Saturday, 26 May 2012


• Cable is the medium through which information usually moves from one network device to another.
• Several types of cable are commonly used with LANs.
• In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types.

 -Types of Cables
• Unshielded Twisted Pair (UTP) Cable
• Shielded Twisted Pair (STP) Cable
• Co-axial Cable
• Fiber Optic Cable

        1)      Unshielded Twisted Pair (UTP) Cable

  •  The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices.
Category 1
Voice (Wayer Telefon)
Category 2
Data to 4 Mbps (LocalTalk)
Category 3
Data to 10 Mbps (Ethernet)
Category 4
Data to 20 Mbps (16 Mbps Token Ring)
Category 5
Data to 100 Mbps (Fast Ethernet

  •   The standard connector for unshielded twisted pair cabling is an RJ-45 connector


  •  A disadvantage of UTP cable is that it may be susceptible to radio and electrical frequency interference.

      2)      Shielded Twisted Pair (STP) Cable


-         - STP is a type of cable consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication.
Suitable for environments with electrical interference;
• However, the extra shielding can make the cables quite bulky.
• Often used on networks using Token Ring topology.

      3)      Co-axial Cable
  • Coaxial cabling has a single copper conductor at its center.
  •  A plastic layer provides insulation between the center conductor and a braided metal shield
  • The metal shield helps to block any outside interference from fluorescent lights, motors, and  other computers.

-Coaxial Cable Connectors

• The most common type of connector used with coaxial cables is the Bayonet-Neill-Concelman (BNC) connector
• Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator.

       4)      FIBRE OPTICS

consists of a center glass core surrounded by several layers of protective materials
• It transmits light rather than electronic signals eliminating the problem of electrical interference.
Ideal for certain environments that contain a large amount of electrical interference
Able to transmit signals over much longer distances than coaxial and twisted pair.

Summary of:

Ethernet Cabling
Cable Type
Maximum length
Unshielded Twisted Pair
100 meters
Thin Coaxial
185 meters
Thick Coaxial
500 meters
Fiber Optic
2000 meters

Cable Topology
Physical Topology
Linear Bus

Twisted Pair

Twisted Pair
Star-Wired Ring
Twisted Pair
Token Ring

Twisted Pair

Network Operating System (NOS)

·         Software that controls a network and its message (e.g. packet) traffic and queues, controls access by multiple users to network resources such as files, and provides for certain administrative functions, including security.
·         coordinate the activities of multiple computers
·         Across a network.
·         Acts as a director to keep the network running smoothly.

·         A NOS is not the same as the networking tools provided by some existing OSs, Windows XP for instance.
·         An NOS is an OS that has been specifically written to keep networks running at optimal performance.
·         Some popular NOSs include:
o   Windows NT , IBM AIX, Sun Solaris, Windows 2000 Server, Windows Server 2003,Inferno Novell NetWare, Red Hat Linux, BSD.

·         There are two major types of network operating system:
1.      Peer-to-Peer
2.      Client/Server

1)      Peer- to-Peer

• In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network
• Allow users to share resources and files located on their computers and to access shared resources found on other computers.
• Do not have a file server or a centralized management source
• Designed primarily for small to medium local area networks.
• AppleShare and Windows for Workgroups are examples of programs that can function as peer-to-peer network operating systems.
• Less initial expense - No need for a dedicated server.
• Setup - An operating system such as Windows XP/…) already in place may only need to be reconfigured for peer-to-peer operations.

• Decentralized - No central repository for files and applications.
• Security - Does not provide the security available on a client/server network.

2)      Client/Server

o   Allow the network to centralize functions and applications in one or more dedicated file servers
o   The file servers become the heart of the system, providing access to resources and providing security.
o   Individual workstations (clients) have access to the resources available on the file servers.
o   Novell Netware and Windows 2000 Server are examples of client/server network operating systems.


• 10/100/1000 Mbps Ethernet
• 100 Mbps FDDI
• 155/620 Mbps ATM
• 4/10/45 Mbps Wireless

What is a Protocol?

• A protocol is a set of rules that governs the communications between computers on a network.
• These rules include guidelines that regulate the following characteristics of a network:
– Access method,
– allowed physical topologies,
– Types of cabling, and
– Speed of data transfer
• Protocol (communications protocol) = standards that specifically address how the devices on a network communicate, i.e
– How the data is packaged for transmission
– How receiving devices acknowledge signals from sending devices
– How errors are detected and handled

Logical topologies are bound to network protocols and describe how data is moved across the network.
Ethernet, Local Talk, Token ring for wired networks
• TCP/IP and WAP for internet
• Wi-Fi for wireless networks
• Bluetooth, for short range wireless network

     A)    Ethernet

• The most widely used wired networks protocol
• Early Ethernet network were half duplex, uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection) a system where each computer listens to the cable before sending anything through the network to avoid collisions.
• Since 1997 Ethernet uses full duplex communication, that does not require listening to other messages and no collisions occur.
• The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted over wireless access points, twisted pair, coaxial, or fiber optic cable.
• Early Ethernet protocols (10BASE-T) support 10BASE transmissions rate 10 Mbps
• Today
– 100BASE-T or 100BASE-TX – 1000Mbps (1Gbps
– 10Gigagbit Ethernet – 10Gbps

     B)    LOCALTALK

• A network protocol that was developed Macintosh computers.
• Used a method called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), where a computer signals its intent to transmit before it actually does so.
• Allows for linear bus, star, or tree topologies using twisted pair cable.
Disadvantage: slow speed (only 230 Kbps).

     C)    TOKEN RING

• developed by IBM in the mid-1980s.
Access method involves token-passing.
• The computers are connected so that the signal travels around the network from one computer to another in a logical ring.
• A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant- the data is captured by the receiving computer.
-The Token Ring protocol requires a star-wired ring using twisted pair or fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps.

     D)    FDDI

• Fiber Distributed Data Interface - a network protocol that is used primarily to interconnect two or more local area networks, often over large distances.
Access method involves token-passing.
Uses a dual ring physical topology. Transmission normally occurs on one of the rings; if a break occurs, the system keeps information moving by automatically using portions of the second ring to create a new complete ring.
• A major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps.