cisco ccna ocg

cisco ccna ocg.connection. However, as a prerequisite to understanding how the various protocols work, it is important to understand the main TCP/IP modelprinciples behind the scenes.1.2.2 The Open Systems Interconnection Reference Model The Open Systems Interconnection (OSI) reference model is another model that uses an abstraction layer to represent the operation of a communication system. The OSI model is designed to be both comprehensive enough to accommodate the evolution of network communications and general enough to allow several existing communication system models to be converted to the OSI model. The OSI model has several similarities to the TCP/IP model introduced in Section 1.2.1, the main similarity being the use of an abstraction layer. Like the TCP/IP model, each layer of the OSI model provides services to the upper layer within the same computing device, and interacts with the same layer of other computing devices. The OSI reference model is divided into seven abstraction layers, each of which represents a different function and service within the communication network.I ling codification Physical Layer One One Layer One (L1): provides services for the transmission of bits (bits) over the data link. Data Link Layer - Layer 2 (L2): deals with the protocols and functions for passing information over a link between two devices directly connected to each other. As an example, the data link layer can provide flow control functions and L1 error detection functions. Network Layer - Layer 3 (L3): deals with the functions needed to pass information across the network and provides abstractions based on the underlying connectivity. The network layer defines L3 addressing, routing, and packet forwarding. Transport Layer - Layer 4 (L4): this layer provides services that include end-to-end connection establishment and information delivery. Let's say that the transport layer may provide functions such as error detection, retransmission, and multiplexing. . Session layer - Layer 5 (L5): provides services to the representation layer and serves to establish sessions and exchange representation layer data. Representation layer - layer 6 (L6): serves the application layer and serves to handle specific syntax, i.e., to determine how data is presented to the end user. Application layer - layer 7 (L7): the highest or first layer of the OSI model (what exactly to say depends on the reader's opinion), covering all services provided by the user application, this layer will involve interaction with the end user.The OSI model layers correspond in function to similar functions provided by the TCP/IP model. When referring to protocols that operate at certain layers, people also often use the terminology of the OSI reference model to refer to that layer, even if the communication device implements the TCP/IP model rather than the OSI model (for example, people will often say IP protocols that operate at the network layer rather than IP protocols that operate at the Internet layer).Figure 1-5 shows the correspondence between the layers of the OSI model and the layers of the TCP/IP model.1.2 TCP/IP and. SI Reference Model 111. OfferingApplication layer Application layer