In an embodiment, a source node assigns a first number to a probe data packet in a probe data flow in a sending sequence, where the first number is used to select a transmission path for the probe data packet. The source node sends the probe data packet in the probe data flow to a destination node at a first sending rate. Each time the source node receives a probe data packet backhauled by the destination node, the source node sends a service data packet in a service data flow, where the service data packet is assigned a second number corresponding to the probe data packet, and the second number is used to select a transmission path for the service data packet.