TcpHeader

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).

Usage diagram

The following diagram shows usage relationships between types. Unresolved types are missing from the diagram.

Inheritance diagram

The following diagram shows inheritance relationships for this type. Unresolved types are missing from the diagram.

Extends

Name Type Description
TransportHeaderBase class

This base class provides an abstraction for different transport layer packets.

Fields

Name Type Description
chunkLength b
srcPort unsigned short

Source Port

destPort unsigned short

Destination Port

sequenceNo unsigned int

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 unsigned int

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 - default: 20 bytes if header options are used the headerLength is greater than 20 bytes (default)

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 unsigned short

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 unsigned short

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

sourcePort unsigned int
destinationPort unsigned int
mutable bool
complete bool
correct bool
properlyRepresented bool
rawBin string[]
rawHex string[]
tags RegionTagSet::cObjectRegionTag[]

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
    unsigned short srcPort;

    // Destination Port
    unsigned short 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)
    unsigned int sequenceNo;

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

    // TCP Header Length - default: 20 bytes
    // if header options are used the headerLength is greater than 20 bytes (default)
    B headerLength = TCP_MIN_HEADER_LENGTH; // TCP_MIN_HEADER_LENGTH = 20 bytes

    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
    unsigned short 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.
    unsigned short 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