SR OS creates a single Selective P-Multicast Service Interface (S-PMSI) per multicast stream: (S,G) or (*,G). To better manage bandwidth allocation in the network, multiple multicast streams are often bundled starting from the same root node into a single, multi-stream S-PMSI. Network bandwidth is usually managed per package or group of packages, rather than per channel.
Multi-stream S-PMSI supports a single S-PMSI for one or more IPv4 (C-S, C-G) or IPv6 (C-S, C-G) streams. Multiple multicast streams starting from the same VPRN going to the same set of leafs can use a single S-PMSI. Multi-stream S-PMSIs can:
carry exclusively IPv4 or exclusively IPv6, or a mix of channels
co-exist with a single group S-PMSI
To create a multi-stream S-PMSI, an S-PMSI policy needs to be configured in the VPN context on the source node. This policy maps multiple (C-S, C-G) streams to a single S-PMSI. Because this configuration is done per MVPN, multiple VPNs can have identical policies, each configured for its own VPN context.
When mapping a multicast stream to a multi-stream S-PMSI policy, the data will traverse the S-PMSI without first using the I-PMSI. (Before this feature, when a multicast stream was sourced, the data used the I-PMSI first until a configured threshold was met. After this, if the multicast data exceeded the threshold, it would signal the S-PMSI tunnel and switch from I-PMSI to S-PMSI.)
For multi-stream S-PMSI, if the policy is configured and the multicast data matches the policy rules, the multi-stream S-PMSI is used from the start without using the default I-PMSI.
Multiple multi-stream S-PMSI policies could be assigned to a specific S-PMSI configuration. In this case, the policy acts as a link list. The first (lowest index) that matches the multi-stream S-PMSI policy is used for that specific stream.
The rules for matching a multi-stream S-PMSI on the source node are listed here.
S-PMSI to (C-S, C-G) mapping on Source-PE, in sequence:
The multi-stream S-PMSI policy is evaluated, starting from the lowest numerical policy index. This allows the feature to be enabled in the service when per-(C-S, C-G) stream configuration is present. Only entries that are not shut down are evaluated. First, the multi-stream S-PMSI (the lowest policy index) that the (C-S, C-G) stream maps to is selected.
If (C-S, C-G) does not map to any of multi-stream S-PMSIs, per-(C-S, C-G) S-PMSIs are used for transmission if a (C-S, C-G) maps to an existing S-PMSI (based on data-thresholds).
If S-PMSI cannot be used, the default PMSI is used.
Multi-stream S-PMSI P-tunnel failure handling:
If an S-PMSI P-tunnel is not available, a default PMSI tunnel is used. When an S-PMSI tunnel fails, all (C-S, C-G) streams using this multi-stream S-PMSI move to the default PMSI. The groups move back to S-PMSI after the S-PMSI tunnel is restored.