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Identifying the OSI Layers at Which Various Network Components Operate

When you have an understanding of the OSI model, it is possible to relate network connectivity devices to the appropriate layer of the OSI model. Knowing at which OSI level a device operates allows you to better understand how it functions on the network. Table 2 identifies various network devices and maps them to the OSI model.

Table 2 Mapping Network Devices to the OSI Model

Device

OSI Layer

Hub

Physical (Layer 1)

Switch

Data-link (Layer 2)

Bridge

Data-link (Layer 2)

Router

Network (Layer 3)

NIC

Data-link (Layer 2)

WAP

Data-link (Layer 2)


Differentiating Among Protocols

You might find yourself working with a number of protocols in today's networked environments. The primary function of these protocols is to facilitate communication between network devices. This section reviews the main characteristics of the most widely used protocols.

Connectionless and Connection-oriented Protocols

Before getting into the characteristics of the various network protocols and protocol suites, it's important to first identify the difference between connection-oriented and connectionless protocols.

In a connection-oriented communication, there is guaranteed delivery of the data. Any packet that is not received by the destination system is resent by the sending device. Communication between the sending and receiving devices continues until the transmission has been verified. Because of this, connection-oriented protocols have a higher overhead and place greater demands on bandwidth.

In contrast to connection-oriented communication, connectionless protocols offer only a best-effort delivery mechanism. Basically, the information is sentthere is no confirmation that the data has been received. If there is an error in the transmission, there is no mechanism to resend the data, so transmissions made with connectionless protocols are not guaranteed. Connectionless communication requires far less overhead than connection-oriented communication, so it is popular in applications such as streaming audio and video where a small number of dropped packets might not represent a significant problem.

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