qos
DESCRIPTION
Revealing the basics of quality of service. The slide includes significant parameters that define quality of service along with brief descriptions.TRANSCRIPT
Fundamentals of Quality of Service
Gopan Govindan
QoS
Introduction
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Definition metrics
Characteristics of network that define QoS
• Bandwidth
• Latency
• Jitter
• Packet loss
The “Model”
DiffServ
• Each packet in the network contains a marking that indicates the required QoS
• Each network device applies QoS based upon this marking
Signaling QoS Requirements
Markers
• ToS – RFC 791
• CoS – QoS at MAC level
• DSCP – RFC 2474
ToS
Bits that matter
CoS
Bits that matter
* Push of packets with a specific CoS has dependency on Switch
Bits that matter
DSCP
Treatment
PHB
• Default PHB – RFC 2474 – DSCP 0 – Traditional best-effort service (FIFO)
• Class-selector PHB – RFC 2474 – for backward compatibility with IP precedence – xxx000
• Assured Forwarding PHB – RFC 2597 - 4 AF classes - AF1, AF2, AF3, AF4
• Expedited Forwarding PHB – RFC 2598 – place packets to priority queue – DSCP 46
• Voice Admit PHB – RFC 5865 - identical characteristics to the EF PHB – also admitted by the network using CAC procedure – DSCP 44
The “FLOW”
QoS process
Configuration…
Class map
Class map
To classify traffic of our interest.
Policy map
Defines a series of actions (functions) that we wish to apply to a set of classified inbound traffic.
Configuration…
Mathematics ;)
Minor algebra
Class map
• AR• CIR• Bc• Be• Tc
Lets relate….
Class map
• AR - Access Rate - full line speed in bps, maximum transmit value - 128000 in our example
• CIR - Committed Information Rate - target value for transmission, normal transmit value
• Bc - Normal Burst - Equals CIR/Tc
• Be - Excess Burst - Equals or can be upto (AR/Tc)-Bc
• Tc will vary. 1/8 sec in data and 1/100 in voice.
Lets relate….
Class map
AR/Tc = Bc+Be Bc = CIR/Tc
Before entering the show…
Class map
Queuing
• FIFO Queuing
• WFQ – Fair-queue (#packets) (#dynamic) (#reserved)
• CBWFQ
• Priority Queues – implemented as heap
Queue Management (Discard)
• Tail drop
• RED
• WRED
Algorithms
Traffic Shaping
• Leaky Bucket
• Token Bucket
The baggage scanner !
Class map
Ready for a better QoS ?