Modelo Osi
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Publicado: 23 de enero de 2013
Expert Reference Series of White Papers
The OSI Model: Understanding the Seven Layers of Computer Networks
1-800-COURSES www.globalknowledge.com
The OSI Model: Understanding the Seven Layers of Computer Networks
Paul Simoneau, Global Knowledge Course Director, Network+, CCNA, CTP
Introduction
The Open Systems Interconnection (OSI) model is a reference tool for understanding datacommunications between any two networked systems. It divides the communications processes into seven layers. Each layer both performs specific functions to support the layers above it and offers services to the layers below it. The three lowest layers focus on passing traffic through the network to an end system. The top four layers come into play in the end system to complete the process. This whitepaper will provide you with an understanding of each of the seven layers, including their functions and their relationships to each other. This will provide you with an overview of the network process, which can then act as a framework for understanding the details of computer networking. Since the discussion of networking often includes talk of “extra layers”, this paper will address theseunofficial layers as well. Finally, this paper will draw comparisons between the theoretical OSI model and the functional TCP/IP model. Although TCP/IP has been used for network communications before the adoption of the OSI model, it supports the same functions and features in a differently layered arrangement.
An Overview of the OSI Model
Copyright ©2006 Global Knowledge Training LLC. All rightsreserved.
Page 2
A networking model offers a generic means to separate computer networking functions into multiple layers. Each of these layers relies on the layers below it to provide supporting capabilities and performs support to the layers above it. Such a model of layered functionality is also called a “protocol stack” or “protocol suite”. Protocols, or rules, can do their work ineither hardware or software or, as with most protocol stacks, in a combination of the two. The nature of these stacks is that the lower layers do their work in hardware or firmware (software that runs on specific hardware chips) while the higher layers work in software. The Open System Interconnection model is a seven-layer structure that specifies the requirements for communications between twocomputers. The ISO (International Organization for Standardization) standard 7498-1 defined this model. This model allows all network elements to operate together, no matter who created the protocols and what computer vendor supports them. The main benefits of the OSI model include the following: • Helps users understand the big picture of networking • Helps users understand how hardware and softwareelements function together • Makes troubleshooting easier by separating networks into manageable pieces • Defines terms that networking professionals can use to compare basic functional relationships on different networks • Helps users understand new technologies as they are developed • Aids in interpreting vendor explanations of product functionality
Layer 1 – The Physical Layer
The physicallayer of the OSI model defines connector and interface specifications, as well as the medium (cable) requirements. Electrical, mechanical, functional, and procedural specifications are provided for sending a bit stream on a computer network.
Copyright ©2006 Global Knowledge Training LLC. All rights reserved.
Page 3
Components of the physical layer include: • Cabling system components •Adapters that connect media to physical interfaces • Connector design and pin assignments • Hub, repeater, and patch panel specifications • Wireless system components • Parallel SCSI (Small Computer System Interface) • Network Interface Card (NIC) In a LAN environment, Category 5e UTP (Unshielded Twisted Pair) cable is generally used for the physical layer for individual device connections....
The OSI Model: Understanding the Seven Layers of Computer Networks
1-800-COURSES www.globalknowledge.com
The OSI Model: Understanding the Seven Layers of Computer Networks
Paul Simoneau, Global Knowledge Course Director, Network+, CCNA, CTP
Introduction
The Open Systems Interconnection (OSI) model is a reference tool for understanding datacommunications between any two networked systems. It divides the communications processes into seven layers. Each layer both performs specific functions to support the layers above it and offers services to the layers below it. The three lowest layers focus on passing traffic through the network to an end system. The top four layers come into play in the end system to complete the process. This whitepaper will provide you with an understanding of each of the seven layers, including their functions and their relationships to each other. This will provide you with an overview of the network process, which can then act as a framework for understanding the details of computer networking. Since the discussion of networking often includes talk of “extra layers”, this paper will address theseunofficial layers as well. Finally, this paper will draw comparisons between the theoretical OSI model and the functional TCP/IP model. Although TCP/IP has been used for network communications before the adoption of the OSI model, it supports the same functions and features in a differently layered arrangement.
An Overview of the OSI Model
Copyright ©2006 Global Knowledge Training LLC. All rightsreserved.
Page 2
A networking model offers a generic means to separate computer networking functions into multiple layers. Each of these layers relies on the layers below it to provide supporting capabilities and performs support to the layers above it. Such a model of layered functionality is also called a “protocol stack” or “protocol suite”. Protocols, or rules, can do their work ineither hardware or software or, as with most protocol stacks, in a combination of the two. The nature of these stacks is that the lower layers do their work in hardware or firmware (software that runs on specific hardware chips) while the higher layers work in software. The Open System Interconnection model is a seven-layer structure that specifies the requirements for communications between twocomputers. The ISO (International Organization for Standardization) standard 7498-1 defined this model. This model allows all network elements to operate together, no matter who created the protocols and what computer vendor supports them. The main benefits of the OSI model include the following: • Helps users understand the big picture of networking • Helps users understand how hardware and softwareelements function together • Makes troubleshooting easier by separating networks into manageable pieces • Defines terms that networking professionals can use to compare basic functional relationships on different networks • Helps users understand new technologies as they are developed • Aids in interpreting vendor explanations of product functionality
Layer 1 – The Physical Layer
The physicallayer of the OSI model defines connector and interface specifications, as well as the medium (cable) requirements. Electrical, mechanical, functional, and procedural specifications are provided for sending a bit stream on a computer network.
Copyright ©2006 Global Knowledge Training LLC. All rights reserved.
Page 3
Components of the physical layer include: • Cabling system components •Adapters that connect media to physical interfaces • Connector design and pin assignments • Hub, repeater, and patch panel specifications • Wireless system components • Parallel SCSI (Small Computer System Interface) • Network Interface Card (NIC) In a LAN environment, Category 5e UTP (Unshielded Twisted Pair) cable is generally used for the physical layer for individual device connections....
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