SR Policy for enhanced DetNet

Segment Routing Policy is defined in . A SR Policy is a set of candidate path which consist of one or more segment lists. The headend node instructs the source routing and writes it into package. The packets steered into an SR Policy have an ordered list of segments associated with that SR Policy written into them. provides the overall architecture for Deterministic Networking (DetNet), which provides the capability to carry specified unicast or multicast data flows with extremely low data loss rates and bounded end-to-end latency within a network domain. Based on this, proposed a timing model for sources, destinations, and DetNet transit nodes. Using the model, it provides a methodology to compute end-to-end latency and backlog bounds for various queuing methods. enhances the DetNet data plane by introducing Bounded Latency Information (BLI) which facilitates DetNet transit nodes to guarantee the bounded latency transmission in data plane. Based on that, defines how to leverage Segment Routing (SR) and Segment Routing over IPv6 (SRv6) to implement bounded latency. For An automatic network, the SR Policy with Bounded Latency Information can facilitate the bounded latency transmission and enable the automation of SR service. This document defines the SR policy enhancement to carry the Bounded Latency Information with a candidate path of SR policy. So that BLI behavior can be enabled automatically when the SR Policy is applied.

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.

The abbreviations used in this document are: BLI: Bounded Latency Information SR: Segment Routing SID: Segment Identifier

The BLI is proposed by to facilitate DetNet transit nodes to guarantee the bounded latency transmission in data plane. In order to specify the bounded latency features that the candidate path is associated with, this document defines two types of new sub-TLV in the BGP Tunnel Encapsulation Attribute for SR Policy for different scenarios.

When all of the nodes/adjacencies in the explicit path indicated by the segment list request different BLI to guarantee bounded latency, a BLI list sub-TLV is defined. The BLI list sub-TLV is formatted as follows.

Where: Type: to be assigned by IANA. Length: 16 bits length value to indicate the length of BLI list in octet. BLI List [1… m]: 64 bits length BLI structure, representing the nth BLI in the BLI list. The BLI in the BLI List corresponds to the Segment in the Segment List one by one. The length of the BLI List depends on the num of Segment in the Segment List. The encoding structure of BGP SR Policy with the BLI list sub-TLV is expressed as below:

Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Priority Policy Name Explicit NULL Label Policy (ENLP) Segment List BLI List Weight Segment Segment ... ... ]]>

When all of the nodes/adjacencies in the explicit path indicated by the segment list request BLI to guarantee bounded latency with the same BLI value, the Shared BLI sub-TLV is defined. The Shared BLI sub-TLV is defined as follows:

Where: Type: to be assigned by IANA. Length: 16 bits value indicate the length of BLI. BLI: 64 bits value of Bounded Latency Information to guarantee the bounded latency, the format of it is defined in section 3.1. The encoding structure of BGP SR Policy with the Per-segment BLI sub-TLV is expressed as below:

Attributes: Tunnel Encaps Attribute (23) Tunnel Type: SR Policy Binding SID Preference Priority Policy Name Explicit NULL Label Policy (ENLP) Segment List Shared BLI Weight Segment Segment ... ... ]]>

When a candidate path of SR Policy is a bounded-latency routing path, the originating node of SR policy MUST include the associated bounded latency information in the BGP Tunnel Encapsulation Attribute of the BGP SR Policy. The other fields and attributes in BGP SR Policy should follows the mechanism as defined in. When a BGP speaker receives an SR Policy which is acceptable and usable according to the rules as defined in , and the SR Policy candidate path selected as the best candidate path is a bounded-latency path, the receiver node of the SR Policy MUST encapsulate the specific bounded latency information to the header of packets steered to the SR Policy. For SR Policy with IPv6 data plane and MPLS data plane, the possible approach is to encapsulate the BLI to the packet using the mechanism defined in and.

IANA is requested to make the assignment from the "BGP Tunnel Encapsulation Attribute sub-TLVs" registry as follows.

TBD