Native SCION Multicast Proposal

[martenwallewein]

Hey everyone,

we're currently working on a native SCION multicast approach that allows scalable inter-domain multicast over SCION. It's a master thesis project on which a very talented student from the Ovgu Magdeburg is working on. We want to raise this issue to create awareness about this work and to get feedback as early as possible. In the following you can find some general notes, followed by detailed descriptions in our proposal draft and some slides.

Core Approach:

• We introduce a "SCION Multicast Extension Header", which consists of multiple "Multihop Fields (MHF)"
• Processing an MHF, the AS authenticates it and replicates the packet to all desired destinations
• We define multicast groups, and endhost can subscribe to one or more groups to receive multicast traffic
• Endhosts can obtain all ASes that have receivers for a given group, and compute the full extension header based on this

Design Goals:

1. Separation of inter- and intra-domain: SCION delivers each multicast packet a single time to a destination AS, the AS is responsible to deliver the packet to all local receivers (intra-domain multicast agnostic)
2. Multicast Services use the SCION Control plane for orchestration: Multicast Services announce to which Groups they have at least one subscriber to others
3. Efficient format to save space in header: Following BIER-TE Use global interface IDs in bit string to represent multicast hops
4. Endhost-based path selection: Encode a full multicast tree into the packet with all links to reach all recipient ASes
5. Authentication of Hops: Traversal of actual paths is verifiable similar to SCION Unicast

We plan to follow on this proposal in two different directions:

1. Implement a PoC version with as less changes in SCION as possible: we're currently looking into having everything covered in a "multicast-service", so that each AS operator can decide to enable multicast by running this service or not.
2. Implement the native version, where changes in the SCION components are required, e.g. multicast packets are processed in the Border Router

We think that it might be very useful to deploy, run and evaluate the PoC before raising PR's to change the SCION core components.

So please feel free to comment or give feedback to the process or to our approach, we appreciate any kind of input!

Further Resources:
We have a raw draft proposal of the idea which can be found here and a list of slides that we presented
PDF: https://drive.google.com/file/d/12PL3esQ8ang5maP9xmw178gQkycvKTxD/view?usp=sharing
Slides: https://docs.google.com/presentation/d/1ZvrG1IxgPuClonYf0U52M3LEPTYU6Ca2HN9kocjZAZU/edit?usp=sharing

Best,
Marten