2024-01-22 10:12:47

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)

UNB/Year 4/Semester 2/CS3873/2024-01-17.md

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

UNB/Year 4/Semester 2/CS3873/2024-01-19.md

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+Lecture Topic: Network Core
+
+Resource Sharing with circuit switching:
+- Network resources divided into pieces allocated to connections 
+- Frequency division multiplexing (FDM). Dividing over bandwidth, and each end user gets a portion of the bandwidth for the entire portion of time.
+- Time division multiplexing (TDM). Dividing over time, and each end user gets the full bandwidth for a portion of allocated time. Similar to round robin.
+
+Table of some information of cellular network technologies:
+CS: Circuit Switching
+
+1G (FDMA)
+2G (TDMA) (GSM/CS)
+3G (CDMA) (CS/PS)
+4G (PS)
+5G (millimeter wave)
+
+With circuit switching you can guarantee a certain level of performance, while with packet switching there is no/less of a guarantee of performance, which is why circuit switching was important for mobile networks as emergency calls need a certain level of performance to be guaranteed.
+
+Packet Switching:
+- Internet is based on packet switching
+- ARPANET was the first packet-switched network and is an ancestor of the internet
+- A sending host breaks a message into packets (numbered sequentially) and sends them into the network one by one
+- Packets are transmitted individually through the network and reassembled at the receiving host to recover the original message
+
+Packet switching is a very adaptive to changing network conditions. Due to packet chunking, packets in transit can be routed through different routes depending on the used bandwidth of other nodes on the network, and this can occur between two packets of the same chunk of data. This is because packets are numbered and are reordered at the destination.
+
+A packet follows a path:
+- First hop router: This is the first router that inspects the packet and forwards it to the next hop
+- Then next router does the same, and so on
+- The packets eventually arrives at the destination and are decoded
+
+Packets follow a protocol called "store and forward" 
+
+Resource sharing with packet switching:
+- Is very easy, as you can just send all packets over a link, according to different priorities
+
+Multiplexing comparison:
+- With circuit switching, if you allocate bandwidth to two services, it may end up unused and wasted, as the format of data is fixed and if service A is not using any traffic service B cannot use that other bandwidth
+- Statistical multiplexing: Packet switching is on demand, so no bandwidth is explicitly allocated, and bandwidth is dynamically allocated based on current network usage
+
+There are some downsides to packet switching to be aware of however:
+-  In next lecture