Network Model Illustration

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Network Model :: Physical Layer

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The physical layer in a network model coordinates the functions required to carry a bit stream over a physical medium. It deals with the mechanical and electrical specifications of the interface and transmission medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur. Figure 2.5 shows the position of the physical layer in a network model with respect to the transmission medium and the data link layer of the network model.


Physical layer in a network model
Figure 2.5

Physical layer in a network model



The physical layer in network model is responsible for movements of individual bits from one hop (node) to the next.

The physical layer in a network model is also concerned with the following:

Physical characteristics of interfaces and medium.

The physical layer in a network model defines the characteristics of the interface between the devices and the transmission medium. It also defines the type of transmission medium.

Representation of bits.

The physical layer data consists of a stream of bits (sequence of Os or Is) with no interpretation. To be transmitted, bits must be encoded into signals — electrical or optical. The physical layer in a network model defines the type of encoding (how 0's and 1's are changed to signals).

Data rate.

The transmission rate — the number of bits sent each second — is also defined by the physical layer in a network model. In other words, the physical layer in a network model defines the duration of a bit, which is how long it lasts.

Synchronization of bits.

The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level. In other words, the sender and the receiver clocks must be synchronized.

Line configuration.

The physical layer in a network model is concerned with the connection of devices to the media. In a point-to-point configuration, two devices are connected through a dedicated link. In a multipoint configuration, a link is shared among several devices.

Physical topology.

The physical topology defines how devices are connected to make a network model. Devices can be connected by using a mesh topology (every device is connected to every other device), a star topology (devices are connected through a central device), a ring topology (each device is connected to the next, forming a ring), a bus topology (every device is on a common link), or a hybrid topology (this is a combination of two or more topologies).

Transmission mode.

The physical layer in a network model also defines the direction of transmission between two devices: simplex, half-duplex, or full-duplex. In simplex mode, only one device can send; the other can only receive. The simplex mode is a one-way communication. In the half-duplex mode, two devices can send and receive, but not at the same time. In a full-duplex (or simply duplex) mode, two devices can send and receive at the same time.


Next

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Network Model

Layered Tasks in a Network Model

Network Model: THE OSI MODEL

Network Model :: Physical Layer

Network Model :: Data Link Layer

Network Model :: Network Layer

Network Model :: Transport Layer

Network Model :: Session Layer

Network Model :: Presentation Layer

Network Model :: Application Layer

TCP/IP protocol suite in a Network Model

Addressing system in a Network Model

Important Points about Network Model


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