Your Office Network: Part 3 of 10
In the first post of this series, we walked through every piece of equipment in your network closet. The router got a lot of attention. The modem was easy to understand. The patch panel was straightforward. But the switch, the box with all the blinking lights and all the cables plugged into it, probably seemed like the least interesting piece in the closet.
It is actually the piece that ties everything together. And for offices running VoIP, the type of switch you have and how it is configured can be the difference between calls that sound great and calls that are a daily source of frustration.
What a switch does
A switch is a device that connects all the wired devices on your network. Every desk phone, computer, printer, access point, and server that has an Ethernet cable plugs into a port on the switch. The switch's job is to move data between those ports.
When your phone sends a voice packet destined for the router (and ultimately, the internet), the switch receives the packet on the port where your phone is connected, reads the destination address in the packet header, looks up which port the router is connected to, and forwards the packet there. This happens for every single packet on your network, millions of times per second in a busy office.
A modern gigabit switch can do this at wire speed, meaning it forwards packets as fast as they arrive with no meaningful delay. The processing time is measured in microseconds. For a single packet, you would never notice the switch is even there.
The issues arise when you start asking the switch to do more than just forward packets, or when the switch is not capable of doing the things your network needs.
Unmanaged switches
An unmanaged switch is the simplest type. You take it out of the box, plug in power, plug in Ethernet cables, and it works. There is no login screen, no configuration interface, no settings to change. It learns which devices are on which ports by watching the traffic, and it forwards packets based on destination addresses. That is all it does.
When unmanaged works fine
For a small office with five or six people, a basic internet connection, and no VoIP phones, an unmanaged switch is perfectly adequate. It costs $30 to $100, it works immediately, and there is nothing to misconfigure because there is nothing to configure.
If your VoIP situation is simple, say three or four phones in a quiet office where the internet connection is never heavily loaded, an unmanaged switch will probably work fine for that too. The voice traffic is so light and the network is so uncongested that the lack of prioritization does not matter. There is no line to wait in because nobody else is in line.
When unmanaged falls short
The problems start as the office grows. Here is what an unmanaged switch cannot do.
No traffic prioritization. Every packet gets equal treatment. A voice packet carrying part of an active phone conversation is treated exactly the same as a packet from a Windows update downloading in the background. When the switch's internal buffers fill up during a traffic burst, it drops packets without any consideration for what those packets contain. If it drops a voice packet, you hear a glitch or gap in the audio. If it drops a file transfer packet, the file transfer retransmits automatically and nobody notices.
No VLANs. An unmanaged switch puts all devices on one flat network. Your phones, computers, printers, security cameras, and guest devices all share the same broadcast domain. Every broadcast packet (and there are more of these than you might think) is sent to every device on every port. In a network with 30 or 40 devices, broadcast traffic can consume a meaningful amount of bandwidth and processing time on every connected device.
No monitoring. You cannot see traffic levels per port, error counts, or utilization statistics. When something is wrong, you have no diagnostic tools beyond unplugging cables and seeing what changes. This makes troubleshooting slow and frustrating, especially for intermittent problems.
No PoE. Most unmanaged switches do not provide Power over Ethernet. This means every VoIP phone needs its own power adapter plugged into a wall outlet, which adds cost, clutter, and another point of failure. (There are some unmanaged PoE switches, but they are essentially managed switches without the management interface, and the cost difference starts to close the gap.)
The daisy chain problem
One of the most common network mistakes in growing offices is daisy-chaining unmanaged switches. The original 8-port switch filled up, so someone bought another 8-port switch and plugged it into the first one. Then a third. Sometimes a fourth.
Each switch in the chain adds a small amount of processing delay. More importantly, the link between the two switches becomes a bottleneck. All traffic from devices on the second switch that needs to reach the router has to pass through that single link to the first switch. If eight devices on the second switch are all active, they are sharing one gigabit link where they used to each have their own.
Daisy-chaining also makes troubleshooting nearly impossible. When calls on one desk sound bad, is it the phone, the cable, the second switch, the link between the switches, the first switch, or the router? With no monitoring or diagnostics on any of the switches, you are guessing.
The fix is almost always to replace the chain with a single managed switch that has enough ports for everything. We will get to what managed switches offer in a moment, but even replacing daisy-chained unmanaged switches with a single, larger unmanaged switch is an improvement.
Managed switches
A managed switch does everything an unmanaged switch does, plus a set of features that give you control over how traffic is handled, monitored, and organized. You access these features through a web interface, a command line, or a management application, depending on the manufacturer.
The word "managed" might sound like it means "complicated." It does not have to be. Many modern managed switches have setup wizards and default configurations that handle the most common scenarios with minimal effort. And the features that matter most for VoIP are straightforward to enable.
Quality of Service
This is the big one. A managed switch can read the priority markings on packets and treat them accordingly. When your VoIP phone sends a voice packet marked with DSCP 46 (Expedited Forwarding), the managed switch recognizes that marking and puts the packet in a high-priority queue. When the switch needs to choose which packet to forward next, voice packets go first.
On an unmanaged switch, that same voice packet sits in line behind whatever else is waiting, which could be a multi-gigabyte file copy between two computers. The file copy does not care about an extra millisecond of delay. The voice call does.
Quality of Service on the switch matters most when the internal network is busy. If you have people transferring large files between departments, running backups to a local server, or doing video editing that involves moving large files across the network, voice traffic benefits enormously from switch-level QoS.
Even if the internal network is not usually busy, QoS on the switch provides insurance. It protects voice quality during the unexpected moments when a software update deploys to 20 machines simultaneously, or someone accidentally starts a massive file copy during business hours.
VLANs
VLANs (virtual local area networks) let you divide one physical switch into multiple logical networks. You can put voice devices on one VLAN and data devices on another, even though they are plugged into the same physical switch.
This is such an important concept that we dedicate the entire next post to it. The short version is that VLANs give you traffic isolation (voice and data do not interfere with each other), easier troubleshooting (you can immediately see whether a problem is on the voice side or the data side), and a foundation for effective QoS enforcement.
PoE (Power over Ethernet)
Power over Ethernet is one of those features that, once you have it, you wonder how you ever lived without it.
A PoE-capable switch delivers electrical power to connected devices through the same Ethernet cable that carries data. For VoIP phones, this means the phone gets its data connection and its power from a single cable. No separate power adapter, no extra wall outlet needed, no additional cable to manage.
Beyond the convenience, PoE provides a meaningful operational benefit. When you connect the switch to an uninterruptible power supply (UPS), your phones stay powered during a power outage, just like old analog phones used to work during outages because the phone company powered them through the phone line. This can be important for businesses that need phone access during emergencies.
PoE comes in several standards. The original PoE (802.3af) provides up to 15.4 watts per port, which is enough for most desk phones. PoE+ (802.3at) provides up to 30 watts, sufficient for phones with color screens and sidecar modules. PoE++ (802.3bt) goes up to 60 or 90 watts depending on the type, which can power wireless access points and other higher-draw devices.
When shopping for a PoE switch, pay attention to the total power budget, not just the per-port rating. A 24-port PoE switch with a 200-watt total budget can only provide about 8 watts per port if all ports are drawing power. That is fine for basic phones but tight if you are also powering access points. Make sure the total power budget covers your actual deployment.
Port monitoring and diagnostics
When something goes wrong on your network, a managed switch gives you tools to investigate. You can see how much traffic is flowing through each port, whether any ports are experiencing errors, which ports are at or near capacity, and what devices are connected where.
This matters enormously for VoIP troubleshooting. If a specific phone is having quality problems, you can look at the switch port it is connected to and see whether there are CRC errors (which suggest a cable problem), high utilization (which suggests congestion), or packet drops (which suggest a buffer overflow). On an unmanaged switch, you have no access to this information.
Some managed switches also support port mirroring, which lets you copy all traffic from one port to another for analysis. This is invaluable for advanced VoIP troubleshooting when you need to capture and examine actual packets.
The passthrough port on VoIP phones
Most VoIP desk phones have two Ethernet ports on the back. One connects upstream to the wall jack (and ultimately to the switch). The other connects to the user's computer.
This design exists so that each desk only needs one cable run from the network closet. The phone sits in the middle, acting as a tiny, two-port switch. Traffic from the computer passes through the phone to reach the network, and traffic for the computer passes through the phone on the way back.
This works well, and it is the standard deployment in most offices. But there are a few things to understand about it.
VLAN tagging
When VLANs are in use (and we will cover this in detail in the next post), the phone typically tags its own voice traffic with the voice VLAN ID and passes the computer's traffic through untagged (or tagged with the data VLAN). The phone learns which VLAN to use from the switch via LLDP-MED or CDP, which are discovery protocols that let the switch tell the phone "your voice traffic should be on VLAN 100."
This is elegant and mostly automatic, but it depends on the switch being properly configured to advertise the voice VLAN on that port. If the switch is unmanaged, there is no way to configure this, and VLAN separation is not possible.
Traffic prioritization through the phone
The phone's internal mini-switch typically prioritizes its own voice traffic over the passthrough computer traffic. This means that even if the computer is downloading a large file, the phone's voice packets get sent first through the upstream link to the wall jack.
However, this only prioritizes traffic on the single link between the phone and the wall jack. Once the traffic reaches the main switch, prioritization depends on the switch's QoS configuration. If the switch is unmanaged, the prioritization the phone applied is effectively lost.
The passthrough port limitation
The passthrough port on most phones is limited to 100 megabits per second, even if the phone's network port supports gigabit. This was a common limitation on older phones and persists on some current models. If the computer user needs gigabit speeds (for large file transfers, for example), they may need a second cable run to the desk instead of passing through the phone.
Newer phones increasingly support gigabit on both ports, so this is becoming less of an issue. Check the specs of your specific phone model if it matters for your environment.
What to look for when buying a switch
If you are in the market for a switch, whether to replace an aging unmanaged switch or to upgrade as part of improving VoIP quality, here are the features that matter.
Port count with room to grow
Count every device that needs a wired connection: phones, computers, printers, access points, cameras, and anything else. Then add 20 to 30 percent for growth. Running out of ports leads to daisy-chaining, which is what you are trying to avoid.
Common sizes are 8, 16, 24, and 48 ports. For a 15-person office where each desk has a phone and a computer sharing a single cable run (using the phone's passthrough port), you need 15 ports for the phones plus ports for printers, access points, and the router uplink. A 24-port switch handles this with room to spare.
Gigabit ports
Every port should be gigabit (1000BASE-T). 10/100 switches are obsolete for any new deployment. The price difference is negligible and gigabit ensures your switch is not a bottleneck for any device.
PoE support
If you are deploying VoIP phones, PoE simplifies installation and provides power resilience. Make sure the total power budget covers your deployment with margin.
VLAN support
Essential for separating voice and data traffic. Any managed switch supports VLANs, but verify that the switch supports 802.1Q VLAN tagging, which is the standard that makes voice VLAN tagging on phone passthrough ports work.
QoS support
The switch should support DSCP-based QoS and priority queuing. Look for support for at least four queues (most managed switches offer this) so that voice, video, important data, and background traffic can be handled separately.
LLDP-MED or CDP support
These protocols let the switch automatically tell phones which VLAN to use and how to tag their traffic. This makes phone deployment much simpler and more reliable than manually configuring each phone.
Management interface
A web-based management interface is standard on modern managed switches and sufficient for most small and medium offices. If you have an IT team or managed service provider, they may prefer switches that support centralized management through a cloud controller or on-premises management platform.
The cost question
The price gap between unmanaged and managed switches has narrowed significantly over the past several years. A basic 24-port unmanaged gigabit switch costs around $80 to $150. A 24-port managed gigabit switch with PoE costs $250 to $600, depending on the brand, the total PoE budget, and the feature set.
That difference is meaningful, but put it in context. A managed PoE switch that costs $400 and lasts five or more years provides VoIP-essential features for the cost of a few dollars per month per port. Compare that to the cost of ongoing call quality problems: lost productivity, frustrated employees, poor impressions on clients, and hours spent on troubleshooting without the diagnostic tools to find the answer.
For any office where VoIP quality matters, and that includes most offices since the phone system is how you talk to customers, a managed PoE switch is one of the best investments you can make in your infrastructure.
When to replace your switch
If you recognize any of these situations, it is probably time.
You are daisy-chaining switches. Replace the chain with a single managed switch that has enough ports.
Your phones need separate power adapters. A PoE switch eliminates the adapters and gives you power resilience.
You cannot see what is happening on your network. A managed switch provides the visibility you need for effective troubleshooting.
Your VoIP provider or IT support has recommended VLANs or QoS. You need a managed switch to implement either.
You are experiencing intermittent call quality problems and have ruled out the internet connection. The local network is next on the list, and the switch is a critical piece of it.
Your switch only supports 10/100 Mbps. Gigabit is the minimum for any current deployment. An old 100-megabit switch is a bottleneck for your entire network.
If you suspect your switch is affecting call quality but are not sure, running a VoIP quality test from a device on your network can help quantify the jitter, latency, and packet loss that your current setup is introducing.
What comes next
Now that you understand what switches do and why managed switches matter for VoIP, the next post covers one of the most important features a managed switch enables: VLANs. We will explain what VLANs are, why separating your voice and data traffic onto separate virtual networks is one of the best things you can do for call quality, and how the pieces fit together.
This is Part 3 of the Your Office Network series. Part 4: VLANs: Giving Your Phones Their Own Lane explains how to separate voice and data traffic for better performance and easier troubleshooting.
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