Wireless Networking

Overview

Wireless networking enables communication without physical cables, using radio waves, microwaves, or infrared signals. This section covers WiFi standards, 5G cellular, and modern network paradigms like SDN and NFV. Understanding wireless technologies is essential for networking interviews, as mobile and wireless increasingly dominate connectivity.

Wireless Technologies

graph TD
    A[Wireless Technologies] --> B[Short Range]
    A --> C[Medium Range]
    A --> D[Long Range]
    A --> E[Cellular]
    B --> F["Bluetooth (10m)"]
    B --> G["NFC (0.1m)"]
    B --> H["Zigbee (100m)"]
    C --> I["WiFi (100m+)"]
    D --> J["WiMAX (50km)"]
    D --> K["Satellite"]
    E --> L["4G LTE"]
    E --> M["5G NR"]

WiFi Standards (IEEE 802.11)

WiFi 6 (802.11ax) Key Features

WiFi 7 (802.11be) Key Features

2.4 GHz vs 5 GHz vs 6 GHz

5G (Fifth Generation Cellular)

5G vs 4G LTE

5G Usage Scenarios (ITU IMT-2020)

graph TD
    A[5G Scenarios] --> B[eMBB<br/>Enhanced Mobile Broadband]
    A --> C[URLLC<br/>Ultra-Reliable Low-Latency]
    A --> D[mMTC<br/>Massive Machine-Type]
    B --> B1["4K/8K video, AR/VR"]
    C --> C1["Autonomous vehicles, remote surgery"]
    D --> D1["IoT sensors, smart cities"]

5G Architecture

Network Slicing

Create multiple virtual networks on the same physical infrastructure:

graph TD
    P[Physical 5G Network] --> S1[Slice 1: eMBB<br/>High bandwidth, streaming]
    P --> S2[Slice 2: URLLC<br/>Low latency, reliability]
    P --> S3[Slice 3: mMTC<br/>Massive IoT connections]

Each slice has independent: bandwidth, latency, security policies, and resource allocation.

SDN (Software-Defined Networking)

Core Concept

Separate the control plane (routing decisions) from the data plane (packet forwarding). A central controller manages network devices programmatically.

graph TD
    subgraph "Traditional"
        T1[Router 1: Control + Data] --- T2[Router 2: Control + Data]
        T2 --- T3[Router 3: Control + Data]
    end
    subgraph "SDN"
        C[Centralized Controller]
        C --> D1[Switch 1: Data only]
        C --> D2[Switch 2: Data only]
        C --> D3[Switch 3: Data only]
    end

SDN Architecture

OpenFlow Protocol

The standard protocol between SDN controller and switches:

Controller → Switch: "For packets matching (src=10.0.0.1, dst=10.0.0.2), forward out port 3"
Switch → Controller: "Packet doesn't match any flow, what should I do?"
Controller → Switch: "Forward out port 2, install flow rule"

SDN Benefits

SDN Use Cases

• Data center networking: Dynamic VM migration, micro-segmentation
• WAN optimization: SD-WAN for branch office connectivity
• Network security: Centralized firewall policy, traffic analysis
• Traffic engineering: Optimize paths based on real-time conditions

NFV (Network Function Virtualization)

Core Concept

Replace dedicated hardware appliances (firewalls, load balancers, routers) with software running on commodity servers.

graph LR
    subgraph "Traditional"
        FW[Firewall Appliance] --> LB[Load Balancer Appliance] --> R[Router Appliance]
    end
    subgraph "NFV"
        S[Commodity Server] --> VFW[vFirewall]
        S --> VLB[vLoad Balancer]
        S --> VR[vRouter]
    end

NFV Architecture (ETSI)

NFV Benefits

SDN + NFV Together

graph TD
    SDN[SDN: Control Plane Separation] --> Combined[Programmable, Virtualized Network]
    NFV[NFV: Virtualize Network Functions] --> Combined
    Combined --> Benefits["Cost reduction, agility, automation"]

• SDN provides programmable network control
• NFV provides virtualized network functions
• Together they enable fully software-defined, virtualized networks

Interview Questions

1. Q: What’s the difference between 2.4 GHz and 5 GHz WiFi? A: 2.4 GHz has longer range and better wall penetration but more interference (only 3 non-overlapping channels, shared with Bluetooth/microwaves). 5 GHz has shorter range but 24+ channels and less interference. 6 GHz (WiFi 6E) adds 59 more channels for even less congestion.

2. Q: What is SDN and why does it matter? A: Software-Defined Networking separates the control plane (routing decisions) from the data plane (packet forwarding). A central controller manages network devices programmatically via OpenFlow. Benefits: centralized visibility, rapid policy changes, automation, vendor independence. Essential for data centers and WAN.

3. Q: What is NFV? A: Network Function Virtualization replaces dedicated hardware (firewalls, load balancers) with software (VNFs) running on commodity servers. Reduces cost, enables rapid deployment and scaling. Together with SDN, enables fully programmable, virtualized networks.

4. Q: What is network slicing in 5G? A: Creating multiple virtual networks on the same physical 5G infrastructure. Each slice is tailored for a specific use case: eMBB (high bandwidth for video), URLLC (low latency for industrial), mMTC (massive IoT). Slices have independent SLAs, security, and resource allocation.

5. Q: Explain WiFi 6’s key improvements. A: (1) OFDMA — multiple users per channel simultaneously (vs one-at-a-time in WiFi 5). (2) MU-MIMO uplink — serve multiple clients in both directions. (3) BSS Coloring — reduces interference between overlapping networks. (4) TWT — devices sleep and wake on schedule, improving battery life. (5) 1024-QAM — 25% more data per symbol.

6. Q: What is the difference between eMBB, URLLC, and mMTC? A: eMBB (Enhanced Mobile Broadband): high speed for video/AR (20 Gbps). URLLC (Ultra-Reliable Low-Latency): 1ms latency for autonomous vehicles, remote surgery. mMTC (Massive Machine-Type Communications): 1M devices/km² for IoT sensors. 5G supports all three via network slicing.

7. Q: How do SDN and NFV relate? A: SDN separates control from data plane (programmable network). NFV virtualizes network functions (software replaces hardware). They’re complementary: SDN provides the programmable control, NFV provides the virtualized functions. Together: software-defined, virtualized, automated networks.

8. Q: What is MLO in WiFi 7? A: Multi-Link Operation allows a device to simultaneously use multiple frequency bands (2.4, 5, 6 GHz). Instead of switching between bands, WiFi 7 transmits on all bands at once, increasing throughput and reducing latency. If one band has interference, traffic shifts to others seamlessly.

Summary

Wireless networking spans from short-range (Bluetooth/NFC) to cellular (5G). WiFi has evolved from 11 Mbps (802.11b) to 46 Gbps (WiFi 7), with each generation adding efficiency improvements (MIMO, OFDMA, wider channels). 5G introduces three distinct usage scenarios (eMBB, URLLC, mMTC) via network slicing. SDN and NFV represent the shift toward programmable, virtualized networks. Understanding these technologies and their trade-offs is essential for modern networking interviews.

Cross-References

• WiFi — Detailed WiFi protocols
• 5G — 5G architecture deep dive
• SDN — Software-Defined Networking details
• NFV — Network Function Virtualization details
• Bluetooth — Short-range wireless
• Network Security — Wireless security (WPA3)
• Load Balancing — L4/L7 load balancing

References

• IEEE 802.11 Standards — WiFi specifications
• 3GPP 5G Specifications — 5G NR standards
• ONF — SDN Definition — SDN architecture
• ETSI NFV ISG — NFV specifications
• WiFi Alliance — WiFi certifications
• Kurose & Ross, Computer Networking, Chapter 7: Wireless and Mobile Networks
• OpenFlow Specification