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)