1. A method performed by a network node of using an application specific service ping packet, comprising: receiving, at the network node, the application specific service ping packet including: a special packet identification field that identifies the application specific service ping packet as a special packet, and an application identification field that identifies an application to which the application specific service ping packet corresponds; performing deep packet inspection on the application specific service ping packet using a deep packet inspection element of the network node; identifying the application specific service ping packet as a special packet; determining that the application specific service ping packet is mapped to the application; identifying the application; setting a flow represented by the application specific service ping packet to the application; and performing application processing based on the set application.