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Fundamentals of Networking
Doc Part Number, Version Number
5-3
Draft Level—Hitachi Confidential
The LLC sublayer defines the logical connection to the upper layer
services based on a socket or Service Access Point (SAP). This allows two
processes on the same network to maintain a “logical connection” with
each other for the purpose of data exchange.
Examples of Layer 2 devices are bridges and switches.
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er 3: Network La
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This layer is where the network provides its routing functionality. The
Network Layer uses a packet to transport data from one network to another.
A 32-bit address is used to define the network’s logical location and is
referred to as the network address or IP address.
Examples of Layer 3 devices are routers.
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er 4: Transport La
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This layer ensures reliable delivery of data between networks. All error
checking, acknowledgments, retransmissions, and data sequencing are
handled by the Transport Layer.
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er 5: Session La
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This layer provides for the ability for two processes on two different
stations to form a connection for the purpose of communication with one
another. This is often referred to as a dialogue layer. Host-to-host
communication is established, managed, and terminated at this layer.
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er 6: Presentation La
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This layer converts the actual data that is being transferred into a readable
and proper form.
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er 7: Applications La
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This layer provides network-based services to a user’s application. The
application layer communicates with the end user via programs such as file
transfers (FTP, TFTP), electronic mail (SMTP), and other applications.