COMP347 (Revision 10) | TrustOpen University
Upon completion of this expanded tutorial, students will be able to:
The network edge is where users and applications connect to the Internet. This tutorial provides a rigorous examination of the end systems (hosts) that generate and consume data, and the access networks that link them to the global infrastructure. We explore the client‑server and peer‑to‑peer architectural models, then dive into the physical and data‑link layer technologies that enable connectivity: DSL, cable, fibre, Ethernet, Wi‑Fi, and cellular. We also analyse the characteristics of physical media and the multiplexing techniques that maximise their utilisation. A detailed comparison table helps evaluate trade‑offs in cost, performance, and scalability.
End systems (hosts) are the devices at the edge that run applications. They include:
In the client‑server model:
Advantages: centralised management, predictable performance. Disadvantages: single point of failure, scalability limits. Load balancing and horizontal scaling mitigate these issues.
Peers act as both clients and servers, sharing resources directly. Examples: BitTorrent, early Skype. P2P is self‑scaling and resilient but faces challenges in security, discovery, and incentive design (free‑riding). Hybrid models (e.g., superpeers) combine centralisation and decentralisation.
Uses existing telephone copper pairs. Employs Discrete Multi‑Tone (DMT) modulation, dividing the frequency spectrum into many sub‑channels. Variants:
Uses coaxial cable and the DOCSIS standard. DOCSIS 3.1 supports 10 Gbps down, 1 Gbps up. The medium is shared; performance degrades during peak usage. Components: cable modem (customer) and CMTS (headend).
Optical fibre directly to the premises. Passive Optical Network (PON) architectures (GPON, XGS‑PON) use passive splitters to share fibre among subscribers. GPON: 2.5 Gbps down, 1.25 Gbps up. Active Ethernet provides dedicated bandwidth.
The dominant wired LAN technology. Speeds from 10 Mbps to 400 Gbps. Switched Ethernet uses full‑duplex, eliminating collisions. Typically uses twisted‑pair (Cat5e/6) or fibre.
Wireless LAN in unlicensed bands (2.4, 5, 6 GHz). Standards: 802.11ax (Wi‑Fi 6) up to 10 Gbps; 802.11be (Wi‑Fi 7) up to 30 Gbps. Uses CSMA/CA with RTS/CTS for collision avoidance. Range: 10–100 m indoors.
Wide‑area wireless using licensed spectrum. 5G supports eMBB (10 Gbps), URLLC (<1 ms), mMTC (1M devices/km²). Uses OFDM, MIMO, beamforming.
GEO satellites: high latency (500–600 ms), 10–100 Mbps. LEO satellites (e.g., Starlink): latency 20–50 ms, 100–500 Mbps. Weather‑dependent.
Attenuation increases with distance and frequency. Fibre has the lowest attenuation (~0.2 dB/km), copper much higher. Bandwidth is limited by the medium and modulation scheme.
| Technology | Downstream | Upstream | Medium | Shared? | Latency | Typical Use |
|---|---|---|---|---|---|---|
| ADSL | 8–24 Mbps | 1–3 Mbps | Copper | No | 10–40 ms | Residential |
| VDSL2 | 100–200 Mbps | 10–20 Mbps | Copper | No | 5–20 ms | Residential |
| Cable (DOCSIS 3.1) | 1–10 Gbps | 200 Mbps–1 Gbps | Coax | Yes | 10–30 ms | Residential |
| FTTH (GPON) | 2.5 Gbps | 1.25 Gbps | Fibre | Yes (PON) | 1–5 ms | Residential/Business |
| FTTH (Active Ethernet) | 10 Gbps | 10 Gbps | Fibre | No | <1 ms | Business/Enterprise |
| Ethernet (1 GbE) | 1 Gbps | 1 Gbps | Copper/Fibre | No | <1 ms | Enterprise |
| Wi‑Fi 6 | 1–10 Gbps | 1–10 Gbps | Radio | Yes | 1–10 ms | Home/Office/Public |
| 4G LTE | 10–100 Mbps | 5–50 Mbps | Radio | Yes | 30–50 ms | Mobile |
| 5G | 100 Mbps–10 Gbps | 100 Mbps–10 Gbps | Radio | Yes | <10 ms | Mobile/FWA |
| Satellite (LEO) | 100–500 Mbps | 20–100 Mbps | Radio | Yes | 20–50 ms | Rural/Remote |
Modulation converts digital bits to analog signals. Common schemes: QAM (Quadrature Amplitude Modulation) – higher orders (e.g., 256‑QAM) carry more bits per symbol but require higher SNR. PSK (Phase Shift Keying) and ASK (Amplitude Shift Keying) are also used.
Typically combines modem/ONT, router, switch, and Wi‑Fi AP. Provides NAT, DHCP, and firewall functions.
Q1: What is the fundamental difference between a client and a server in the client‑server model?
A client initiates requests and is typically intermittently connected; a server is always‑on and provides services.
Q2: Name two access technologies that use guided media and two that use unguided media.
Guided: DSL (copper), FTTH (fibre). Unguided: Wi‑Fi (radio), satellite.
Q3: What is the DOCSIS standard used for?
DOCSIS defines data transmission over cable TV infrastructure, enabling cable Internet.
Q4: Explain the role of a PON in FTTH.
PON (Passive Optical Network) uses passive splitters to share a single fibre among multiple subscribers, reducing infrastructure cost.
Q5: What is the main advantage of fibre optic over copper?
Fibre offers extremely high bandwidth, low attenuation, and immunity to electromagnetic interference.
Q6: Why is cable Internet a shared medium?
All users in a neighbourhood share the same coaxial cable and headend capacity; bandwidth is distributed among them.
Q7: What is the difference between TDM and FDM?
TDM allocates time slots; FDM allocates frequency bands.
Q8: In DSL, what is the purpose of DMT modulation?
DMT divides the spectrum into many sub‑channels, each modulated independently based on signal‑to‑noise ratio, maximising data rate.
Q9: What is the approximate latency of GEO satellite communication?
500–600 ms round‑trip time due to the 36,000 km altitude.
Q10: How does Wi‑Fi avoid collisions?
Wi‑Fi uses CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), which uses RTS/CTS and random backoff.
Q11: What is the role of a cable modem?
It modulates/demodulates signals for transmission over coaxial cable and handles the DOCSIS protocol.
Q12: Why are access networks often asymmetric (downstream > upstream)?
Typical user behaviour involves more downloading (web, streaming) than uploading, so bandwidth is allocated accordingly.
Exercise 1 – Choosing an access technology
A rural area has three options: satellite (100 Mbps down, 600 ms latency), fixed wireless (50 Mbps, 20 ms), and DSL (10 Mbps, 10 ms). Which is best for VoIP, large downloads, gaming, and 4K streaming? Justify.
Exercise 2 – Office building connection
An office with 100 employees, VoIP, video conferencing, and guest Wi‑Fi needs an Internet connection. Recommend a technology and justify.
Dedicated fibre (Active Ethernet or leased line) with symmetric 1 Gbps or higher. Provides dedicated bandwidth, low latency, and scalability. Cable or DSL would be insufficient due to sharing and asymmetry.
Exercise 3 – DSL vs cable
A homeowner is comparing 100 Mbps DSL and 100 Mbps cable. What factors beyond speed matter?
Upload speed, shared vs dedicated (cable shared), latency, reliability, contract terms, future upgradability.
Exercise 4 – PON operation
Describe the downstream and upstream transmission in a GPON.
Downstream: OLT broadcasts to all ONTs; each ONT filters based on its identifier. Uses TDM. Upstream: ONTs transmit in assigned time slots (TDMA) to avoid collisions, scheduled by the OLT.
Exercise 5 – Modulation comparison
Compare QAM‑16 and QAM‑64 in terms of bits per symbol and required SNR.
QAM‑16 carries 4 bits per symbol; QAM‑64 carries 6 bits per symbol. QAM‑64 requires higher SNR to maintain the same error rate due to closer constellation points.
Exercise 6 – Wi‑Fi vs cellular
Compare Wi‑Fi and 5G for a mobile device. Discuss speed, coverage, cost, and security.
Wi‑Fi: high speed, limited coverage, free (after infrastructure), WPA3 security. 5G: wide coverage, high speed, paid data plans, carrier‑managed security. Choose Wi‑Fi when stationary and high bandwidth needed; choose 5G when mobile or outside Wi‑Fi coverage.
Homework 1 – Evolution of access technologies
Research the evolution of access networks from dial‑up to 5G. How have data rates increased? What technologies became obsolete?
Dial‑up (56 kbps) → ISDN (128 kbps) → ADSL (8 Mbps) → Cable (50 Mbps) → FTTH (1 Gbps) → 5G (10 Gbps). Obsolete: dial‑up, ISDN, early DSL.
Homework 2 – Digital divide
Explain the digital divide and its causes. Propose solutions using access technologies.
Digital divide is unequal access to Internet. Causes: geographic, economic, demographic. Solutions: government subsidies, LEO satellite, fixed wireless, shared infrastructure.
Homework 3 – Physical media comparison
Compare fibre, copper, and wireless in terms of bandwidth, latency, error rate, and security.
Fibre: high bandwidth, low latency, low error, high security. Copper: lower bandwidth, higher error, susceptible to EMI. Wireless: variable bandwidth, higher error, requires encryption.
Homework 4 – Multi‑access edge computing
Research MEC (Multi‑access Edge Computing). How does it relate to 5G and access networks?
MEC brings cloud computing to the edge of the network, reducing latency for 5G applications. It integrates with 5G network slicing.
Homework 5 – Converged access
What is “triple‑play” (voice, video, data) and how does a single access network support it?
Triple‑play bundles Internet, TV, and phone over one connection. Technologies: DOCSIS, GPON, with QoS to prioritise real‑time traffic.
This tutorial provided a comprehensive exploration of the network edge:
Understanding the network edge is critical for designing and troubleshooting network applications. In the next tutorial, we will move to the network core, examining packet switching, circuit switching, and the routing infrastructure that underpins global communication.