Paging and Intercom Setup in VoIP: Multicast vs Unicast Methods Explained

Setting up paging and intercom in a VoIP system isn’t just about plugging in speakers and dialing a number. If you’ve ever tried to broadcast a message across your office, hospital, or warehouse and had it fail halfway through-muffled audio, delayed replies, or no sound at all-you know how frustrating it can be. The problem isn’t always the hardware. More often, it’s how you’re sending the signal: multicast or unicast. These aren’t just technical terms. They’re the difference between a system that works reliably and one that drives your team crazy.

What’s the Difference Between Multicast and Unicast?

Think of multicast like a radio broadcast. You send one audio stream, and every device tuned to that frequency hears it. That’s how paging works in large facilities. You press a button, and 50 phones, speakers, and intercom units all play the message at once. It’s efficient. It uses less bandwidth. And it’s fast-latency stays under 250ms even across 100 devices.

Unicast is different. It’s a direct call. When you use intercom to talk to someone’s desk phone, the system creates a one-to-one connection. It’s like dialing a number, except the phone picks up automatically. This is perfect for two-way conversations. But if you try to use unicast to page 50 people? You’re making 50 separate calls. That eats up bandwidth. It slows down. And if your network isn’t rock-solid, the audio cuts out.

When to Use Multicast Paging

Multicast is the go-to for one-way announcements. Think morning facility alerts, emergency notifications, or shift change reminders. It’s used in places like hospitals, schools, and warehouses where timing matters and everyone needs to hear the same message at the same time.

Grandstream’s UCM6200 series, for example, lets you schedule daily paging messages-like an automated 8 a.m. announcement. Yeastar lets you create custom groups: “Nurses,” “Warehouse Staff,” “Front Desk.” Each group can have its own greeting tone and even display a custom name on the phone screen.

But multicast has rules. Your network switches must support IGMP snooping. Without it, the audio floods the whole network like a broken faucet. Cisco’s 2022 guide says proper IGMP setup cuts latency to 150-250ms. Without it? You’re looking at 500ms or more. That’s noticeable. People hear delays. They think the system is broken.

Also, multicast only works on local networks. If you’re using a cloud PBX like RingCentral, you’ll need to disable answering rules and voicemail for paging extensions. Otherwise, the system tries to route the page like a regular call-and it fails. CyberData’s 2021 integration guide says 33% of failed deployments miss this step.

When Unicast Intercom Makes More Sense

Unicast is your best bet for two-way talk. Need to ask the warehouse guy if the shipment arrived? Or check with the front desk if a visitor is waiting? Unicast lets you press a button, and the other phone instantly goes hands-free. You talk. They respond. No dialing. No waiting.

Yeastar’s S-Series PBX supports full-duplex intercom-meaning both people can talk at once, like a regular phone call. Grandstream uses *80 as the default prefix. You press *80, then the extension number, and boom-you’re connected.

But here’s the catch: unicast uses way more bandwidth. Each active intercom session uses about 87 kbps. Multicast? Only 35 kbps per endpoint. If you’ve got 30 people chatting at once, unicast could eat up 2.6 Mbps. That’s a lot for a small business network. And if you chain intercoms-say, you page Person A, who then pages Person B-latency jumps to 450ms or more. The conversation stutters.

Network Setup Is Non-Negotiable

You can have the best PBX in the world, but if your network is messy, paging and intercom will fail. Here’s what you need:

• Power over Ethernet (PoE): Most IP speakers and phones need 802.3af or 802.3at. No power? No audio.
• 100 Mbps or Gigabit switches: Older 10 Mbps switches can’t handle VoIP traffic. You’ll hear choppy audio or dropped calls.
• VLANs for paging traffic: Separate your paging devices onto their own network segment. A 2019 VoIP Supply case study showed this cuts interference with voice and data by 42%.
• QoS with EF (Expedited Forwarding): Mark paging and intercom traffic as high priority. Dr. Lisa Breaux from Cisco says this prevents 92% of audio quality issues in mixed networks.
• Firewall rules: Open UDP ports 5004-5005 for RTP traffic. 73% of failed deployments? Blocked ports. Not the PBX. Not the phones. The firewall.

DTMF Settings: The Silent Killer

One of the most overlooked issues? DTMF signaling. That’s the tones your phone sends when you press buttons. For intercom to work, every device-phone, PBX, speaker-must use the same method: RFC2833, SIP INFO, or in-band audio.

RFC2833 is the most reliable. It’s built into most modern SIP devices. But if one phone uses in-band and your PBX expects RFC2833? The intercom won’t trigger. You press *80. Nothing happens.

VoIP Supply’s 2019 guide says this is the #1 reason people say, “Paging works, but intercom doesn’t.” It’s not a bug. It’s a config mismatch. Check every device. Make sure they’re all on the same page.

Vendor Differences Matter

Not all VoIP systems are built the same. Here’s how the big players compare:

Comparison of Major VoIP Paging and Intercom Systems

Vendor	Default Paging Prefix	Default Intercom Prefix	Max Endpoints	Special Features
Grandstream	*81	*80	100+ (multicast)	Scheduled paging, AI noise cancellation (firmware 1.0.20.113+)
Yeastar	*81	*80	250+ (multicast)	Custom group prompts, Intercom Barge (join live calls)
Ooma Office	*81	*80	250 (multicast)	Department-specific groups, high user satisfaction
3CX	*81	*80	50+ (unicast)	Integration with CyberData speakers, mobile app support

Grandstream leads in automation. Yeastar wins on group control. Ooma gets the highest user ratings for reliability. But if you’re in a hospital or school, you’ll want to look at CyberData speakers-they integrate cleanly with 3CX and have been shown to cut emergency response times by 22 seconds in real-world tests.

What’s Holding SMBs Back?

A 2022 Spiceworks survey found 68% of small businesses don’t use VoIP paging. Why? Perceived complexity. They think it’s for big IT teams. But it’s not. The real issue? Documentation.

Grandstream’s guide scores 4.7/5 on their forum. Yeastar’s is detailed but dense. Smaller vendors? Half the steps are missing. One user on Trustpilot spent 14 hours across three techs just to set up paging for 87 retail locations.

The fix? Start small. Pick one group. Test multicast paging to three speakers. Then add intercom between two phones. Get it working before scaling. And always, always test DTMF settings.

Future Trends and Hidden Risks

By 2026, Gartner predicts 75% of new paging systems will use spatial audio-directing announcements to specific zones in a building. Imagine a fire alarm that only sounds in the kitchen, not the entire warehouse. That’s coming.

But there’s a dark side. Multicast is a security risk if not isolated. In a lab test, researchers intercepted paging audio from 300 feet away using a misconfigured network tap. If your paging traffic runs on the same VLAN as your payroll system? You’re broadcasting sensitive info to anyone on the network.

The fix? VLAN segmentation. Don’t just enable it-enforce it. Use firewall rules to block paging traffic from leaving your facility.

Implementation Checklist

Here’s what you need to do before you hit “save”:

1. Confirm your network switches support IGMP snooping.
2. Assign paging devices to a dedicated VLAN.
3. Set QoS to mark paging and intercom traffic as EF (Expedited Forwarding).
4. Open UDP ports 5004-5005 on your firewall.
5. Set all devices to use RFC2833 for DTMF signaling.
6. Disable voicemail and answering rules for paging extensions.
7. Test multicast paging with 3+ devices.
8. Test unicast intercom between two phones.
9. Document your group names, prefixes, and device lists.

Frequently Asked Questions

Next Steps

If you’re setting this up for the first time, start with a single group. Pick one room or floor. Use multicast to send a test page. If it works, add intercom between two phones. Don’t try to configure 20 devices at once. Take notes. Test each step. And if you’re stuck, check your DTMF settings first. It’s the most common fix.

For larger deployments, hire a VoIP specialist. The average technician needs 17 hours of training to do this right. Don’t risk downtime because you tried to cut corners. A well-configured system saves time, improves safety, and keeps your team connected-without the frustration.