QoS Configuration: Traffic Priority for VoIP and Video Conferencing

Summary: QoS (Quality of Service) is the discipline of assigning different priorities to different traffic types on a network. In an SME office, limited internet bandwidth is split between VoIP calls, Teams / Zoom meetings, file transfers, web browsing, and YouTube; without QoS, the noisiest application (e.g. YouTube) hurts the most important one (VoIP). Properly configured QoS lifts VoIP to the highest priority, puts video conferencing second, file transfers third, and pushes "background" traffic to the back. It's applied on switches and routers via DSCP marking; at SME scale it can be set up in an afternoon and runs quietly for years.

In SMEs, the "internet is slow" complaint usually isn't about raw bandwidth — it's about traffic mix. On a single link, 50 devices do different things at once: accounting pushes data into the ERP, sales is on a Teams call, the office is on Zoom, someone is on Netflix during a break, the cloud backup started its nightly batch two hours early. Without QoS, all that traffic carries the same priority — and the customer's VoIP call breaks up.

In this article we cover SME-scale QoS configuration, the VoIP / video prioritisation strategy, and switch / router-level implementation. Target audience: IT managers, network administrators, and managers who keep getting complaints about VoIP / video-conference quality.

Why QoS Is Necessary

The internet / LAN runs "best effort" — packet order and delay aren't guaranteed. QoS overlays a prioritisation rule on that default.

An Environment Without QoS

[VoIP packet] | [Backup packet] | [VoIP packet] | [Backup packet]
            queue

Backup is large (1500 bytes), VoIP is small (~200 bytes) and needs regular intervals. If backup packets fill the queue, VoIP gets delayed and breaks up.

An Environment With QoS

[VoIP packet] | [VoIP packet] | [Backup packet] | [Backup packet]
            high priority             low priority

VoIP always goes first. Backup isn't hurt by waiting (no human is watching).

Classifying Traffic

QoS needs traffic split into categories.

Typical QoS Classes

Class	Application	Latency	Bandwidth
Voice (Real-Time)	VoIP, IP phones	<150 ms	Low (~100 kbps)
Video (Real-Time)	Teams, Zoom, Meet	<150 ms	High (1–5 Mbps)
Critical Data	ERP, CRM, corporate portal	<500 ms	Medium
Important Data	Email, file transfer	<1 second	Medium-high
Best Effort	Web browsing	Tolerant
Bulk	Backup, OS update	Doesn't matter	Low priority
Scavenger	YouTube, social media	Doesn't matter	Lowest

A Lean Model for SMEs

Three classes can be enough:

1. High: VoIP, video conferencing
2. Medium: Business-critical applications (ERP, M365)
3. Low: Web, backup, entertainment

DSCP Marking

QoS rollout uses the DSCP (Differentiated Services Code Point) standard.

Typical DSCP Values

DSCP	Name	Recommended use
EF (46)	Expedited Forwarding	VoIP
AF41 (34)	Assured Forwarding	Video conferencing
AF31 (26)	Critical Apps	ERP, business-critical
AF21 (18)	Important	Email
0	Default (Best Effort)	Web browsing
CS1 (8)	Scavenger	YouTube, personal

DSCP is a field in the IP header — wherever the packet goes, it carries the signal "I'm high priority".

Where to Mark

DSCP marking can happen in three places:

1. In the application: the VoIP software marks its own packet as EF
2. On the switch: trust port (accepts the application's marking)
3. On the router: mark outbound traffic before it hits the WAN

Typical SME approach: VoIP / video applications set their own markings, the switch trusts them, the router / firewall sends them out prioritised onto the WAN.

QoS Architecture at SME Scale

QoS Inside the LAN

On the switch side:

• Voice VLAN (for VoIP devices)
• DSCP trust enabled
• Queue priority (4–8 queues depending on hardware)
• Strict priority (the highest queue goes first)

QoS Toward the WAN

On the router / firewall:

• Outbound shaping (shape traffic to WAN bandwidth)
• Class-based queuing
• Bandwidth guarantees (e.g. 10% for VoIP)
• Maximum caps (Scavenger limited to 20%)

Controlling Inbound

Inbound QoS is limited — without ISP-side QoS you don't have full control. But:

• BBR / CUBIC congestion control
• Application-aware shaping
• More advanced in SD-WAN setups

QoS for VoIP — A Practical Example

VoIP is the most sensitive traffic type.

VoIP Requirements

• Latency: <150 ms one-way
• Jitter: <30 ms
• Packet loss: <1%
• Bandwidth (G.711 codec): 87 kbps one-way

VoIP QoS Configuration

1. A separate VLAN for VoIP devices (phones, softphones)
2. Default DSCP EF (46) on the Voice VLAN
3. Switch port: trust dscp / trust voice
4. Voice queue on the router: strict priority
5. Bandwidth: at least 10–15% guaranteed for VoIP

Example Cisco Switch Commands

interface GigabitEthernet1/0/1
 switchport mode trunk
 switchport voice vlan 40
 switchport access vlan 20
 mls qos trust device cisco-phone
 mls qos trust dscp

QoS for Video Conferencing

Applications like Teams, Zoom, Google Meet.

Requirements

• Latency: <150 ms
• Jitter: <30 ms
• Packet loss: <1% (audio), <1.5% (video)
• Bandwidth: 1–5 Mbps one-way (HD)

Configuration

• Microsoft 365: Teams traffic uses DSCP 46/34/24 (Microsoft's guidance)
• Zoom: DSCP 46 (audio), 34 (video)
• For configuration, consult the Microsoft Teams QoS documentation

A Common Issue

Cloud SaaS applications (Teams, Zoom) may have the DSCP marker rewritten on the provider side, and ISPs may zero out DSCP. In that case, DSCP marking on the SME side has limited effect; but it still improves things inside the local network.

Bandwidth Management

QoS is not just about priority; it's also about bandwidth planning.

A Typical SME Pipe

• 100/100 Mbps fibre
• 30 employees
• Active use: 50 devices

Typical Consumption

• Background (OS updates, downloads): 30–40%
• Web browsing, email: 20–30%
• Cloud apps (M365, Salesforce): 15–25%
• Teams / Zoom video: 20–40% (with many participants)
• VoIP: 1–5%

Total: can exceed 100% → congestion → user complaints.

Resolution

Managed prioritisation via QoS + (if needed) more bandwidth. Just adding bandwidth without QoS doesn't fix it — someone on Netflix can consume 50 Mbps; you need the right limits.

Traffic Shaping

A slightly different concept from QoS: capping bandwidth.

Typical Uses

• Guest Wi-Fi: 10 Mbps max per user
• A specific IP / device: 20 Mbps max
• A specific application: 30 Mbps max (e.g. YouTube)

Configuration

In modern firewalls (FortiGate, Palo Alto, Sophos):

• Application-aware shaping
• Limits by IP / user / group
• Schedules (strict during working hours, looser outside)

A Typical SME Policy

User / Traffic	Limit
Guest Wi-Fi	10 Mbps/user
Employee total	50 Mbps/user
Streaming (YouTube, Netflix)	20% of total bandwidth
Backup traffic	Wide overnight, narrow during the day
OS updates	Overnight only

Testing and Verification

How do you check QoS is doing its job?

Tools

• Wireshark: to see whether DSCP markers are correct
• iperf3: bandwidth tests
• Pingplotter / Smokeping: latency / jitter monitoring
• MOS score: VoIP-quality measurement (automatic on VoIP gateways)

KPIs

• VoIP MOS score: should be >4.0
• Latency (inside LAN): <5 ms
• Latency (WAN): <50 ms (local), <150 ms (long-distance)
• Jitter: <30 ms
• Packet loss: <1%

Common QoS Mistakes

Typical issues in SMEs:

• I'm marking DSCP but trust is missing: if the switch port doesn't trust, the marking is overwritten
• Everything's marked high priority: nothing is
• No inbound QoS: download congestion can't be eased
• No VLAN separation: voice traffic mixes with data
• No bandwidth shaping: background traffic balloons
• Not reviewed in years: new applications aren't in the QoS plan
• SaaS DSCP isn't preserved: rewritten in the cloud — but marking still helps inside the LAN

What Yamanlar Bilişim Offers

Our QoS support areas at SME scale:

• Current traffic analysis (NetFlow, sniffing)
• VoIP / video quality measurement
• QoS policy design
• Switch and router configuration
• A DSCP-marking standard
• Bandwidth planning
• Annual QoS review
• VoIP MOS monitoring

Frequently Asked Questions

Conclusion

QoS is the quiet discipline that prevents VoIP, video conferencing, and business-critical traffic from slowing down in a bandwidth-constrained environment. At SME scale, DSCP marking + switch/router configuration + an annual review goes up in an afternoon and runs in the background for years. "Slow internet" complaints are often caused by missing QoS, not insufficient bandwidth.

Yamanlar Bilişim provides traffic analysis, QoS design, and rollout services sized to your needs — moving the quality of customer calls in your office from "good if we're lucky" to confidently guaranteed.