Multiple channels are multiplexed into a single connection. Channels are identified by numbers at each end. The number referring to a channel may be different on each side. Requests to open a channel contain the sender's channel number. Any other channel-related messages contain the recipient's channel number for the channel.
Channels are flow-controlled.
No data may be sent to a channel until a message is received to indicate that window space is available. When either side wishes to open a new channel, it allocates a local number for the channel. It then sends the following message to the other side, and includes the local channel number and initial window size in the message. The channel type is a name as described in the SSH architecture document, with similar extension mechanisms. The client MAY show the additional information to the user.