Network Media, Coding, Topology, and Ethernet Standards

Posted on Feb 16, 2025 in Computer Engineering

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:

100Mb Ethernet

Gigabit Ethernet

10 Gigabit Ethernet