Wireless Networks, Protocols & Mobile App Integration

TAKEAWAYS:

• Wireless connectivity relies on radio waves (Wi-Fi), microwaves (cellular), or infrared/Bluetooth (short-range), each with distinct speed, range, and power constraints.
• TCP/IP and HTTP/HTTPS are the backbone of mobile app communication, while MQTT enables lightweight IoT/mobile messaging.
• Security protocols (WPA3, TLS) protect data in transit, but mobile apps must handle offline scenarios and reconnection logic.
• Latency and bandwidth directly impact app performance (e.g., video streaming vs. chat apps).
• Nepali examples: eSewa uses HTTPS + OAuth for secure payments; Pathao relies on GPS + cellular data for ride tracking; Ncell’s 4G/LTE network manages voice/data traffic via SIP for VoIP.
• Exam focus: Compare protocols (Wi-Fi vs. Bluetooth vs. cellular), trace packet flows, and explain how apps handle disconnections/reconnections.

Wireless Communication Technologies

Wireless connectivity enables mobile apps to interact with networks without physical cables. The three primary technologies are:

1. Wi-Fi (IEEE 802.11 Standards)

• Uses radio waves (2.4 GHz or 5 GHz) for short-to-medium range (up to 100 meters indoors).
• Standards:
  • 802.11n (Wi-Fi 4): Up to 600 Mbps, MIMO technology.
  • 802.11ac (Wi-Fi 5): Up to 3.5 Gbps, wider channels.
  • 802.11ax (Wi-Fi 6): Improved efficiency in crowded networks (e.g., airports).
• Security: WPA3 (replaces WPA2) uses SAE (Simultaneous Authentication of Equals) to prevent brute-force attacks.
• Use in Nepal:
  • eSewa app uses Wi-Fi for secure transactions when users are at home/businesses.
  • NTC’s public Wi-Fi hotspots (e.g., in Kathmandu) rely on 802.11ac for high-speed internet.

Figure 1: Wi-Fi communication flow (eSewa transaction example).

2. Bluetooth (IEEE 802.15.1)

• Uses short-range radio waves (2.4 GHz), ideal for device pairing (e.g., headphones, printers).
• Versions:
  • Bluetooth Classic: Low speed (up to 24 Mbps), used in audio devices.
  • Bluetooth Low Energy (BLE): Optimized for low power (e.g., fitness trackers, beacons).
• Use in Nepal:
  • Khalti’s POS machines use BLE for contactless payments.
  • Health apps (e.g., pulse oximeters) connect via BLE to smartphones.

Figure 2: BLE connection steps (Khalti POS example).

3. Cellular Networks (3G/4G/5G)

• Uses microwaves for long-range communication via base stations (cell towers).
• Generations:
  • 3G: Up to 42 Mbps (e.g., Ncell’s early 3G).
  • 4G/LTE: Up to 1 Gbps (Nepal’s current standard).
  • 5G: Ultra-low latency (<1 ms), higher bandwidth (Ncell testing in Kathmandu).
• Protocols:
  • SIP (Session Initiation Protocol): Used for VoIP (e.g., Ncell’s internet calling).
  • MQTT: Lightweight protocol for IoT/mobile messaging (e.g., Daraz’s inventory updates).

Figure 3: 4G VoIP call flow (Ncell internet calling).

Wireless Protocols for Mobile Apps

Mobile apps use protocols to communicate over wireless networks. Key protocols include:

1. TCP/IP Suite

• TCP (Transmission Control Protocol): Reliable, connection-oriented (e.g., web browsing, emails).
• UDP (User Datagram Protocol): Faster, connectionless (e.g., video streaming, online games).
• IP (Internet Protocol): Addresses packets for routing (IPv4 vs. IPv6).

Comparison Table:

Example: eSewa uses TCP for secure transactions (reliable data transfer) but may use UDP for real-time chat notifications.

2. HTTP/HTTPS

• HTTP (Hypertext Transfer Protocol): Stateless protocol for web requests (e.g., loading Daraz product pages).
• HTTPS: Secure HTTP with TLS/SSL encryption (used by all banking apps like NMB Bank).
• Methods:
  • GET: Retrieve data (e.g., fetching stock prices from NEPSE).
  • POST: Send data (e.g., submitting a Pathao ride request).
  • PUT/DELETE: Update/delete resources.

sequenceDiagram
  participant User
  participant App
  participant Server
  User->>App: Clicks "Book Ride" (Pathao)
  App->>Server: POST /rides (HTTPS)
  Server-->>App: 201 Created (Ride ID)
  App-->>User: Displays "Ride Confirmed"

Figure 4: HTTPS request flow (Pathao ride booking).

3. MQTT (Message Queuing Telemetry Transport)

• Lightweight protocol for IoT/mobile messaging (e.g., Daraz’s warehouse inventory updates).
• Uses publish-subscribe model:
  • Broker: Middleman (e.g., Mosquitto).
  • Topics: Channels (e.g., daraz/inventory/books).
• QoS Levels:
  • 0: Fire-and-forget (e.g., sensor data).
  • 1: At least once delivery (e.g., order confirmations).
  • 2: Exactly once (critical updates).

Example: A Daraz app subscribes to daraz/inventory/books to update stock levels in real time.

Security in Wireless Communication

Wireless networks are vulnerable to attacks (e.g., man-in-the-middle, eavesdropping). Security measures include:

1. Wi-Fi Security: WPA3

• Replaces WPA2 with stronger encryption (SAE instead of PSK).
• Features:
  • Forward Secrecy: Past sessions can’t be decrypted if a key is stolen.
  • Protected Management Frames: Prevents deauthentication attacks.
• Use in Nepal: NTC’s public Wi-Fi now uses WPA3 in major cities.

2. TLS/SSL for HTTPS

• Encrypts data between app and server (e.g., Khalti payments).
• Handshake Process:
  1. Client sends supported cipher suites.
  2. Server responds with its digital certificate.
  3. Client verifies certificate (via CA like Let’s Encrypt).
  4. Symmetric key exchange (e.g., AES).

flowchart TD
  A["Client"] -->|"Hello"| B["Server"]
  B -->|"Certificate"| A
  A -->|"Key Exchange"| B
  B -->|"Encrypted Data"| A

Figure 5: TLS handshake (Khalti payment example).

3. Mobile App Security Best Practices

• Certificate Pinning: Bind app to a specific server certificate (prevents MITM).
• Data Encryption: Use SQLCipher for local databases (e.g., eSewa’s offline transactions).
• Secure Authentication: OAuth 2.0 (e.g., eSewa login via Facebook/Google).

Handling Network Disconnections in Mobile Apps

Mobile networks are unreliable (e.g., Kathmandu traffic jams drop 4G signals). Apps must handle:

1. Offline-First Design:

   • Store data locally (e.g., Room Database in Android) and sync later.
   • Example: Pathao app caches ride history for offline access.

2. Reconnection Logic:

   • Use exponential backoff to retry failed requests.
   • Example: Daraz app retries failed order placements every 5 seconds (then 10, 20, etc.).

3. Conflict Resolution:

   • Last-write-wins: For non-critical data (e.g., chat messages).
   • Merge strategies: For critical data (e.g., banking transactions).

   // Pseudocode for offline-first sync (Android)
   public void syncData() {
       if (isOnline()) {
           uploadLocalChanges();
       } else {
           scheduleRetry(); // Exponential backoff
       }
   }
   

   Trace:

   Step	Network Status	Action
   1	Online	Uploads 3 pending orders
   2	Offline	Schedules retry in 5 seconds
   3	Online (later)	Retries, uploads remaining 1

Real-World Applications in Nepal

1. eSewa App:

   • Technology: HTTPS (TLS 1.3) + OAuth for authentication.
   • Wireless Use: Wi-Fi for home transactions, 4G for mobile payments.
   • Challenge: Handles disconnections by caching transactions and syncing later.

2. Pathao Ride-Hailing:

   • Technology: GPS (via cellular data) + WebSockets for real-time driver tracking.
   • Protocol: MQTT for lightweight driver location updates.
   • Example: When a user books a ride, the app:
     1. Sends a POST /rides request (HTTPS).
     2. Subscribes to pathao/ride/{id}/updates (MQTT) for ETA changes.

3. Ncell’s 4G Network:

   • Protocol: SIP for VoIP calls (e.g., Ncell’s internet calling).
   • Optimization: Uses load balancing to distribute traffic across cell towers during peak hours (e.g., 7–9 PM in Kathmandu).

4. Daraz Marketplace:

   • Wireless Stack: HTTP/2 for product pages, MQTT for inventory updates.
   • Offline Handling: Caches product listings; syncs when back online.

Exam Tip

1. Diagrams Are Key:
   • Draw OSI vs. TCP/IP model comparisons.
   • Trace TLS handshake or MQTT publish-subscribe flows.
2. Compare Protocols:
   • Wi-Fi vs. Bluetooth vs. Cellular (speed, range, power).
   • TCP vs. UDP (reliability vs. speed).
3. Real-World Scenarios:
   • Explain how eSewa uses HTTPS + OAuth or Pathao uses MQTT for GPS.
   • Describe offline-first sync with a trace table.
4. Security Focus:
   • Differentiate WPA2 vs. WPA3 and TLS 1.2 vs. 1.3.
   • Mention certificate pinning and OAuth 2.0 in app security.
5. Common Pitfalls:
   • Don’t confuse HTTP (stateless) with WebSockets (persistent).
   • Remember: MQTT is for IoT/mobile messaging, not general web requests.

Visual Summary: