 Signal) option provides control information to enable the reassembly of streams from different TCP connections and its reliable and orderly delivery of data for the application at the destination level. To deliver the data in sequence, the DSS option contains the mapping between the data sequence number (DSN) of the MPTCP connection and the sub-flow sequence number (SSN) of the TCP connection (Figure 12.10). Wi-Fi Integration to the 4G Mobile Network SSN (LTE access) SSN (Wi-Fi access) MPTCP Proxy Server access accessi Option : DSS (DSN = 1, SSN = 1) Option DSS (DATA ACK = 1401) Option : DSS (DSN = 1401, SSN = 1) Option : DSS (DATA ACK = 2801) Option : DSS (DSN = 2801, SSN = 1401) Option : DSS (DATA ACK = 4201) Figure 12.10. Data transfer The DSS option uses the Data ACK field to acknowledge data from the MPTCP connection. This acknowledgment indicates to the sender that the data corresponding to the DSN number has been received and specifies the next DSN to be transmitted. For a normal TCP connection, the recipient of a segment notifies the source of the available size for the receive memory in the Window field. The MPTCP connection uses a single receive window for all TCP connections, which allows each TCP connection to transmit data if the size of the receive memory allows. The value of the receive window is indicated in the Window field of the TCP connection, whose associated DSS option contains in the DATA_ACK field the number of the next expected byte relative to the DSN MPTCP Aggregation sequence (Figure 12.10). The source can transmit on all TCP connections segments whose DSN number is between DATA_ACK and DATA_ACK + Window. For a normal TCP connection, congestion control introduces another limitation provided by the congestion window (cwnd). Executing the existing algorithms independently for each TCP connection would give very high flow rate for MPTCP connection if these TCP connections cross a single bottleneck. In addition, it is desirable for a source with multiple available accesses to use the leas