A communication system provides a clear channel link for transport of encrypted payload across a network of the communication system. When a source access network receives, via an air interface, a frame that is formatted pursuant to an air interface protocol and that comprises encrypted payload, the source access network demultiplexes the frame to separate the encrypted payload and assembles an Intersystem Link Protocol (ISLP) frame that comprises the encrypted payload. The source access network adds a link layer header to the ISLP frame that identifies one or more of frame type information and a sequence value associated with the frame and conveys the ISLP frame and added header across the network, for example, to a destination access network. Based on the added header, the source and destination access networks are able to perform clear channel synchronization.