2.4 KiB
2.4 KiB
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