Transcript Demystifying QoS Peter Thompson Chief Scientist U4EA Technologies

Demystifying QoS
Peter Thompson
Chief Scientist
U4EA Technologies
[email protected]
1
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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2
Why is ‘QoS’ Necessary?
Jitter of
VoIP stream
mixed with
TCP over a
T1 link
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3
Why is ‘QoS’ Necessary?
PESQ score
of G711
subject to
packet loss
and jitter
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4
QoS is Affected at Many Levels
•
•
•
•
•
Layer
Layer
Layer
Layer
Layer
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1:
2:
3:
4:
5:
S/N ratio
protocol overheads
buffer overflow, queuing delays
error correction, jitter buffers
session management
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5
QoS: Reliable Packet-based Services
• Dynamic sharing of resources makes packetbased 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
Ensure the
right amount
Admission control
Identify the
right packets
Packet classification
Allocate the
right resources
Packet queuing and scheduling
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Is Standard QoS Enough?
Offered load
Bursts for which loss and
delay are increased
Can manage
with standard
techniques
e.g. 802.1p
Capacity
Average
Time
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Is Standard QoS Enough?
Offered load
Bursts where loss and/or
delay become excessive
Needs an
advanced
multi-media
QoS solution
Capacity
Average
Time
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Summary: Reliable IP-based Services
1. Make sure the lower layers don’t 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
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