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Demystifying QoS

Demystifying QoS. Peter Thompson Chief Scientist U4EA Technologies Peter.Thompson@u4eatech.com. 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)

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Demystifying QoS

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  1. Demystifying QoS Peter Thompson Chief Scientist U4EA Technologies Peter.Thompson@u4eatech.com

  2. 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

  3. Jitter of VoIP stream mixed with TCP over a T1 link Why is ‘QoS’ Necessary?

  4. PESQ score of G711 subject to packet loss and jitter Why is ‘QoS’ Necessary?

  5. 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

  6. 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

  7. Ensure the right amount Identify the right packets Allocate the right resources Elements of QoS Admission control Packet classification Packet queuing and scheduling

  8. Bursts for which loss and delay are increased Average Is Standard QoS Enough? Can manage with standard techniques e.g. 802.1p Capacity Offered load Time

  9. Bursts where loss and/or delay become excessive Is Standard QoS Enough? Needs an advanced multi-media QoS solution Offered load Capacity Average Time

  10. Summary: Reliable IP-based Services • Make sure the lower layers don’t cause trouble • Use session control to limit the amount of traffic needing protection • Use standard techniques (802.1p, Diffserv etc.) to protect/prioritize traffic where the average load is low • Look for advanced mechanisms to make efficient use of more loaded links • Manage the congestion where it occurs

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