What Is VoIP?
VoIP (Voice over Internet Protocol) is a technology that carries voice calls over the internet instead of traditional phone lines (PSTN). Voice data is converted into packets and transmitted via the internet. In Japan, 050-number IP phone services are the most common example, and services like NTT's Hikari Denwa that use traditional area-coded numbers are also available. If you are considering switching from a landline to Hikari Denwa, see Hikari Denwa Migration Guide.
Handling voice as data is used for everything from app-based calls to corporate phone systems. Knowing how it works makes practical decisions easier - pricing, call quality, and how emergency calls are handled.
How VoIP Works
Digitization and Packetization of Voice
Voice captured by a microphone is converted to digital data, split into small packets, and transmitted over the internet. The receiving end reassembles the packets and plays them back as audio. This entire process happens in real time, providing a conversation experience similar to a regular phone call.
Voice compression uses codecs. G.711 prioritizes quality at the cost of more bandwidth, while G.729 saves bandwidth at the cost of slightly lower quality. Which one is used depends on the service and the equipment settings.
Key Protocols
VoIP uses SIP (Session Initiation Protocol) to manage call setup and teardown, and RTP (Real-time Transport Protocol) to carry the actual voice data. These protocols work together to deliver stable calls. SIP is a text-based protocol similar to HTTP, offering high extensibility.
Advantages of VoIP
- Pricing not tied to distance: Because voice travels as IP packets, pricing leaves behind the assumption that a line is occupied for the distance and duration of a call, so it depends on how each provider designs it. Some services charge nothing for calls between users of the same app, while others, such as 050-number IP phones, have a monthly base fee plus call charges
- Location flexibility: Make and receive calls from the same number anywhere with an internet connection. Ideal for remote work
- Rich add-on features: Call forwarding, recording, IVR (interactive voice response), and call analytics can be added via software
- Multi-device support: Use simultaneously on smartphones, PCs, and dedicated handsets
- Lines are easy to add or remove: Adjust the number of lines as the business grows or contracts
Disadvantages and Considerations
- Quality depends on the network: Call quality is directly tied to internet speed and stability. Jitter and packet loss cause audio degradation
- Unusable during power outages: Power stops reaching the ONU (optical network unit) and the router, so calls are not possible without a backup such as a UPS (uninterruptible power supply)
- Emergency call limitations: 050-number IP phones cannot place emergency calls to 110 or 119. Hikari Denwa and other services that support 0AB-J numbers do reach 110 and 119
- Social credibility of 050 numbers: 050 numbers may be perceived as less credible than landline numbers. For business use, consider services supporting 0AB-J numbers
- Security risks: Being internet-based, there are risks of eavesdropping and spoofing. Encryption (SRTP) is recommended
Comparing Major VoIP Services
Consumer services include OCN's "050 plus" and Rakuten Mobile's "Rakuten Link." For businesses, carriers offer services combined with a cloud PBX, and platforms from outside Japan such as Zoom Phone and Microsoft Teams Phone are also used domestically.
When choosing a service, comprehensively compare call quality, pricing, supported numbers (050 or 0AB-J), emergency call support, and customer service.
VoIP Deployment Steps
Step 1: Check Your Network Environment
VoIP call quality depends directly on your internet connection. Voice itself uses less bandwidth than video, but as jitter (variation in delay) and packet loss increase, the audio starts to drop out or lag. Where the line is shared with other traffic, QoS settings on the router that give voice packets priority matter.
Step 2: Select a Service
For personal use, a 050-number IP phone service is the easiest option. For business, choose a service supporting 0AB-J numbers (with area codes). Combining with a cloud PBX enables advanced features like extensions, forwarding, and IVR.
Step 3: Prepare Equipment
VoIP requires an IP phone handset, an ATA (Analog Telephone Adapter), or a softphone app (for PC/smartphone). If you want to keep using an existing analog phone, connect it through an ATA. Softphones require no additional hardware and pair well with remote work.
VoIP Security Measures
Since VoIP communicates over the internet, it faces security risks that traditional phone lines do not. Proper measures ensure safe VoIP usage.
- Call encryption: Use SRTP (Secure Real-time Transport Protocol) to encrypt voice data, lowering the risk of the audio being read in transit
- Strengthen SIP authentication: Set complex passwords for SIP accounts and change them regularly to prevent brute-force attacks
- Firewall configuration: Allow only SIP traffic (ports 5060/5061) and RTP traffic (ports 10000-20000), closing unnecessary ports
- Use VPN: In remote work environments, route VoIP through a VPN to encrypt the entire communication path
When to Use VoIP vs. Traditional Landlines
VoIP and traditional landlines each have distinct strengths. Choosing based on your needs leads to the optimal communication setup.
- When pricing matters: VoIP is a candidate where calls to distant areas are frequent, since pricing no longer follows distance. International rates are set per destination and per provider, so check your provider's rate table for the destination country before calling
- Reliability priority: Traditional landlines win. They work during power outages via exchange power and offer higher emergency call accuracy
- Flexibility priority: VoIP wins. Make and receive calls from anywhere on the same number, ideal for remote work
- Social credibility: VoIP with 0AB-J numbers is equivalent to landlines. 050 numbers may be seen as slightly less credible
Another option is a hybrid setup that keeps both: VoIP for everyday calls, with a landline left in place as a fallback for power outages and line faults. Decide what matters most for the intended use, then check supported numbers and emergency call handling before choosing a service.