Namespace inet::tcp

TcpHeader

class

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).

Extends

Name	Type	Description
TransportHeaderBase	(unknown -- not in documented files)

Fields

Name	Type	Description
chunkLength
srcPort	uint16_t	Source Port
destPort	uint16_t	Destination Port
sequenceNo	uint32_t	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)
ackNo	uint32_t	Acknowledgement Number: if ACK flag is set, this field contains the next sequence number the sender of this segment is expecting to receive
headerLength	B	TCP Header Length including options
cwrBit	bool	CWR: congestion window reduced bit (RFC 3168)
eceBit	bool	ECE: ECN-echo bit (RFC 3168)
urgBit	bool	URG: urgent pointer field significant if set
ackBit	bool	ACK: ackNo significant if set
pshBit	bool	PSH: push function
rstBit	bool	RST: reset the connection
synBit	bool	SYN: synchronize seq. numbers
finBit	bool	FIN: finish - no more data from sender
window	uint16_t	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
urgentPointer	uint16_t	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.
crc	uint16_t
crcMode	CrcMode
headerOption	TcpOption[]	Header options (optional) Currently only EOL, NOP, MSS, WS, SACK_PERMITTED, SACK and TS are implemented

Packet operations (observed)

action	module
insertAtFront	Tcp, TcpConnection, TcpCrcInsertionHook, TcpLwip
peekAtFront	Tcp, TcpLwip
popAtFront	PcapRecorder
removeAtFront	TcpCrcInsertionHook, TcpLwip

Source code

//
// 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 crc = 0;
    CrcMode crcMode = CRC_MODE_UNDEFINED;

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

File: src/inet/transportlayer/tcp_common/TcpHeader.msg