Fast Convergence of Multicast Traffic

When a CCEP or MCT peer fails, multicast traffic that used to go through the failed CCEP link or node switches to the surviving CCEP link in approximately one second or less.

Sub-second convergence requires both MCT peers to maintain the state for traffic and pull down traffic for all multicast flows from the core, regardless of whether the chassis is forwarding this stream out of the local CCEP. This means that streams forwarded by the remote CCEP are pulled down to the local MCT peer but dropped in the absence of other receivers on the local router, thus potentially wasting the bandwidth inside the core on uplink. This is deemed a fair trade-off because otherwise the MCT peer that takes over the job of forwarding a stream when the remote CCEP or peer fails must establish a new multicast path through the core, which can potentially black out the stream for many seconds.