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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