October, 2025

You’re in your Chicago, IL call-centre, mid-call your customer hears you but you don’t hear them. That’s the dreaded PBX one-way audio issue. Or maybe you’re at your New York headquarters and your sales rep in Miami can’t hear a prospect while the prospect hears them clearly. 

At KingAsterisk Technology, we’ve helped hundreds of contact-centres, service desks, global enterprise offices, and regional SMBs fix exactly this kind of problem. In this friendly, straight-talk blog we’ll walk you through why this PBX issue happens, how to fix it, and what you should check so you don’t lose revenue or damage your brand.

What is a PBX one-way audio issue?

It’s when a call connects normally through your PBX or VoIP system, but audio works only in one direction—either you can hear the other party and they can’t hear you, or vice versa. This often stems from NAT/firewall problems, codec mismatches, or mis-routing of RTP streams.

Why This Matters (And Why You Should Care)

• In a Houston, TX oil-&-gas enterprise phone system, a single long call dropping audio means lost revenue and angry clients.
  
• In a London-based international support team, one-way audio erodes trust with global customers.
  
• In a Las Vegas hospitality contact-centre, poor audio means higher repeat calls and lower quality scores.
  

Though specific global numbers for PBX one-way audio aren’t widely published, many forum posts describe “every 1 in 6 or 7 calls” encountering one-way audio when NAT/firewall mis-configurations exist. 

Given the boom in remote work, global contact-centres and multi-site operations (US cities like Atlanta, Seattle, Dallas; APAC hubs like Singapore, Manila; EMEA hubs like Berlin), a smooth PBX experience is no longer optional—it’s essential.

Understanding the PBX One-Way Audio Issue

Let’s break the term down so it doesn’t sound like tech jargon. What exactly happens during a PBX one-way audio issue?

• The call connects. Ring tone, answered, all seems fine.
• One party speaks. The other party either cannot hear them, or vice versa.
• Often it happens when calling in from another region, or when a call crosses a site boundary (e.g., New York → Manila, Chicago → Mexico City).
• Internally calls may work fine, but external or trunked calls mis-behave.
• Frequently random: one call works, next call fails, then works again.

Common root-causes of PBX one-way audio

Having deployed and troubleshooted many systems, here are the frequent culprits:

1. NAT / Firewall / Router Issues

Your PBX (for example an Asterisk-based system) sits behind NAT. The signalling (SIP) works, but the voice-stream (RTP) gets blocked or mis-routed.

2. Double NAT / Multiple Firewalls

Example: You have a branch in Vancouver, BC connecting into a US HQ in Denver, CO. The VPN does NAT, your firewall at HQ also does NAT. The RTP path gets confused.

3. RTP Port Range Blocked/Mis-Routed

Your firewall might only open SIP (5060) but not the full UDP range your carrier uses. A common symptom: one audio direction only.

4. SIP ALG / SIP Helper Issues

Some routers try to “help” SIP by rewriting headers—but often they corrupt the media path, leading to one-way audio.

5. Codec Incompatibility or Packet Loss

If your call flows from your LA-based support desk to a New Delhi, India branch and the codec is mismatched or packet loss extreme, you might not hear the other side. The signalling succeeded, but audio failed.

6. Multi-Site/Conference Topologies 

If a global enterprise in Melbourne, Australia links into a LA support centre and also uses a data centre in Miami, routing loops or mis-configured media servers can cause asymmetric flow (only one direction audio).

7. Carrier/Trunk Issues

Sometimes the external SIP/Trunk provider mis-advertises media IP/port or uses a different range that your firewall doesn’t catch — you’ll see “calls working one moment, failing next”.

Proven Fixes to Resolve PBX One-Way Audio Issue

This is where things get actionable. If you’re running a contact-centre in San Francisco, CA; a global operations centre in Singapore; or a retail support hub in Dallas, TX—these steps apply.

Start with basic checks and quick fixes

Ensure the audio flow is truly one-way (you hear them but they don’t hear you, or vice versa). That confirms the manifestation of the PBX one-way audio issue. Test with a local call (same office) vs external trunk call. If local work, the problem is likely network/internet/trunk. Check equipment: phones/headsets, cables, firmware. Equipment issues seldom cause one-way only (they tend to cause no audio or both directions bad).

Firewall, NAT & RTP Port Fixes

Define your RTP port range in your PBX (e.g., UDP 10000-20000). Document it. Open that range on your external firewall/NAT device. Also allow inbound/outbound. Ensure NAT is correct — in your PBX settings, list the external IP address, local network ranges, and make sure “External Address / Local Networks” fields are correct. (In Asterisk, for example, these appear under “Asterisk SIP Settings”.) 

Disable SIP ALG on your firewall/router unless your provider explicitly uses it. SIP ALG often breaks media by rewriting SDP headers incorrectly. Avoid double NAT if possible — If your branch office (say Austin, TX) uses NAT + VPN to HQ in Atlanta, GA and then HQ NATs again to the internet, consider using VPN tunnel or single NAT point to simplify. Test with Wireshark / packet capture: Check RTP flows in both directions. If you see flow one way only (192.168.x.x → external, but no return), you’ve found the culprit.

Configuring Call Routing & Multi-site Media

In global setups (e.g., servicing APAC from LA), route media to the closest media server to reduce latency and mismatched NAT hops. Segment SIP signalling and RTP media where possible: signalling may go to HQ, media may stay local. Use STUN/TURN servers when remote agents (e.g., home-based agents in Chicago, IL or London, UK) call in. 

That helps with NAT traversal. In cloud-PBX or hybrid setups, request your carrier/trunk provider to send you their media IP/port list, and whitelist them.

Codec, Packet Loss & Quality Considerations

Use common codec sets across sites (G.711, G.722) and avoid exotic ones unless necessary. Some endpoints may not support them properly. Monitor your packet loss/latency/jitter especially between tied sites (e.g., New York ↔ Manila). High one-way packet loss = potential one-way audio. Set QoS / DSCP properly in your WAN links so voice packets get priority.

Example: For a retail contact-centre in Phoenix, AZ with backup site in Dublin, Ireland — if the Dublin link is congested at 40 ms+ latency and 3% packet loss one direction, you’ll likely see the PBX one-way audio issue crop up.

Vendor/Carrier/Trunk Interface Checks

Ensure the trunk provider is sending the correct IP/port for media and that your firewall has allowed them. Ask the provider if they are using “Media Anchoring” where the voice media flows through their servers; then you must allow those IP ranges inbound/outbound. For global operations (e.g., LA-based support and London partner call centres), pick a trunk provider that has geographically distributed media centres else you’ll suffer regional latency and potential one-way audio.

Case Study Snapshot: Multi-City Support in the US & APAC

Our LA-based service desk for a tech vendor had agents in Los Angeles, Dallas and Sydney. Calls to the Sydney team from California occasionally dropped audio one direction. Root cause: Sydney branch NAT’d VPN + local firewall NAT + trunk provider used unexpected media IP. We re-configured: allowed correct RTP range, disabled SIP ALG, and used STUN server for remote agents. Result: >98% reduction in one-way incidents within a week.

How KingAsterisk Technology Can Help You Globally

Here at KingAsterisk Technology, we serve enterprises and contact centre operations across the US, EMEA, APAC and Latin America. Whether you’re in Boston MA, Denver CO, Toronto ON, Singapore, Melbourne or Johannesburg—this one-way audio issue doesn’t respect time zones.

We audit your PBX/VoIP stack (on-prem, cloud, hybrid) for root causes of PBX one-way audio issues. We work with your network/firewall teams in Houston, TX or Frankfurt, Germany to align NAT, RTP, signalling correctly. We help integrate your global SMB or multi-site operations (for instance: a retailer in Miami + branch in São Paulo) to ensure flawless voice across regions. 

We provide continuous monitoring and reporting so you can show your C-suite in New York or Chicago the improvement in call quality KPIs after fix. We drive tool-discovery: you’ll get visibility of your call-flow, bridging technology and network performance across sites in Mumbai and San Francisco.

Ready to generate leads and improve your call clarity? Let’s talk.

FAQs

Q1: I hear them, they don’t hear me — is that the PBX one-way audio issue?

Yes—that’s a classic manifestation of the PBX one-way audio issue. It means signalling worked, but media (RTP) is blocked or not returning in one direction.

Q2: Does this issue only happen with on-prem PBX systems?

No. It can happen in cloud-PBX, hybrid, or on-prem systems. Anywhere VoIP + NAT + firewall + trunking are involved. For example a cloud-hosted PBX servicing Latin America and the US can still suffer one-way media flow issues.

Q3: How fast can this be fixed?

With the right people looking, many setups fix basic NAT/port issues in 2–4 hours; multi-site global deployments might take 1–3 days to validate and roll out. At KingAsterisk we aim to deliver root-cause and patch within one business day for most regional sites.

Summary

If you run a contact-centre in Los Angeles, a service desk in Seattle, a retail support team in Dallas, or a multi-region enterprise with hubs in New York, London, Mumbai and Sydney — the PBX one-way audio issue is more than a nuisance. It hurts your brand, frustrates your agents, and costs you revenue.

Here’s what you should do now:

1. Run a quick self-check: place internal vs external calls and observe one-way audio.
2. Check your NAT/firewall settings against the RTP port range and disable SIP ALG where applicable.
3. If you’re multi-site, map your media path global-wide and note delay/packet-loss asymmetries.
4. Reach out to a voice-expert partner (like us at KingAsterisk Technology) to audit your PBX and network stack.

Let’s fix this together. Ready for clarity? Reach out today.

Choosing a new phone system for your contact center? You’re likely wondering what’s best: a shared Multi-Tenant PBX vs Single-Tenant PBX. That one question shapes your cost, flexibility, security, and future roadmap.

In this post, I’ll walk you through the PBX Solution key differences, benefits, and ideal use cases — with real data, opinions, and advice tailored for U.S. enterprises, SMBs, and contact centers. Along the way, I’ll drop trending keywords (cloud contact center, CCaaS, AI-driven routing, hybrid architectures) so this blog stands strong in 2025 search results.

Let’s dive in — and by the end, you’ll know which model fits your business best (and how KingAsterisk can help you deploy it smoothly).

What Are Multi-Tenant PBX and Single-Tenant PBX — Quick Comparison

Multi-Tenant PBX (aka shared-instance PBX)

A single PBX platform (in the cloud) serves multiple customers (tenants). In this shared setup, every user stays separate and secure despite using the same underlying systems, updates, and resources. Better yet, your vendor takes care of all the upkeep, sizing, and new versions.

Single-Tenant PBX (aka dedicated instance / private PBX)

Each customer gets its own instance, server(s), and database. No sharing with other customers. With a single-tenant, you get full control — but you also bear more responsibility.

Why the Debate Matters

Before choosing one, let’s stir the pot a bit. What are the trade-offs? What risk do you assume with each? You invest in a system and it can’t scale when your call volume doubles. surprise costs or vendor lock-in after going live. You fear performance hiccups, latency, or noisy neighbors in shared infrastructure. These are real concerns. And they tip the balance for many enterprise buyers.

Multi-Tenant PBX vs Single-Tenant PBX — Benefits & Ideal Use Cases

We’ll examine where each system excels, the benefits you get, and the trade-offs you make. The core distinction typically between Multi-Tenant and Single-Tenant PBX comes down to how your company handles matters of growth, data safety, and budget. These distinct PBX setups offer different perks that will define how adaptable and efficient your communication is.

Benefits of Multi-Tenant PBX

It’s the top pick for those  VoIP service providers in the U.S. that don’t want to spend a fortune on equipment.

Cost Efficiency & Lower CAPEX/OPEX

Because infrastructure is shared, hosting costs typically get amortized across multiple tenants. That reduces your total cost of ownership (TCO).

Rapid Deployment & Agility

You don’t need to wait for provision servers or typically install software. Multi-tenant systems often go live in days or weeks.

Automatic Upgrades & Maintenance

The provider usually rolls out new features, bug fixes, and patches centrally. You get all the benefits without having to schedule upgrades yourself in general.

Built-in Scalability & Elasticity

As your team or call volume grows, the system can scale horizontally without gross overhauls.

Shared Innovation & Continuous Improvement

Because providers serve many customers, feature development is often faster. AI routing, analytics, and new modules arrive more quickly.

Lower Barrier for Smaller Businesses

SMBs or contact centers in smaller U.S. cities (e.g. Dayton, OH; Boise, ID) can typically adopt enterprise-grade features without enterprise budgets in general.

Benefits of Single-Tenant PBX

Perfect for large U.S. corporations and regulated industries, Single-Tenant PBX delivers stability, scalability, and the freedom to tailor every communication workflow.

Maximum Isolation & Security

Since typical instances don’t share infrastructure, you control firewalls, network segmentation, encryption, and compliance. For regulated sectors—healthcare, finance, legal—this often is non-negotiable.

Deep Customization & Flexibility

You can build bespoke workflows, custom call routing, API integrations, and tailor the system end to end.

Predictable Performance / QoS Guarantees

Without “noisy neighbors,” you can guarantee resource reservations and performance metrics.

Vendor Independence / Control

You decide upgrade timing, backup strategies, migration plans—no surprise forced upgrades.

Real Data, Trends & 2025 Insights You Should Know

Whitepapers now caution that while multi-tenant PBX is budget-friendly, it may not meet the security or scaling demands of high-growth enterprises. Some companies that migrated to multi-tenant public stacks are now migrating part of their critical workloads back to dedicated or hybrid models due to cost and latency issues.

The future is hybrid. Many smart buyers adopt a multi-tenant core for standard workloads while pushing mission-critical voice paths to single-tenant or private lanes.

Multi-Tenant PBX vs Single-Tenant PBX — Ideal Use Cases (U.S. Focus)

Let’s walk through what types of organizations in the U.S. benefit from each Advanced Asterisk PBX Configuration model. (Yes, I’ll mention some U.S. state / city contexts.)

Best Fit for Multi-Tenant PBX

• Growing startups / scaleups in cities like Austin, TX or Denver, CO
• Contact centers with 50–300 agents that want to avoid heavy upfront cost
• Customer support teams in e-commerce, SaaS, travel, or retail
• Regional franchises / multi-local operations needing unified telephony
• Businesses that prioritize rapid time-to-value and want managed infrastructure
  

Example: A mid-sized SaaS company in Seattle wants to spin up call support and chatbot integrations. Multi-tenant PBX gives them fast deployment without requiring telecom engineers.

Best Fit for Single-Tenant PBX

• Enterprises in highly regulated industries
• Organizations with strict compliance, such as HIPAA, PCI, or FedRAMP
• Big contact centers (1,000+ agents) in major metros
• Companies that already maintain a hybrid cloud approach
• Those that demand predictable performance, SLAs, QoS guarantees

Decision Guide — Which One Should You Choose?

Choosing between Multi-Tenant PBX vs Single-Tenant PBX depends on your business size, compliance needs, and growth goals. If you want a cost-effective, scalable, and low-maintenance setup, go for a multi-tenant PBX. But if your focus is security, customization, and total control, a single-tenant PBX is the smarter long-term investment for your contact center success. Here’s a checklist + decision logic to help your team pick.

Security / Compliance Needs

If you must meet regulatory standards (HIPAA, GLBA, etc.), lean single-tenant or hybrid.

Budget and CapEx Sensitivity

Tight budgets favor multi-tenant (OPEX model), while large budgets might absorb single-tenant overhead.

Customization Requirements

If you foresee deep integrations, unique workflows, or custom plug-ins, single-tenant is safer.

Operational Maturity

Do you have internal teams to manage telecom, network, backups, DR? If not, outsource (multi-tenant) might be safer.

Performance Sensitivity

If latency, jitter, or QoS is critical, single-tenant gives you tighter control.

Suggested Paths

If you’re an SMB or mid-sized firm launching new voice operations, start with multi-tenant PBX and grow. As your volume, regulation, or complexity escalates, migrate or bifurcate into a hybrid / single-tenant architecture for your core workloads. Always test via pilot runs (e.g., a site in Phoenix, AZ) to validate performance, integration, and manageability.

Objections & Common Questions

“Will multi-tenant PBX be less secure because it’s shared?” You’re right to ask. But reputable providers isolate tenants at the logical level, use encryption, and apply strict firewalling. For many organizations, that is sufficient. If you demand full physical isolation, single-tenant is safer.

“Can I switch from multi-tenant to single-tenant later?” Yes—you can migrate. But you should plan for lift & shift of configurations, data, number migrations, and ensure minimal downtime. We at KingAsterisk help clients through that migration road.

“Is single-tenant always more expensive?” Not always. Over time, scale and optimized management may make it comparable. But upfront, single-tenant demands infrastructure and operational cost.

“Will performance degrade for multi-tenant in peak times?” It depends on provider architecture. A well-engineered multi-tenant network isolates resources. Still, in heavy usage, the provider’s underlying infrastructure becomes critical. Over time, as you scale or require stricter controls, migrating parts to single-tenant may pay off.

Does single-tenant PBX eliminate vendor lock-in? It reduces some types of lock-in (you can control upgrades, migration, backup), but you still depend on software vendors or platform support. Well-chosen platforms support portability.

Final Thoughts 

If you’re weighing Multi-Tenant PBX vs Single-Tenant PBX, there’s no universal “winner.” Your ideal choice depends on your scale, security needs, customization appetite, and team capabilities.

At KingAsterisk Technology, we often guide U.S. clients through selection, pilot deployments (e.g. in Dallas, TX or Charlotte, NC), and migrations. We help you avoid pitfalls, optimize cost, and adopt next-gen features (AI routing, analytics, hybrid models).

Want a free audit or architecture review? Drop us a line. Let’s build your future-ready PBX / contact center stack — whichever model fits you best. Ready to take the next step? Contact us at KingAsterisk — we’ll map out your ideal setup, pilot deployment, and long-term roadmap.