Archive for May 2012
MESH TOPOLOGY
In a Mesh Topology, every node has a dedicated
point-to-point link to every other node. Messages sent on a mesh network can
take any of several possible paths from source to destination. A fully
connected mesh network has n (n-1)/2 physical links to link n devices.
Advantages of Mesh Topology
§ The use of large number of links eliminates network
congestion.
§ If one link becomes unusable, it does not disable the
entire system.
Disadvantages of Mesh Topology
§ The amount of required cabling is very large.
§ As every node is connected to the other, installation
and reconfiguration is very difficult.
§ The amount of hardware required in this type of
Topology can make it expensive to implement.
TREE TOPOLOGY
A Tree Topology combines
characteristics of linear bus and star topologies. It consists of groups of
star-configured workstations connected to a bus backbone cable.
Advantages
of Tree Topology
§ The distance to which a signal can travel increases as
the signal passes through a chain of hubs.
§ Tree Topology allows isolating and prioritising
communications from different nodes.
§ Tree Topology allows for easy expansion of an existing
network, which enable organizations to configure a network to meet their needs.
Disadvantages of Tree Topology
§ If the backbone line breaks, the entire segment goes
down.
§ It is more difficult to configure and wire than other
Topologies.
STAR TOPOLOGY
In Star Topology devices are
connected via a centralised network component known as hub or concentrator. The
hub acts as a central controller and if a node wants to send data to another
node, it boosts up the message to the intended node. This topologies commonly
uses twisted pair cable, however, coaxial cable or fiber optic cable can also
be used.
Advantages of Star Topology
§ Star Topology is easy to install and wire.
§ The network is not disrupted even if a node fails or
is removed from the network.
§ Fault detection and removal of faulty parts is easier
in Star Topology.
Disadvantages of Star Topology
§ It requires a longer length of cable.
§ If the hub fails, nodes attached to it are disabled.
§ The cost of the hub makes the network expensive as
compared to bus and Ring Topology.
RING TOPOLOGY
In Ring Topology, computers
are placed on a circle of cable. Every node has exactly two neighbors for
communication purposes.
All messages
travel through a ring in the same direction (clockwise or counterclockwise)
until it reaches its destination. Each node in the ring incorporates a
repeater. When a node receives a signal intended for another device, its
repeater regenerates the bits and passes them along the wire.
Advantages of Ring Topology
§ Ring Topology is easy to install and reconfigure.
§ Every computer is given equal access to the ring.
Hence, no single computer can monopolies the network.
Disadvantages of Ring Topology
§ Failure in any cable or node breaks the loop and can
take down the entire network.
§ Maximum ring length and number of nodes are limited.
BUS TOPOLOGY
Bus topology uses a common bus or backbone (a single
cable) to connect all devices with terminators at both ends. The backbone acts
as a shared communication medium and each node (file, server, workstations, and
peripherals) is attached to it with an interface connecter.
Whenever a message is to be transmitted on the network, it is passed
back and forth along the cable, past the stations and between the two
terminators, from one end of the network to the other. As the message passes
each station, the station checks the message’s destination address. If the
address in the message matches the station’s address, the station receives the
message. If the address does not match, the bus carries the message to the next
station, and so on.
Advantages of BUS Topology
§ Connecting a computer or peripheral to a linear bus is
easy.
§ This topology requires least amount of cabling to
connect the computers and, therefore, less expensive than other cabling
arrangement.
§ It is easy to extend a bus since two cables can be
joined into one longer cable with a connector.
Disadvantages of Bus Topology
§ Entire network shuts down if there is a failure in the
backbone.
§ Heavy traffic can slow down a bus because computers on
such networks do not coordinate with each other to reserve time to transmit.
NETWORK TOPOLOGY
Network topology is 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. The term
topology refers to the way a network is laid out, either physically or
logically. A topology can be considered as the network’s shape.
There are five basic topologies: Bus, Ring, Star, Tree, and Mesh.
- BUS TOPOLOGY
- RING TOPOLOGY
- STAR TOPOLOGY
- TREE TOPOLOGY
- MESH TOPOLOGY
WIDE
AREA NETWORK
Wide Area Network (WAN) is a computer
network that covers a broad area (i.e., any network whose communications
links cross metropolitan, regional, or national boundaries).
Several options are
available for WAN connectivity:
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Option:
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Description
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Advantages
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Disadvantages
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Bandwidth range
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Sample protocols used
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Point-to-Point connection between two computers or Local Area
Networks (LANs)
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Most secure
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Expensive
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Less Expensive
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Call Setup
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28 Kb/s - 144 Kb/s
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Devices transport packets via a shared single point-to-point or
point-to-multipoint link across a carrier internetwork. Variable length
packets are transmitted over Permanent Virtual Circuits (PVC) or
Switched Virtual Circuits (SVC)
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Shared media across link
| ||||
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Similar to packet switching, but uses fixed length cells instead
of variable length packets. Data is divided into fixed-length cells and then
transported across virtual circuits
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best for simultaneous use of Voice and data
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Overhead can be considerable
|
Transmission rate usually range from 1200 bits/second to 6 Mbit/s,
although some connections such as ATM and Leased lines can reach speeds greater
than 156 Mbit/s. Typical communication
links used in WANs are telephone lines, microwave links & satellite
channels.
METROPOLITAN
AREA NETWORK
A MAN, or Metropolitan
Area network, is a network of computers spread over a ‘metropolitan’ area such
as a city and its suburbs.
Some technologies used for this purpose are ATM, FDDI, and SMDS. These
older technologies are in the process of being displaced by Ethernet-based
MANs (e.g. Metro Ethernet) in most areas. MAN links radio, or infra-red laser links.
DQDB,
Distributed Queue Dual Bus, is the Metropolitan Area Network standard for data
communication. It is specified in the IEEE
802.6 standard. Using DQDB, networks can be up to 30 miles long and
operate at speeds of 34 to 155 Mbit/s.
LOCAL AREA NETWORK
A local area network (LAN) is a computer
network covering a small geographic area, like a home, office, or groups of
buildings e.g. a school.
LAN configurations consist
of:
§ A file server - stores all of the software that controls the
network, as well as the software that can be shared by the computers attached
to the network.
§ A workstation - computers connected to the file server (Mac or
PCs). These are less powerful than the file server
§ Cables - used to connect the network interface cards in each
computer.
Ethernet over unshielded twisted pair cabling, and Wi-Fi are the
two most common technologies currently for LAN, but ARCNET, Token
Ring and many others have been used in the past. Usually
LAN offers a bandwidth of 10 to 100 Mbps.Networking
==========================================
A computer network is a collection of two or more computers, which
are connected together to share information and resources. Computers in a
network are interconnected by telephone lines, coaxial cables, satellite links,
radio and/or some other communication technique. A network can be as few as
several personal computers on a small network or as large as the internet, a
worldwide network of computers.
Advantages of NETWORK
Speed. Sharing and transferring files within Networks are very rapid. Thus
saving time, while maintaining the integrity of the file.
Cost. Individually licensed copies of many popular software programs can be
costly. Networkable versions are available at considerable savings. Shared
programs, on a network allows for easier upgrading of the program on one single
file server, instead of upgrading individual workstations.
Security. Sensitive files and programs on a network are
passwords protected (established for specific directories to restrict access to
authorized users) or designated as "copy inhibit," so that you do not
have to worry about illegal copying of programs.
Centralized Software Management. Software can
be loaded on one computer (the file server) eliminating that need to spend time
and energy installing updates and tracking files on independent computers
throughout the building.
Resource Sharing. Resources such as, printers, fax machines and modems
can be shared.
Electronic Mail. E-mail aids in personal and professional
communication. Electronic mail on a LAN can enable staff to communicate within
the building having tot to leave their desk.
Flexible Access. Access their files from computers throughout the
firm.
Workgroup Computing. Workgroup software (such as Microsoft BackOffice)
allows many users to work on a document or project concurrently.
§ Server faults stop applications being available.
§ Network faults can cause loss of data.
§ Network fault could lead to loss of resources.
§ User work dependent upon network.
§ System opens to hackers.
§ Decisions tend to become centralized.
§ Could become inefficient.
§ Could degrade in performance.
§ Resources could be located too far from users.
§ Network management can become difficult.
