WEEK 7 : CABLES


CABLES
·      LAN Technology  Cabling.
·      A wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers without using wires.
·      LAN utilizes spread-spectrum based on radio waves to enable communication between devices in a limited area, also known as the basic service set.


Types Of Cables
Ø  Unshielded Twiested Pair (UTP) cable
Ø  Shielded Twisted Pair (STP) cable
Ø  Coaxial Cable
Ø   Fiber Optic Cable
Ø  Wireless LANs

UNSHIELDED TWISTED PAIR (UTP) CABLE
§  4 pairs of wires inside the jacket
each pair is twisted with a different number of twisted per inch

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5 categories:
category 1 : voice ( telephone wire)
category 2 : data to 4Mbps (local talk)
category 3 : data to 10Mbps (ethernet)
category 4 : data to 20Mbps (16Mbps token ring)
category 5 : data to 100Mbps (fast ethernet)
standard connector is an RJ-45 connector
Disadvantage of UTP : may be susceptible to radio and electrical frequency interference.

SHEILDED TWISTED PAIR (STP) CABLE
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Consist of tw0 individual wires wrapper in a foil shielding-help provide a more realiable data communication suitable for environments with electrical interference. Extra shielding can make the cables quite bulky.


COAXIAL CABLE
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Ø  has a single copper conductor at its center
Ø  a plastic layer provides insulation between the center conductor and a braided metal shield
Ø  the metal shield helps to block any outside interference from fluorescent lights,motors, and other computers.



coaxial cable connector:
Bayone-Neill-Concelman (BNC) connector
different types of adapters are available for BNC connectors, including:
v T-connector
v barrel connector
v terminator

FIBRE OPTIC CABLES
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v consists of a center glass core surrounded
v transmits lightrather than electronic signals eliminating the problem of electrical interference.
v large amount of electrical interference
v able to transmit signals over much longer distances than coaxial and twisted pair.



WIRELESS LANS
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Wireless telecommunications is the transfer of information between two or more points that are not physically connected.










WEEK 6 : NETWORK TOPOLOGY


Network topologies are categorized into the following basic types:
§                               BUS
§                               RING
§                                STAR
§                               TREE
§     MESH

More complex networks can be built as hybrids of two or more of the above basic topologies 

BUS  TOPOLOGY

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Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.



      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.



RING TOPOLOGY
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In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.
To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Advantages

·       There is no need for network server to control the connectivity between workstations.
·       Additional components do not affect the performance of network.
·       Each computer has equal access to resources.


Disadvantages

·       If one workstation or port goes down, the entire network gets affected.
·        Network is highly dependent on the wire which connects different components. 
·        MAU’s and network cards are expensive as compared to Ethernet cards and hubs. 




STAR TOPOLOGY
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Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hubswitch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)


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.



TREE TOPOLOGY
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Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Advantages
·        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.


MESH TOPOLOGY

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Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.


ETHERNET
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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


LOCALTALK

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LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s.CSMA/CA was implemented as a random multiple access method.













































 
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