2.2.1.1 Control Flags

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The control flag is 1 byte after the SMID field and indicates the type of the packet. Only DATA packets have payload data. The sender MUST NOT send a combination of flags in the same packet. For example, a FLAGS field value of 0x06 (ACK plus FIN) is an invalid value.

Value

Meaning

SYN

0x01

Indicates that a new connection is to be established (see SYN packet). The session ID for the session is the number that is stored in the SID field.

ACK

0x02

Informs the peer about a change in window size when consecutive unanswered DATA packets are received (see ACK packet).

FIN

0x04

Indicates that the sending entity will no longer use the session to send data.

DATA

0x08

Indicates that the packet carries user data after the header (see DATA packet).