Transcript Slide 1

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
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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:
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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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Get lost
QoS
Lost speech:
“ing”, “is easy here honey”
Internet
Network parameters
•Packet loss
•Delay
•Jitter
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Getting
lost is
easy here
honey.
Where did
he go?
QoS
Delay 1000 ms
Silence
Internet
Network parameters
•Packet loss
•Delay
•Jitter
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Getting
lost is
easy here
honey.
What the
QoS
G ettinglos tis
easyhere h on ey
Internet
Network parameters
•Packet loss
•Delay
•Jitter – variability in delay
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Delay 1000 ms
Getting
lost is
easy here
honey.
Types of Traffic
• Different applications generate different
types of traffic e.g.
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Web pages (delay sensitive)
FTP (BW sensitive)
Streamed Media (BW sensitive)
Conversational Multimedia (delay and BW)
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Building blocks
Routers
Edge Router
End host
Networ
k
Region
Routers
Edge Router
Networ
k
Region
•End – to – end signalling
•Routers: Queuing and Scheduling
•Edge Routers: Add admission control
•Aofdefined
set of rules or classes to request
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End host
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 perflow 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
Router
Router
Router
OK
Flow
End Host
End Host
Can I get?
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•
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Can I get?
Can I get?
Can I get?
Sender announces meta-info of flow
Receiver app fills in Traffic specification (T-Spec)
Each router: admission control
If requirements met: make reservations
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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
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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)
– 122122122…
• 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 domain
Ingress
Router
PHB
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Core
Router
Core
Router
PHB
Egress
Router
PHB
Dimensioned to meet
Ingress router admission
control
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
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©J.F Kurose and K.W. Ross
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
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©J.F Kurose and K.W. Ross
DiffServ
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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!
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