A period mapping method, comprising: determining, by a first network device, m based on a first jitter of the first network device, wherein m is a quantity of label numbers used to identify the periods of a first network device; receiving, by the first network device, second information sent by a second network device, wherein the second information indicates n based on a second jitter of the second network device, n is a quantity of label numbers used to identify the periods of the second network device, and m and n are positive integers; and wherein the first jitter of the first network device is inconsistent with the second jitter of the second network device; and numbering, by the first network device, each period of the first network device based on m and n, wherein the numbering is based on a common multiple of the quantity of label numbers m and n, after the numbering, receiving, by the first network device, first information sent by the second network device, wherein the first information carries a first number, the first number is a number of the first period of the second network device, and the first number comprises a first label number and a first group number; determining, by the first network device, based on the received first information and the first jitter of the first network device a first period that can be used to send the first information, wherein a second number of the first period comprises a second label number and a second group number, the first label number and the first group number meet a mapping relationship with the second label number and the second group number; and establishing, by the first network device, mapping relationships for packet forwarding between numbers of a plurality of periods of the first network device and numbers of a plurality of periods of the second network device based on the mapping relationship of the first label number and the first group number with the second label number and the second group number. determining, by a first network device, m based on a first jitter of the first network device, wherein m is a quantity of label numbers used to identify the periods of a first network device; receiving, by the first network device, second information sent by a second network device, wherein the second information indicates n based on a second jitter of the second network device, n is a quantity of label numbers used to identify the periods of the second network device, and m and n are positive integers; and wherein the first jitter of the first network device is inconsistent with the second jitter of the second network device; and numbering, by the first network device, each period of the first network device based on m and n, wherein the numbering is based on a common multiple of the quantity of label numbers m and n, after the numbering, receiving, by the first network device, first information sent by the second network device, wherein the first information carries a first number, the first number is a number of the first period of the second network device, and the first number comprises a first label number and a first group number; determining, by the first network device, based on the received first information and the first jitter of the first network device a first period that can be used to send the first information, wherein a second number of the first period comprises a second label number and a second group number, the first label number and the first group number meet a mapping relationship with the second label number and the second group number; and establishing, by the first network device, mapping relationships for packet forwarding between numbers of a plurality of periods of the first network device and numbers of a plurality of periods of the second network device based on the mapping relationship of the first label number and the first group number with the second label number and the second group number.