University of British Columbia Cpsc 527 Advanced Computer Communications Lecture 7b DiffServ Overview

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University of British Columbia Cpsc
527Advanced Computer CommunicationsLecture 7b
DiffServ Overview

• Instructor Dr. Son T. Vuong
• Email vuong_at_cs.ubc.ca
• The World Connected

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Outline

• Overview of QoS and DiffServ
• Our research on DiffServ
• A Class of Protocols
• Dynamic (Fair) Distribution DiffServ
• Conclusions

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What is the Service on Internet

• A "Service" defines some significant
  characteristics of packet transmission in one
  direction across a set of one or more paths
  within a network.
• These characteristics may be specified in
  quantitative or statistical terms of
• throughput, delay, jitter, loss.

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Current Problems with the Internet

• Best-effort service has strained its current
  infrastructure capabilities.
• A challenge is to design routers that can provide
  service differentiation for various types of
  traffic.
• Two solutions proposed in IETF
• Integrated service (IntServ) individual flows
  with specific QoS requirements, e.g. RSVP flows
• Differentiated services (DiffServ) aggregate of
  flows and per-hop behavior.

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What is QoS and why we need it?

• QoS has many different measures
• Delay, delay variance (jitter), rate
• Fairness, flow isolation
• Reliability, e.g. drop rate
• QoS is needed in packet networks to support
  multimedia applications IP Telephony, mobile
  web-access, Video teleconferencing, net-PC
  applications, Grid services, etc.

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Application QoS requirements

• Different applicationsdifferent QoS
  requirements.
• Delay-sensitive real-time applications Voice,
  Interactive Video.
• Delay-tolerant real-time applications Streaming
  Video.
• Elastic applications that tolerate a wide range
  of delay variations FTP, Telnet and e-mail.

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How to Provide QoS in a Best-Effort Internet?

• More bandwidth does not solve the problem it only
  moves it to the core of the network
• IP router technology has a limit to its
  computational capabilities.
• Also, fairness is not solved when bandwidth is
  increased.
• Solution packet scheduling and resource
  reservation.

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Improving QOS in IP Networks

• IETF groups are working on proposals to provide
  better QOS control in IP networks, i.e., going
  beyond best effort to provide some assurance for
  QOS
• Work in Progress includes RSVP, Differentiated
  Services, and Integrated Services
• Simple model for sharing and congestion
  studies

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Principles for QOS Guarantees

• Consider a phone application at 1Mbps and an FTP
  application sharing a 1.5 Mbps link.
• bursts of FTP can congest the router and cause
  audio packets to be dropped.
• want to give priority to audio over FTP
• PRINCIPLE 1 Marking of packets is needed for
  router to distinguish between different classes
  and new router policy to treat packets accordingly

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Principles for QOS Guarantees (more)

• Applications misbehave (audio sends packets at a
  rate higher than 1Mbps assumed above)
• PRINCIPLE 2 provide protection (isolation) for
  one class from other classes
• Require Policing Mechanisms to ensure sources
  adhere to bandwidth requirements Marking and
  Policing need to be done at the edges

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Principles for QOS Guarantees (more)

• Alternative to Marking and Policing allocate a
  set portion of bandwidth to each application
  flow can lead to inefficient use of bandwidth if
  one of the flows does not use its allocation
• PRINCIPLE 3 While providing isolation, it is
  desirable to use resources as efficiently as
  possible

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Principles for QOS Guarantees (more)

• Cannot support traffic beyond link capacity
• PRINCIPLE 4 Need a Call Admission Process
  application flow declares its needs, network may
  block call if it cannot satisfy the needs

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Summary
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Scheduling And Policing Mechanisms

• Scheduling choosing the next packet for
  transmission on a link can be done following a
  number of policies
• FIFO in order of arrival to the queue packets
  that arrive to a full buffer are either
  discarded, or a discard policy is used to
  determine which packet to discard among the
  arrival and those already queued

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Scheduling Policies

• Priority Queuing classes have different
  priorities class may depend on explicit marking
  or other header info, eg IP source or
  destination, TCP Port numbers, etc.
• Transmit a packet from the highest priority class
  with a non-empty queue
• Preemptive and non-preemptive versions

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Scheduling Policies (more)

• Round Robin scan class queues serving one from
  each class that has a non-empty queue

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Scheduling Policies (more)

• Weighted Fair Queuing is a generalized Round
  Robin in which an attempt is made to provide a
  class with a differentiated amount of service
  over a given period of time

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Policing Mechanisms

• Three criteria
• (Long term) Average Rate (100 packets per sec or
  6000 packets per min??), crucial aspect is the
  interval length
• Peak Rate e.g., 6000 p p minute Avg and 1500 p p
  sec Peak
• (Max.) Burst Size Max. number of packets sent
  consecutively, ie over a short period of time

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Policing Mechanisms

• 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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Policing Mechanisms (more)

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

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What Is Scheduling and Why Do We Need It?

• In real networks, a large number of flows may
  require different guarantees from the network.
• Scheduling determines the next eligible packet,
  among all the arriving packets, to be sent out in
  order to satisfy the required guarantees.
• Attributes of a good scheduler
• Rate and delay guarantees.
• Fairness.
• Utilization.
• Simplicity.

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Scheduling (revisited)

• Scheduling per-flow or aggregated flows.
• Per-flow (IntServ)
• Provides exact delay and fairness guarantees.
• Requires maintaining state information for all
  active sessions on a link.
• Aggregation (DiffServ)
• Delay and fairness are not as easy to guarantee.
• No (or minimal amount of) states need to be
  maintained.

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Types of Schedulers

• Rate-controlled Delay / jitter Earliest Due Date
  (D-EDD and J-EDD).
• Non-rate-controlled Generalized Processor
  Sharing (GPS) and Weighted Fair Queueing (WFQ).

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How GPS Works

• Every session has its own queue and share.
• Weighted Round Robin (WRR) service order with an
  infinitesimal amount serviced from each session.
• Empty queues are skipped when their turn arrives.

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End-to-End Network Delay

• DelayHost DelayAccess DelayNetwork Delay
• Even if the network provided the required QoS
  without the host applications or access networks
  providing their guarantees then the end-to-end
  guarantees will not be met.

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WFQ vs. GPS
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Scheduling Policies (more)

• Weighted Fair Queuing is a generalized Round
  Robin in which an attempt is made to provide a
  class with a differentiated amount of service
  over a given period of time

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Proactive Packet Discard

• Congestion management by proactive packet discard
• Before buffer full
• Used on single FIFO queue or multiple queues for
  elastic traffic
• E.g. Random Early Detection (RED)

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Random Early Detection (RED)Motivation

• Surges fill buffers and cause discards
• On TCP this is a signal to enter slow start
  phase, reducing load
• Lost packets need to be resent
• Adds to load and delay
• Global synchronization
• Traffic burst fills queues so packets lost
• Many TCP connections enter slow start
• Traffic drops so network under utilized
• Connections leave slow start at same time causing
  burst
• Bigger buffers do not help
• Try to anticipate onset of congestion and tell
  one connection to slow down

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RED Design Goals

• Congestion avoidance
• Global synchronization avoidance
• Current systems inform connections to back off
  implicitly by dropping packets
• Avoidance of bias to bursty traffic
• Discard arriving packets will do this
• Bound on average queue length
• Hence control on average delay

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RED Algorithm Overview

• Calculate average queue size avg
• if avg lt THmin
• queue packet
• else if THmin ? avg ? Thmax
• calculate probability Pa
• with probability Pa
• discard packet
• else with probability 1-Pa
• queue packet
• else if avg ? THmax
• discard packet

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RED Buffer
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RED Algorithm Detail
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Architecture of DiffServ

• DiffServ Domain
• A Set of per-hop (forwarding) behaviors (PHB).
• Packet classification functions.
• Traffic conditioning functions including
• metering
• marking
• shaping
• policing

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DS Nodes

• DS boundary Nodes
• Classify the ingress packets.
• Perform traffic conditioning according to a
  traffic conditioning agreement (TCA)
• DS Interior Nodes
• Perform limited traffic conditioning functions
  such as DS codepoint re-marking.

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DS Definition

• 000000 Best - effort behavior
• Pool Codepoint space Policy
• 1 xxxxx0 Standards
  Action
• 2 xxxx11 EXP/LU
• 3 xxxx01 EXP/LU ()
• () May be used for future Standards Action
  allocations as necessary

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Example of DiffServ Domains
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Per-Hop Behaviors (PHB)

• PHB is a description of forwarding behavior of a
  DS node for a particular DS behavior aggregate.
• Via PHBs, a node allocates its resources (buffer
  , bandwidth , delay, loss) to behavior
  aggregates.
• PHBs are implemented via buffer management and
  packet scheduling mechanisms.
• A PHB is selected at a node by a mapping of the
  DS codepoint in a received packet.

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Traffic Conditioning Specification

• The TCS specifies detailed service parameters for
  each service level
• Service performance parameters such as expected
  throughput, drop probability, latency.
• Traffic profiles which must be adhered to for the
  requested service to be provided, such as token
  bucket parameters.
• Disposition of traffic submitted in excess of the
  specified profile.
• Marking services provided.
• Shaping services provided.

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Packet Classifier and Traffic Conditioner

• Classifier select packets in a traffic stream
  based on packet header.
• Meter measures the temporal properties of the
  stream of packets selected by a traffic profile.
• Marker sets the DS field of a packet to a
  particular codepoint, add marked packet to a DS
  behavior aggregate.
• Shaper shapes the traffic stream to bring it
  into compliance with a traffic profile.
• Dropper discards some or all packets in a
  traffic stream to bring it into compliance with
  a traffic profile.

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Service Level Specification (SLS)

• In addition to TCS, the SLS specifies more
  general service
• Availability/Reliability
• Encryption services.
• Routing constraints.
• Authentication mechanisms.
• Mechanisms for service monitoring and auditing.
• Responsibilities such as location of the
  equipment and functionality, action if the
  contract is broken, support capabilities.
• Pricing and billing mechanisms.

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Profile in Router

• Profile ----gt behavior of the router
• There may be many profiles in the router at any
  time.
• Profile contains
• Name
• Attribute (in/out)
• Policy Scope
• Other information (Address , port, permission,
  month mask, time of day, direction )

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Example of Profile

• Name Entry2
• PolicyScope DataTraffic
• TimeOfDayRange 090000 to 170000
• IncomingTOS 111
• SourceAddressRange 139.24.2.12
• 
  to 139.24.2.255
• Direction Outgoing
• MaxeRate 5000
• OutgoingTOS 101

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Examples of Services

• Better than Best-Effort (BBE) Service
• This is a qualitative service which promises to
  carry specific web server traffic at a higher
  priority than best-effort traffic.
• Premium Service
• Customer purchases a peak rate
• Packets below that rate carried with no delay
• Packets above that rate dropped

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Our research on DiffServ

• We focus on differentiated service since this
  aggregate service scales better than the per-flow
  integrated service.
• We focus on developing a class of protocols
  including the Meter, Marker, Shaper at the
  Boundary nodes and the per-hop behavior of all
  interior nodes in a DS Domain.
• For performance evaluation, the network simulator
  NS2 was used.

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DiffServ and BestEffort Queues
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The simulation of DiffServ and BestEffort for
TCP/IP traffic
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The Dynamic Distribution DiffServ

• The scheme unites DiffServ flows with Dynamic
  Distribution to the aggregate before sending
  them to the network.
• Dynamic Distribution prevents any aggregate from
  taking all the bandwidth in a period of time,
  thus allows every aggregate a chance of passing
  through the router at all times.
• Dynamic Distribution also guarantees Multimedia
  applications an upper bound on packet delay
  inside the DiffServ domain without the per-flow
  requirement.

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Multiple Queues in DiffServ Router
Backlogged packets
DiffServ queues
Figure 1.
Multiple-Queues in a Router of the DiffServ
Domain
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The Scheme of Dynamic Distribution Differentiated
Service

• This scheme simplifies processing at routers in
  DiffServ domain (cf. the IntServ scheme) while
  maintaining QoS guarantee for every flow.
• At Boundary Nodes, packets are classified by
  their flows, which may number in thousands at one
  node or tens of thousand in the whole domain
• At Inside Nodes, packets classified by their
  aggregates, numbered in hundreds at a node.

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The Scheme at Boundary Node

• Classifier selects packets in a traffic stream
  based on DiffServ byte in header.
• Meter The leaky-bucket meter scheme for every
  flow with its subscribed bandwidth.
• Dropper drops all out-profile packets.
• Shaper Fair-Queue scheme for every DiffServ flow
  depending on the subscribing bandwidth.
• Marker an aggregate marking scheme
• PHB exact Fair-Queue forwarding scheme.

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The Scheme for Interior Nodes

• Classifier selects packets in a traffic stream
  based on DiffServ byte and places them in
  appropriate queues.
• Shaper time divided into equal slots, each
  further divided mini-slots. Each aggregate
  receives a number of mini slots based on
  calculation at the beginning of the slot.
• PHB Frame-based forwarding scheme with Dynamic
  Distribution of resources.

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Summary

• The proposed Dynamic Distribution DiffServ scheme
  is flexible, simple and efficient
• Guarantees delay bound without the per-flow
  complexity, suitable for multimedia traffic.
• Future work
• Various types of multimedia application traffic
  such as video teleconferencing
• Various performance measures, including delay,
  throughput and jitter
• Multicasting and security DS services