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