Quality of Service

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Quality of Service Traffic Engineering (QoS
TE)Khaled MohamedCredit some of the sides are
from Cisco Systems
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Agenda

• QOS and TE in IP Network
• The QoS and TE Architectures
• QOS and TE Service Types
• The Technical Scenarios Reasons
• The Applications and Their Needs
• QA

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QoS in IP Networks

• Thus far making the best of best effort
• Future next-generation Internet with QoS
  guarantees
• Differentiated Services differential guarantees
• Integrated Services firm guarantees
• Example guarantees an audio application 1Mbps
  the remaining to 0.5Mbps to Web transfer

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Principles for QoS Guarantees
packet classification router can distinguish
between different classes
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Principles for QoS Guarantees

• prevents applications from misbehaving (e.g.,
  multimedia app. sends higher than declared rate)

scheduling and policing provide protection
(isolation)
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Principles for QoS Guarantees

• Allocating fixed (non-sharable) bandwidth to
  flow inefficient use of bandwidth if flows
  doesnt use its allocation

high utilization while providing isolation, it
is desirable to use resources as efficiently as
possible
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Principles for QoS Guarantees

• Basic fact of life cannot support traffic
  demands beyond link capacity

call admission flow declares its needs, network
may block call (e.g., busy signal) if it cannot
meet needs
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Summary of QoS Principles
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Traffic Specification

• Three common-used criteria
• (Long term) Average Rate how many pkts can be
  sent per unit time (in the long run)
• crucial question what is the interval length
  100 packets per sec or 6000 packets per min have
  same average!
• Peak Rate e.g., 6000 pkts per min. (ppm) avg.
  1500 ppm peak rate
• (Max.) Burst Size max. number of pkts sent
  consecutively (with no intervening idle)

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Traffic Specification

• Token Bucket limit input to specified Burst Size
  and Average Rate.
• bucket can hold b tokens
• tokens generated at rate r token/sec unless
  bucket full
• over interval of length t number of packets
  admitted less than or equal to (r t b).

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Scheduling Mechanisms

• scheduling choose next packet to send on link
• FIFO (first in first out) scheduling send in
  order of arrival to queue
• discard policy if packet arrives to full queue
  who to discard?
• tail drop drop arriving packet
• priority drop/remove on priority basis
• random drop/remove randomly

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Scheduling Policies more

• Priority scheduling transmit highest priority
  queued packet
• multiple classes, with different priorities
• class may depend on marking or other header info,
  e.g. IP source/dest, port numbers, etc..

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Scheduling Policies still more

• round robin scheduling
• multiple classes
• cyclically scan class queues, serving one from
  each class (if available)

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Scheduling Policies still more

• Weighted Fair Queuing
• generalized Round Robin
• each class gets weighted amount of service in
  each cycle

.
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Delay Guarantees

• token bucket, WFQ combine to guarantee upper
  bound on delay, i.e., QoS guarantee!

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QOS Type of Services

• Integrated services
• Differentiated services

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IETF IntServ Services

• Architecture for providing QoS guarantees in IP
  networks for individual application sessions
• Assumptions
• use a common infrastructure for both real-time
  and non-real-time communications
• resource must be explicitly managed in order to
  meet the requirements of real-time applications
• resource reservation routers maintain state info
  (a la VC) of allocated resources, QoS reqs

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Intserv QoS Service Models rfc2211, rfc 2212

• Guaranteed service
• worst case traffic arrival leaky-bucket-policed
  source
• simple (mathematically provable) bound on delay
  Parekh 1992, Cruz 1988

• Controlled load service
• "a quality of service closely approximating the
  QoS that same flow would receive from an unloaded
  network element."

• Controlled link sharing
• Sharing link among different classes

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Reference Architecture
Routing
Routing Messages
RSVP
RSVP messages
Control Plane
Admission Control
Data Plane
Forwarding Table
Per Flow QoS Table
Data In
Scheduler
Classifier
Route Lookup
Data Out
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A Closer Look at the Data Path
Per-flow State

flow 1
flow 2
Scheduler
Classifier
flow n
Buffer management
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Intserv QoS Guarantee Scenario

• Resource reservation
• call setup, signaling (RSVP)
• traffic, QoS declaration
• per-element admission control

request/ reply
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RSVP Protocol

• A flow needs performance guarantee must
• declare its QoS requirement
• R-spec defines the QoS being requested
• characterize traffic it will send into network
• T-spec defines traffic characteristics
• signaling protocol needed to carry R-spec and
  T-spec to routers (where reservation is required)
• RSVP

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RSVP Soft-state Receiver-initiatedEnd-to-End
Reservation

• Sender periodically sends PATH messages to
  receiver R, each router updates the PATH message
  by increasing hop count and adding its
  propagation delay
• When receiver R gets the PATH message, it knows
• Traffic characteristics (tspec) (r,b,R)
• Number of hops, propagation delay introduced by
  the routers
• Receiver R sends back this information required
  worst-case delay in RESV
• Each router along path provides a per-hop delay
  guarantee and forwards RESV with updated info
• In the simplest case, the routers can just split
  the delay
• State timed out if not refreshed

R
R2
S
R1
R3
RESV
PATH
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Implementing IntServ

• Use WFQ to implement controlled link sharing
  among different organizations
• WFQ provides guaranteed service
• Controlled-load and best-effort flows are
  separated by priority

WFQ
CS department gets 50
WFQ
30
10
priority
guaranteed flow n
guaranteed flow 1
best effort flows
controlled flows
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IETF Differentiated Services

• Concerns with Intserv
• Scalability signaling, maintaining per-flow
  router state difficult with large number of flows
  
• Flexible Service Models Intserv has only two
  classes. Also want qualitative service classes
• behaves like a wire
• relative service distinction Platinum, Gold,
  Silver
• Diffserv approach
• simple functions in network core, relatively
  complex functions at edge routers (or hosts)
• Dont define service classes, provide functional
  components to build service classes

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The DiffServ Traffic Conditioner Block (TCB)

• Classifier Identifies packets for assignment to
  Classes
• Meter Checks compliance to traffic parameters
  (Token Bucket) and passes result to Marker and
  Shaper/Dropper to trigger particular action for
  in/out-of-profile packets
• Marker Writes/rewrites the DSCP value
• Shaper Delays some packets for them to be
  compliant with the profile
• Dropper Drops packets that exceed the profile
  (Bc or Be)

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DiffServ Architecture
Edge router - per-flow traffic management -
marks packets as in-profile and out-profile
Core router - per class traffic management -
buffering and scheduling based on marking at
edge - preference given to in-profile packets -
Assured Forwarding
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Edge-router Packet Marking

• profile pre-negotiated rate A, bucket size B
• packet marking at edge based on per-flow profile

User packets
Possible usage of marking

• class-based marking packets of different classes
  marked differently
• intra-class marking conforming portion of flow
  marked differently than non-conforming one

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Classification and Conditioning

• Packet is marked in the Type of Service (TOS) in
  IPv4, and Traffic Class in IPv6
• 6 bits used for Differentiated Service Code Point
  (DSCP) and determine PHB that the packet will
  receive
• 2 bits are currently unused

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Classification and Conditioning

• may be desirable to limit traffic injection
  rate of some class
• user declares traffic profile (eg, rate, burst
  size)
• traffic metered, shaped if non-conforming

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Forwarding (PHB)

• PHB result in a different observable (measurable)
  forwarding performance behavior
• PHB does not specify what mechanisms to use to
  ensure required PHB performance behavior
• Examples
• Class A gets x of outgoing link bandwidth over
  time intervals of a specified length
• Class A packets leave first before packets from
  class B

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Forwarding (PHB)

• PHBs being developed
• Expedited Forwarding pkt departure rate of a
  class equals or exceeds specified rate
• logical link with a minimum guaranteed rate
• Assured Forwarding 4 classes of traffic
• each guaranteed minimum amount of bandwidth
• each with three drop preference partitions

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Why QoS?Congestion Scenario 1Speed Mismatch

• The 1 Reason for Congestion!
• Possibly Persistent when going from LAN to WAN
• Usually Transient when going from LAN to LAN!

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Why QoS?Congestion Scenario 2Aggregation

• Transient Congestion fairly typical!

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Why QoS?? Congestion Scenario 3Confluence
Net-1
Core1
Core2
STM-64/OC-192c
Net-2
STM-16/OC-48c
Net-n

• Always need mechanisms to provide guarantees!
• Transient Congestion occurs!

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Typical ApplicationQoS Requirements
ERP andMission-Critical
Voice
FTP
Low toModerate
Moderateto High
Bandwidth
Low
ModerateTo High
Random Drop Sensitive
Low
High
Low toModerate
Delay Sensitive
High
Low
Jitter Sensitive
High
Low
Moderate
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• Q A
• Thank You