The study of the arrangement or mapping
of the elements (links, nodes, etc.) of a network, especially the physical
(real) and logical (virtual) interconnections between nodes.
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Topology
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Topology
PHYSICAL TOPOLOGY
Any given node in the LAN will have one or more
links to one or more other nodes in the network and the mapping of these links
and nodes onto a graph results in a geometrical shape that determines the physical
topology of the network..
LOGICAL TOPOLOGY
the mapping of the flow of data between the nodes in the network determines the
logical topology of the network ..
Types/Classification of physical topologies:
- LINEAR BUS
-A linear bus topology consists of a main run
of cable with a terminator at each end.
-All nodes (file server, workstations, and
peripherals) are connected to the linear cable.
-Ethernet and LocalTalk networks use a linear
bus topology.
*Advantages
-Easy to connect a computer or peripheral to a
linear bus.
-Requires less cable length than a star
topology.
*Disadvantages
-Entire network shuts down if there is a break
in the main cable.
-A faulty cable or workstation will take the
entire LAN down
-Terminators are required at both ends of the
backbone cable.
-Difficult to identify the problem if the
entire network shuts down.
-Not meant to be used as a stand-alone solution
in a large building.
-A star topology is designed with each node (file server, workstations, and peripherals)
connected directly to a central network hub or concentrator .
-This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.
*Advantages
-Easy to install, and wire.
-Easy to add new workstations
-No disruptions to the network when connecting
or removing devices.
-Any non-centralised failure will have very
little effect on the network
-Easy to detect faults and to remove parts.
-Centralized control
-Centralized network/hub monitoring
*Disadvantages
-Requires more cable length than a linear
topology.
-If the hub or concentrator fails, nodes
attached are disabled.
-More expensive than linear bus topologies
because of the cost of the concentrators
- STAR-WIRED RING
-A star-wired topology may appear (externally)
to be the same as a star topology.
-Internally, the MAU (multistation access unit) of a star-wired
ring contains wiring that allows information to pass from one device to another
in a circle or ring
- TREE
-A tree topology combines characteristics of
linear bus and star topologies.
-It consists of groups of star-configured
workstations connected to a linear bus backbone cable. Tree topologies allow
for the expansion of an existing network, and enable schools to configure a
network to meet their needs.
*Advantage
-Point-to-point wiring for
individual segments
*Disadvantages
-Overall length of each segment is limited by
the type of cabling used.
-If the backbone line breaks, the entire
segment goes down.
-More difficult to configure and wire than
other topologies.
WHAT IS MEAN BY???
- NIC
-stands
for Network Information Center
-For
example, the organization named "InterNIC" is a NIC that provides information
to the general public on Internet domain names.
provides
the hardware interface between a computer and a network. A NIC technically is
network adapter hardware in the form factor of an add-in card such as a PCI
or PCMCIA
card.
-Some NIC cards work with wired connections while others are wireless. Most NICs support either wired Ethernet or WiFi wireless standards. Ethernet NICs plug into the system bus of the PC and include jacks for network cables, while WiFi NICs contain built-in transmitters / receivers (transceivers).
-In new computers, many NICs are now pre-installed by the manufacturer. All NICs feature a speed rating such as 11 Mbps, 54 Mbps or 100 Mbps that suggest the general performance of the unit.
- NOS
-Network
Operating System
-System
that is designed primarily to support workstation, personal computer, and, in
some instances, older terminal that are connected on a local area network
(LAN). Artisoft's LANtastic, Banyan VINES, Novell's NetWare, and Microsoft's
LAN Manager are examples of network operating systems.
-In
addition, some multi-purpose operating systems, such as Windows NT and
Digital's OpenVMS come with capabilities that enable them to be described as a
network operating system.
-A
network operating system provides printer sharing, common file system and
database sharing, application sharing, and the ability to manage a network name
directory, security, and other housekeeping aspects of a network.
- CONCENTRATOR
-For example, ISPs use concentrators to combine their dial-up modem connections onto faster T-1 lines that connect to the Internet.
-Concentrators are also used in local-area networks (LANs) to combine transmissions from a cluster of nodes. In this case, the concentrator is often called a hub or MAU.
- REPEATER
-Repeaters are used in transmission systems to regenerate analog or digital signals distorted by transmission loss. Analog repeaters frequently can only amplify the signal while digital repeaters can reconstruct a signal to near its original quality.
-In a data network, a repeater can relay messages between subnetworks that use different protocols or cable types. Hubs can operate as repeaters by relaying messages to all connected computers. A repeater cannot do the intelligent routing performed by bridges and routers.
- SWITCH
-In
a telecommunications network, a switch is a device that channels incoming data
from any of multiple input ports to the specific output port that will take the
data toward its intended destination. In the traditional circuit-switched
telephone network, one or more switches are used to set up a dedicated though
temporary connection or circuit for an exchange between two or more parties.
-On
an Ethernet local area network (LAN), a switch determines from the physical
device (Media Access Control or MAC) address in each incoming message frame
which output port to forward it to and out of. In a wide area packet-switched
network such as the Internet, a switch determines from the IP address in each
packet which output port to use for the next part of its trip to the intended
destination.
- GATEWAY
In homes, the gateway is the ISP that connects the user to the internet.
In enterprises, the gateway node often acts as a proxy server and a firewall.
-The gateway is also associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway.
-A computer system located on earth that switches data signals and voice signals between satellites and terrestrial networks.
An earlier term for router, though now obsolete in this sense as router is commonly used.
- ETHERNET
-Ethernet
is a type of network cabling and signaling specifications developed by Xerox in
the late 1970. While Internet is a global network, Ethernet is a local area
network (LAN).
Ethernet is the most
widely-installed local area network ( LAN) technology.-Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel.
-An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD ) protocol.
-Read this:
http://www.creative-wisdom.com/teaching/network/ethernet.shtml
- LOCALTALK
-Such networks are sometimes called LocalTalk networks .
Although LocalTalk networks are relatively slow, they are popular because they are easy and inexpensive to install and maintain. An alternative cabling scheme that is faster is Ethernet.
