**Session Date/Time:** 11 Nov 2021 14:30

# bier

## Summary

The BIER working group met to discuss the status of several drafts, including `mldp-bier-v2`, `pce-based-bier`, and `slicing-traffic-differentiation`. A new draft proposing a "Recursive Bitstring Structure" for BIER was also presented, aiming to simplify BIER-TE complexity. The group noted concerns about the slow pace of progress due to low mailing list activity and discussed the need for an interim meeting. The chair provided an update on `isis-bier-te`'s ISG review. Discussions also covered `te-lan-bfr` and `bier-protection` drafts.

## Key Discussion Points

*   **Meeting Logistics:** Tony volunteered to take minutes. The chair clarified the process for collaborative note-taking via the shared notepad and jabber logs.
*   **Working Group Pace:** Concerns were raised regarding the slow progress of drafts due to limited mailing list activity and short meeting slots. Alvaro suggested scheduling an interim meeting.
*   **Dependency on BIER Ping:** Human highlighted that the `BIER Ping` document has expired, blocking progress on Path MTU Discovery in BIER.
*   **`draft-ietf-bier-mldp-bier-v2` (Human):**
    *   Aims to facilitate incremental upgrades from MPLS LDP multicast (MLDP) to BIER without extensive software or configuration changes.
    *   Leverages RFC 7060, T-LDP between BIER edge routers for FEC signaling.
    *   Discussion points included ensuring proper cross-WG visibility (MPLS, BESS) during Working Group Last Call (WGLC).
    *   The draft was incorrectly marked as "informational" and lacked normative references, requiring correction.
*   **`draft-ietf-bier-pce-based-bier` (Juan Ali):**
    *   Introduced updates to PCE objects for BIER, defining new TLVs for multicast source/group addresses, VPN information (RD, forwarding label), and BIER information (router ID, subdomain ID, BF RID, BSL).
    *   Discussion included suggestions for a more precise document title and questions about the handling of "non-BIER" scenarios within BIER-specific objects. Torless suggested broadening the scope to a general BIER PCE architecture beyond just IP multicast.
*   **`draft-ietf-bier-slicing-traffic-differentiation` (Jeffrey):**
    *   Explored methods for network slicing and traffic differentiation in BIER.
    *   Proposed mapping slice aggregates (SAs) to BIER subdomains or directly to BIER Routing Tables (BIRT) for scalability, requiring IGP/BGP extensions.
    *   Suggested a "BIER Extension Header" to carry slice selectors for finer-grained traffic differentiation, aligning with similar concepts in IPv6 and MPLS for generic delivery functions and stateless QoS.
    *   Discussion touched upon the relationship with `flex-algo` and `IPA` drafts, which address similar slicing concepts.
*   **`draft-ietf-bier-isis-bier-te` (Torless):**
    *   Status update: ISG review completed in August, with one DISCUSS point (a typo) and numerous comments.
    *   The author is working on version -11, addressing feedback, including clarifying terminology (e.g., "BIER," "non-TE BIER," "BIER-TE").
*   **`draft-wibg-bier-rbs` (Torless):**
    *   Proposed "Recursive Bitstring Structure (RBS)" to address complexities and scalability limitations of BIER-TE's flat bit strings, particularly for sparse multicast trees.
    *   RBS structures the bit string to reflect the distribution tree, with "recursive units" extracted and rewritten at each hop, simplifying controller logic and reducing state on BFRs.
    *   The forwarding plane would incur some additional processing for address rewriting.
    *   Packet encoding could potentially use RFC 8296 as a new BIFT mode.
    *   The chair confirmed this work is within the BIER WG charter.
*   **`draft-chen-bier-te-lan-bfr` (Chen Liya):**
    *   Addressed potential duplicate packets on broadcast links (LANs) in existing BIER-TE.
    *   Proposed introducing "pursuit nodes" and having real nodes act as proxies, managing two forwarding tables.
    *   The problem statement regarding duplicates was questioned, suggesting it might stem from sub-optimal mask generation by the PCE.
*   **`draft-chen-bier-protection` (Chen Liya):**
    *   Extended BIER protection mechanisms to cover "Case B," where a backup node protects a primary node, but they send packets to *different* CE receivers (unlike "Case A," where they send to the same receivers).
    *   Utilizes a flag (`s=0`) to indicate different CE receivers and requires BFRs to extend forwarding tables with backup entries.

## Decisions and Action Items

*   **General:**
    *   Tony volunteered as the minute taker for this session.
    *   The chairs will coordinate an interim meeting, targeting mid-late January, to address the backlog of documents and foster more active discussion.
    *   The chair will review the status of all current BIER documents and communicate updates on the mailing list, particularly for the expired `BIER Ping` draft.
*   **`draft-ietf-bier-mldp-bier-v2`:**
    *   **ACTION:** Human to correct the draft's status to "standards track" and add necessary normative references.
    *   **ACTION:** Chairs to coordinate with Human to send WGLC notification emails to the MPLS and BESS working groups when the WGLC begins.
*   **`draft-ietf-bier-pce-based-bier`:**
    *   **ACTION:** Juan Ali to clarify the purpose of the "known beer" flag on the mailing list and consider expanding the draft's scope to a more general BIER PCE architecture.
*   **`draft-ietf-bier-slicing-traffic-differentiation`:**
    *   **ACTION:** Jeffrey to review `flex-algo` and `IPA` drafts to understand their relationship and potential synergy.
    *   **ACTION:** Jeffrey to initiate a discussion on BIER extension headers within the BIER working group for broader generic delivery functions and stateless QoS.
*   **`draft-ietf-bier-isis-bier-te`:**
    *   **ACTION:** Torless to submit `v-11` addressing ISG review comments, including clarifying terminology.
*   **`draft-chen-bier-te-lan-bfr`:**
    *   **ACTION:** Chen Liya to provide further clarification on the problem statement (duplicate packets on broadcast links) and solution details on the mailing list.
*   **`draft-chen-bier-protection`:**
    *   **ACTION:** Chen Liya to clarify the use cases and the relationship between "Case A" and "Case B" for BIER protection on the mailing list.

## Next Steps

*   The working group will focus on increasing activity on the mailing list to facilitate discussion and document review.
*   An interim meeting will be scheduled for mid-to-late January.
*   Authors are encouraged to progress their drafts and address identified action items, particularly those related to WGLC and ISG review.
*   Further discussions on new concepts like BIER Extension Headers and Recursive Bitstring Structure are expected.