 less than or equal to 2,304 bytes. Prot. Protocol Sub type Retry Order Frame Duration Address 1 Address 2 Address 3 Address 4 Trame LLC Control Fragment Sequence Number Number Figure 2.1. MAC header structure Frame Control: this field consists of a sequence of several subfields: - Protocol Version: this subfield is coded on two bits and takes the value 00; - Type and Subtype: the subfields are coded, respectively, on two and four bits. They identify the function of the frame. There are three types of Wi-Fi Integration to the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2018. Published by ISTE Ltd and John Wiley & Sons, Inc. Wi-Fi Integration to the 4G Mobile Network frames, namely the traffic frame, the control frame and the management frame. For each type of frame, subtypes are defined; - To DS and From DS: these two subfields are coded on one bit. They indicate the direction of transmission of the frame (Table 2.1); - More Fragments: this subfield is coded on a bit. It takes the value of ONE for traffic or management frames, if other fragments follow; - Retry: this subfield is coded on a bit. It takes the value of ONE to signal the retransmission of a frame; - Power Management: this subfield is coded on a bit. It takes the value of ONE when the station signals the switch to standby state; - More Data: this subfield is coded on a bit. It takes the value of ONE when the access point signals to the terminal that frames are stored in the buffer; - Protected Frame: this subfield is coded on a bit. It takes the value of ONE when the frame payload is secured by the WPA1 (Wi-Fi Protected Access) or WPA2 mechanism; - Order: this subfield is coded on a bit. It takes the value of ONE to indicate that the frame is transmitted as part of an ordered service. To DS From DS Meaning All control and management frames Traffic frames in ad hoc mode Traffic frames to the local area network (LAN) Traffic frames from the LAN Traffic frames exchanged between access points Table 2.1. To DS and From DS subfield values Dura