Backpressure in federative live streaming

Resistance or force opposing the desired flow of data through software.

Situation

Client --> ShigA --> ShigB --> Streamer

Congestion

Receiver Estimated Max Bitrate

We have three Estimation in a pipe

Client -> ShigA
ShigA -> ShigB
ShigB -> Streamer

Questions:

Would we calculate and accumulate all three to One?
Is Simulcast enough? When ShigB has small bitrate we would call sende don't send max track size?