What is Transport domain, Domain controller and Transport Layer?

• Transport Domain: A transport domain consists of all systms that you plan to manage using the same TMS (Transport Management System). Within the transport domain, all systems must have unique System IDs (SID) and only one if these systems is identified as the (transport) domain controller.
• The Trasport Domain Controller is the system where all TMS configuration settings are maintained. Any changes to the configuration settings are distributed to all systems in the landscape. This ensures that TMS configuration settings are consistent throught out the domain. The domain controller stores the referrence configuration and all other systems receive a copy of the referrence configuration.
• Customizing and repository objects are assigned to a specific consolidation route by meands of a Transport layer.