bile IP packet. The IP transport network that allows communication between the entities of the EPS network routes the IP packet that is the S1 or S5 bearer. The eNB and SGW entities do not perform routing. They only provide the connection between the bearers. I.2. Wi-Fi network I.2.1. Network architecture The Wi-Fi (Wireless Fidelity) network consists of an access point (AP) that bridges the Wi-Fi radio interface with the Ethernet interface to the local area network (LAN) (Figure I.3). Router Figure I.3. Wi-Fi network architecture xxviii Wi-Fi Integration to the 4G Mobile Network The BSS (Basic Service Set) cell is the radio zone covered by the access point. The BSS identifier (BSSID) of the BSS cell is the MAC address of the access point. Several BSS cells can be deployed to cover an area. The set of cells constitute an ESS (Extended Service Set) network. The ESS network is identified by the service set identifier (SSID). Wi-Fi technology has defined the data link layer and physical layer of the radio interface (Figure I.4): - the data link layer consists of two sub-layers, namely the LLC (Logical Link Control) sub-layer and the MAC (Medium Access Control) sub-layer; - the physical layer has defined two sub-layers, namely the PLCP (Physical Layer Convergence Protocol) sub-layer and the PMD (Physical Medium Dependent) sub-layer. Bridging consists of modifying the data link layer and the physical layer used on both sides of the access point. Station Access Point Router Wi-Fi Ethernet Wi-Fi Ethernet Figure I.4. Protocol architecture The LLC sub-layer is not specific to Wi-Fi technology. It is also used for other data link layer protocols, such as the Ethernet MAC sub-layer. It indicates the nature of the encapsulated data, for example an IP packet. Introduction The MAC sub-layer defines the procedure of access to the physical medium shared between the different mobiles of the cell. The CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) procedure solves the collision problems that occur when two mobiles sim