59 lines
1.6 KiB
Markdown
59 lines
1.6 KiB
Markdown
Lecture Topic: Bandwidth and Data Rate
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Analog: x(t)
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Discrete: x(n)
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Digital: from formula, range / set, bit sequence
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Bandwidth:
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$x(t) = \sum^{\infty}_{k=-\infty}A_k cos(2\pi f_k + \phi_k)$
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Fourier series
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Shannon Theorem:
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For a Gaussian channel the data rate that can be achieved over a channel of a given bandwidth satisfies
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$R \leq B_w log_2(1+\frac{S}{N}) \triangleq C$
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R = Achievable data rate (bps)
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$B_w$ = Channel bandwidth in Hz
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S/N = Signal to noise ratio (SNR)
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S = Signal power, N = noise power
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Internet Architecture:
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- Network Edge
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- End systems: Host apps, not only computers and mobile devices but also wearables, sensors and large servers
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- Access Networks: (Last hop, last mile), Connect end systems to the first router (aka edge router)
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- Network Core:
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- Packet switches: Routers, link layer switches
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A hierarchical look at A network of network:
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- Hosts connect to the internet via access ISPs, residential, cooperate ISPs, university ISPs, cellular data ISPs.
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- Access ISPs in turn are interconnected through regional ISPs and tier 1 ISPs
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(Diagram in slides)
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Internet Access and Physical Media:
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- Wired
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- Dial up
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- DSL
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- Cable
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- Fibre Optics
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- Ethernet
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- Wireless
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- WiFi
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- Cellular
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- Satellite
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Wired media: EM waves are guided along a solid medium (twisted pair copper, coaxial cable, fibre optics)
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Wireless media: EM waves propagate through the air (Different electromagnetic spectrum/frequency bands)
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Dial-Up:
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Use existing telephony infrastructure
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- Low Speed (56k)
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- Can't use phone and internet at the same time (not always present)
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- Modems modulate and demodulate data over phone lines
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DSL:
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Digital Subscriber Line
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(Slides went fast) |