[MUSIC] The digital revolution has changed the way we work and communicate almost beyond recognition. Yet the smart interconnected world we live in is still neither smart nor as connected as we would like it to be. Until in the mid 1980s, the ISO or International Standard Organization develops networking model to provide standards that will become the basis for network designs. This is the OSI model. Several layers build up the open systems interconnection or OSI model. Let's take the flow of data and represent it with the train system. Sending a file or clicking a link in your computer ignites the flow of information. The first layer to receive the command is the application layer. The application layer serves as the window for the users and application processes to access the network services. This layer contains a variety of commonly needed functions like resource sharing and device for your direction. Data are packed and ready to take on a long journey. [MUSIC] After the data is read, the next layer or the presentation layer formats the data to represent it to the application layer. It can be viewed as the translator for the network. This layer may translate data from a format used by the application layer into a common format at the sending station. It then translates the common format to a format known to the application layer at the receiving station. The presentation layer also encrypts control information into the data, in this case the train, to be read by the next layers. [MUSIC] Now, this layer allows session establishment, maintenance and termination, which allow two application processors on different machines to establish, use, and terminate a connection called a session. This session support which performs the functions that allow these processors to communicate over the network performing security, name recognition, logging and so on. This layer remembers everyone who passes by. [MUSIC] After another journey, the data pass through a layer of security and validity, the transport layer. This layer scans and make sure the data is reliable and valid and that the messages are delivered error-free, and then broken down or acknowledged into segments. The security firewall is usually in action at this layer, data that do not pass will be rejected or destroyed. And because the session layer before remembers the data that gets through, data are retransmitted when there is no connection acknowledgment. This is the safe haven of the data whenever data packets are lost. [MUSIC] Down to another layer is the network player. Here the segments are encapsulated into packets, routing takes place in this layer where the path the packets will take is determined. [MUSIC] Packet filtering routers and firewalls sometimes take place in this layer. The lower the firewall the layer is, the more secure the network. [MUSIC] An additional responsibility of the network layer is that it adds a source and destination Internet Protocol or IP address to the segment. [MUSIC] The next layer is the data link layer. The packets are turned into frames for the specific networks. The data link layer provides air-free transfer of data frames from one node to another over the physical layer, allowing layers above it to assume virtually error-free transmissions over the link. A switch in networking takes place in this layer where packets are read with its control information and then encoded with the media access control or MAC address. The MAC address contains 12 hexi decimal digits and prevents collision in the same media. [MUSIC] Finally, the physical layer transforms the frames into bits and then sent over the network via physical hardware or media, in this case, the Ethernet. Data are logically arranged and encoded before they get sent to a physical media to another computer, and is then received by another computer's physical layer. [MUSIC] Some data or information in the upper layers are destined to be sent through the Internet, a vast interconnection of information and data. Either way, the data sent will then be received by the seven layers of another computer. From the physical layer which encodes the bits, back to the data link layer where the bits become frames and is transferred error-free to the network layer where frames turn back into packets and then sent to the upper layers. And to the transport layer where validation and firewalls take place. Sent up to the session layer where connections called sessions are maintained or terminated, back to the presentation layer where the data turned back into a format that can be read by the presentation layer. And finally, sent and presented to the user via the application layer where you will be provided with your request or command. [MUSIC] So every time you click on a link on the Internet or send a file from one computer to another, remember the journey the data have taken to make sure that everything is connected for a common network standard. The enormous complications the data must take just to serve you well, from the physical connections at the lowest layer after the layer that has the user's applications, all wrapped up in a network model called the OSI model. [MUSIC]
