*What is a Network?
Network is defined as having two or more devices (like workstations, printers, and servers) linked together for the purpose of sharing information, resources, or both.
*A local-area network (LAN) interconnects computers within a limited geographical area, such as within a building or campus
*When two or more LANs are linked within a city or limited geographic area, it is considered a metropolitan-area network (MAN).
*A wide-area network (WAN) has few geographic limits. WANs can cover a city, country, or even the entire world. The Internet is an example of a WAN.
*Topologies - Describe the actual physical layout of the network. Common physical topologies are the bus, ring, star, extended star, hierarchical, and mesh.
In 1984, the International Organization for Standardization (ISO) developed the OSI
Reference Model to describe how information is transferred from one networking
component to another
The OSI Reference Model defines the process of connecting two layers of networking
functions. The application layer provides the user interface. The presentation layer
determines how data is represented to the user. The session layer is responsible for
setting up and tearing down connections. The transport layer is responsible for the
mechanics of connections, including guaranteed services. The network layer provides
a logical topology and layer 3 addresses: routers operate here. The data link layer
defines MAC addresses and how communication is performed on a specific media
type: switches, bridges, and NICs operate here. The physical layer defines physical
properties for connections and communication: repeaters and hubs operate here.
Wireless solutions are defined at the physical layer.
As this information is
passed from higher to lower layers, each layer adds information to the original
data�typically a header and possibly a trailer. This process is called encapsulation
Data--------- Application, presentation, and session layers
Segment ---Transport layer
Packet ------Network layer (TCP/IP calls this a datagram)
Frame -------Data link layer
Bits--------- --Physical layer
TABLE 2-3
Ethernet is a LAN technology that functions at the data link layer. Ethernet uses
the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) mechanism
to send information in a shared environment. Ethernet was initially developed with
the idea that many devices would be connected to the same physical piece of wiring.
The acronym CSMA/CD describes the actual process of how Ethernet operates on a
shared medium.
Bandwidth:The capacity of media to transmit data, and a range of frequencies.
When discussing signals on networks, the speed at which the signals travel and the type of transmission are important to keep in mind. The speed of the signals is called bandwidth while the type of transmission can be either baseband or broadband. This section discusses both issues.
Bandwidth (the width of a band of electromagnetic frequencies) is used to describe (1) how fast data flows on a given transmission path and (2) the range of frequencies that a signal occupies on a given medium.
A digital or analog signal has a bandwidth. Today this is expanded to include fiber-optic based light impulses. Typically the amount of bandwidth is measured by the amount of data that can be transferred in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second (Bps). For analog devices, the bandwidth is expressed in cycles per second, or hertz (Hz).
Bandwidth, generally speaking, is proportional to the amount of data that can be transmitted or received in a certain amount of time.
baseband describes a communications system in which the media carries one signal only.
Broadband:A transmission method that takes multiple signals and places it on one cable
LANs with bandwidth of 10 Mbps:
� 10BASE2 (Uses a thin coaxial cable, known as thinnet, with a maximum segment length of 185 m)
� 10BASE5 (Uses a thick coaxial cable, known as thicknet, with a maximum segment length of 500 m)
� 10BASE-T (Uses twisted-pair cable with a maximum segment length of 100 m)
LANs with bandwidth of 100 Mbps:
� 100BASE-T (four pairs of twisted-pair wire)
� 100BASE-TX (two pairs of data grade twisted-pair wire)
� 100BASE-FX (a two-strand fiber-optic cable)
Backbone
A pathway or cable that runs between telecommunications rooms (TRs) and buildings.
