A host device is either the source or destination of a message transmitted over the network.docx

7/27/2019 A host device is either the source or destination of a message transmitted over the network.docx

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A host device is either the source or destination of a message transmitted over the network. In order to

distinguish one host from another, each host on a network is identified by an address.

Servers are hosts that have software installed that enables them to provide information and services,

like e-mail or web pages, to other hosts on the network

Clients are hosts that have software installed that enables them to request and display the information

obtained from the server.

Data

Node

Peer

Network adapter

Hub

Switch

Router

Media- provides the channel over which the message travels from source to destination.

Transport Protocol

Bandwidth

A LAN- is usually administered by a single organization. The administrative control that governs thesecurity and access control policies are enforced on the network level.

Ethernet operates in the lower two layers of the OSI model: the of the Data Link layer and the Physical

layer.

Ethernet at Layer 1 involves signals, bit streams that travel on the media, physical components that put

signals on media, and various topologies. Ethernet Layer 1 performs a key role in the communication

that takes place between devices, but each of its functions has limitations.

As the figure shows, Ethernet at Layer 2 addresses these limitations. The Data Link sublayers contribute

significantly to technological compatibility and computer communications. The MAC sublayer is

concerned with the physical components that will be used to communicate the information and

prepares the data for transmission over the media..


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The Logical Link Control (LLC) sublayer remains relatively independent of the physical equipment that

will be used for the communication process.

The Layer 2 notation for network devices connected to a common medium


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network interface card (NIC), which inserts into the system bus of a computer and makes the connection

between running software processes on the computer and physical media. The NIC is not solely a

physical entity, however. Software associated with the NIC enables the NIC to perform its intermediary

functions of preparing data for transmission and encoding the data as signals to be sent on the

associated media.


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Topology - How the connection between the nodes appears to the Data Link layer

The topology of a network is the arrangement or relationship of the network devices and the

interconnections between them. Network topologies can be viewed at the physical level and the logical

level.

The physical topology is an arrangement of the nodes and the physical connections between them. The

representation of how the media is used to interconnect the devices is the physical topology. These will

be covered in later chapters of this course.

A logical topology is the way a network transfers frames from one node to the next. This arrangement

consists of virtual connections between the nodes of a network independent of their physical layout.

These logical signal paths are defined by Data Link layer protocols. The Data Link layer "sees" the logical

topology of a network when controlling data access to the media. It is the logical topology that

influences the type of network framing and media access control used.


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Logical topology of a network is closely related to the mechanism used to manage network access.

Access methods provide the procedures to manage network access so that all stations have access.

When several entities share the same media, some mechanism must be in place to control access.

Access methods are applied to networks regulate this media access. Access methods will be discussed in

more detail later.

Logical and physical topologies typically used in networks are:

Point-to-Point

Multi-Access

Ring

In point-to-point networks, if data can only flow in one direction at a time, it is operating as a half-

duplex link. If data can successfully flow across the link from each node simultaneously, it is a full-duplex

link.


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A logical multi-access topology enables a number of nodes to communicate by using the same shared

media. Data from only one node can be placed on the medium at any one time. Every node sees all the

frames that are on the medium, but only the node to which the frame is addressed processes the

contents of the frame.


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a logical ring topology, each node in turn receives a frame. If the frame is not addressed to the node, the

node passes the frame to the next node. This allows a ring to use a controlled media access control

technique called token passing.


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A WAN is a data communications network that operates beyond the geographic scope of a LAN.

When permanent dedicated connections are required, a point-to-point link is used to provide a pre-

established WAN communications path from the customer premises through the provider network to a

remote destination. Point-to-point lines are usually leased from a carrier and are called leased lines.


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Standard IEEE 802.15 - Wireless Personal Area Network (WPAN) standard, commonly known as

"Bluetooth", uses a device pairing process to communicate over distances from 1 to 100 meters.

Standard IEEE 802.16 - Commonly known as WiMAX (Worldwide Interoperability for Microwave Access),

uses a point-to-multipoint topology to provide wireless broadband access.

Global System for Mobile Communications (GSM) - Includes Physical layer specifications that enable the

implementation of the Layer 2 General Packet Radio Service (GPRS) protocol to provide data transfer

over mobile cellular telephony networks.

The Wireless LAN

A common wireless data implementation is enabling devices to wirelessly connect via a LAN. In general,

a wireless LAN requires the following network devices:

Wireless Access Point (AP) - Concentrates the wireless signals from users and connects, usually through

a copper cable, to the existing copper-based network infrastructure such as Ethernet.

Wireless NIC adapters - Provides wireless communication capability to each network host.

Standards include:

IEEE 802.11a - Operates in the 5 GHz frequency band and offers speeds of up to 54 Mbps. Because this

standard operates at higher frequencies, it has a smaller coverage area and is less effective at

penetrating building structures. Devices operating under this standard are not interoperable with the

802.11b and 802.11g standards described below.

IEEE 802.11b - Operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mbps. Devices

implementing this standard have a longer range and are better able to penetrate building structures

than devices based on 802.11a.

IEEE 802.11g - Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps. Devices

implementing this standard therefore operate at the same radio frequency and range as 802.11b but

with the bandwidth of 802.11a.

IEEE 802.11n


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The IEEE 802.11n standard is currently in draft form. The proposed standard defines frequency of 2.4

Ghz or 5 GHz. The typical expected data rates are 100 Mbps to 210 Mbps with a distance range of up to

70 meters.

A host device is either the source or destination of a message transmitted over the network.docx

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