Re: [spring] 答复: Comments on draft-geng-spring-sr-redundancy-protection

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

Hi Fan,

In this thread I’ll address another point that I deferred. I snipped unrelated text.



Zzh6> It’s important to distinguish between control plane and data plane. In data plane it is always a simple SID (replication or redundancy). In control plane (that sets up the replication/redundancy state on relevant nodes), it could be whatever.

Fan> I try to compare the two solutions redundancy protection and P2MP replication as follows, hope it can help the understandings.

Format: <solution> ,  <identifier of service> ,  <how it works>
<redundancy protection> , <Redundancy SID> ,  <service is identified by Red-SID, Red-SID triggers redundancy policy to assign candidate paths between redundancy node and merging node>
<P2MP replication> ,  <P2MP policy identifier (root-id, tree-id)> ,  <P2MP policy gives the tree structure of the P2MP service, replication segment is an atomic building block for packet replication and stays in root, bud and leaf>

Although each solution includes a SID and a SR-Policy, there are totally different mechanisms. I don’t think it is just a representation difference.


In your representation for Redundancy solution, you mentioned “candidate paths”. I would change it to “replication branches”, because “candidate paths” in SR policies have a different meaning. Basically, the redundancy policy would replicate incoming traffic and send them down to different paths. No additional replication is done downstream and this corresponds to the “Ingress Replication” concept in multicast/p2mp.

For <identifier of service>, you used “redundancy SID” and “P2MP policy identifier” respectively. As I mentioned before, in the data plane both just use a SID. In the control plane (i.e., how the replication/redundancy segment is installed), the identifier could be anything for both solutions, including a SID.

For replication segment based solution, unless the replication is to more than two copies and done by a multi-level tree (node 1 replicating to node 2 and 3, and then node 2 replicating to node 4 and 5), then it is “Ingress Replication” and no different from the redundancy segment solution.

BTW, P2MP policy (with tree identification, candidate paths, set of leaves, etc.) are really just control plane information on the root. It does not give the tree structure either. Instead, the entire replication tree are just concatenated replication segments on root, leaves and intermediate replication nodes. The intermediate replication nodes are optional (i.e., Ingress Replication), and in that case there is no difference from the redundancy segment.

Jeffrey


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