Liaison statement
Title: LS on work progress on quantum key distribution network (QKDN) in SG11

Note: See attachment for document with functioning links.

ITU-T SG11 is pleased to inform you of SG11 progress on quantum key
distribution network (QKDN) topics.

1. The published Recommendations
ITU-T SG11 has published five Recommendations on QKDN as follows:

1) Recommendation ITU-T Q.4160: Quantum key distribution networks – Protocol
framework

2) Recommendation ITU-T Q.4161: Protocols for Ak interfaces for quantum key
distribution networks

3) Recommendation ITU-T Q.4162: Protocols for Kq-1 interfaces for quantum key
distribution networks

4) Recommendation ITU-T Q.4163: Protocols for Kx interfaces for quantum key
distribution networks

5) Recommendation ITU-T Q.4164: Protocols for Ck interfaces for quantum key
distribution networks

2. The items consented at ITU-T Study Group 11 meeting (Geneva, 17-26 November
2025) ITU-T SG11 consented one Recommendation on QKDN as follows:

1) Recommendation ITU-T Q.4165 (ex Q.QKDNi_profr) Quantum key distribution
networks interworking - Protocol framework.

Summary:
Recommendation ITU-T Q.4165 (ex Q.QKDN_profr) specifies a protocol framework
for signalling and protocols for quantum key distribution network interworking
(QKDNi).

3. On-going work items progressed at ITU-T Study Group 11 meeting (Geneva,
17-26 November 2025) ITU-T SG11 made progress on five draft Recommendations on
QKDN as follows:

1) Draft Recommendation ITU-T Q.QKDNi_KM “Protocols for interfaces between key
managers for quantum key distribution network interworking”

Summary
Recommendation ITU-T Q.QKDNi_KM specifies protocols for Kxi and Kxi’ interfaces
in quantum key distribution network interworking (QKDNi).

2) Draft Recommendation ITU-T Q.QKDN_Mk “ Protocols for interfaces on quantum
key distribution network manager for quantum key distribution networks”

Summary
Recommendation ITU-T Q.QKDN_Mk specifies protocols for interfaces on a quantum
key distribution network manager (QKDN manager) in quantum key distribution
networks (QKDN). Reference points on a QKDN manager are defined in [ITU-T
Y.3802] which are Mq, Mqrp, Mops, Mk, Mc, Mu and Mx. A QKDN manager performs
FCAPS functions through these interfaces to QKD modules, KMs, QKDN controllers,
QKD links, user network managers and corresponding QKDN managers. Also, Mxi
reference point for interworking of QKDN management layers is defined in
[Y3810] for sharing QKDN management information between QKDN providers through
the QKDN management layer.

3) Draft Recommendation ITU-T Q.QKDN_Cq “Protocols for Cq interfaces for
quantum key distribution networks”

Summary
Recommendation ITU-T Q.QKDN_Cq specifies key generation control protocols for
Cq interfaces for quantum key distribution networks.

4) Draft Recommendation ITU-T Q.QKDN_GC “General control protocols for
interfaces on quantum key distribution network controller for quantum key
distribution networks”

Summary
Recommendation ITU-T Q.QKDN_GC specifies general control protocols at
interfaces on a quantum key distribution network controller (QKDN controller)
in quantum key distribution networks (QKDNs). Reference points on a QKDN
controller are defined in [ITU-T Y.3802] which are Cq, Cqrp, Cops, Ck and Cx
and in [ITU-T Y.3810] which is Cxi. A QKDN controller performs control
functions through these interfaces to QKD modules, KMs, QKD links and other
QKDN controller.

Signalling procedures, messages and parameters at Ck interfaces for key relay
and Cq interfaces for key generation are specified in [ITU-T Q.4164] and [draft
Q.QKDN_Cq]. This draft Recommendation describes protocols for general control
functions which can be applied commonly to interfaces on the QKDN controller.
These specifications are additional to [ITU-T Q.4164] and [draft Q.QKDN_Cq] and
will not override them.

4. New work items initiated at ITU-T Study Group 11 meeting (Geneva, 17-26
November 2025) ITU-T SG11 initiated one Recommendation on QKDN as follows:

1) Recommendation ITU-T Q.QKDN_Pro-car "Protocols for cryptographic application
registration in quantum key distribution networks".

Summary
Draft ITU-T Recommendation Y.QKDN_car-fr "Quantum key distribution networks –
Framework of cryptographic application registration" specifies functional
architecture model, functional elements, reference points and operational
procedures for cryptographic application registration procedures.
Recommendation ITU-T Q.QKDN_Pro-car specifies protocols on relevant interfaces
including Ar, Ck, Mu and Mc to support cryptographic application registration
procedures to be aligned with Y.QKDN_car-fr.

5. Conclusion
ITU-T SG11 looks forward to close cooperation with you and relevant groups for
future standardization on QKDNs.

Attachments:
1) SG11-TD712/GEN: Consent - draft new Recommendation ITU-T Q.4165 (ex
Q.QKDNi_profr) "Quantum key distribution network interworking - Protocol
framework" (Geneva, 17-26 November 2025).

2) SG11-TD701/GEN: Output - draft new Recommendation Q.QKDNi_KM "Protocols for
interfaces between key managers for quantum key distribution network
interworking" (Geneva, 17-26 November 2025).

3) SG11-TD704/GEN: Output - draft new Recommendation Q.QKDN_Mk "Protocols for
interfaces on quantum key distribution network manager for quantum key
distribution networks" (Geneva, 17-26 November 2025).

4) SG11-TD702/GEN: Output - draft new Recommendation Q.QKDN_Cq "Protocols for
Cq interfaces for quantum key distribution networks" (Geneva, 17-26 November
2025).

5) SG11-TD703/GEN: Output - draft new Recommendation Q.QKDN_GC "General control
protocols for interfaces on quantum key distribution network controller for
quantum key distribution networks" (Geneva, 17-26 November 2025).

6) SG11-TD710/GEN: Output - draft baseline of new work item Q.QKDN_Pro-car
"Protocols for cryptographic application registration in quantum key
distribution networks" (Geneva, 17-26 November 2025).