The Internet Protocol (IP) resides on the Network layer.
The Transport layer ensures that data is delivered error-free, in sequence, and with no losses or duplications. This layer also can break large messages from the Session layer into smaller segments to be handed down to the Network layer and sent to the destination computer; it then reassembles segments into messages to be presented to the Session layer. The Transport layer can send an acknowledgment to the originator for messages received (as in Figure 1.6). Most of these services are optional and are not required in the implementation of ccna exam
all Transport layer protocols. The one feature common to all protocols at the Transport layer is upper-layer protocol multiplexing, allowing multiple higher-layer protocol flows to operate simultaneously.
In terms of TCP/IP, this means you could, for example, navigate to a website and download a file at the same time.
Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are examples of protocols that exist at the Transport layer.
The Transport layer provides end-to-end communication with integrity and performance guarantees.
The Session Layer
The Session layer allows applications on separate computers to share a connection called a session . This layer provides services that allow two programs to find each other and establish the communication link, such as name lookup and security. The Session layer also provides for data synchronization and check pointing so that in the event of a network failure, only the data sent after the point of failure would need to be re-sent. This layer also controls the dialogue between two processes and determines who can transmit and who can receive at what point during the communication (see Figure 1.7).
NetBIOS, RPC, Named Pipes, PPTP, and SQL are examples of protocols on the Session layer.
The Presentation Layer
The Presentation layer translates data between the formats the network requires and the for- mats the computer expects. The Presentation layer microsoft exam
performs protocol conversion; data trans- lation, compression, and encryption; character set conversion; and the interpretation of graphics commands.
The network redirector, long a part of Windows networking, operates at this level. The redi- rector is what makes the files on a file server visible to the client computer. The network redirector also makes remote printers act as though they were attached to the local com- puter. Figure 1.8 shows the Presentation layer’s role in the protocol stack.
Graphic formats such as PICT, TIFF, and JPEG are examples of Presentation layer protocols.
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