Know and understand the use of mobile devices for communication including SMS messaging, phone calls, voice over Internet Protocol (VoIP), video calls, accessing the internet

ICT Applications – Mobile Devices for Communication

This set of notes fulfils Cambridge IGCSE/AS‑Level ICT Section 6.1 – Mobile communication. It covers the range of mobile‑communication methods, the technical concepts behind each service, their advantages and limitations, e‑safety issues, and the wider social, ethical and environmental impact. A practical activity at the end develops AO2 skills.

1. Overview of Mobile‑Communication Methods

  • SMS (Short Message Service) – text‑only messages (max 160 characters, 70 characters with Unicode).

  • MMS (Multimedia Messaging Service) – SMS‑style messages that can include images, video, audio or contacts.

  • USSD (Unstructured Supplementary Service Data) – session‑based, real‑time communication with the network (e.g., balance checks, menu‑driven services).

  • Traditional voice call – circuit‑switched voice communication over the mobile network.

  • VoIP (Voice over Internet Protocol) – voice transmitted as IP data packets via Wi‑Fi or mobile data.

  • Video call – simultaneous audio and video streams sent over IP.

  • Messaging apps (e.g., WhatsApp, iMessage, Telegram) – internet‑based instant messaging that can carry text, voice notes, images, video and files.

  • Internet access – using a mobile device to browse the web, stream media, use cloud services, etc.

2. Technical Foundations

  • Cellular generations – the underlying radio technology determines bandwidth, latency and coverage:

    • 2G (GSM) – voice & SMS, low data rates (≈ 0.1 Mbps), high latency.

    • 3G (UMTS/HSPA) – better data (≈ 2 Mbps), lower latency, supports video calls.

    • 4G (LTE) – high‑speed data (≈ 20‑100 Mbps), low latency, ideal for VoIP & video.

    • 5G (NR) – very high data rates (> 1 Gbps), ultra‑low latency (< 10 ms), enables high‑definition video and AR/VR.

  • Network layers – all services use the OSI/TCP‑IP model:

    • Physical & Data Link – radio interface (GSM, LTE, 5G NR).

    • Network – routing of IP packets (for VoIP, video, messaging apps, Internet).

    • Transport – TCP (reliable) or UDP (low‑latency) used by voice/video codecs.

    • Application – SMSC, MMS Relay, USSD gateway, SIP (VoIP), WebRTC (video), HTTP/HTTPS (Internet).

  • Bandwidth & latency – key performance indicators:

    • SMS/MMS/USSD – negligible bandwidth, latency measured in seconds.

    • Traditional voice – ~ 12 kbps per direction, latency < 150 ms.

    • VoIP audio – 8‑64 kbps (codec dependent), latency < 100 ms for good quality.

    • Video call – 300 kbps (low‑def) to 2 Mbps (HD), latency < 200 ms.

3. Detailed Service Notes

3.1 SMS (Short Message Service)

  • How it works: Sent via the cellular signalling (control) channel to the Short Message Service Centre (SMSC); the centre stores and forwards the message to the recipient’s device.

  • Key characteristics

    • Cost: per‑message charge or included in flat‑rate plans.

    • Data usage: 0 MB (uses signalling, not mobile data).

    • Coverage: works in very low‑signal areas (2G‑GSM sufficient).

    • Device compatibility: all mobile phones, including feature phones.

    • Bandwidth: negligible; latency typically < 5 s.

  • Typical uses: Alerts, verification codes, short information to students or staff.

  • Advantages: Low cost, works on basic phones, high reliability in weak signal.

  • Limitations: Text‑only, 160‑character limit, no delivery guarantee.

  • e‑Safety tip: Beware of smishing (SMS phishing) – never click unknown links.

3.2 MMS (Multimedia Messaging Service)

  • How it works: Uses the same signalling channel as SMS but forwards the multimedia content via the MMS Relay/Server, which may route through the Internet.

  • Key characteristics

    • Cost: higher than SMS (often per‑message or per‑MB).

    • Data usage: typically 0.1‑1 MB per message (depends on media size).

    • Coverage: requires at least 3G for reliable transfer of larger files.

    • Device compatibility: smartphones and most feature phones with a camera.

    • Bandwidth: modest; latency a few seconds to a minute.

  • Typical uses: Sharing photos from a school event, short video clips, audio notes.

  • Advantages: Adds visual/audio content to text; works without a data plan.

  • Limitations: Higher cost, size limits (usually ≤ 300 KB), may be blocked by some carriers.

  • e‑Safety tip: Do not send personal images to unknown contacts; check app permissions.

3.3 USSD (Unstructured Supplementary Service Data)

  • How it works: Real‑time, session‑based communication between the handset and the mobile network’s USSD gateway; uses the signalling channel (no storage).

  • Key characteristics

    • Cost: usually free or minimal charge.

    • Data usage: 0 MB.

    • Coverage: works on 2G and above.

    • Device compatibility: all phones.

    • Typical latency: < 2 s.

  • Typical uses: Balance enquiries, menu‑driven services (e.g., “*123#” for airtime top‑up), mobile banking prompts.

  • Advantages: Instant feedback, works without a data plan.

  • Limitations: Text‑only, limited to short commands, no multimedia.

  • e‑Safety tip: Only use USSD codes provided by trusted operators; avoid unknown “*#*#” codes.

3.4 Traditional Voice Call

  • How it works: Circuit‑switched connection set up via the mobile network’s control channel; voice is digitised, compressed (e.g., AMR codec), and sent over a dedicated voice channel.

  • Key characteristics

    • Cost: per‑minute charge or included in voice‑minute allowance.

    • Data usage: 0 MB.

    • Coverage: requires adequate signal on the voice channel (2G‑GSM or higher).

    • Device compatibility: all mobile phones.

    • Bandwidth: ≈ 12 kbps per direction.

    • Latency: < 150 ms in good conditions.

  • Typical uses: Personal conversations, emergencies, voice‑only support calls.

  • Advantages: Reliable voice quality in good signal, works on basic phones.

  • Disadvantages: Higher cost for long‑distance, no visual component, call drops in weak signal.

  • e‑Safety tip: Do not share personal details with unknown callers; use caller‑ID blocking if required.

3.5 VoIP (Voice over Internet Protocol)

  • How it works:

    1. Microphone captures analog voice → ADC → digital audio.

    2. Audio is compressed using a codec (e.g., Opus, G.711).

    3. Compressed frames are packetised (RTP) and sent over IP (Wi‑Fi or mobile data).

    4. At the receiver, packets are re‑ordered, decoded, and converted back to analog (DAC).

  • Requirements

    • Internet connection (Wi‑Fi, 3G/4G/5G data).

    • VoIP client/app (Skype, WhatsApp, Viber, Google Voice, etc.).

    • Microphone & speaker or headset.

  • Key characteristics

    • Cost: data‑based; often free beyond the data charge.

    • Data usage: ≈ 0.5 MB / min (audio only).

    • Bandwidth: 64‑128 kbps (depends on codec).

    • Latency: < 100 ms for good quality.

    • Coverage: depends on data signal strength (3G‑5G).

  • Advantages: Low cost for long‑distance, works on any internet‑enabled device, often bundled with instant messaging and file‑sharing.

  • Disadvantages: Requires stable data connection; quality suffers with congestion; security depends on app encryption.

  • e‑Safety tip: Use apps with end‑to‑end encryption (e.g., Signal, WhatsApp); avoid VoIP on unsecured public Wi‑Fi without a VPN.

3.6 Video Call

  • How it works:

    1. Front‑facing camera captures video; microphone captures audio.

    2. Video is compressed (e.g., H.264/AVC, VP8/VP9) and audio with a codec (Opus).

    3. Both streams are packetised (RTP/RTCP) and sent over IP.

    4. Receiver decodes, synchronises, and displays video while playing audio.

  • Requirements

    • Camera, microphone, speakers/headset.

    • Internet connection with sufficient bandwidth (≥ 1 Mbps for SD, ≥ 3 Mbps for HD).

    • Compatible app or web client (Zoom, Teams, FaceTime, Google Meet, WhatsApp Video).

  • Key characteristics

    • Cost: data‑based; often free beyond data charge.

    • Data usage: ≈ 2 MB / min (standard SD) – up to 5 MB / min for HD.

    • Bandwidth: 500 kbps‑2 Mbps (depends on resolution).

    • Latency: < 200 ms for smooth interaction.

    • Battery impact: high (camera + video encoding).

  • Advantages: Visual cues improve understanding; supports remote learning, tele‑health, business meetings; often includes screen‑share and collaboration tools.

  • Challenges: High data and battery consumption; requires good lighting and stable high‑speed connection; privacy risk if camera access is misused.

  • e‑Safety tip: Keep camera cover when not in use; check app permissions; use a VPN on public Wi‑Fi.

3.7 Messaging Apps (Internet‑Based Instant Messaging)

  • How they work: Messages are sent as data packets over the Internet using proprietary or standard protocols (e.g., XMPP, MQTT). They may carry text, voice notes, images, videos, documents, and even location data.

  • Key characteristics

    • Cost: free beyond data usage.

    • Data usage: varies – ~ 0.1 MB per 10‑text‑message exchange; larger for media.

    • Bandwidth: low for text, moderate for images (≈ 0.5‑2 MB each), high for video clips.

    • Latency: typically < 1 s for text, a few seconds for large media.

    • Device compatibility: smartphones, tablets, PCs (app or web).

  • Typical uses: Group chats for class projects, sharing homework photos, voice notes, quick coordination.

  • Advantages: Rich media, group functionality, often includes end‑to‑end encryption.

  • Limitations: Requires data connection; privacy concerns if permissions are overly broad.

  • e‑Safety tip: Review privacy settings; avoid sharing personal details with unknown contacts; keep apps updated.

3.8 Accessing the Internet on Mobile Devices

  • Connection methods

    • Cellular data: 3G, 4G (LTE), 5G – provided by the mobile operator; billed per GB or via unlimited plans.

    • Wi‑Fi: Local area network, usually faster and cheaper for large transfers.

  • Key technical concepts

    • IP address: Numeric identifier (e.g., 192.168.1.45) that enables routing of packets.

    • DNS (Domain Name System): Translates domain names (e.g., www.bbc.co.uk) to IP addresses.

    • HTTPS: Secure version of HTTP; encrypts data between device and web server using TLS/SSL.

    • Bandwidth & latency: Determines speed of browsing, streaming and file downloads.

  • Typical activities: Web browsing, email, social media, cloud storage, streaming music/video, e‑learning platforms.

  • Considerations

    • Data limits – exceeding the plan may incur extra charges.

    • Battery drain – high‑speed data and video streaming consume more power.

    • Security – prefer HTTPS sites, avoid sensitive transactions on public Wi‑Fi unless using a VPN.

4. Comparison of Mobile Communication Methods

FeatureSMSMMSUSSDPhone CallVoIPVideo CallMessaging AppsInternet Access
Typical costLow – per messageMedium – per message/sizeFree or minimalMedium – per minuteLow – data onlyLow – data onlyLow – data onlyVariable – data plan or Wi‑Fi
Required networkCellular signalling (2G‑5G)Cellular signalling + data (3G+)Cellular signalling (2G‑5G)Cellular voice channel (2G‑5G)Internet (Wi‑Fi or 3G‑5G)Internet (high‑bandwidth)Internet (Wi‑Fi or 3G‑5G)Internet (any speed)
Device compatibilityAll phonesAll phones with cameraAll phonesAll phonesSmartphone, tablet, PC (app)Smartphone, tablet, PC (camera)Smartphone, tablet, PC (app/web)Smartphone, tablet, PC
Data usage (approx.)0 MB0.1‑1 MB0 MB0 MB≈ 0.5 MB / min≈ 2‑5 MB / min0.1 MB / 10 texts; higher for mediaVaries – web page ≈ 0.1 MB, streaming > 5 MB / min
Battery impactVery lowLow‑moderateVery lowLowModerate (audio processing)High (camera + video encoding)Low‑moderate (depends on media)Variable – high with streaming
Reliability in low‑signal areasHigh (uses signalling)Moderate (needs 3G+)HighLow‑moderateLow (depends on data signal)Low (needs good bandwidth)Low‑moderateLow‑moderate (Wi‑Fi often better indoors)
Typical usesAlerts, verification codesPhoto/video sharing, event invitesBalance checks, service menusVoice conversation, emergenciesLong‑distance/audio calls, businessRemote meetings, tutoring, family chatsGroup chats, file sharing, voice notesBrowsing, email, streaming, e‑learning
Security risksSMS spoofing, smishingMalware in attachments, spoofingSocial engineering via fake codesCaller ID spoofing, interceptionUnencrypted traffic (if app lacks encryption)Same as VoIP + unauthorized camera accessData leakage, over‑broad permissionsPhishing sites, unsecured Wi‑Fi, malware

5. Social, Ethical and Environmental Impact

  • Social inclusion: Mobile communication enables remote learning, keeps families connected across distances, and supports people with limited mobility.

  • Digital divide: Not all pupils have smartphones or affordable data plans, creating inequality in access to information and learning resources.

  • Privacy & surveillance: Location data, call‑metadata and message logs can be collected by operators or apps; students must understand consent and data‑protection rights.

  • Distraction: Constant notifications can disrupt classroom focus; schools often implement device‑use policies.

  • Environmental impact: Production of smartphones, batteries and network infrastructure generates e‑waste and carbon emissions; 5G rollout increases energy demand.

6. e‑Safety Checklist for Mobile Communication

  • Set a strong, unique password or use biometric lock for the device and each app.

  • Enable two‑factor authentication (2FA) for email, banking and any service that offers it.

  • Never click on links or open attachments in unexpected SMS, MMS or instant‑message chats – they may be phishing (smishing) attempts.

  • Download apps only from official app stores; read reviews and check the permissions requested.

  • Keep the operating system and all apps up to date to patch security vulnerabilities.

  • When using public Wi‑Fi, avoid accessing personal or financial information unless you use a reputable VPN.

  • Review app privacy settings regularly – limit camera, microphone, contacts and location access to what is essential.

  • Cover the camera when not in use and disable microphone access for apps that do not need it.

  • Report any suspicious messages, calls or app behaviour to your carrier, school IT staff or a trusted adult.

7. Practical Activity – Evaluating a VoIP/Video Call

Objective: Apply knowledge of VoIP and video‑call technology, record data usage, assess quality and reflect on security.

  1. Select a free VoIP or video‑call service (e.g., Skype, WhatsApp, Zoom, Microsoft Teams).

  2. Connect the device to Wi‑Fi (or note the mobile data type if using cellular).

  3. Make a 2‑minute audio call to a classmate or family member.

    • Record the data usage shown by the app or by the device’s data‑usage monitor.

    • Note any audio quality issues (lag, echo, drop‑outs).

  4. Repeat the test with a 2‑minute video call (standard definition).

    • Record data usage and battery level before and after the call.

    • Observe video quality (pixelation, freezing) and any latency.

  5. Answer the following questions in a short report (≈ 200 words):

    • How did the data usage compare between audio‑only and video calls?

    • What network conditions (signal strength, Wi‑Fi speed) affected the call quality?

    • Identify any security features the app provides (encryption, 2FA, privacy settings).

    • Based on your findings, recommend when it is appropriate to use VoIP/audio vs. video for school communication.

Assessment criteria (AO2): Demonstrates understanding of technical concepts (bandwidth, latency, data usage), evaluates the practical outcomes, and reflects on e‑safety considerations.