A packet transmission method for a first network node in a shared medium network, the shared medium network comprises at least two broadcast domains, each of the at least two broadcast domains comprises at least two network nodes and packet identity, ID, numbers each including a variable packet sequence number m and a domain number n that uniquely identifies a broadcast domain in which the network node is located used by all network nodes in a first broadcast domain to identify packets, said packet ID numbers being the same at a same moment for all network nodes in the same broadcast domain and being different from packet ID numbers used by a network node in another broadcast domain to identify packets, the first broadcast domain is any broadcast domain in the shared medium network, the first network node is any network node in the first broadcast domain, and the method comprises: broadcasting a first ID sending request in the first broadcast domain, wherein the first ID sending request is used to request to send specified information and comprises a first ID number, and the first ID number is a packet ID number used by each network node in the first broadcast domain at a current moment to identify a packet; when receiving, within a preset time period, no ID sending request sent by another network node, sending a first packet to a second network node, wherein the first packet comprises the first ID number, and the another network node is a node in the first broadcast domain other than the first network node; and after sending the first packet to the second network node, updating the ID number in synchronization with the another network node in the first broadcast domain, to obtain a second ID number, wherein the second ID number and the first ID number meet a preset change rule, and the change rule is a monotonically increasing rule or a monotonically decreasing rule, wherein the first broadcast domain is a one-hop broadcast domain and the another network node in the first broadcast domain detects the packet ID number of the first network node through listening; and the method further comprises: when receiving, within the preset time period, an ID sending request sent by the another network node, comparing a sending priority of the first network node with a sending priority of the another network node; and when the sending priority of the first network node is higher than the sending priority of the another network node, sending the first packet to the second network node; or when the sending priority of the first network node is lower than the sending priority of the another network node, broadcasting a second ID sending request after a preset backoff time period, wherein the second ID sending request is used to request to send the specified information, the second ID sending request comprises a second ID number, and the second ID number is an ID number synchronously updated by the first network node after the another network node sends a packet. broadcasting a first ID sending request in the first broadcast domain, wherein the first ID sending request is used to request to send specified information and comprises a first ID number, and the first ID number is a packet ID number used by each network node in the first broadcast domain at a current moment to identify a packet; when receiving, within a preset time period, no ID sending request sent by another network node, sending a first packet to a second network node, wherein the first packet comprises the first ID number, and the another network node is a node in the first broadcast domain other than the first network node; and after sending the first packet to the second network node, updating the ID number in synchronization with the another network node in the first broadcast domain, to obtain a second ID number, wherein the second ID number and the first ID number meet a preset change rule, and the change rule is a monotonically increasing rule or a monotonically decreasing rule, wherein the first broadcast domain is a one-hop broadcast domain and the another network node in the first broadcast domain detects the packet ID number of the first network node through listening; and the method further comprises: when receiving, within the preset time period, an ID sending request sent by the another network node, comparing a sending priority of the first network node with a sending priority of the another network node; and when the sending priority of the first network node is higher than the sending priority of the another network node, sending the first packet to the second network node; or when the sending priority of the first network node is lower than the sending priority of the another network node, broadcasting a second ID sending request after a preset backoff time period, wherein the second ID sending request is used to request to send the specified information, the second ID sending request comprises a second ID number, and the second ID number is an ID number synchronously updated by the first network node after the another network node sends a packet.