1 Demystifying QoS Peter Thompson Chief Scientist U4EA Technologies

© U4EA Technologies 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

© U4EA Technologies Why is QoS Necessary? Jitter of VoIP stream mixed with TCP over a T1 link

© U4EA Technologies Why is QoS Necessary? PESQ score of G711 subject to packet loss and jitter

© U4EA Technologies 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

© U4EA Technologies 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

© U4EA Technologies Elements of QoS Admission control Packet classification Packet queuing and scheduling Allocate the right resources Identify the right packets Ensure the right amount

© U4EA Technologies Is Standard QoS Enough? Bursts for which loss and delay are increased Offered load Time Average Capacity Can manage with standard techniques e.g p

© U4EA Technologies Is Standard QoS Enough? Bursts where loss and/or delay become excessive Offered load Time Capacity Needs an advanced multi-media QoS solution Average

© U4EA Technologies 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