school of information technologies ip quality of service nets3303/3603 weeks 10-11
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School of Information Technologies
IP Quality of Service
NETS3303/3603
Weeks 10-11
School of Information Technologies
Outcomes
• Understanding components of IP QoS– What they do– Why they are used or proposed
• Have knowledge of some case study technologies
• Understanding the relevance to real-time multimedia delivery
School of Information Technologies
What is QoS ?
• Many definitions in literature
• Comer’s definition:– Bounds on loss, delay, jitter and minimum
throughput that a network guarantees to deliver
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IP QoS
• IP provides only Best Effort service:– No guarantees full stop– No guaranteed packet delivery– No guaranteed time– No guaranteed order
• IP is ignorant of packet content• No “Flows” in IP• Compare telephony network
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QoS
Internet Internet
Network parameters•Packet loss•Delay•Jitter
Getting lost is
easy here honey.
Lost speech:“ing”, “is easy here honey”
Get lost
School of Information Technologies
QoS
Internet Internet
Network parameters•Packet loss•Delay•Jitter
Getting lost is
easy here honey.
Delay 1000 ms
Where did he go?
Silence
School of Information Technologies
QoS
Internet Internet
Network parameters•Packet loss•Delay•Jitter – variability in delay
Getting lost is
easy here honey.
Delay 1000 ms
What the
G ettinglos tis easyhere h on ey
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Types of Traffic
• Different applications generate different types of traffic e.g.– Web pages (delay sensitive)– FTP (BW sensitive)– Streamed Media (BW sensitive)– Conversational Multimedia (delay and BW)
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Building blocks
Network Region
Network Region
Network Region
Network Region
End host End host
Edge Router Edge Router
Routers Routers
•End – to – end signalling•Routers: Queuing and Scheduling•Edge Routers: Add admission control•A defined set of rules or classes to request
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Integrated Services (IntServ)
• First QoS proposal for IP• Offers a set of service classes per flow
– Guaranteed Service• Hard guarantees (Conversational MM)
– Controlled Load Service• Same behaviour as lightly loaded BE network (adaptive MM
etc.)
– Best Effort Service• All other types of traffic
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IntServ Functions• Admission control
– Check bw availability and make reservation– For specific QoS, reservation required for new
flow• Resource reSerVation Protocol (RSVP) used
• Forwarding– Base decision on QoS parameters
• Queuing and scheduling discipline– Take account of different flow requirements
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Is there a problem with the per-flow specification?
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Resource Reservation Protocol (RSVP)
• Create notion of flow in IP:– E2E Signalling
• IETF proposal– Resource Reservation Protocol, RSVP
• Allows applications to make reservations
• But only keeps soft-state
• If routing path change, need to re-reserve on new routers!!
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RSVP
• Sender announces meta-info of flow• Receiver app fills in Traffic specification (T-Spec)• Each router: admission control• If requirements met: make reservations
End Host End Host
Router RouterRouter
Can I get?Can I get? Can I get?Can I get?
OKFlow
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Queuing
• Traditional queuing: one queue and FIFO service
• For QoS, need to separate traffic into classes– So can provide different priority to different
classes
• Need to manage the different queues
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Priority Queuing
• K queues– 1 ≤ k ≤ K– Queue k+1 higher prio. than queue k– Higher prio. served first
• Simple implementation• Low processing overhead • No fairness
– low prio. queues can be starved!!
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QoS Router
• Standard QoS Router Components– Routing Policy (rules for classification)– Routing table (Where to send packets)– Input Lines (where packets come in, no queue)– Output queues (where packets wait to be sent)– Classifier (puts packets into queues acc. to
policy)– Scheduler (decides which queue to empty)
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Scheduling
• Generally, the scheduler assigns resources to tasks
• In a computer: divide CPU time to processes
• In a router: divide available BW (output queues) to packets– Operates based on router policy
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Weighted Fair Queuing (WFQ)
• Involves multiples queues• Generalized Round Robin• Each class gets weighted amount of service in
each cycle => enables prioritisation• E.g. 2 queues with weight ratio 1:2 (both queues
full)– 1 2 2 1 2 2 1 2 2 …
• Variant implemented by manufacturers
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Question:Can we do QoS management
without Queuing / Scheduling?
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Differentiated Services (DiffServ)
• A newer QoS framework for IP• IntServ per-flow has scalability problem• Solution: aggregate flows
– Treat classes not individual flows
– Thus, tables kept small
• IP TOS field becomes DSCP– 6 bit identifier of class
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DiffServ domainIngressRouter
EgressRouter
CoreRouter
CoreRouter
Dimensioned to meetIngress router admissioncontrol
PHB PHBPHB
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DiffServ Architecture
Edge/Boundary router:-per-flow traffic management-admission control
Core/Interior router:
- per class traffic management
- queuing and scheduling
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Forwarding (PHB)
• Per Hop Behaviour results in a different observable (measurable) forwarding performance behaviour
• PHB does not specify what mechanisms to use to ensure required behavior
• PHB examples: – Class A gets x% of outgoing link bandwidth over time
intervals– Class A packets leave first before packets from class B
©J.F Kurose and K.W. Ross
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Forwarding (PHB) II
Two PHBs introduced:• Expedited Forwarding: pkt departure rate of a
class equals or exceeds specified rate – c.f. logical link with a minimum guaranteed rate
• Assured Forwarding: 4 classes of traffic– each guaranteed minimum amount of bandwidth
– each class with three drop preference partitions
©J.F Kurose and K.W. Ross
School of Information Technologies
DiffServ
• Scales well• Provides statistical guarantee only• There are also hybrids of IntServ + DiffServ• Other popular mechanisms outside IP
– Multi-Protocol Label Switching (MPLS)– Better type of tx media such as optical fibre
with wavelength division multiplexed (WDM) systems
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Summary
• IP, no flows, no traffic separation
• Different types of traffic, different needs
• QoS management:– Admission control
– Classification
– Queuing/scheduling
• IntServ and DiffServ
• Supports higher level protocols such as RTP – next!