In order for parachain to communicate with each other, they need to have a HRMP channel opened first.
Currently the maximum number of HRMP channel allowed on Kusama 10.
We have 27 parachains at moment and Karura is already have 6 channels and working with many more parachains on opening more channels. 10 channels is simply not enough.
There are overheads on relaychain per each established HRMP channels and therefore we needs an upper limit. However similar to number of parachains, we do not know the upper limit value and will want to gradually increase the limit and observe the performance of Kusama. This also helps to configure a safe limit for Polkadot.
This proposal aims to increase the maximum number of HRMP channels from 10 to 30. Note that number of inbound and outbound channels are separate configuration and therefore this is a batch call to update both values.
30 channels should be enough for at least next few months. We have another proposal to increase further if any parachains are approaching this limit and Kusama is still operating fine.