Message transmission method, apparatus and system in integrated access and backhaul systems

A message transmission apparatus, applicable to a first integrated access and backhaul node (IAB-node), the apparatus comprises:

• a receiver configured to:
• receive a second radio resource control (RRC) reconfiguration message for path migration of a second IAB-node while the first IAB-node is still connected with source parent node, the second radio resource control (RRC) reconfiguration message being transmitted by a donor central unit (donor-CU), the second IAB-node is a downstream child node of the first IAB-node;
• and
• receive a first RRC reconfiguration message for path migration of the first IAB-node, the first RRC reconfiguration message being transmitted by the donor-CU;
• and
• a transmitter configured to withhold the second RRC reconfiguration message to be forwarded to the second IAB node until the first IAB-node has successfully performed a random access procedure to the target parent node,
• wherein the second RRC reconfiguration message is carried by a first downlink F1AP message transmitted by the donor-CU, and
• wherein the first RRC reconfiguration message includes a first parameter configured for the first IAB-node to change a transmission path, the first parameter including:
• a default backhaul RLC channel configured for the first IAB-node,
• a default BAP route configured for the first IAB-node, or
• an IP address configured for the first IAB-node.