DNSOP                                                        D. Eastlake
Internet-Draft                                               Independent
Intended status: Standards Track                                 H. Song
Expires: 22 March 2025                      Futurewei Technologies, Inc.
                                                       18 September 2024


 Expressing Quality of Service Requirements (QoS) in Domain Name System
                             (DNS) Queries
          draft-eastlake-dnsop-expressing-qos-requirements-05

Abstract

   A method of encoding quality of communication service (QoS)
   requirements in a Domain Name System (DNS) query is specified through
   inclusion of the requirements in one or more labels of the name being
   queried.  This enables DNS responses including addressing and packet
   labeling information that is dependent on such requirements without
   changes in the format of DNS protocol messages or DNS application
   program interfaces (APIs).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 22 March 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components



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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology and Acronyms  . . . . . . . . . . . . . . . .   3
   2.  Including Service Requirements in DNS Queries . . . . . . . .   4
     2.1.  Including Information in DNS Queries  . . . . . . . . . .   4
     2.2.  Encoding Service Requirements in DNS Names  . . . . . . .   5
       2.2.1.  Service Requirement TLV Encoding  . . . . . . . . . .   5
       2.2.2.  Requirements Types and Value Encoding . . . . . . . .   6
       2.2.3.  Complete QoS DNS Names  . . . . . . . . . . . . . . .   7
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Restricted LDH Label Prefixes . . . . . . . . . . . . . .   8
       4.1.1.  R-LDH Registry  . . . . . . . . . . . . . . . . . . .   9
       4.1.2.  R-LDH Expert Guidance . . . . . . . . . . . . . . . .   9
     4.2.  Requirements Label Type Codes . . . . . . . . . . . . . .  10
       4.2.1.  Coarse Requirements Label Values  . . . . . . . . . .  11
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   7.  Informative References  . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   The Domain Name System (DNS, [RFC1034] [RFC1035]) is a distributed
   database that stores data under hierarchical domain names and
   supports redundant servers, data caching, and security features.  The
   data is formatted into resource records (RRs) whose content type and
   structure are indicated by the RR Type field.  A typical use of DNS
   is that, by implementing the DNS protocol, a host can retrieve IP
   addresses stored at a domain name from DNS servers through that
   host's DNS resolver.  Many other types of data besides IP addresses
   can be stored in and returned by the DNS.














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   There are instances where different DNS answers are desired depending
   on the type of destination service to be connected to and/or the
   communication protocol to be used for that communication.  This can
   be indicated in a query through the use of designated initial labels
   beginning with the underscore codepoint ("_", 0x5F).  This was
   initially specified for the SRV RR Type [RFC2782].  For example, a
   query for type SRV to DNS name _ldap._tcp.example.com requests
   information on connecting to the example.com LDAP service with the
   TCP transport.  This underscore label prefix method has been extended
   with additional types of leading-underscore labels for use with the
   TLSA, URI, TXT, and other RR Types [RFC8552].

   Similarly, there is a need to encode different communication service
   quality requirements in DNS queries.  Then different DNS answers can
   be returned depending, for example, on whether high bandwidth or low
   delay is the most important factor in the communication.  Different
   answers could cause packets to be handled, constructed, or addressed
   differently which in turn could affect the path taken and/or the
   behavior of network switches along the communications path so as be
   to more likely to satisfy the desired communication service
   requirements.

   Such encoding into the name being queried ensures that requirements
   will be forwarded by any recursive DNS servers between the querying
   resolver and the responding authoritative server.  It also avoids any
   change in DNS protocol messages or application program interfaces
   (APIs).

   This document specifies how quality of communication service
   requirements may be encoded in DNS queries through inclusion of the
   requirements in one or more labels of the name being queried enabling
   an authoritative server to take such requirements into account in
   determining its answers.

1.1.  Terminology and Acronyms

   The following terminology and acronyms are used in this document.
   General familiarity with DNS terminology [RFC9499] is assumed.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   ABNF - Augmented Backus-Naur Form [RFC5234].

   API - Application Program Interface.



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   DNS - Domain Name System.

   LDH - Letters, Digits, and Hyphen (DNS label) [RFC5890].

   R-LDH - Restricted LDH (DNS label) [RFC5890].

   RR - Resource Record [RFC9499].  Ths unit of data stored in the DNS.

   TLV - Type, Length, Value.

2.  Including Service Requirements in DNS Queries

   This section specifies how to encode quality of communication service
   requirements in one or more domain name labels and discusses why some
   alternatives methods of including requirements in a DNS query are
   less desirable.

2.1.  Including Information in DNS Queries

   There exist methods to include information in a DNS request that are
   conveyed only from a resolver to a server, that is, one DNS hop.
   These are primarily through the inclusion of "meta-RRs" in the
   Additional Information section of a DNS request [RFC1035] including
   the OPT meta-RR [RFC6891] which can carry an extensible set of
   options.  These methods are generally not suitable to use for the
   inclusion of QoS requirements for two reasons:

   *  Typical APIs do not provide for meta-RRs to be specified on a
      query or retrieved from a response.

   *  Because meta-RRs designate transient data associated with a
      particular DNS message.  Thus, if a query is forwarded by a
      recursive DNS server, such requirements will be lost.

   Other methods of including information in a DNS query that are
   preserved when a query is forwarded are the Name, Class, and RR Type.

   Class is an additional dimension of DNS data besides Name and RR
   Type.  However, only the "IN" or Internet Class has significant
   deployment or utilization and DNS messages specifying other Classes
   are frequently blocked by middle-boxes.  Thus this dimension is not
   useful in practice.

   RR Type is only 16-bits and is already used to indicate the type of
   RRs being requested.

   This leaves only the name being queried for the encoding of service
   requirement as specified below.



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2.2.  Encoding Service Requirements in DNS Names

   Domain names consist of a sequence of labels, with labels further to
   the right being a higher level in the name hierarchy and labels to
   the left of a particular label identifying nodes in the hierarchical
   tree below that particular label.  Each label is limited to 63 octets
   in length and the zero length null label is reserved to identify the
   root node.  In a complete, valid domain name, the sum of the length
   of each label in the name plus one octet of overhead per label
   (including the terminating null label) cannot exceed 255 octets.

   Communication service requirements are encoded into names being
   queried.  This is done by including a QoS label, constructed as
   described below, in the name, usually as the left most label.  A QoS
   label consists of a special prefix followed by a sequence of one or
   more encoded TLVs indicating the QoS requirements.  The use of such a
   special prefix, which affects the interpretation of the remainder of
   the label, is similar to the use of the "xn--" prefix to indicate
   internationalized domain names [RFC5890].

2.2.1.  Service Requirement TLV Encoding

   Each TLV expressing a service requirement can be thought of as being
   binarily encoded as shown in Figure 1 although the specified encoding
   below in a DNS label is more readable.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     |     Type      |    Length     |
                     +---+---+---+---+---+---+---+---+
                     |  Value (Length Bytes Long)    .
                     .                               .
                     .                               .
                     .................................

                Figure 1: Service Requirement TLV Structure

   Type:  4-bit unsigned integer indicating the type of service
      requirement.

   Length:  4-bit unsigned integer indicating the length of the value
      associated with the service requirement in bytes.  The presence of
      an explicit length makes it possible to skip unknown /
      unimplemented service requirements.

   Value:  The value, if any, associated with the service requirement.





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   Although the DNS does not constraint the octet values within a label,
   for ease of use and due to user interface restrictions, label octets
   are commonly limited to a subset of printing ASCII [RFC0020]
   character values.  Furthermore, for name matching purposes, the DNS
   does not distinguish between octets having the upper case and lower
   case codes for an ASCII letter and in some cases the storage of a
   label in the DNS and/or its later retrieval may change the value of
   an octet in that label between the values for upper and lower case
   version of an ASCII letter [RFC4343].

   To avoid possible problems with this DNS case insensitivity or
   possibly problematic byte values such as zero, the TLV or sequence of
   TLVs is included in the DNS name label in hexadecimal notation with
   one hex digit per byte using ASCII [RFC0020].  For "A" through "F",
   either upper or lower case may be used.  Although there are more
   compact encoding that avoid most of these problems, for example as a
   customization of Bootstring similar to Punycode [RFC3492] or Base32
   [RFC4648], hexdecimal is used for simplicity, to make the encoding
   into names more easily readable for debugging and other purposes, and
   to provide ample reserved code points for future extensions.

   Such future extensions MUST use the same four prefix bytes and be
   structured as TLVs but may assign meaning to Type byte values
   reserved in this document and may extend the meaning of the Length to
   accomodate longer values by allowing letters "G" through "Z" (or "g"
   through "z") indicating Value length of 17 through 36 bytes.  Length
   byte MUST NOT be any value than "0" through "9", "A" through "Z", or
   "a" through "z" and if such a prohibited value ocurrs, that TLV and
   the reaminder of he label MUST be ignored.

2.2.2.  Requirements Types and Value Encoding

   The following types of QoS requirements are initially defined.  If
   more than one requirements TLV of the same type occurs in a DNS name,
   all but the first (leftmost) occurrance MUST be ignored.

      Coarse: A general indication of the most important service being
      sought encoded as a one byte integer patterned after the IPv4 ToS
      (Type of Service) value specified in [RFC1349].  (This is "coarse"
      in contrast with the more precise service requirements defined
      further below.)  The following coarse values are defined:

         0x00 - Normal service.

         0x01 - Minimize cost.

         0x02 - Maximize reliability.




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         0x04 - Maximize throughput.

         0x08 - Minimize delay.

         0x10 - Minimize jitter.

      Bandwidth: The bandwidth requirement is encoded as a float32
      (32-bit IEEE floating point format [ieee754] number).  The unit is
      bits per second.

      Delay: The delay requirement is encoded in 24-bit integer format.
      The unit is microseconds.

      Jitter: The jitter (i.e., delay variation) is encoded in 24-bit
      integer format.  The unit is microseconds.

      Loss Rate: This lost rate (i.e., the percentage of packet loss) is
      encoded in 24-bit integer format.  The basic unit is 0.000001%
      (i.e., one packet drop per 100 million packets), where (2^24 - 2)
      = 16.777214% is the largest loss rate defined, 2^24-1 means no
      loss rate requirement, and 0 means the drop rate should be smaller
      than 0.000001%.

   Using IEEE 32-bit floating point for the values when appropriate
   provides a compact notation that can encode up to approximately 10^38
   and down to approximately 10^-38 with 6 to 9 significant digits of
   precision [ieee754].

2.2.3.  Complete QoS DNS Names

   The on-the-wire encoding of a domain name beginning with a service
   requirement label would be as shown in Figure 2 below.  (In the DNS
   wire encoding, each label is preceded by a byte that indicates its
   length.)

    +-------+-------+-----+   +-----+--------------------------------+
    |length |prefix |TLV1 |...|TLVn |Encoded Remainder of Domain Name|
    +-------+-------+-----+   +-----+--------------------------------+

                    Figure 2: Name Wire Encoding Style 1

   Alternatively, service requirements could split among a sequence of
   two or more labels in a DNS name to be queried, as shown in Figure 3.

      +-------+------+----+   +-------+------+----+-----------------+
      |length |prefix|TLV1|...|length |prefix|TLVn|Remainder of Name|
      +-------+------+----+   +-------+------+----+-----------------+




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                      Figure 3: Name Encoding Style 2

   A display presentation of a DNS name requesting a coarse QoS
   requirement for minimum delay for communication with example.com
   would be as shown in Figure 4.

                               qs--  Prefix
                                  1  TLV Type
                                  1  TLV Length
                                 08  TLV Value
                        example.com  Remainder of domain name

              qs--1108.example.com.  Complete domain name

                         Figure 4: Example DNS Name

3.  Security Considerations

      TBD

4.  IANA Considerations

   This section conforms to [RFC8126].

   IANA is requested to create the following registries.

4.1.  Restricted LDH Label Prefixes

   LDH labels are specified in [RFC5890] as consisting of letters,
   digits, and hyphen but not beginning or ending with a hyphen.  That
   is, strings of length from 1 through 63 that match the ABNF
   (Augmented Backus-Naur Form [RFC5234]) expression for LDH below.

   *  LD = ( a-z / 0-9 )   ;letter or digit (case insensitive)

   *  HYPH = %x2D   ;hyphen / minus

   *  LDH = LD / HYPH

   *  LDH-LABEL = LD / LD 0*61LDH LD

   R-LDH (Restricted LDH) labels are specified in [RFC5890] as the
   subset of LDH-LABELs that begin with two letters/digits followed by
   two hyphens.  That is, they are LDH-LABELs that match the ABNF
   regular expression [RFC5234] below.

   *  R-LDH-LABEL = 2LD HYPH HYPH 0*58LDH LD




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4.1.1.  R-LDH Registry

   IANA is requested to create a registry on the Domain Name System
   (DNS) Parameters webpage as follows:

   Name: DNS Restricted LDH (R-LDH) Label Prefixes

   Registration Procedure: Expert Review

   Reference: [this document]

            +========+======================+=================+
            | Prefix | Description          | Reference       |
            +========+======================+=================+
            | qs--   | QoS Requirements     | [this document] |
            +--------+----------------------+-----------------+
            | xn--   | Internationalization | [RFC5890]       |
            +--------+----------------------+-----------------+

                                  Table 1

4.1.2.  R-LDH Expert Guidance

   In reviewing applications for the assignment of an R-LDH prefix, the
   Expert should keep in mind the following guidance:

   1.  The use of labels with the requested prefix must be documented in
       an Internet Draft or RFC,

   2.  not significantly duplicate the use of any other R-LDH prefix,

   3.  not require any changes to DNS protocol messages or DNS
       mechanisms such as the handling of CNAME or DNAME RRs or
       wildcards, and

   4.  provide a substanial additional capability.

   5.  Prefixes where the first or second character is any of the digits
       "0", "1", and "5" or the letters "O", "I", and "L" should not be
       assigned, due to the possibilities of confusion, unless there are
       strong reasons to use these characters.

   6.  Assignment of more than one R-LDH for a purpose is prohibited.
       The remainder of an R-LDH label MUST include an appropriate
       extension mechanism such as a version number or multiple
       unassigned code points such that later versions or extensions can
       be accodated without the assignment of a new R-LDH label.  If it
       is necessary to distinguish sub-uses under an R-LDH prefix, this



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       should be done by encoding within the R-LDH label after the
       prefix or by a further label or labels before and/or after the
       R-LDH label, such as a label beginning with underscore ("_").

4.2.  Requirements Label Type Codes

   IANA is requested to create a registry on the Domain Name System
   (DNS) Parameters webpage as follows:

   Name: DNS QoS Requirements Label Type Codes

   Registration Procedure: Expert review

   Reference: [this document]

           +=======+===========+=============+=================+
           | Code  | Hex       | Description | Reference       |
           +=======+===========+=============+=================+
           |     - | 0x00-0x2F | reserved    |                 |
           +-------+-----------+-------------+-----------------+
           |     0 |      0x30 | reserved    |                 |
           +-------+-----------+-------------+-----------------+
           |     1 |      0x31 | Coarse QoS  | [this document] |
           +-------+-----------+-------------+-----------------+
           |     2 |      0x32 | Bandwidth   | [this document] |
           +-------+-----------+-------------+-----------------+
           |     3 |      0x33 | Delay       | [this document] |
           +-------+-----------+-------------+-----------------+
           |     4 |      0x34 | Jitter      | [this document] |
           +-------+-----------+-------------+-----------------+
           |     5 |      0x35 | Loss Rate   | [this document] |
           +-------+-----------+-------------+-----------------+
           |   6-9 | 0x33-0x39 | unassigned  |                 |
           +-------+-----------+-------------+-----------------+
           |     - | 0x3A-0x40 | reserved    |                 |
           +-------+-----------+-------------+-----------------+
           | 10-15 | 0x41-0x46 | unassigned  |                 |
           +-------+-----------+-------------+-----------------+
           |     - | 0x47-0x60 | reserved    |                 |
           +-------+-----------+-------------+-----------------+
           | 10-15 | 0x61-0x66 | unassigned  |                 |
           +-------+-----------+-------------+-----------------+
           |     - | 0x67-0xFF | reserved    |                 |
           +-------+-----------+-------------+-----------------+

                                  Table 2





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4.2.1.  Coarse Requirements Label Values

   IANA is requested to create a sub-registry on the Domain Name System
   (DNS) Parameters webpage under the Requirements Label Type Codes
   registry as follows:

   Name: DNS QoS Coarse Requirements Label Values

   Registration Procedure: Expert review

   Reference: [this document]

         +==============+======================+=================+
         |    Value     |     Description      |    Reference    |
         +==============+======================+=================+
         |         0x00 | Normal service       | [this document] |
         +--------------+----------------------+-----------------+
         |         0x01 | Mimimize cost        | [this document] |
         +--------------+----------------------+-----------------+
         |         0x02 | Maximize reliability | [this document] |
         +--------------+----------------------+-----------------+
         |         0x04 | Maximize throughput  | [this document] |
         +--------------+----------------------+-----------------+
         |         0x08 | Minimize delay       | [this document] |
         +--------------+----------------------+-----------------+
         |         0x10 | Minimize jitter      | [this document] |
         +--------------+----------------------+-----------------+
         | Other Values | unassigned           |                 |
         +--------------+----------------------+-----------------+

                                  Table 3

5.  Acknowledgments

   The suggestions of the following are gratefully acknowledged:

   *  TBD

6.  Normative References

   [ieee754]  IEEE 754 WG, IEEE., "IEEE 754-2019 - IEEE Standard for
              Floating-Point Arithmetic", 2019,
              <https://standards.ieee.org/standard/754-2019.html>.

   [RFC0020]  Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <https://www.rfc-editor.org/info/rfc20>.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4343]  Eastlake 3rd, D., "Domain Name System (DNS) Case
              Insensitivity Clarification", RFC 4343,
              DOI 10.17487/RFC4343, January 2006,
              <https://www.rfc-editor.org/info/rfc4343>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, DOI 10.17487/RFC5890, August 2010,
              <https://www.rfc-editor.org/info/rfc5890>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

7.  Informative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [RFC1349]  Almquist, P., "Type of Service in the Internet Protocol
              Suite", RFC 1349, DOI 10.17487/RFC1349, July 1992,
              <https://www.rfc-editor.org/info/rfc1349>.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              DOI 10.17487/RFC2782, February 2000,
              <https://www.rfc-editor.org/info/rfc2782>.




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   [RFC3492]  Costello, A., "Punycode: A Bootstring encoding of Unicode
              for Internationalized Domain Names in Applications
              (IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003,
              <https://www.rfc-editor.org/info/rfc3492>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <https://www.rfc-editor.org/info/rfc6891>.

   [RFC8552]  Crocker, D., "Scoped Interpretation of DNS Resource
              Records through "Underscored" Naming of Attribute Leaves",
              BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019,
              <https://www.rfc-editor.org/info/rfc8552>.

   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/info/rfc9499>.

Authors' Addresses

   Donald Eastlake
   Independent
   2386 Panoramic Circle
   Apopka, FL 32703
   United States of America
   Phone: +1-508-333-2270
   Email: d3e3e3@gmail.com


   Haoyu Song
   Futurewei Technologies, Inc.
   2220 Central Expressway
   Santa Clara, CA 95050
   United States of America
   Email: haoyu.song@futurewei.com











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