



Internet Engineering Task Force                                   A. Zhu
Internet-Draft                                                  Y. Zhang
Intended status: Experimental                                 R. Broberg
Expires: 4 May 2026                                              L. Feng
                                                               JM. Smith
    University of Pennsylvania School of Engineering and Applied Science
                                                         31 October 2025


  Quantum Datagram Control Protocol (QDCP) for IP Optical Environments
                         draft-zhu-qirg-qdcp-00

Abstract

   This document specifies the Quantum Datagram protocol a lightweight
   transport protocol designed to operate over UDP in IP optical
   environments.  QDCP (formerly QFCP) enables the transmission of
   control- plane parameters required for transporting quantum
   information and associated optical configurations, including
   polarization stabilization, timestamp alignment, ROADM port
   selection, and spectral parameters.  The protocol uses a Type-Length-
   Value (TLV) structure to support versioning and extensibility and is
   prototyped for the transport of third-order nonlinear generated
   quantum information on IP optical infrastructure.  This work is
   motivated by recent demonstrations of a classical-decisive quantum
   internet using integrated photonics.

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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   This Internet-Draft will expire on 4 May 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   3
   3.  QDCP Packet Format  . . . . . . . . . . . . . . . . . . . . .   3
   4.  TLV Structures  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Example Use Cases . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Dynamic ROADM Configuration . . . . . . . . . . . . . . .   5
     5.2.  Real-Time Error Mitigation  . . . . . . . . . . . . . . .   5
     5.3.  Hybrid IP Packet Orchestration  . . . . . . . . . . . . .   5
     5.4.  Timestamp Alignment . . . . . . . . . . . . . . . . . . .   6
     5.5.  WDM/TDM Extensions  . . . . . . . . . . . . . . . . . . .   6
   6.  Example TLV Blocks  . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  0x08: Error Mitigation Vector . . . . . . . . . . . . . .   6
   7.  UDP Port Assignment . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Hybrid quantum-classical networking is emerging as a foundation for
   distributed quantum information processing.  Recent experiments on
   commercial fiber networks have shown that quantum states can be
   dynamically routed by classical headers embedded in IP-like packets.
   To configure downstream optical switches and mitigate errors, a
   lightweight, extensible protocol is needed.  QDCP is intended to be
   that protocol, running over UDP [RFC768] and supporting modular Type-
   Length-Value (TLV) extensions.  QDCP supports applications aligned
   with scenarios defined by the IRTF Quantum Internet Research Group
   (QIRG) [RFC9583].






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   By the no-cloning theorem, quantum information cannot be copied,
   buffered, or retransmitted without disturbing the underlying state.
   In the present work, where practical quantum memories and error-
   corrected storage are not yet available at network scale, quantum
   information is therefore transmitted as a datagram: loss is terminal,
   and retransmission is physically meaningless.  The accompanying
   classical control header is sent without guaranteed delivery.  If the
   classical information is lost in transit, the associated quantum
   state is presumed lost as well.  Future implementations may leverage
   advances in quantum memory, error correction, or entanglement-
   assisted repeaters to decouple classical and quantum reliability,
   potentially incorporating reliable classical transports such as QUIC
   or TCP for control-plane robustness.

1.1.  Requirements Language

   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.

2.  Protocol Overview

   QDCP defines a fixed header followed by TLV-encoded fields.  The
   header carries version and flag information; TLVs encode control-
   plane parameters such as quantum link layer protocol, polarization
   state, center frequency, or error-mitigation metadata.  UDP provides
   transport simplicity and compatibility with existing IP
   infrastructure.  Unknown TLVs MUST be ignored to ensure forward
   compatibility.

   While UDP imposes a maximum datagram length (65,535 bytes), this
   limitation has no impact on the amount of quantum information
   conveyed.  The quantum payload is not encapsulated within the UDP
   packet itself but is passed through at the physical layer, with UDP
   carrying only the associated classical control header.  Thus the UDP
   size constraint applies solely to the metadata, not to the optical or
   quantum state being transported.

3.  QDCP Packet Format

   The QDCP packet consists of a fixed header followed by a sequence of
   Type-Length-Value (TLV) payloads.

   Packet Format:





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    0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Version  | Flags |          Length            |   Reserved   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                         TLV Payloads                         ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: QDCP Packet Header and TLV Payloads

   *  Version (4 bits): Protocol version number (currently 0x1).

   *  Flags (4 bits): Reserved for future use.

   *  Length (16 bits): Specifies length of entire packet.

   *  Reserved (8 bits): Set to zero; ignored on receipt.

   *  TLV Payloads: Sequence of variable-length TLVs.

4.  TLV Structures

   Each TLV consists of a type, a reserved field, a length (in bytes),
   and a value.  The length specifies the length of the value, not the
   entire TLV.  All fields are in network byte order.

   TLV Format:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Type     |    Reserved   |           Length              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         Value (variable)                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                            Figure 2: TLV Format

   Defined TLV Types:










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    Type   Name                       Value Format
    ----   -------------------------  ------------------------------
    0x01   Quantum Protocol           32-bit int (e.g., encoding)
    0x02   Polarization State         32-bit float
    0x03   Timestamp of Origination   128-bit int (ps)
    0x04   ROADM Output Port ID       32-bit int
    0x05   Quantum Packet Delay       128-bit int (ps)
    0x06   Duration of quantum        128-bit int (ps)
           information
    0x07   Center Frequency (GHz)     32-bit float
    0x08   Optical Linewidth (GHz)    32-bit float
    0x09   Polarization Correction    Variable Polarizations

                   Figure 3: Initial TLV Type Assignments

5.  Example Use Cases

   This section illustrates how the Quantum Datagram Control Protocol
   (QDCP) can be applied in practical network environments.

5.1.  Dynamic ROADM Configuration

   QDCP packets carrying TLVs for ROADM Output Port ID ([RFC4950]) allow
   classical headers to steer entangled photons through commercial
   reconfigurable optical add-drop multiplexers (ROADMs).  This enables
   dynamic path selection across metro and campus-scale optical
   networks, as demonstrated in recent hybrid IP packet experiments
   ([Zhang2025]).

5.2.  Real-Time Error Mitigation

   TLVs containing polarization parameters and error-mitigation vectors
   (Type 0x08) allow active compensation of SU(2) rotations induced by
   deployed fiber ([ZhangSM2025]).  Classical light encodes detection
   signals in the header, enabling dynamic updates to the error
   mitigator without disturbing quantum states.

5.3.  Hybrid IP Packet Orchestration

   The QDCP framework aligns with the IRTF QIRG goals and use-cases
   ([RFC9583]).  By transporting control-plane metadata in TLVs,
   classical headers and quantum payloads can be synchronized and routed
   through existing IP infrastructure.








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5.4.  Timestamp Alignment

   TLVs carrying local and photon arrival timestamps can provide
   synchronization similar to RTP ([RFC3550]).  This enables sub-
   nanosecond correlation of entangled photon arrivals across nodes.
   The mechanisms to achieve such precision for distributed-clock
   synchronization (e.g. NTP, PTP, White Rabbit) are out of scope for
   this document.

   TLVs carrying "Duration of Quantum Information" specify the period
   during which the optical bypass must remain active to support quantum
   information transport.  After the indicated duration expires, the
   bypass is automatically reverted back to its normal state to resume
   classical control-plane processing.

5.5.  WDM/TDM Extensions

   Additional TLVs may specify per-wavelength parameters, enabling
   wavelength-division multiplexing (WDM) or time-division multiplexing
   (TDM) of entangled states ([ZhangSM2025]).  This supports scaling of
   quantum internet bandwidth across multiple frequency channels while
   preserving compatibility with ITU-T DWDM grids ([ITU-T.G694.1]).

6.  Example TLV Blocks

   This section specifies the TLV structure for specific TLV types.

6.1.  0x08: Error Mitigation Vector

   Error mitigation can be done by sending different known polarization
   states with respect to the output of the chip and identifying the
   SU(2) transformation applied to these states by the fiber once they
   reach the receiver ([ZhangSM2025]).  To account for hardware
   limitations in preparing certain known states, the reserved bits in
   the TLV will be used to specify which polarization states are
   transmitted.  For simplicity, assume transmitted states must be in a
   horizontal, vertical, diagonal, anti-diagonal, right-circular, or
   left-circular polarization.  The transmitted states can then be
   specified by setting the bit corresponding to a specific polarization
   to one (1), with the following mapping from bit to polarization.

   Polarization to Reserved Bit Mapping:









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                          Bit   Polarization
                          ---   ------------------
                           0    Horizontal
                           1    Vertical
                           2    Diagonal
                           3    Anti-Diagonal
                           4    Right-Circular
                           5    Left-Circular

              Figure 4: Polarization to Reserved Bit Mappings

   Using this mapping, if eg. the desired transmitted polarization
   includes only Horizontal and Right-Circular, then the reserved byte
   would be "00010001" or equivalently "0x11".

   To accurately identify the SU(2) transformation, multiple repetitions
   of each transmitted polarizations is necessary.  Zhang et al.
   experimentally determined that eight (8) repetitions of each
   polarization is sufficient.  They were also able to recover the full
   SU(2) transformation with only two polarizations.

   Thus, to balance stability and simplicity, the length of the Error
   Mitigation TLV is limited to 32 bits, allowing up to four (4)
   different polarizations each repeated eight times.  The order that
   the polarizations are sent will be fixed by their bit position in the
   Polarization to Reserved Bit Mapping table such that a polarization
   with a greater bit position will be sent before one with a smaller
   bit position.  If the number of polarizations flagged in the reserved
   byte exceeds 4, the behavior is undefined.

   If the number of polarizations flagged in the reserved byte is less
   than 4, then in the spirit of [RFC8701], we define GREASE8 as the
   following set of octaves:

                          {0x0A, 0x1A, 0x2A, 0x3A,
                           0x4A, 0x5A, 0x6A, 0x7A,
                           0x8A, 0x9A, 0xAA, 0xBA,
                           0xCA, 0xDA, 0xEA, 0xFA}

                          Figure 5: GREASE8 Values

   To fill the extra bytes after sending the desired polarizations, the
   sender MUST randomly select from these GREASE8 values to pad the end
   of the packet.  The receiver MUST ignore the GREASE8 values upon
   receipt.

   For concreteness, consider the example where only Horizontal and
   Right-Circular polarizations are transmitted for error correction.



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   Example Error Mitigation TLV Structure:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      0x08     |     0x11      |            0x20               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    R * 0x08   |    H * 0x08   |    GREASE8   |     GREASE8    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 6: Error Mitigation TLV for Right-Circular and Horizontal
        Polarizations. 0x08 is the TLV type. 0x11 is the hexadecimal
        encoding of 00010001 in binary, which specifies that Right-
     Circular and Horizontal polarizations will be sent in this packet
       according to Figure 4. 0x20 Specifies the length of the value,
      which is 32 bits.  The actual value then contains eight bits of
          Right-Circular polarized light followed by eight bits of
       Horizontal polarized light, followed by two randomly selected
                              GREASE8 values.

7.  UDP Port Assignment

   Implementations SHOULD use a configurable default port.  IANA is
   requested to allocate a well-known port for QDCP.

8.  IANA Considerations

   - Allocate a UDP port for QDCP.

   - IANA is also requested to establish a QDCP TLV Types Registry with
   initial assignments as defined in Section 4.

9.  Security Considerations

   QDCP inherits the risks of UDP: spoofing, injection, replay.  It MUST
   be run in trusted environments or protected by DTLS/IPsec.  TLVs may
   reveal network state information and MUST be protected if
   confidentiality is required.

   Use of DTLS/IPsec and reliable classical transport mechanisms are
   reserved for future work.










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10.  Acknowledgements

   The authors would like to thank Steve Schwartz and Wes Harding for
   their constructive feedback and detailed comments.  Their suggestions
   helped broaden the scope of this document beyond the initial
   implementation and guided refinements to the protocol design and
   terminology.

11.  References

11.1.  Normative References

   [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>.

   [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>.

   [RFC768]   Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [RFC4950]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "ICMP
              Extensions for Multiprotocol Label Switching", RFC 4950,
              DOI 10.17487/RFC4950, August 2007,
              <https://www.rfc-editor.org/info/rfc4950>.

   [RFC8701]  Benjamin, D., "Applying Generate Random Extensions And
              Sustain Extensibility (GREASE) to TLS Extensibility",
              RFC 8701, DOI 10.17487/RFC8701, January 2020,
              <https://www.rfc-editor.org/info/rfc8701>.

11.2.  Informative References

   [RFC9583]  Wang, C., Rahman, A., Li, R., Aelmans, M., and K.
              Chakraborty, "Application Scenarios for the Quantum
              Internet", RFC 9583, DOI 10.17487/RFC9583, June 2024,
              <https://www.rfc-editor.org/info/rfc9583>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/info/rfc3550>.





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   [ITU-T.G694.1]
              International Telecommunication Union (ITU-T), "Spectral
              grids for WDM applications: DWDM frequency grid",
              Recommendation G.694.1, February 2012,
              <https://www.itu.int/rec/T-REC-G.694.1/en>.

   [Zhang2025]
              Zhang, Y., Broberg, R., Zhu, A., Li, G., Ge, L., Smith,
              J.M., and L. Feng, "Classical-decisive quantum internet by
              integrated photonics", DOI: 10.1126/science.adx6176,
              Science Vol. 389, pp. 940-944, August 2025,
              <https://doi.org/10.1126/science.adx6176>.

   [ZhangSM2025]
              Zhang, Y., Broberg, R., Zhu, A., Li, G., Ge, L., Smith,
              J.M., and L. Feng, "Supplementary Materials for Classical-
              decisive quantum internet by integrated photonics",
              Science Supplementary Materials, August 2025.

Authors' Addresses

   Alan Zhu
   University of Pennsylvania School of Engineering and Applied Science
   Philadelphia, PA 19104
   United States
   Email: alzhu@seas.upenn.edu


   Yichi Zhang
   University of Pennsylvania School of Engineering and Applied Science
   Philadelphia, PA 19104
   United States
   Email: zyc@seas.upenn.edu


   Robert Broberg
   University of Pennsylvania School of Engineering and Applied Science
   Philadelphia, PA 19104
   United States
   Email: rbroberg@seas.upenn.edu


   Liang Feng
   University of Pennsylvania School of Engineering and Applied Science
   Philadelphia, PA 19104
   United States
   Email: fenglia@seas.upenn.edu




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   Jonathan M. Smith
   University of Pennsylvania School of Engineering and Applied Science
   Philadelphia, PA 19104
   United States
   Email: jms@seas.upenn.edu














































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