|  | 3.3 | Basics of Data Flow Through LANs
| 3.3.5 |
Packet flow through clouds and through Layer 1-7 devices
The graphic shows that certain devices operate at all seven layers. Some devices (e.g. your PC) are Layer 1-7 devices. In other words, they perform processes that can be associated with every layer of the OSI model. Encapsulation and decapsulation are two examples of this. A device called a gateway (essentially a computer which converts information from one protocol to another) is also a Layer 7 device. An example of a gateway would be a computer on a LAN that allows the network to connect to an IBM mainframe computer or to a network-wide facsimile (fax) system. In both of these examples, the data would have to go all the way up the OSI model stack to be converted into a data format the receiving device, either the mainframe or the fax unit, could use. Finally, clouds may contain several kinds of media, NICs, switches, bridges, routers, gateways and other networking devices. Because the cloud is not really a single device, but a collection of devices that operate at all levels of the OSI model, it is classified as a Layer 1-7 device.
| Web Links
| Encapsulation
| Packets
| Data Encapsulation
| Encapsulation Slide
| Encapsulation of PDUs