 of this layer, as well as addressing, error handling, and congestion control. 6. Layer 2, data link layer: This layer furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control, and frame syn- chronization. The data link layer is divided into two sub layers: the media access control (MAC) layer and the logical link control (LLC) layer. The MAC sublayer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, physical flow con- trol, and error checking. 7. Layer 1, physical layer: This layer conveys the bit stream-electrical impulse, light or radio signal-through the network at the electrical (or optical) and mechanical level. It provides the hardware means of sending and receiving data. 3.2.3 Internet The Internet model is a complete model for the packet network and the IP suite is the set of protocols used at the various levels of the pure Internet network model [19,20]. In its pure version, the Internet is a datagram switched network: that is, a network where the data stream from one termination to the other is divided into packets traveling inde- pendently through the network The fact that packets belonging to the same message can be routed through different paths in the network potentially causes a disordered arrival of packets at the destination and a difficulty to recognize packet lost. The layer model of the Internet is shown in Figure 3.20 [21,22]. The layered model is composed of four layers plus the physical layer that collects all the equipment used for transmission and that is not part of the Internet stack. Due to the datagram nature of the Internet, control signals travels through trails in the various layers either as headers of the data packets or as dedicated protocol packets, depending on the protocol. This means that when a layer passes a packet to the lower layer, the packet is envel- oped with a header and at link layer also a tail SO that the whole packet 