CIM 2465 Network Connectivity 1
Network Connectivity(Topic 2)
Textbook:
Networking Basics, CCNA 1 Companion Guide, Cisco Press
Cisco Networking Academy Program, CCNA 1 and 2, Companion Guide, Cisco Press, Latest Edition
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Analog Signal Vs Digital Signal
• Analog data is continuous data• The world we live in is mainly an analog
world. E.g. light, video, voice • Digital data is discrete, values are distinct
from one another.• Digital computers process data in digital
form (0 or 1)• A/D D/A conversion (e.g. modem)
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Analog Signal Vs Digital Signal
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Properties of an Analog Signal
• Amplitude
• Frequency
• Phase
• Modulation and Demondulation
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Factors AffectingTransmission of Signals
• Noise– Refers to any interference on the physical medium that makes it
difficult for the receiver to detect the data signal– Crosstalk
• Noise created on one wire as a result of current flowing over a nearby wire
• Attenuation– Attenuation in an electrical signal is a decrease in voltage as the
signal crosses the wire– Can be caused by
• Resistance of wires• Energy loss• Frequency of signal
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Digital Transmission
• Digital Transmission is a general term that refers to how computing devices transmit the binary bits from one to another
• Can be done by (Modulation)– Varying (modulating) an electrical signal as it
passes over a copper wire– Varying the power of light as sent over an
optical fiber– Varying the radio waves sent through space,
wireless communications
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Transmission Media
• Major types– Copper Wires
• Coaxial Cable, Shielded Twisted Pair (STP), Unshielded Twisted Pair (UTP)
– Optical– Wireless
• Considerations– Transmission speed– Digital or Analog transmission– Transmission distance
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Coaxial Cable
• Composed of a single copper wire, surrounded by an insulating shell, then a second conductor shield, and a plastic outer shell– Types:
• Thick Coaxial (10Base5)• Thin Coaxial (10Base2)
• Today’s modern LANs no longer use 10BASE5 and 10BASE2
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Coaxial Cable
• Advantages– Longer transmission distance than STP and UTP, few
er repeaters needed– Less expensive than fiber-optic, more expensive than
STP and UTP– High bandwidth medium that can carry thousands of
signals, support broadband transmission of cable TV, a single cable is divided into many channels for transmission. Commonly used to deliver cable-television signals and high-speed Internet access
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Coaxial Cable
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Twisted Pair Wire
• Most commonly used data transmission medium
• Its core consists of pairs of copper wires twisted together to create magnetic field and thus reduce interference
• 2 types: – Shielded Twisted Pair (STP)– Unshielded Twisted Pair (UTP)
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Shielded Twisted Pair (STP)
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Shielded Twisted Pair (STP)
• Shielding provides a cleaner electrical current by reducing attenuation and noise, thus longer cabling lengths
• More expensive, heavier, and difficult to bend when installing them (compare with UTP)
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Unshielded Twisted Pair (UTP)
• Grouped into categories based on quality
• Generally used in LAN
• Cat 5 cable• RJ45
connector
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Unshielded Twisted Pair (UTP)
• Adv– Does not require grounding like STP, easier to add co
nnectors– Thinner, more flexible to install– Same data speeds as other copper media
• Disadv– More susceptible to electrical noise and interference– Shorter cabling distance (100m when used for Ethern
et LANs)
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Twisted Pair Wire
• Advantages– Commonly available and relative low cost,
especially where telephone lines have already been installed
• Disadvantages– Subject to signal distortion, noise and
interference, and the relatively low transmission rates
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Fiber Optic Cable
• Thin wire (usually very pure glass or plastic) surrounded by a reflective cladding that is used to transmit optical signals (light)
• Copper wire cables transmit signals electrically, whereas fiber-optic cables transmit signals by means of light
• More expensive than copper wires, more skill to install
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Fiber Optic Cable
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Fiber Optic Cable
• Not susceptible to lightning, electromagnetic interference (EMI), or radio frequency interference (RFI), and does not generate EMI or RFI
• Much greater bandwidth• Greater transmission distances• Excellent signal quality
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Fiber Optic Cable
• More secure (difficult to tap)
• Thin, requires little space in a conduit
• Lightweight, easy to install
• Better resistance to environment factors, e.g. water
• Generally used to link LANs, WANs, or as backbone of large networks
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Fiber Optic Cable
• Fiber Optics Types:– Multi-mode cable
• Less expensive• Less expensive LED transmitters are used• Larger core, multiple angles of entry
– Single-mode cable• More expensive• More expensive laser transmitters are used• Significant longer cabling distances• Skinny core, only one angle of entry
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Fiber Optic Cable
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Wireless Media (1)
• Infrared
• Radio wave– Bluetooth– Wifi– Mobile Phone network (e.g. GSM, 3G)– Microwave– Satellite
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Wireless Media (2)
• WLAN Components– PCs with WLAN NICs– Access Points (APs), which act as a LAN hub for wirel
ess devices
• Infrastructure mode– Uses APs, with the PCs sending and receiving data to
and from the AP
• Ad-hoc mode– Formed by any two wireless devices, find and associa
te with each other
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Wireless Media (3)
• To install a WLAN that works with the existing LAN infrastructure– At least one AP– A straight-through cable to connect AP to an e
xisting LAN switch– Wireless NICs in end-user devices to commun
icate with the APs
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Wireless Media (4)
• WLAN Organization and Standards– IEEE defines WLAN standards 802.11– Wi-Fi alliance (www.wi-fi.org)
Standard Spectrum Used Max Data Rate
802.11a 5GHz 54Mbps
802.11b 2.4GHz 11Mbps
802.11g 2.4GHz 54Mbps
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LAN Cabling
• Considerations– Ethernet Types– Media– Speed– Distance– Connector
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LAN UTP Cabling Standards
Category Purpose Comments
1 Telephones Not suitable for data
2 Token Ring Supports 4Mbps Token Ring
3 Telephones and 10BASE-T
4 Token Ring Supports 16Mbps Token Ring
5 Ethernet 10BASE-T and 100BASE-T
5e Ethernet Supports Gigabit Ethernet
6 Ehernet Officially supports 1Gbps, working for 10Gbps support
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Ethernet LAN Media and Connectors
Ethernet Types Media Max Segment Length
Connector
10BASE2 50-ohm coax(Thinnet)
185m BNC
10BASE5 50-ohm coax
(Thicknet)
500m Attachment unit interface (AUI)
10BASE-T Cat 3,4,5 UTP 100m RJ45
100BASE-TX Cat 5 UTP 100m RJ45
100BASE-FX 62.5/125 micron multimode fiber
400m Duplex media interface connector (MIC), ST, or SC
1000BASE-T Cat 5 UTP 100m RJ45
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UTP Cable Pinouts
• Key concepts– Ethernet devices (at 10 and 100Mbps Ethenet) use on
e pair of wires to transmit data– Ethernet devices (at 10 and 100Mbps Ethenet) use a
nother pair of wires to receive data– Two pairs of wires are required
• Types– Straight-Through Cable– Crossover Cable– Console Connection and Rollover Cable
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Straight-Through Cable
• To connect an end-user device and a LAN hub or switch
• PC’s NIC uses– Pin 1, 2 to transmit– Pin 3, 6 to receive
• LAN hubs, switches (the other end)– Pin 3, 6 to transmit– Pin 1, 2 to receive
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Straight-Through Cable• TIA/EIA-T568-B or A on BOTH ends of the cable
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TIA/EIA 568-A
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Crossover Cable
• To connect two devices that both want to send on the same pins (two devices of similar ‘type’, e.g. two PCs)
• BOTH sides use– Pin 1, 2 to transmit– Pin 3, 6 to receive
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Crossover Cable• One side is T568-A and T568-B one the other (10BaseT,
100BaseT)• Special arrangement for 1000BaseT
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How to choose?
• Two groups of devices– PC, router, server, AP (use pins 1 and 2 to transmit)– Switch, hub, bridge, repeater (use pins 3 and 6 to transmit)
• When connecting two devices that are similar in regard to which pins they use to transmit, use a crossover cable– e.g. Switch to Switch, Switch to Hub, Hub to Hub, Router to Rout
er, PC to PC, Router to PC
• When connecting two devices that differ in regard to which pins they use to transmit, use a straight-through cable– e.g Switch to Router, Switch to PC, Hub to PC
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Basic Models for PC Communications (1)
• Peer-to-peer– A computer acts as a peer with other computer by acti
ng both as a client and a server– E.g. Sharing a folder in a Windows workgroup– Adv
• Simple to install• No special hardware required• Most OS support peer-to-peer networking• No network administrators required
– Disadv• Security• Loss control
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Basic Models for PC Communications (2)
• Client/Server– A computer acts as either a client or a server– Server usually is more powerful, and requires a more
expensive network operating system (NOS)– Adv
• Centralized control• Security control• Easier data backup
– Disadv• Cost• Network administrators required• If server fails, ….
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Comparing Peer-to-Peer and Client/Server
Comparison Point P-to-P C/S
Requires a dedicated server
Requires a more expensive NOS
Requires a dedicated network administrator
End users must be trained in network administration
More secure
Easier to back up data
Scales well
Single point of failure
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