Lesson 2 Data Transmission Bounded Media Unbounded Media

Lesson 2

Data Transmission Bounded Media Unbounded Media Confines the data to specific physical pathways. Transmits the data-carrying signal through space, independent of cable. Examples: • STP/UTP Cable • Coaxial Cable • Optical Fiber Cables • Cable TV Examples: • Broadcast radio and television • Micro. Wave transmission

Bounded Media Generally… Watch for… • Most common 1. • Low cost • Reliable Resistance to electromagnetic interference (EMI) 2. Bandwidth 3. Attenuation 4. Cost

Cable Types • Electrical Conductors (“copper”) • Coaxial • Twisted Pair • Fiber Optic (“fiber” or “glass”)

Coaxial Cable Coax for short as two conductors share a COmmon AXis. Components: • Center Conductor • Insulation Layer • Outer Conductor or Shield • Jacket or Sheath Desirable Characteristics: • Highly Resistant to EMI • Can support high bandwidths

Coaxial Cable Pay Attention There is a wide variety of coax available. You MUST use cable that exactly matches the requirements of a particular type of network. Coax cables vary in impedance (measured in ohms), which is an indication of the cable’s resistance to current flow. Common Examples of Coax used in LANs: • RG-8 and RG-11: 50 ohm cables required for thickwire ethernet (10 Base 5 – Thick. Net) • RG-58: smaller 50 ohm cable required for use with thinwire ethernet (10 Base 2 – Thin. Net) • RG-59: 75 ohm cable mostly used for cable TV and broadband ethernet (10 Broad 36) • RG-62: 93 ohm cable used for ARCnet.

Coaxial Cable Advantages… Disadvantages… • Highly sensitive to EMI • Vulnerable to EMI in harsh conditions like factories • Supports high bandwidths • Easy to expand • Heavier types of coax are sturdy and can withstand harsh environments • Represents a mature technology that is well understood and consistently applied among vendors • Expensive when compared to twisted pair • Bulky • Single cable failure can fail the entire network

STP & UTP

Twisted Pair (TP) • Two conductors are twisted together to form twisted pair • Twists reduce cable’s sensitivity to EMI and cross talk • Twists reduce the degree to which the cable radiates radio frequency signals (RF) • Copper core is generally 22 -AWG or 24 -AWG (American Wire Gauge standard) • Early networks used TP surrounded by a braided shield to reduce EMI sensitivity and radio emissions. • Examples: STP IBM Type 1, Type 6, & Type 9 for token ring

Twisted Pair (TP) Advantages… Disadvantages… • Telephone cable standards are mature and well established. • STP can be expensive and difficult to work with. • May be possible to use in-place telephone wiring if it’s high enough quality. • Compared to fiber, all UTP cable is more sensitive to EMI. • UTP is lowest cost cabling. STP is higher and comparable to the cost of coax. • UTP especially may be unsuitable for use in high-EMI environments. • Cable segment lengths are also more limited with UTP. • UTP cables are regarded as being less suitable for highspeed transmissions than coax or fiber optic.

Unshielded Twisted Pair (UTP) • UTP is more common than STP Characteristics: • Inexpensive • Low cost • 10 Base-T, 100 Base-TX, and Gigabit Ethernet standards define Ethernet configurations that utilize UTP • Easy to install • High speed capacity Can be used for some configurations of Token Ring, Ethernet, and ARCnet. • High attenuation • Effective to EMI UTP is implemented using modular connectors • 100 meter limit • • Examples: • • RJ-11: 2 pair • RJ-45: 4 pair • Can be either voice grade or data grade depending on condition • Normally has impedance of 100 ohm.

Unshielded Twisted Pair (UTP) Pay Attention UTP looks like the cable used to wire voice grade telephones. In newer phone installations, it may be possible to use the wiring installed as data grade cable in a network. UTP comes in a variety of grades, from CAT 3 (low quality) to CAT 6 (high quality). Be sure to determine what is required for your network. 6 Levels of Data Cabling: • Category 1: Used in telephone lines and low speed data • Category 2: Can support up to 4 mps implementation • Category 3: Supports up to 16 mps and are mostly used in 10 mps • Category 4: Used for large distance and high speed. Can support 20 mps. • Category 5: Can support up to 100 mps. • Category 6: Highest quality

Unshielded Twisted Pair (UTP) Advantages… Disadvantages… • Easy installation • Short distance due to attenuation • Capable of high speeds for LANs • Low cost

Shielded Twisted Pair (STP) • Has a mesh shielding that protects it from EMI Characteristics: • Standard cables for IBM’s Token Ring Networks and Apple’s Local. Talk • Easy to install • IBM categories for STP • Type 1: two pairs of 22 -AWG • Type 2: includes type 1 with 4 telephone pairs • Type 6: two pairs of standard shielded 26 -AWG • Type 7: 1 pair of standard shielded 26 -AWG • Type 9: shielded 26 -AWG wire • Medium cost • Higher capacity than UTP • Medium immunity from EMI • 100 meter limit

Shielded Twisted Pair (STP) Advantages… Disadvantages… • Shielded • More expensive than UTP and coaxial cable • Faster than UTP and coaxial cable • More difficult to install • High attenuation rate

Fiber Optic Cable • Utilize light waves to transmit data through a thin glass or plastic fiber • Structure: • Light conductor is very fine fiber or glass core. • Cladding is a glass layer surrounding the optical fiber core. • Sheath or jacket protects the cable from damage. A single sheath can be used to bundle multiple core/cladding fibers into a multi-fiber cable.

Fiber Optic Cable • Light signals generated by light emitting diodes (LEDs) or injection laser diodes (ILDs). • The signals are received by photodiodes (solid state devices that detect variations in light intensity. • The interface devices required for fiber are more expensive than those required for copper. • Cost is higher because: • Cost of components • Tighter design characteristics because fiber is operated at high data rates. • Cost of installation is starting to go down so not as much of a factor anymore.

Fiber Optic Cable • Require greater skill to install than copper • Cables cannot be bent too sharply and connectors required special tools in the past • Desirable characteristics: • Fibers are small in diameter so a single cable can contain more fibers than copper wire pairs. • Use light pulses instead of electrical signals and so offer very high bandwidth. • 100 Mbps is common • Gigabit and 10 Gigabit range are available • Signal cannot be affected by EMI because it’s light pulses. • Cables don’t radiate RF noise and so are suitable for the noisiest, most sensitive environments • Radiate NO electromagnetic energy so it’s impossible to intercept the data signal with electronic eavesdropping equipment. • More secure

Fiber Optic Cable Advantages… Disadvantages… • Very high bandwidth speeds • Very costly • Immune to EMI • Hard to install • No RF emmisions • Low attenuation

Summary of Cable Characteristics Cable Type Cable Cost Installation Cost EMI Sensitivity Data Bandwidth UTP Lowest Highest Lowest STP Medium Moderate Low Moderate Coax Medium Moderate Low High Fiber Optic Highest None Very High