The transport channel service manage client connections and I/O processing for HTTP and JMS requests. These services provide a highly scalable foundation to WebSphere Application Server request processing. Java NIO based architecture has limitations in terms of performance, scalability and end user usability. Therefore, integration of true asynchronous I/O is implemented. This implementation provides significant benefits in usability, reduces the complexity of I/O processing and reduces that amount of performance tuning you have to perform.Changing the default values for settings on one or more of the transport channels associated with a transport chain can improve the performance of that chain.
I copied this diagram from IBM Redbook, it explains how the Transport channel service works.
You can access the the transportation related configuration in WAS Admin Console by going to Servers - server_name -> Web Container settings - Web Container transport chains, then select WCInboundDefault, which is the virtual host for handling all the requests to web application on that server.
As you can see there is a hyper link for configuring settings related to each of the three channels