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:
Cable | Topology | Coding | Max Length | Observations |
---|---|---|---|---|
10Base5 -> Thick Coaxial, RG8, Z = 50Ω | Bus | Manchester | 500m | 5 segments connected with repeaters, 100 stations/segment |
10Base2 -> Thin Coaxial, RG58, 50Ω | Bus | Manchester | 185m | 30 devices/segment, 90 max (3 segments) |
10BaseT -> Twisted Pair (Cat3 or higher) | Star | Manchester | 100m to concentrator | |
10BaseFL -> Fiber Optic (Cat3 or higher) | Star | Manchester | 2 km | |
10BROAD36 -> Coaxial, 75Ω | 3.6 km |
100Mb Ethernet
Standard | Cable | Topology | Max Length | Observations |
---|---|---|---|---|
100BaseTX | Cat5 or higher | Star | 100m (station-concentrator) | |
100BaseT4 | Cat3 | Star | 100m | |
100BaseFX | Multimode Fiber Optic (62.5/125, 50/125) | Star | One cable for transmission and another for reception. |
Gigabit Ethernet
Standard | Cable | Coding | Max Length | Observations |
---|---|---|---|---|
1000BaseLX | Fiber Optic | 8B/10B | Singlemode (9μm, 5km); Multimode (50μm 550m, 62.5μm 500m) | Long Wavelength 1300nm |
1000BaseSX | Multimode Fiber Optic | 8B/10B | 50μm 550m, 62.5μm 220-275m | Long Wavelength 850nm |
1000BaseCX | Twisted Pair (shielded STP) | 8B/10B | 25m | Applies to 802.3z |
1000BaseT | Twisted Pair (Cat5e or higher) | 8B/10B | 100m | 802.3ab. 4 pairs are used for sending and receiving (Ethernet) |
10 Gigabit Ethernet
Standard | Cable | Max Length | Wavelength |
---|---|---|---|
10GBaseSR | Multimode Fiber Optic | 300m | 850nm |
10GBaseLR | Singlemode Fiber Optic | 10km | 1310nm |
10GBaseER | Singlemode Fiber Optic | 40km | 1550nm |
10GBaseLX4 | Singlemode & Multimode Fiber Optic | Singlemode 10km, Multimode 300m |