Packet TCPSegment

File: src/transport/tcp/TCPSegment.msg

C++ definition: click here

Represents a TCP segment, to be used with the TCP module.

TCP header fields not explicitly modelled:

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:

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Inheritance diagram:

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Fields:

Name Type Description
pshBit bool

PSH: push function

srcPort short

Source Port

payloadLength int

Payload length in octets (not an actual TCP header field). This may not always be the same as encapsulatedPacket()->getByteLength(); e.g. when simulating a virtual data stream there's no encapsulated packet at all.

finBit bool

FIN: no more data from sender

payload TCPPayloadMessage[]

Message objects (cMessages) that travel in this segment as data. (This field is used only with TCPMsgBasedSendQueue/RcvQueue and not with TCPVirtualBytesSendQueue/RcvQueue.) Every message object is put into the TCPSegment that would (in real life) carry its last octet. That is, if message object 'msg' with length=100 bytes occupies sequence number range 10000..10099, it will travel in the TCPSegment which carries the octet 10099. This way it is easily achieved that the receiving TCP passes up the message object to its client when the last byte of the message has arrived.

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

ackBit bool

ACK: ackNo significant if set

window unsigned long

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

urgBit bool

URG: urgent pointer field significant if set

rstBit bool

RST: reset the connection

synBit bool

SYN: synchronize seq. numbers

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)

urgentPointer unsigned long

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.

destPort short

Destination Port

Source code:

//
// Represents a \TCP segment, to be used with the TCP module.
//
// \TCP header fields not explicitly modelled:
// - 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()
// - Options: none supported currently (MSS comes from config)
// - Padding
//
// cMessage::getKind() may be set to an arbitrary value: TCP entities will
// ignore it and use only the header fields (synBit, ackBit, rstBit).
//
packet TCPSegment
{
    @customize(true);
    // Source Port
    short srcPort;

    // Destination Port
    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;

    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: no more data from sender

    // Window: 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 long 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 long urgentPointer;

    // Payload length in octets (not an actual \TCP header field).
    // This may not always be the same as encapsulatedPacket()->getByteLength();
    // e.g. when simulating a virtual data stream there's no encapsulated
    // packet at all.
    int payloadLength;

    // Message objects (cMessages) that travel in this segment as data.
    // (This field is used only with TCPMsgBasedSendQueue/RcvQueue and
    // not with TCPVirtualBytesSendQueue/RcvQueue.)  Every message object
    // is put into the TCPSegment that would (in real life) carry its
    // last octet. That is, if message object 'msg' with length=100 bytes
    // occupies sequence number range 10000..10099, it will travel in the
    // TCPSegment which carries the octet 10099. This way it is easily achieved
    // that the receiving TCP passes up the message object to its client
    // when the last byte of the message has arrived.
    abstract TCPPayloadMessage payload[];
}