9 and 13 are used by domestic image transmitters and analog and digital Webcams. The 2.450 GHz frequency is that of microwave ovens that can disrupt, more or less, Wi-Fi channels 7 to 10. The maximum authorized power, inside and outside buildings, is 100 mW. Channel number 2.412 2.417 2.422 2.427 2.432 2.437 2.442 2.447 2.452 2.457 2.462 2.467 2.472 2.484 Central frequency (GHz) 22 MHz Figure 3.9. ISM band at 2.4 GHz Source: http://en.wikipedia.org/wiki/IEEE_802.11g-2003 802.11n Interface 4.1. MAC layer evolution Table 4.1 summarizes the features provided by the MAC (Medium Access Control) layer. Features Mandatory/optional Description Reception A-MPDU Mandatory Transmission MAC frame aggregation Optional A-MPDU Reception A-MSDU Mandatory Transmission Aggregation of MAC frame payload Optional A-MSDU Block Ack Mandatory Acknowledgment for a block of MAC frames Detection of radio channel occupancy time Protection Mandatory by non-802. 11n compatible stations Mandatory Reduced inter-frame interval Spatial Multiplexing Power save by reducing Mandatory Power Save the number of spatial flows Power Save Power save by modifying the radio access Optional Multi-Poll procedure for smaller frames Non-TKIP Mandatory TKIP is no longer allowed Phased Coexistence Alternating radio channels Optional Operation at 20 and 40 MHz Table 4.1. Features of MAC layer 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 4.1.1. Management frames 4.1.1.1. HT Capabilities information element The management frames indicate that the access point has an 802.11n interface by including the HT (High Throughput) Capabilities information element. The information provided by the HT Capabilities Info field is described in Table 4.2. Information Designation LDPC Coding Capability LDPC error correction code Bandwidth of the radio channel Supported Channel Width Set (20 MHz / 40 MHz) SM Power Save Power save for spatial multiple