QoS Configuration on Network Equipment
We often see this situation: at 100% WAN channel utilization, VoIP calls break up due to jitter, video conferences freeze, and backups or software updates compete for bandwidth on equal footing. Proper QoS configuration using DSCP marking, LLQ, and CBQ solves this problem by guaranteeing priority for critical traffic. With QoS, VoIP jitter is reduced by over 10 times compared to best-effort networks. Additionally, QoS saves you $500–$2,000 per month on bandwidth upgrades. We can assess your project in one day — contact us for a consultation. QoS is not a universal patch but precise traffic engineering that requires analysis and configuration for your specific network. Advanced mechanisms like WRED (Weighted Random Early Detection) can further reduce congestion on real-time traffic.
Key understanding: QoS only works at the saturation point. If the channel is not congested, all packets flow without delay and QoS does not affect traffic behavior.
How QoS Solves Packet Loss
QoS mechanisms (LLQ, CBQ) arrange packets into queues by class. VoIP receives strict priority (LLQ), business applications get a minimum bandwidth guarantee (CBQ), and bulk traffic gets the remainder. This reduces jitter and loss for voice even at 100% channel load. Long queues (WFQ) improve interactive traffic performance by a factor of 5 compared to simple FIFO. DiffServ performs packet marking via DSCP (Differentiated Services Code Point, 6 bits in the IP header). Priority is determined on each hop by the label. DiffServ scales well and is what is configured in real networks. More details: DiffServ on Wikipedia.
| Criteria | IntServ | DiffServ |
|---|---|---|
| Mechanism | RSVP reservation | DSCP marking |
| Scalability | Low (state per flow) | High (aggregation) |
| Configuration complexity | High | Moderate |
| Application | Very rare | Ubiquitous |
DSCP values per RFC 4594:
| Class | DSCP | Decimal | Traffic Type |
|---|---|---|---|
| EF | 101110 | 46 | VoIP, video calls |
| CS5 | 101000 | 40 | Signaling (SIP) |
| AF41 | 100010 | 34 | Interactive video |
| CS3 | 011000 | 24 | Critical business apps |
| AF21 | 010010 | 18 | Normal business traffic |
| CS1 | 001000 | 8 | Bulk, backup, updates |
| BE | 000000 | 0 | Best Effort (default) |
Source: RFC 4594
Why Re-mark DSCP at Network Ingress?
A corporate network should not trust DSCP marking from untrusted hosts. A user could set DSCP EF on a torrent client, causing backup traffic to receive VoIP priority. A rule on Cisco: trust marking only from IP phones and corporate video conferencing systems; re-mark everything else to BE (0):
class-map TRUSTED-ENDPOINTS
match access-group name VOIP-PHONES
match access-group name VIDEO-ENDPOINTS
policy-map INGRESS-TRUST
class TRUSTED-ENDPOINTS
set dscp dscp-table
trust
! preserve marking
class class-default
set dscp default
! everything else = BE
interface GigabitEthernet1/0/1
service-policy input INGRESS-TRUSTCisco IOS: MQC (Modular QoS CLI)
Cisco QoS is built on three blocks: class-map (what to classify), policy-map (what to do), service-policy (where to apply).
Cisco MQC Configuration Example
! Traffic classification
class-map match-any VOICE
match dscp ef
match dscp cs5
class-map match-any VIDEO
match dscp af41
match dscp af42
class-map match-any BUSINESS-CRITICAL
match dscp cs3
match dscp af31
class-map match-any BULK
match dscp cs1
match protocol ftp
match protocol bittorrent
!
QoS policy (applied on WAN outbound)
policy-map WAN-EGRESS-QOS
class VOICE
priority percent 20
! LLQ: guaranteed priority, 20% of bandwidth
police rate percent 20
class VIDEO
bandwidth percent 30
! CBQ: minimum 30% when channel is loaded
fair-queue
class BUSINESS-CRITICAL
bandwidth percent 25
class BULK
bandwidth percent 5
shape average 2000000
! Shape backup to 2 Mbps
class class-default
fair-queue
bandwidth percent 20
!
Apply to WAN interface
interface GigabitEthernet0/1
description "WAN Uplink"
service-policy output WAN-EGRESS-QOS
priority (LLQ) — for VoIP: packets are sent immediately, bypassing the queue. Without police, a VoIP burst could consume the entire channel. With police, you limit the maximum.
bandwidth (CBQ) — minimum guarantee as a percentage. If the channel is not loaded, the class can use more. At saturation, it receives the guaranteed minimum.
MikroTik: Simple Queue and Queue Tree
MikroTik supports two mechanisms. Simple Queue is simpler but only for leaf nodes (specific hosts). Queue Tree is more flexible, works with DSCP, and allows hierarchical queues.
MikroTik Queue Tree Example
# Mangle: mark traffic
/ip firewall mangle
add chain=forward protocol=udp dst-port=5060,5061 \
action=mark-packet new-packet-mark=voip-signaling passthrough=yes
add chain=forward protocol=udp dst-port=10000-20000 \
action=mark-packet new-packet-mark=voip-media passthrough=yes
add chain=forward dst-address=192.168.20.0/24 \
action=mark-packet new-packet-mark=backup-traffic passthrough=yes
# Queue Tree: hierarchical policy
/queue tree
add name=WAN-QOS parent=ether1-wan max-limit=100M
add name=voip parent=WAN-QOS packet-mark=voip-media \
priority=1 max-limit=20M limit-at=10M
add name=voip-sig parent=WAN-QOS packet-mark=voip-signaling \
priority=2 max-limit=5M limit-at=1M
add name=backup parent=WAN-QOS packet-mark=backup-traffic \
priority=8 max-limit=10M limit-at=2M
add name=default parent=WAN-QOS priority=5 max-limit=100Mpriority=1 is the highest priority in RouterOS (1 = highest, 8 = lowest). Reverse logic compared to some other platforms.
What's Included in QoS Configuration?
The result of the work includes documentation with baseline configuration, classification scheme, and before/after metrics (jitter, channel load). We train the duty team on basic show commands and verification. We guarantee VoIP stability after implementation — packet loss reduced to 0% and jitter reduction. We provide a runbook for typical situations. Get a consultation — contact us for a network assessment.
Process and Timelines
- Analysis of current channel utilization and traffic profile (5-7 days).
- Design of classes and policies (1-2 days).
- Configuration on a pilot site with monitoring (1-2 days).
- Rollout to all sites (2-4 days).
- Monitoring and adjustment (1-2 weeks).
Timelines range from 3 to 10 days depending on network complexity. Cost typically ranges from $1,500 for a small office to $10,000 for a distributed network. Savings on bandwidth upgrades can reach 20%, amounting to $500–$2,000 per month. Our QoS implementation reduces jitter by 10x and packet loss to 0% compared to non-QoS networks. Contact us for a personalized quote.
Our team has 5+ years of experience configuring QoS on Cisco, MikroTik, and Juniper equipment. We have completed more than 20 projects for companies with distributed networks. After implementation, clients report VoIP packet loss reduced to 0% and improved video conferencing quality. Order QoS configuration today.