53 lines
2.4 KiB
Markdown
53 lines
2.4 KiB
Markdown
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Lecture Topic: Network Edge & Internet Access Technologies
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Bandwidth and Data Rate recap:
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The data rate cannot exceed the capacity of the bandwidth of a given channel, this is where the formula $R \leq B_w log_2(1+\frac{S}{N}) \triangleq C$ comes from
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Doubling the data rate means that you need a bandwidth that has at least as much capacity to handle the new data rate
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Internet Access Technologies:
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- DSL:
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- Using Frequency Division Multiplexing (FDM) it caries digital data through phone lines
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- Example: Voice 0-4 kHz, Upstream 4-50 kHz, Downstream 50 kHz-1 MHz
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- Twisted Pair Cable Wire:
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- Constitute a fine antenna
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- Cancel out cross talk and produce less radiation
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- A number of pairs are bundled together in a cable
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- Used in telephone systems, unheralded twisted pair (UTP) for local area networks, computer networks within a building (Ethernet)
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- Data Rate: 10Mbps - 10Gbps
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- Cable:
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- Use cable TV companies existing cable infrastructure
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- Hybrid fibre coaxial (HFC) access network
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- Coaxial cables are shared to reach individual homes
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- Fibre optics connect neighbourhood level junctions to CMTS
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- Asymmetric 40Mbps - 1.2Gbps downstream, 30Mbps - 100Mbps upstream
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- Data/TV are transmitted at different frequencies over shared cable
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- At the home, splits the signals into TV and Internet signals
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- Coaxial Cable
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- More complex structure
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- Better performance
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- Excellent noise immunity because cable is very shielded
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- Can span longer distances
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- Bandwidth is close to 1 Ghz
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- Data rates are higher than other technologies, 100s Mbps per channel
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- Fibre to the home (FTTH)
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- Optical network terminal in individual homes (ONT)
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- Optical line terminal in central office (OLT)
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- Fibre optic cables are similar to coax cables (lots of layers)
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- Class core with higher index of refraction than the outer glass
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- Light propagates through glass core
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- Thin plastic jacket to protect glass cladding
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- Fibres are typically grouped in bundles protected by an outer sheath
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- The outer layer keeps the light inside, not leaking any energy by reflecting the signal off an outer sheath
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- Has a few excellent features:
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- Very low signal attenuation up to 100km
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- Immune to electromagnetic interference
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- Larger bandwidth, support data rate up to 10s or 100s of Gbps
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- Hard to tap
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Network Core:
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- How is data moved through a network of links and packet switches?
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- There are two fundamental approaches
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- Circuit switching
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- Packet switching
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