Internet-Draft Abbreviated Title March 2024
Zhang, et al. Expires 4 September 2024 [Page]
Intended Status:
Standards Track
Z. Zhang
ZTE Corporation
H. Wu
ZTE Corporation
J. Wang
China Mobile

IS-IS and OSPF extensions for TVR (Time-Variant Routing)


TVR needs IGP to calculate different results depending on the time, without convergence after the detection of link or nodes. IGP nodes need to learn the predictable and scheduled changes in advance. This document defines the IGP extensions for predictable and scheduled changes of TVR.

Status of This Memo

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This Internet-Draft will expire on 4 September 2024.

Table of Contents

1. Introduction

This draft was submitted as [].

[I-D.ietf-tvr-use-cases] and [I-D.ietf-tvr-requirements] describe a new challenge for non-terrestrial networks. In these networks, there are predictable and scheduled changes of link or nodes. The affected nodes which connected the changing link or node advertise the changes after finding the changes. After convergence all the nodes calculate a new routing table. But for the predictable and scheduled changes, the nodes can advertise the changes and do the calculation in advance to reduce the convergence time.

   |                 Satellite Network                 |
   |                                                   |
   |   ----------------            ----------------    |
   ----| Satellite R1 |------------| Satellite R2 |-----
       ----------------            ----------------
              |                            |
              |                            |
              |                            |
      -------------------         -------------------
  ----| Ground Station1 |---------| Ground Station2 |----
  |   -------------------         -------------------   |
  |                                                     |
  |                                                     |
  |                    Ground Network                   |
Figure 1

For example, in Figure 1, The groud station 1/2 connects the Satellite. Because of the satellite movement, the metric between satellite and ground station changes over time. Because the movement is periodic, the metric is changed periodically. Regardless the unexpected situation like bad weather, the metric variation is predicable and scheduled. The groud station 1/2 advertises the predicable and scheduled metric variation to the ground network. Then the nodes in the ground network can learn the scheduled metric and calculate the routing table in advance.

This document defines the a set of extensions to IS-IS, OSPFv2 and OSPFv3 for predictable and scheduled changes of TVR. These extensions can be advertised by the node self which has predictable and scheduled changes, or by the node which connected or adjacenct to the node which has predictable and scheduled changes.

This document helps the implementation of Intrinsic schedule defined in section 3.1.1 in [I-D.ietf-tvr-requirements]. And the schedule based on Flex Algorithm can solve the time overlap mentioned in section 3.2.7 in [I-D.ietf-tvr-requirements]. The schedule in different FA may be overlapped, but the constrain-based routing calculation will not be affected.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

2. Terminology


3. Time Variant Algorithm

The predictable and scheduled changes can be looked as a set of new constrains which defined in [RFC9350]. The new constrains are advertised as new sub-tlvs.

4. Time Variant sub-TLVs of IS-IS and OSPF FAD Sub-TLV

A new type of Metric-Type is defined for time variant in IS-IS FAD sub-TLV which defined in section 5.1 [RFC9350] and OSPF FAD sub-TLV which defined in section 5.2 [RFC9350].

A new Time Variant sub-TLV is advertised as a sub-TLV of IS-IS FAD sub-TLV and OSPF FAD sub-TLV. The Time Variant sub-TLV has following formats:

    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     |    Length     |
   |                       Recurrence-type                         |
   |                          Metric1                              |
   |                       Time-slot1-begin                        |
   |                       Time-slot1-end                          |
   |                          Metric2                              |
   |                       Time-slot2-begin                        |
   |                       Time-slot2-end                          |
   |                               .                               |
   .                               .                               .
   |                               .                               |
   |                          Metric[m]                            |
   |                       Time-slot[m]-begin                      |
   |                       Time-slot[m]-end                        |
Figure 2
Type: 1-octet. TBD (To be assigned by IANA).
Length: 1-octet. The number of the set of metric and time-slot.
Recurrence-type: 4-octet. The schedule repetitiveness.
Metric: 4-octet. The metric value of specific time slot. The value of 0xffffffff indicates unreachable.
Time-slot-begin: 4-octet. The begin time of this time-slot.
Time-slot-end: 4-octet. The end time of this time-slot.

5. Handling of the time variant sub-TLV

The handling follows the definition in [RFC9350], except one or more timers are scheduled for different time-slot carried in time variant sub-tlv. When a scheduled time-slot is coming, the associated routing table needs to be calculated with the associated metric.

When the Recurrence-type in the time variant sub-TLV is set, the routing table needs to be calculated repeatedly. During the time which is not covered by the time-slot, the default metric is suggested to be used for routing calculation.

6. IANA Considerations

The document requests new allocations from the IANA registries as follows:

6.1. IGP Metric-type Registry

IANA is requested to allocate a new code points from the "IGP Metric-Type" registry.

Table 1: IGP Metric-Type
Type Description Reference
TBD1 Time Variant metric This Document

6.2. IS-IS Registry

IANA is requested to allocate a new code points from the "IS-IS Sub-Sub-TLVs for Flexible Algorithm Definition Sub-TLV" registry.

Table 2: IS-IS TVR sub-TLV
Type Description Reference
TBD2 Time Variant This Document

6.3. OSPF Registry

IANA is requested to allocate a new code points from the "OSPF Flexible Algorithm Definition TLV Sub-TLVs" registry.

Table 3: OSPF TVR sub-TLV
Type Description Reference
TBD3 Time Variant This Document

7. Security Considerations

This document does not introduce more security consideration than [RFC9350].

8. Acknowledgements


9. References

9.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", RFC 9350, DOI 10.17487/RFC9350, , <>.

9.2. Informative References

King, D., Contreras, L. M., and B. Sipos, "TVR (Time-Variant Routing) Requirements", Work in Progress, Internet-Draft, draft-ietf-tvr-requirements-01, , <>.
Birrane, E. J., Kuhn, N., Qu, Y., Taylor, R., and L. Zhang, "TVR (Time-Variant Routing) Use Cases", Work in Progress, Internet-Draft, draft-ietf-tvr-use-cases-09, , <>.
Zhang, Z. and H. Wu, "IS-IS and OSPF extensions for TVR (Time-Variant Routing)", Work in Progress, Internet-Draft, draft-zw-tvr-igp-extensions-02, , <>.

Authors' Addresses

Zheng Zhang
ZTE Corporation
Haisheng Wu
ZTE Corporation
Jing Wang
China Mobile
No.32 XuanWuMen West Street