Network Media, Coding, Topology, and Ethernet Standards

Media Transmission

Wired (transmission signals via electricity):

  • Balanced (2 conductors; if there is interference, the difference is used).
  • Unbalanced (the modified signal is received).

Types of Wired Media:

  • Stranded: 4 twisted pairs.
  • UTP (Unshielded Twisted Pair) (digital): Twisted pairs.
  • FTP (Foiled Twisted Pair) (digital): 4 twisted pairs with a mesh around them.
  • STP (Shielded Twisted Pair) (digital): Shielding on each pair and all pairs.
  • Coaxial (analog & digital): Central core conductor (copper), isolating coating (plastic), metal mesh, plastic outer coating (internal) or metal (external). Used in systems. Balanced.
  • Fiber-optic (transmission via pulsed light):
    • Multimode (short distances, 62.5 and 50 microns core diameter, 125-micron coating): Uses core and coating (plastic). Propagation by reflection. Several signals at once. Problems of reflection and dispersion.
    • Singlemode (Long wavelength and large bandwidth, structured as multimode, diameter 5 microns or less): It spreads along the fiber. No attenuation, greater performance.

Wireless Transmission:

  • Laser: High Speed (1Gb/sec max).
  • Infrared: Short distance.
  • Radio: Higher frequency, more transmission.

Coding

TTL-Communication: Problem is generated current. 1 -> 5V, 0 -> 0V

  • NRZ-L (symmetrical): 1 -> +V, 0 -> -V
  • NRZ-i (differential coding): Si = Si-1 -> 0; If different Si-1 -> 1
  • Manchester (10Mbps Ethernet): Increases the number of transitions per bit, doubles the bandwidth consumed. S-> 1, Z-> 0
  • Differential-Manchester: Information contained above. Si = Si-1 -> 0; If different Si-1 -> 1
  • MLT3 (Internet up to 100Gb): Coding levels. Si = Si-1 -> 0; If different Si-1 -> 1. Problem with sequence of 0’s. Good bandwidth utilization.

Topology

  • Star: Point-to-point. Multiplexing in time, frequency, or none. Total disposition.
  • Extended Star: Point-to-point. Large distance.
  • Ring: Point-to-point. If the signal is lost, each station regenerates it. Greater length, more information lost.
  • Tree: The information in each station need not be in the others.
  • Bus: Half-duplex (diffusion), minimum wiring length.
  • Mesh: Point-to-point. The entire bandwidth is available. High cost and cable adaptation.

Modulation

Transmission of binary data through analog signals.

Ts (symbol time): Constant value depends on bandwidth.

Number of transmission bits per unit time: Depends on modulation type.

Vtx (bits/sec) = (Number of bits/Symbol) / Ts;

Two types of modulation: coherent (advisable, passing through 0), non-coherent (not passing through 0)

  • ASK Modulation (amplitude-shift keying; constant frequency, variable amplitude): Si(t) = (2Ei(t) / Ts)^(1/2) * cos(wt + ?)
  • PSK Modulation (phase-shift keying; phase modulation, information is included in the angular lag): Si(t) = (2Ei(t) / Ts)^(1/2) * cos(wt + 2πi / M)
  • FSK Modulation (frequency-shift keying; constant amplitude and ?, variable w): Si(t) = (2Ei(t) / Ts)^(1/2) * cos(wit + ?)
  • QAM Modulation (quadrature amplitude modulation; modulates amplitude and phase angle): Si(t) = (2Ei(t) / Ts)^(1/2) * cos(wt + ?i(t))

Ethernet

Speed in Mb/s; Length: 100m max segments; Base: Digital signal; Broad: Analog

Ethernet Standards:

CableTopologyCodingMax LengthObservations
10Base5 -> Thick Coaxial, RG8, Z = 50ΩBusManchester500m5 segments connected with repeaters, 100 stations/segment
10Base2 -> Thin Coaxial, RG58, 50ΩBusManchester185m30 devices/segment, 90 max (3 segments)
10BaseT -> Twisted Pair (Cat3 or higher)StarManchester100m to concentrator
10BaseFL -> Fiber Optic (Cat3 or higher)StarManchester2 km
10BROAD36 -> Coaxial, 75Ω3.6 km

100Mb Ethernet

StandardCableTopologyMax LengthObservations
100BaseTXCat5 or higherStar100m (station-concentrator)
100BaseT4Cat3Star100m
100BaseFXMultimode Fiber Optic (62.5/125, 50/125)StarOne cable for transmission and another for reception.

Gigabit Ethernet

StandardCableCodingMax LengthObservations
1000BaseLXFiber Optic8B/10BSinglemode (9μm, 5km); Multimode (50μm 550m, 62.5μm 500m)Long Wavelength 1300nm
1000BaseSXMultimode Fiber Optic8B/10B50μm 550m, 62.5μm 220-275mLong Wavelength 850nm
1000BaseCXTwisted Pair (shielded STP)8B/10B25mApplies to 802.3z
1000BaseTTwisted Pair (Cat5e or higher)8B/10B100m802.3ab. 4 pairs are used for sending and receiving (Ethernet)

10 Gigabit Ethernet

StandardCableMax LengthWavelength
10GBaseSRMultimode Fiber Optic300m850nm
10GBaseLRSinglemode Fiber Optic10km1310nm
10GBaseERSinglemode Fiber Optic40km1550nm
10GBaseLX4Singlemode & Multimode Fiber OpticSinglemode 10km, Multimode 300m