A virtual LAN (VLAN) allows geographically dispersed network nodes to communicate as if they were on the same physical network by logically grouping nodes. A switch that supports VLANs allows the administrator to group specific switch ports together in a VLAN. Data passed between these ports will be isolated from other switch ports. Wired media like twisted pair wire, coaxial cable, and fiber optic cable can be used to physically connect network nodes, with each having advantages and disadvantages regarding attributes like noise absorption, bandwidth, and security.

2. • A virtual local area network (virtual
LAN) is the logical grouping of
network nodes. A virtual LAN allows
geographically dispersed network
nodes to communicate as if they were
physically on the same network.
• A switch that supports VLANs
allows the administrator to select
which ports will participate in the
VLAN. These ports are then grouped
to become one VLAN, and any
broadcasts or information passed
among these ports will not be seen by
the remaining ports on the switch.

3. • There are several types of physical channels through which data can
be sent from one point to another in a LAN.
• Bounded/Guided Media (Wired)
• Unbounded/Unguided Media (Wireless)
• Media differ in the capability for the following reasons:
1. Noise absorption: Susceptibility to external noise
2. Radiation: Leakage of signal
3. Attenuation: decline of magnitude of signal with distance
4. Bandwidth: transmission speed

4. • Wired media
1. Twisted-pair wire : LAN
2. Coaxial cabling : Cable TV
3. Fiber-optic cabling : Broadband

5. • two insulated copper wires (1 mm thick)
• The purpose of twisting the wires is to ensure that each wire is
equally exposed to any external electrical magnetic field that could
induce unwanted noise.
• commonly used in local telephone communication and for digital
data transmission over short distances up to 1 km. (9600 bps)

6. Insulator (Teflon in Cat 5)

7. • being the oldest method, trained manpower is easily available
• In a telephone system, signals can travel several kilometers without
amplification
• can be used for both analog and digital data transmission
• least expensive
• if a portion of a twisted-pair cable is damaged, the entire network is
not shutdown

8. • easily picks up noise signals
• thin (break easily)

9. • Category 3 : 4 pairs
• Category 5 : 4 pairs but more twisted with Teflon insulation
• Category 6 : Gigabyte Ethernet

10. • stiff (rigid) copper wire surrounded by an insulating material
• The insulator is encased within a cylindrical conductor (braided
mesh)
• The signal is transmitted by the inner copper wire

11. • Two types:
1. 50-ohm : digital transmission
2. 75-ohm : analog transmission (Cable TV)

12. Terms Implementation
10Base2 Thin Ethernet (RG-58), 10MBPS, 185m cable segment
10Base5 Thick Ethernet, 10MBPS, 500m cable segment(bus)
10BaseF Fiber-optic cable
10BaseT UTP, uses RJ-45 connectors, Star Topology, 100m length
Thick
Ethernet
0.4 inch thick, 1006m
Thin
Ethernet
0.2 inch thick, 165m, normally used for office
installation

13. • better shielding against EMI(Electromagnetic interference) than
twisted-pair cable
• can be used for both analog and digital
• higher bandwidth (noise immunity)
• more expensive than TP but easy to handle
• capable of carrying over 50 std 6MHz color TV channels

14. • Cables that employ copper conductors can easily be breached by
listening equipment.
• If the main consideration is security, then fiber cable is the only
choice to avoid espionage.

15. • newest form of bounded media
• superior in data handling and security
• transmits light signals rather than electric signals
• each fiber has an inner core of glass/plastic that conducts light

16. • total internal reflection

17. • Two light sources:
1. LEDs (Light Emitting Diodes)
2. LASERs(Light Amplification by Stimulated Emission Radiation)
Photoelectric
diodes
LED/Laser

18. • Two types:
1. Single-mode fiber (8-10µ (microns) core)
2. Multimode fiber (50µ microns core) 1µ = 10-6 m
Laser
LED

19. • Cost: more expensive than copper cable (associated equipments)
• Installation: difficult to install
• Bandwidth capacity: provides data rates from 100MBPS to 2GBPS
• Node capacity: 75 nodes
• Attenuation: much lower attenuation but has a different problem,
namely, chromatic dispersion
• EMI: immune to eavesdropping
• Mode of transmission: half duplex

21. • handle much higher bandwidth with low attenuation
• not affected by power surges, EMI or power failures
• lighter than copper cable
• do not leak light and are quite difficult to tap (excellent security)

22. • unfamiliar technology requiring skills
• Being unidirectional, two-way communication requires either two
fiber cables or two frequency bands on one fiber
• higher cost

23. Factor UTP STP Coaxial Fiber-optic
Cost Lowest Moderate Moderate Highest
Installation Easy Fairly easy Fairly easy Difficult
Bandwidth 1-155 Mbps 1-155 Mbps 100 Mbps 2 Gbps
Attenuation High (few hundred
meter)
High (few
hundred meter)
Lower (few
kilometer)
Lowest (tens of
kilometer)
EMI Most vulnerable to
EMI and
eavesdropping
Less vulnerable
than UTP
Less vulnerable
than UTP
Not affected by
EMI or
eavesdropping

24. • signals are not guided through a solid medium (Air)
• Radio wave (including VHF and microwave links)
• Satellite links
• VSATs(Very Small Aperture Terminals)
• Infrared and millimeter waves

25. • frequencies between 10 KHz and 1 GHz
• broadcast omnidirectionally or unidirectionally
• The power of the Radio Frequency (RF) signal is determined by the
antenna and trans-receiver.

26. • easy to generate
• travel long distances
• penetrate buildings easily
• omnidirectional
• At low frequency, radio waves pass through obstacles easily, but the
power falls off sharply with distance from source.
• At high frequency, radio waves tend to travel in straight lines and
bounce off obstacles.
• absorbed by rain

27. • Above 100 MHz, the waves travel in straight lines and can,
therefore, be narrowly focused.
• Concentrating all the energy into a small beam using a parabolic
antenna gives a much higher signal to noise ratio, but the
transmitting and receiving antennas must be accurately aligned with
each other.
• uses repeaters at intervals of about 25-30 km to amplify weak signal

28. • do not pass through buildings well
• Multipath Fading (delayed waves may arrive out of phase)
• The higher the towers are, the further apart they can be.

29. • transmission depends on weather and frequency. (10GHz)
• widely used for long-distance telephone communication, cellular
telephones, television distribution
• inexpensive as compared to fiber-optic system (congested area)
• 16 Gbps

30. • Two Types:
1. Terrestrial
2. Satellite

31. • use directional parabolic antennas to send and receive signals
• Relay towers and repeaters are used to extend signals
• used whenever cabling is cost-prohibitive such as in hilly areas or
crossing rivers etc.

32. • Frequency range : 4-6 GHz and 21-23 GHz
• Cost : inexpensive for short distance but expensive for long distance
• Installation: difficult due to Line-of-sight requirements
• Bandwidth capacity: 1-10 Mbps
• Attenuation: affected by atmospheric conditions (rain and fog)
• EMI: vulnerable to EMI, jamming and eavesdropping

33. • one antenna is on the satellite in geo-synchronous orbit about
36,000 km above the equator (can reach the most remote places)
• the transmitted frequency is different from the receiving frequency
to avoid interference

34. • Frequency range: 4-6 GHz and 11-14 GHz
• Cost: The cost of building and launching a satellite is extremely
high
• Installation: extremely technical and difficult
• Bandwidth capacity: 1-10 Mbps
• Attenuation: depends on frequency, power, antenna size and
atmospheric conditions. Higher frequency microwaves are more
affected by rain and fog

35. • visible from any point
• transmission and reception costs are independent of the distance
• a transmission station can receive its own transmission (testing)
• cost of placing the satellite
• a signal sent to a satellite is broadcast to all receivers within the
range (security measures need to be taken)

36. • Very Small Aperture Terminals (1m wide antennas)
• the micro-stations do not have enough power to communicate
directly with one another, hence
• a special ground station, the hub, with a large high-gain antenna is
needed to relay traffic between VSATs

37. • connect two LANs in two buildings via lasers mounted on their
roof-tops
• Coherent optical signaling using lasers is inherently unidirectional.
So, each buildings needs its own Laser and photo detector

38. • Advantages:
1. bandwidth is very high at very low cost
2. easy to install
3. does not require any license
• Disadvantages:
1. cannot penetrate rain or thick fog
2. heat from sun causes convection currents

39. • used for short-range communication (remote control in TV)
• directional, cheap and easy to build but do not pass through solid
objects
• Security if Infrared systems against eavesdropping is better than
that of radio systems
• No government license is needed (radio systems must be licensed)

40. Factor LED Laser
Data rate Low High
Mode Multimode Multimode or single-mode
Operating distance 3 Km 30 Km
Lifetime Long life Short life
Temperature sensitivity Minor Substantial
Cost Low Substantial
• Light Source: LED/Laser
• Transmission medium: Fiber-optic cable
• Detector: converter

41. • a network that connects the computer and networks within an
organization by using the hardware and software that is used on the
Internet (TCP/IP protocol)
• secure & can have thousands of users
Intranet
(HCL)
Intranet
(Wipro)Internet
Extranet