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UNB/Year 4/Semester 2/CS3873/2024-01-15.md

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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)