Packet loss detection method, apparatus, and system

A controller, comprising:

• a receiver, configured to receive multiple first results sent by a first network device and multiple second results sent by a second network device, one first result comprising a quantity of packets in one group of packets obtained by the first network device through statistics collection according to packets sent in a sequential order to the second network device and a section identifier of the group of packets, each group of packets sent by the first network device comprising multiple packets belonging to a section corresponding to a section identifier of the group of packets, one second result comprising a quantity of packets in one group of packets obtained by the second network device through statistics collection according to the received packets sent by the first network device and comprising a section identifier of the group of packets obtained by the second network device, each group of packets received by the second network device comprising multiple packets belonging to a section corresponding to a section identifier of the group of packets, wherein packets that are continuous in the sequential order and having at least one bit with a same value in a same position in packet identifier fields in the IP packet headers belong to a same section, wherein when a packet and a previous packet belong to different sections, the packet is used as a first packet of a next packet group, and the previous packet is part of a first group of packets;
• and
• a processor, configured to:
• determine, according to the multiple first results and the multiple second results, whether a packet in the packets sent by the first network device to the second network device has been lost, and
• when the section identifier is in the form of values of multiple bits of an identifier field in a packet header, sequence the multiple second results so that section identifiers of the sequenced multiple second results are in ascending order, and determine, according to the multiple first results and the sequenced multiple second results, whether a packet in the packets sent by the first network device to the second network device has been lost.