9-jun-14data link layer guided media media that provide a conduit from one device to another....
TRANSCRIPT
Apr 10, 2023 Data Link Layer
Guided Media
Media that provide a conduit from one device to another.
Signals travelling along any of these media is directed and contained by the physical limits of the medium.
Examples are: Twisted-pair cable Coaxial cable Fiber-optic cable
Apr 10, 2023 Data Link Layer
Twisted-Pair Cable
Uses two metallic (copper) conductors with individual plastic insulator each.
Accepts and transports signals in the form of electric current.
One wire is used to carry signals to the receiver and the other is used as a ground reference.
The receiver uses the difference between the two signal levels in the wires.
Noise or crosstalk effect is balanced by twisting the wires.
Figure 7.3 Twisted-pair cable
Apr 10, 2023 Data Link Layer
Twisted-Pair (Continued…)
Twisted-pair cable can be divided into: Unshielded (UTP) – The most common
twisted-pair cable used in data communication.
Shielded (STP) – IBM’s version for its use. It has a metal foil of braided-mesh covering encasing each pair of the insulated conductors. It improves the quality of the cable, but it is bulkier.
Figure 7.4 UTP and STP
Apr 10, 2023 Data Link Layer
Twisted-Pair (Continued…)
Standards: The Electronic Industries Association
(EIA) has developed standards to classify UTP cable into seven categories based on their quality.
Category 1 is the lowest in quality and category 7 is the highest.
Connectors: The most common is RJ45, which is a
keyed connector.
Table 7.1 Categories of unshielded twisted-pair cablesTable 7.1 Categories of unshielded twisted-pair cables
Category Bandwidth Data Rate Digital/Analog Use
1 very low < 100 kbps Analog Telephone
2 < 2 MHz 2 Mbps Analog/digital T-1 lines
3 16 MHz 10 Mbps Digital LANs
4 20 MHz 20 Mbps Digital LANs
5 100 MHz 100 Mbps Digital LANs
6 (draft) 200 MHz 200 Mbps Digital LANs
7 (draft) 600 MHz 600 Mbps Digital LANs
Figure 7.5 UTP connector
Apr 10, 2023 Data Link Layer
Twisted-Pair (Continued…)
Performance: A twisted-pair cable can pass a wide
range of frequencies. However, the attenuation (dB/mi) sharply increases with frequencies above 100KHz.
Applications: Voice and data channels in telephone
lines. High data rate connections in DSL lines. 10Base-T and 100Base-T LANs.
Figure 7.6 UTP performance
Apr 10, 2023 Data Link Layer
Coaxial Cable
Uses central core conductor of solid or stranded copper wire enclosed in an insulating sheath.
The insulating sheath is then encased in an outer conductor of metal foil, braid or a combination of the two.
The metallic wrapping serves both as a shield against noise and as a second conductor that completes the circuit.
This outer conductor is also enclosed in another insulating sheath and the whole thing is protected by a plastic cover.
Figure 7.7 Coaxial cable
Apr 10, 2023 Data Link Layer
Coaxial Cable (Continued…)
Standards: Categorised by their radio government
(RG) ratings with each number denotes a unique set of physical specifications.
Category Impedance Use
RG-59RG-59 75 Cable TV
RG-58RG-58 50 Thin Ethernet
RG-11RG-11 50 Thick Ethernet
Apr 10, 2023 Data Link Layer
Coaxial Cable (Continued…)
Connectors: The most commonly used connectors
are the Bayone-Neill-Concelman (BNC) connectors.
The three popular types of BNC are: BNC – used to connect the end of the cable
to a device, such as TV set. BNC T – used in Ethernet networks to branch
out a cable for connection to a computer or other devices.
BNC terminator – used at the end of the cable to prevent the signal reflection.
Figure 7.8 BNC connectors
Apr 10, 2023 Data Link Layer
Coaxial Cable (Continued…)
Performance: Coaxial cable has a much higher
bandwidth compared to the twisted-pair cable. However, the signal weakens rapidly and it requires frequent use of repeaters.
Applications: Analogue and digital telephone
networks. Cable TV. Traditional Ethernet LANs.
Figure 7.9 Coaxial cable performance
Apr 10, 2023 Data Link Layer
Fiber-Optic Cable
Made of glass or plastic and transmits signals in the form of light.
Making use of the property of light that changes direction when travelling through substances of differing density.
A glass or plastic core is surrounded by a cladding of less dense glass or plastic.
The difference in density of the two materials must be such that a beam of light moving through the core is reflected off the cladding instead of being refracted into it.
Figure 7.14 Fiber construction
Figure 7.10 Bending of light ray
Figure 7.11 Optical fiber
Apr 10, 2023 Data Link Layer
Fiber-Optic Cable (Continued…)
Sizes: Defined by the ratio of the diameter of
their core to the diameter of their cladding, both expressed in micrometers.
7/1257/125
100/125100/125
62.5/12562.5/125
50/12550/125
Type
7
100
62.5
50
Core
125
125
125
125
Cladding
Apr 10, 2023 Data Link Layer
Fiber-Optic (Continued…)
Connectors: Uses three types of connectors:
Subscriber channel (SC) – uses push/pull locking system.
Straight-tip (ST) – uses bayonet locking system and more reliable than SC.
MT-RJ – a new connector with the same size as RJ45.
Performance: Attenuation is flatter than in the case of
TP and coaxial cables. Therefore, less repeater is needed for fiber-optic cable.
Figure 7.15 Fiber-optic cable connectors
Figure 7.16 Optical fiber performance
Apr 10, 2023 Data Link Layer
Fiber-Optic (Continued…)
Applications: Used often in the backbone networks. Used in hybrid cable TV network as the
backbone. Used in 100Base-FX and 1000Base-X
LANs