons. If encrypted, each in between router has to
    decrypt the header for providing the required QoS to the packet. As
    the QoS specification requires minimum delay for the packet, decrypting
    each packet's header at each router will not be a good idea because of
    the time required in processing the packet.


11. Conclusion

    This report has dealt extensively with all the suggested formats for
    defining the 20-bit IPv6 Flow Label and finally has suggested a
    hybrid approach for efficiently defining the 20-bit IPv6 Flow Label.
    The emphasis of this work is to result into a practically acceptable
    specification that could be effectively used for a reasonably long
    period of time for implementing IPv6 Quality of Service that so far
    has been elusive in absence of a clear, verifiable and complete
    specification. A separate ID is under preparation specifically building
    upon these specifications so as to explicitly address the scalabilty issues
    related to the IPv6-Multicast-QoS.

Acknowledgements

    Authors acknowledge technical inputs and support from the members of
    the "Project IPv6@BITS" at the Birla Institute of Technology and
    Science, Pilani, India, Dr. Latif Ladid of Ericsson Telebit,
    (Luxembourg); Dr. Torstern Braun of University of Bern
    (Switzerland); Dr. Pascal Lorenz of I.U.T. at the University of
    Haute Alsace, Colmar (France); Dr. S. Rao of Telscom A.G.
    (Switzerland); Dr. Bernardo Martinez of Versaware Inc. (Spain);
    Juan Quemada of UPM, Madrid (Spain) and Dr. Merce and Dr. Paulo
    at the EC and Dr. Zoubir Mammeri of IRIT (France).

    Authors gratefully acknowledge the works of many dedicated brains
    at the IETF and elsewhere, sections or extracts of which have helped
    us to shape this document.

References

    [RFC 2460]    S. Deering and Bob Hinden, "The Internet Protocol
    Specification", RFC 2460, Internet Protocol version 6 Specification.

    [RFC 1809]    C. Partridge, RFC 1809, "Using the Flow Label Field
                  in IPv6".

Rahul Banerjee                                                [Page 25]


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                 Quality of Service using hybrid approach.


    [RFC 2676]    RFC 2676, QoS Routing Mechanisms and OSPF Extensions.

    [RFC 1633]    RFC 1633, Integrated Services in the Internet
                  Architecture: an overview.

    [RFC 2475]    RFC 2475, An Architecture for Differentiated Services.

    [RFC 2676]    RFC 2676, QoS Routing Mechanisms and OSPF Extensions.

References to the work in progress

    [draft-banerjee-ipv6-quality-service-01.txt]   Rahul Banerjee, N.
               Preethi, M. Sethuraman, "Design and Implementation of
               the Quality-of-Service in IPv6 using the modified
               Hop-by-Hop Extension header - A Practicable Mechanism".

   [draft-conta-ipv6-flow-label-02.txt]     A. Conta, B. Carpenter,
               "A proposal for the IPv6 Flow Label".

    [NGNI-MMI-QoS: D1 and D2] Rahul Banerjee (BITS), Juan Quemda (UPM), P.
    Lorenz (UHA), Torsten Braun (UoB), Bernardo Martinez (Versaware):
    "Use of Various Parameters for Attaining QoS in IPv6-based
    Multimedia Internetworks", Nov. 15, 2001  and Feb. 2002 readily
    available at the URL: http://ipv6.bits-pilani.ac.in/ngni/.


Disclaimer

    The views and specification here are those of the authors and are not
    necessarily those of their employers.  The authors and their employers
    specifically disclaim responsibility for any problems arising from
    correct or incorrect implementation or use of this specification.

Author Information

    Rahul Banerjee
    3256, Centre for Software Development
    BITS, Pilani - 333031
    Rajasthan, India.

    Phone: +91-159-7645073 Ext. 335
    Email: rahul@bits-pilani.ac.in


Full Copyright Statement

    Copyright (C) The Internet Society (2002).  All Rights Reserved.




Rahul Banerjee                                                [Page 26]


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                 Quality of Service using hybrid approach.

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Rahul Banerjee                                                [Page 27]