Call Quality Is Fine in the Morning But Bad in the Afternoon

When Your Phones Sound Bad: Part 9 of 12

This pattern is one of the more telling clues in VoIP troubleshooting. Calls are clear and crisp first thing in the morning. By midday, they start getting choppy. By 2 or 3 PM, the quality is noticeably worse. By the end of the business day, things are bad enough that people are complaining. The next morning, everything is fine again.

The daily cycle tells you that the problem is related to usage. Something that isn't happening in the morning is happening in the afternoon, and it's degrading the conditions that voice traffic needs to sound good. The question is what, and whether it's inside your network or outside of it.

The most likely cause: bandwidth saturation

When call quality degrades as the day gets busier, the most common explanation is that your internet connection's available bandwidth is being consumed by everything your office is doing, and voice traffic is suffering because it's competing for space.

In the morning, usage is light. A few people are checking email, someone loads a webpage. Your 50 Mbps upload can handle this easily, and the voice traffic has plenty of room. By early afternoon, more people are active. Someone starts a video conference. The cloud backup kicks in. A few people are uploading files to a shared drive. The marketing team is uploading video content to social media. Now that 50 Mbps upload is being asked to carry a lot more, and voice packets are waiting behind larger data transfers.

Upload is the direction that matters most here. As covered in the Getting the Internet Right series, your upload bandwidth is typically much smaller than your download bandwidth on cable and most shared fiber connections. Voice calls need consistent upload bandwidth for the outgoing audio. When the upload is saturated, voice packets get delayed or dropped, and you hear choppy or degraded audio.

How to confirm this

Run a speed test during the morning when calls sound fine. Note the upload speed. Run the same test during the afternoon when calls sound bad. If the afternoon upload speed is significantly lower than the morning speed, your upload bandwidth is being consumed. Running a VoIP quality test during both windows is even more telling, because it measures jitter and packet loss alongside throughput, which a basic speed test does not.

Better yet, if your router supports bandwidth monitoring, look at the real time upload utilization during the problem periods. If upload utilization is consistently at or near the connection's maximum during the times when calls are bad, you've found the cause.

How to fix it

QoS configuration. Configure Quality of Service on your router to prioritize voice traffic. When QoS is active, the router ensures voice packets are sent first, even when the connection is busy. Other traffic gets slightly delayed to make room for voice, which is the right tradeoff because a web page loading 100 milliseconds slower is invisible to the user, while a voice packet arriving 100 milliseconds late is audible.

Identify and schedule heavy traffic. Cloud backups, large file syncs, software updates, and other bandwidth intensive operations should be scheduled for off hours if possible. Most backup and sync applications have scheduling features. Moving these to evening or overnight hours frees up bandwidth during business hours.

Upgrade the connection. If QoS and scheduling aren't sufficient, the connection itself may need to be upgraded. This might mean a faster plan from the same provider (if one with better upload is available), switching from cable to fiber (for better upload speeds), or adding a dedicated connection for voice traffic.

ISP congestion

If your own bandwidth isn't the issue (your speed tests show full capacity even during the afternoon), the congestion might be on your ISP's network. As covered in the cable internet post, shared internet connections like cable share bandwidth among all customers connected to the same node. When more customers in your area are active during the afternoon, the shared capacity gets divided among more users, and your effective bandwidth drops even though nothing on your end has changed.

ISP congestion shows up as reduced speed test results during peak hours, increased latency on ping tests, and sometimes increased jitter and packet loss. If you're consistently seeing degraded metrics during business hours but full performance early in the morning or late at night, your ISP's infrastructure in your area is likely congested.

This is harder to fix because it's not under your control. You can report the issue to your ISP and ask about node capacity. ISPs do split overloaded nodes periodically, but it's on their timeline. If the congestion is persistent, switching to a less congested ISP (if options exist at your address), upgrading to a dedicated connection that isn't shared, or adding a separate dedicated connection for voice are the most effective long term solutions.

Internal network congestion

Sometimes the congestion isn't on the internet connection at all. It's on the internal network. This happens when your internal switches or access points are oversubscribed during busy periods.

A common scenario: a 100 Mbps switch port connects to a device that's doing large file transfers to a local server. The same switch is handling phone traffic. During heavy file transfer periods, the switch's backplane or a specific uplink port gets congested, and voice packets experience delay.

This is more common with older or cheap switches that don't handle traffic prioritization well. Managed switches with VLAN support and QoS solve this by putting voice traffic on a separate VLAN with priority handling. If your phones and computers are on the same unmanaged switch, upgrading the switching infrastructure can eliminate internally generated congestion.

Video conferencing load

The rise of video conferencing has created a new bandwidth pressure that wasn't there a few years ago. A single video call can consume 2 to 4 Mbps of upload bandwidth. An office with five people on simultaneous video calls could be using 10 to 20 Mbps of upload just for video, which on a connection with 20 to 30 Mbps total upload leaves very little room for voice and everything else.

If the afternoon quality degradation correlates with periods of heavy video conferencing use, the video traffic is likely the competing demand. QoS can help by ensuring voice gets priority over video when both are competing. Reducing video resolution settings on conferencing platforms also helps. Most platforms allow administrators to set default bandwidth limits for video calls.

The pattern as the diagnosis

The daily pattern itself is the most useful diagnostic information. If someone reports "call quality is bad," that's hard to investigate. If someone reports "call quality is bad between 1 and 4 PM every weekday," that's almost certainly a congestion issue and the question is just whether the congestion is on the internet connection, at the ISP level, or on the internal network.

Document the pattern. Note the times when quality is good and when it's bad. Correlate with activities in the office (meeting schedules, backup schedules, video conferencing patterns). Run a VoIP quality test during both good and bad periods. The comparison between good and bad periods will point you directly at the cause.

Next up: Calls Sound Fine Internally But Bad on External Calls, which covers what to check when internal calls are clear but external calls degrade.