Backhaul Adaptation Protocol
Backhaul Adaptation Protocol (BAP) is a layer 2 Routing protocol used in 5G for Integrated Access and Backhaul (IAB) This protocol is specified by 3GPP in TS 38.340. The purpose of BAP is to deliver packets to a destination node over multiple hops. BAP is located on top of the 3GPP RLC-layer. A BAP PDU is either a Data PDU or a Control PDU. Data PDUs are used to transport upper layer data along a path towards a destination. A BAP Data PDU has the following format: Control PDUs are used to indicate backhaul radio  link failures, to poll for flow control information and to provide flow control feedback. A BAP Control PDU has the following format: Further information is dependent on PDU type. For flow control feedback per BH RLC channel, available buffer size is given per BH RLC channel. For flow control feedback per routing ID, available buffer size is given per BAP routing ID (which consists of BAP address and path ID). No further information is given in the flow control feedback polling and the BH RLF indication.