A modem (MODulator-DEModulator) is a hardware device that allows a computer or another device to transmit data over telephone lines or cable lines. The modem modulates and demodulates signals so that digital data can be transmitted over analog communication systems.
How Modems Work
A modem has the following key functions:
- Modulation – Converts digital binary data from computers into analog signals that can be transmitted over phone lines, cable networks, satellite etc. This process is called modulation.
- Demodulation – Converts incoming analog signals back into digital binary data that the receiving computer can understand. This process is called demodulation.
- Encoding/Decoding – Modems encode the modulated signal at sender side and decode the demodulated data at receiver side into compatible digital data.
- Compression/Decompression – Modems compress the digital data for faster transmission rates and decompress the data back to original form at receiving end.
- Error correction – Modems automatically request retransmission of data in case any errors are detected.
Types of modulation schemes used by modems:
- Frequency Shift Keying (FSK)
- Phase Shift Keying (PSK)
- Quadrature Amplitude Modulation (QAM)
Types of Modems
There are several types of modems differentiated by interface, supported network, speed etc.
Internal vs External Modems
- Internal – Modems cards/chips installed within the computer.
- External – External hardware devices connecting to computer.
|Connects via motherboard
|Connects via ports like USB
|Not portable. Fixed to one computer
|Portable and can connect to multiple computers
Broadband vs Narrowband Modems
- Narrowband – Supports transmission upto 56Kbps like dial-up modems over POTS lines
- Broadband – High speed DSL and cable modems supporting multiple Mbps bandwidth
Wired vs Wireless Modems
- Wired Modems – Connect via wired mediums like telephone lines, ethernet cables, cable TV networks etc.
- Wireless Modems – Connect using cellular networks or radio wavebands. Examples:
- Satellite Modems
- Cellular Network Modems
- Radio Modems
Evolution of Modem Technology
Over the decades, modems have evolved supporting higher modulation schemes and transmission rates:
- Early Acoustic coupled modems worked over phone lines at speeds below 1200 bits per second
- V.21/V.22/V.22bis Bell modems increased rates upto 2400 bits/s using PSK and FSK modulation
- V.32/V.34 modems achieved 9600 bps and 33600 bps using Trellis coded modulation
- V.90/V.92 dial-up modems reached 56 Kbps upstream and downstream
- Present day cable and DSL modems based on ITU standards V.90/V.92 provide 100+ Mbps bandwidth over telephone lines and cable TV networks
- 5G NR modems expected to provide upto 20 Gbps speed leveraging higher order QAM modulation
Working of Dial-up Modems
Before broadband became popular, dial-up modems were ubiquitous allowing internet access over POTS telephone lines. Their working steps were:
- The dial-up modem converts digital data from computer into analog audio frequency signals through modulation
- Computer establishes connection over POTS by dialing receiver modem’s phone number
- Modem transmits these analog signals over the phone line to receiving modem
- Receiver demodulates analog signals back into digital data for the remote computer
Advantage – Allow internet connectivity over existing telephone network
Disadvantage – Maximum 56 Kbps speed. Too slow for today’s data applications.
Cable and DSL Broadband Modems
With digital cable and DSL lines replacing analog telephone networks, high speed broadband modems became mainstream.
These modems connect customer end devices to the Internet Service Provider (ISP) broadband network instead of direct computer-to-computer dial-up connection.
Both cable and DSL modems provide 100+ Mbps bandwidth enabling high speed internet and WiFi connectivity to multiple devices in a home or office network.
Key Applications of Modems
Some major applications of modems are:
- Internet Connectivity – DSL, cable or fiber modems provide broadband internet over telephone and cable TV networks
- Computer Connectivity – Establish connectivity between computers over dial-up or leased lines for data transfer
- Telemetry – Wireless modems connect devices and sensors sending remote metrics and reports
- Fax Machines – Enable documents transmission over telephone lines
- POS Terminals – Allow digital POS machines to transmit transaction information to payment networks via phone lines
Buying Considerations for Modems
Some key factors while purchasing a modem are:
- Network – Which connection does it support (Cable, DSL, Satellite, Cellular etc.)
- Speed – Higher Mbps means faster connectivity
- WiFi – Built-in WiFi router allows connecting multiple wireless devices
- Port numbers – More Ethernet ports allows connecting multiple wired devices
- Brand – Reputed brands like Netgear, D-Link, Linksys offer better performance
- Budget – Entry level vs Premium modems balancing cost versus longevity
- Ease of setup – Easy installation procedures for non-technical users
For cable and DSL modems, check the approved modem list and compatibility details from your ISP before purchasing.
Setting up a new Modem
Follow these step-by-step instructions for installing and setting up a new modem at home:
Step 1) Install Hardware
- Turn OFF modem and computer
- Connect coaxial cable from cable wall outlet to cable port in the modem
- Use ethernet cable to link computer and modem LAN port
- Insert power cable and turn ON the modem
Step 2) Configure Connection
- Launch browser and access modem setup page (192.168.100.1)
- Select internet connection type (Automatic/Static IP)
- For automatic, enter ISP details – Server names, Domain etc
- Save settings. Modem will now contact network and establish link
Step 3) Verify Connectivity
- Check status LEDs on modem to confirm connectivity
- Open browser on computer/phone connected to modem
- If connected, you will be able to access internet
Try accessing a few websites. Setup is complete.
- Modem = Modulator + Demodulator. Converts digital bits into and from analog waveforms.
- Different types include internal/external modems and narrowband/broadband modems
- Modems have evolved from early acoustic coupled modems upto present day high speed cable/fiber/5G modems
- Dial-up modems use telephone lines. DSL/Cable modems provide 100+ Mbps over broadband lines
- Choosing right modem depends on network, speed, WiFi features as per usage needs
- Setting up modems is easy. Just connect hardware, configure ISP settings correctly
Hope this detailed guide gives you a good understanding of what is modem, how they work to connect digital devices over analog networks, different types available, evolution of modem technology, their applications and factors to consider while selecting right modem as per your connectivity needs. Modems have been enabling digital communication for over 6 decades and continue to be integral part of networks as they evolve towards 5G and fiber-speeds.
Frequently Asked Questions (FAQs) Related to Modems
Q1. Why are modems required?
Modems enable transmitting digital computer data over analog telephone and cable TV networks by converting between digital bits and analog waveforms through modulation and demodulation.
Q2. How fast can modems be?
Legacy dial-up modems had maximum speed of 56 Kbps. Present day cable and DSL modems provide speed upto 1 Gbps for home users. With 5G, enterprise grade modems can transmit at 20 Gbps over cellular spectrum.
Q3. Do modems come with WiFi?
Yes, most cable and DSL modems available today feature an inbuilt router and WiFi access allowing you to connect multiple devices over the wireless network.
Q4. Can I use external modem on laptop?
Yes, laptops can easily use external USB modems. Just plug the USB cable to connect laptop and modem port to access the internet via the modem.
Q5. How do I check modem connectivity?
You can check the signal levels, connection status and IP address assigned on the modem using it’s configuration login page. Strong signal with valid IP indicates good connectivity.
Q6. Why modem has no dial tone?
If the telephone socket has no dial tone, first check all cable connections. Also ensure line filter is correctly installed for DSL modems. Contact ISP if hardware connections are proper but dial tone still does not come.
Q7. How to troubleshoot slow internet speed on modem?
Try restarting the modem/router, connect nearby to WiFi router, check for interference, contact ISP for line quality checks, upgrade plan if consistently slow during peak usage.
Q8. My new modem is not connecting. What can be wrong?
Most connectivity issues can be fixed by power cycling modems/routers and checking hardware connections. Also call ISP helpline to ensure MAC address is correctly registered if all connections are proper.
Q9. Why is my modem indicator blinking continuously?
A constantly blinking LED light could mean the modem is trying to establish connection with the provider network due to hardware fault, line issues, configuration problems or network outage for the area.
Q10. How to check modem logs and history?
Modem logs can be accessed by logging into the admin interface using default gateway IP address. The logs provide historical events, warnings and errors related to hardware, connectivity etc for troubleshooting.
Q11. Can I set up modem myself or need technician?
No need for a technician if your ISP provides clear setup instructions. Just follow port connection diagrams, configure ISP settings correctly and power on modem to get online.
Q12. My modem has only 1 LAN port. How do I connect multiple devices?
You can connect an inexpensive network switch to the single LAN port, which splits it into multiple ports allowing many devices to connect over the same modem.
Q13. What is the difference between router and modem?
The modem connects to ISP to get internet signal. Router uses the internet connection provided by modem for traffic routing between connected devices and also provides WiFi access.
Q14. Why is modem MAC address required during activation?
ISP verifies unique MAC address embedded on each modem to activate internet connection for the customer as part of security policy.
Q15. Can I reuse existing modem while changing internet provider?
It depends on modem compatibility with new provider equipment. Best is to get a new modem approved for network but sometimes old modems can work by reconfiguring settings.
Q16. Do wireless home networks need a modem?
Yes, cable/DSL modems along with WiFi routers connect cordless devices like mobiles/tablets over wireless home network to the internet. The modem brings the internet signal.
Q17. How frequently should Modems be replaced?
A reliable modem typically lasts between 3-5 years if properly maintained. Get it replaced sooner if experiencing frequent drops, slower speeds or unable to get technical support due to older technologies.
Q18. How do hotel internet modems provide temporary guest access?
Hospitality industry uses server based controller systems to provide time limited temporary credentials and WiFi passwords uniquely to each guest device for secure access over the shared modem connection.
Q19. Why Modem RF shielding required?
RF noise interference can disrupt modem signals leading to slower speed and connectivity issues. Quality modems provide integrated RF shield minimising such radio frequency disturbances for reliability.
Q20. How modems help connect branch office networks to central HQ?
Modems enable site-to-site connectivity between branch locations and central HQ over leased line or broadband links helping build secure corporate WAN and allowing central monitoring.