qos best practices for uc&c within enterprise lans
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Manfred Arndt Distinguished Technologist - UC&C
Advanced Technology Group, HP Networking
Mar 2, 2011
QoS Best Practices for UC&C within Enterprise LANs
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Key Networking Trends with UC&C
– Data Center Migration • UC&C applications running on industry
standard HW
– User Productivity • Media rich collaboration seamlessly integrated
into desktops and a proliferation of new devices
– Additional Demands on the Network • Everything over IP driving upgrades for
bandwidth, QoS, PoE/PoE+, availability,
multicast, security, etc
Data Center / Cloud • Presence & signaling • Rich messaging • Advanced collaboration
Branch Signaling
Media
PSTN
Federated site or branch
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There’s plenty of bandwidth...why use QoS?
100 Mbps
GbE
Link Speed Mismatch
GbE
GbE
Over-Subscription
• Micro bursts faster than egress can drain • Multiple packets arrive at the same time
TCP micro-bursts occur even at 5% average utilization and lack of QoS can result in buffer queue over-runs
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Provision sufficient bandwidth, especially important with video 1.
Best Practices for QoS in the LAN
Control to eliminate unnecessary traffic and don’t admit more high priority traffic than provisioned
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Prioritize time-sensitive traffic ahead of normal traffic, but keep policies simple
3.
Monitor network to assess impact of new applications and traffic
4.
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Understand network topology and traffic flows
Real-Time Media Streams
IP Phones IP Phones
Softphones & desktop video
Softphones & desktop video
Data Center or “Cloud” IPT Call Control OCS / Presence
Video Gatekeeper Conference Bridging, etc
Room Video Conference
Room Video Conference
WAN
Service Provider SIP & PSTN
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Mechanisms for Achieving QoS
• Classification
− Identify traffic requiring preferential treatment into different classes
• Queuing / Scheduling
− Place traffic in queues based on traffic class and service queues
• Marking (no trust)
− Re-write packet priority at client edge or network boundary, to simplify and enforce consistent QoS policies
• Layer 2: VLAN priority (802.1p)
• Layer 3: IP DiffServ (DSCP)
• Call Admission Control
− Protects against over subscription on constrained links
• Rate Limit (optional)
− Protects against QoS DoS attacks and control unwanted traffic
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Traffic Classes for QoS
Priority
(802.1p) Traffic Type Description
7 (Highest) Network Control Insure network stability
6 Voice Low bandwidth RTP/UDP
5 Real-time Video High bandwidth RTP/UDP
4 Signaling Latency sensitive
3 Critical Data Business transactional apps
2 Excellent Higher priority
0 (Default) Best Effort Default bursty TCP data
1 (Lowest) Scavenger Undesirable
• Most LAN switches support 8, 4 or 2 hardware queues per port
• Don’t mix real-time UDP with bursty TCP in the same HW queue
• Lack of sufficient buffering, can defeat the value of QoS
There are no hard rules, but here are some recommendations
Priority if
4 queues
7/6
5/4
3/2
0/1
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UC&C requires an intelligent client edge
To core switch
• PC traffic does not include L2 priority • Softphones and video clients often
don’t set the L3 DSCP • PC applications generally can’t be
trusted
Phone discovers vlan and QoS via LLDP-MED
IP Phone packets include both L2 priority and L3 DSCP
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Edge switch
• Honors DSCP from the IP phone
• Classifies soft phone traffic based on QoS ACL and marks L2/L3 priority
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Tagged voice VLAN
Untagged data VLAN, does not include any L2 priority
Tagged voice and data VLAN
[MAC hdr] ..6.. [IP hdr]
vlan tag
L2 Pri. L3 DSCP
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Different QoS Policies & Untrusted Domains
Need ability to remark QoS policies to match different administrative domains
Classroom (video)
Admin bldg (data) Admin bldg (voice)
Faculty (data) Faculty (voice)
Layer 3 link
Classroom (video)
Main campus Remote site
QoS Policy (5 classes)
802.1p value DSCP queue
Voice: 6 46 7
Video: 5 36 6
Signaling: 4 26 5
Default: 0 0 3
Scavenger: 1 14 1
QoS Policy (3 classes)
802.1p value DSCP queue
Voice: 6 46 4
Video: 5 26 3
Default: 0 0 1
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More robust Codecs can mitigate impairments
Average Packet
Loss Average Jitter Average MOS
HQ – Soft client 0% 1.00 4.10
15% 3.00 3.74
Site 1 – IP Phone 5% 3.50 3.83
15% 4.50 3.70
Site 2 – Soft client 5% 1.50 3.93
15% 3.60 3.60
Site 3 – IP Phone 10% 3.00 3.65
15% 5.00 3.58
Actual voice quality testing between 4 simulated sites
• Simulated packet loss to exercise codec
• Even with substantial 15% packet loss, audio quality was still good
• MOS (Mean Opinion Scores) over 3.5 is considered “Toll Quality”
• More robust codecs can deliver good audio quality during non-ideal conditions
NOTE: does not eliminate the need for QoS
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QoS Summary for UC&C
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• UC by definition, requires multi-vendor interoperability
• Open industry standards are important to insure long-term success
• QoS is important…but so are many other key features
• Reliability, sufficient bandwidth, PoE/PoE+, multicast, security, etc
• Deploy a consistent end-to-end QoS policy
• Use LLDP-MED to auto-config QoS and VLAN policies for phones
• Use monitoring tools to insure ongoing success
• Performance monitoring, network topology, phone inventory
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