A data transmission method performed by a first network device, wherein: ∘ there are multiple pre-setup first bearers between the first network device and a base station, and there are multiple pre-setup second bearers between the first network device and a second network device, ∘ the multiple pre-setup first bearers and the multiple pre-setup second bearers are setup when the first network device is initialized, and ∘ data having a same first service quality characteristic are all transmitted on a same first bearer among the multiple pre-setup first bearers, and data having a same second service quality characteristic are all transmitted on a same second bearer among the multiple pre-setup second bearers; and the method comprises the following steps: • determining a second bearer among the multiple pre-setup second bearers as being a bearer which corresponds to a certain second service quality characteristic of data (step 305); • receiving (step 302), by using one first bearer among the multiple pre-setup first bearers, the data from the base station, wherein the data is sent (step 301) by a terminal to the base station by using an air interface resource, and the first bearer is determined (step 304) by the base station as being a bearer which corresponds to a certain first service quality characteristic of the data, wherein the data received by using the first bearer carry a first identifier of the terminal; • obtaining an IP address of the terminal according to a correspondence between the first identifier of the terminal and the IP address of the terminal, wherein a bit quantity of the first identifier is less than a bit quantity of the IP address (step 306); • sending the data to the second network device by using the second bearer among the multiple pre-setup second bearers, wherein the data sent by the first network device to the second network device carry the IP address of the terminal (step 303). ∘ there are multiple pre-setup first bearers between the first network device and a base station, and there are multiple pre-setup second bearers between the first network device and a second network device, ∘ the multiple pre-setup first bearers and the multiple pre-setup second bearers are setup when the first network device is initialized, and ∘ data having a same first service quality characteristic are all transmitted on a same first bearer among the multiple pre-setup first bearers, and data having a same second service quality characteristic are all transmitted on a same second bearer among the multiple pre-setup second bearers; and • determining a second bearer among the multiple pre-setup second bearers as being a bearer which corresponds to a certain second service quality characteristic of data (step 305); • receiving (step 302), by using one first bearer among the multiple pre-setup first bearers, the data from the base station, wherein the data is sent (step 301) by a terminal to the base station by using an air interface resource, and the first bearer is determined (step 304) by the base station as being a bearer which corresponds to a certain first service quality characteristic of the data, wherein the data received by using the first bearer carry a first identifier of the terminal; • obtaining an IP address of the terminal according to a correspondence between the first identifier of the terminal and the IP address of the terminal, wherein a bit quantity of the first identifier is less than a bit quantity of the IP address (step 306); • sending the data to the second network device by using the second bearer among the multiple pre-setup second bearers, wherein the data sent by the first network device to the second network device carry the IP address of the terminal (step 303). <EOS>