TcpHeader¶

//
// Represents a TCP segment, to be used with the ~Tcp module.
//
// TCP header fields not explicitly modelled: work on going
// - Data Offset (number of 32 bit words in the header): represented
//   by cMessage::length().
// - Reserved (reserved for future use)
// - Checksum (header checksum): modelled by cMessage::hasBitError()
// - Header Options: Currently only EOL, NOP, MSS, WS, SACK_PERMITTED, SACK and TS are implemented
// - Padding
//
// cMessage::getKind() may be set to an arbitrary value: TCP entities will
// ignore it and use only the header fields (synBit, ackBit, rstBit).
//
class TcpHeader extends TransportHeaderBase
{
    chunkLength = TCP_MIN_HEADER_LENGTH;

    // Source Port
    uint16_t srcPort;

    // Destination Port
    uint16_t destPort;

    // Sequence Number: first sequence number of the first data octet
    // in the respective segment (except if SYN is set; then the the
    // seq. number is the initial seq. number (ISS) and the first data
    // octet is ISS + 1)
    uint32_t sequenceNo;

    // Acknowledgement Number: if ACK flag is set, this field contains
    // the next sequence number the sender of this segment is expecting
    // to receive
    uint32_t ackNo;

    // TCP Header Length including options
    B headerLength = TCP_MIN_HEADER_LENGTH;

    bool cwrBit; // CWR: congestion window reduced bit (RFC 3168)
    bool eceBit; // ECE: ECN-echo bit (RFC 3168)
    bool urgBit; // URG: urgent pointer field significant if set
    bool ackBit; // ACK: ackNo significant if set
    bool pshBit; // PSH: push function
    bool rstBit; // RST: reset the connection
    bool synBit; // SYN: synchronize seq. numbers
    bool finBit; // FIN: finish - no more data from sender

    // Window Size: the number of data octets beginning with the one indicated
    // in the acknowledgement field which the sender of this segment is
    // willing to accept
    uint16_t window;

    // Urgent Pointer: communicates the current value of the urgent pointer
    // as a positive offset from the sequence number in this segment. The
    // urgent pointer points to the sequence number of the octet following
    // the urgent data. This field is only be interpreted in segments with
    // the URG control bit set.
    uint16_t urgentPointer;

    uint16_t checksum = 0;
    ChecksumMode checksumMode = CHECKSUM_MODE_UNDEFINED;

    // Header options (optional)
    // Currently only EOL, NOP, MSS, WS, SACK_PERMITTED, SACK and TS are implemented
    TcpOption *headerOption[] @owned;
}