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In case <strong>of</strong> reception, each layer will take the necessary information and will then withdraw its headers to<br />
send the remaining data blocks to the next layer above.<br />
Links<br />
In certain cases, an extra layer is necessary. In case <strong>of</strong> access via a modem (by a serial link), there is no<br />
material address (MAC address) on a modem. This address needing to be used by the physical and<br />
network layers, in theory there can be no communication possible. A modem is not an interface network<br />
but a serial one (communication is done through a COM port), it has no material standard address, nor<br />
does it have any ROM giving an IP communication interface.<br />
An extra s<strong>of</strong>tware layer is thus necessary, in order to simulate and provide an alternative to the use <strong>of</strong> a<br />
MAC address. In the case <strong>of</strong> a TCP/IP link with a modem, a PPP protocol (Point to Point <strong>Pro</strong>tocol) will<br />
generally be used; it will be placed between the network layer and the physical layer. This protocol will<br />
give a s<strong>of</strong>tware solution to IP communications needing a MAC address.<br />
Layers and protocols used<br />
Each layer <strong>of</strong> the IP pile uses one or several protocols to fulfil certain functions (the transport layer uses<br />
TCP or UDP). With this method, layers can standardize incoming and outgoing data flows. Each layer<br />
(and thus each implementation) is therefore independent <strong>of</strong> upper and/or lower layers.<br />
The <strong>Hack</strong>ademy DMP -9/209- SYSDREAM
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