Demystifying QoS

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Demystifying QoS

• Peter Thompson
• Chief Scientist
• U4EA Technologies
• Peter.Thompson_at_u4eatech.com

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What is QoS?

• Quality of Service many meanings
• Service availability
• E.g PSTN backup for VoIP
• Service reliability
• Even when subject to interference (accidental or
  malicious)
• Service observability
• For SLAs

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Why is QoS Necessary?
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Why is QoS Necessary?
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QoS is Affected at Many Levels

• Layer 1 S/N ratio
• Layer 2 protocol overheads
• Layer 3 buffer overflow, queuing delays
• Layer 4 error correction, jitter buffers
• Layer 5 session management

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QoS Reliable Packet-based Services

• Dynamic sharing of resources makes packet-based
  services
• Flexible
• Efficient
• Potentially unreliable!
• Making packet-based services reliable requires
  giving the right resources to the right amount of
  the right packets

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Elements of QoS
Admission control
Packet classification
Packet queuing and scheduling
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Is Standard QoS Enough?
Can manage with standard techniques e.g. 802.1p
Capacity
Offered load
Time
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Is Standard QoS Enough?
Needs an advanced multi-media QoS solution
Offered load
Capacity
Average
Time
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Summary Reliable IP-based Services

1. Make sure the lower layers dont cause trouble
2. Use session control to limit the amount of
   traffic needing protection
3. Use standard techniques (802.1p, Diffserv etc.)
   to protect/prioritize traffic where the average
   load is low
4. Look for advanced mechanisms to make efficient
   use of more loaded links
5. Manage the congestion where it occurs