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Quality of Service - QoS. 2007. Outline. Integrated Services in the Internet service definitions, protocol support architecture framework algorithms support Differentiated service Intserv over Diffserv Engineering for QoS. What is the Problem?.

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outline

Outline

Integrated Services in the Internet

service definitions, protocol support

architecture framework

algorithms support

Differentiated service

Intserv over Diffserv

Engineering for QoS

what is the problem
What is the Problem?
  • Goal: support for wide variety of applications:
    • Interactive TV, IP telephony, on-line gamming, (distributed simulations), VPNs, etc
  • Problem: deal with network congestion
  • During congestion all packets are treated the same
    • All packets get the same delay
  • Only control possible at end-hosts
    • Feedback loop too large (e.g., 100s of ms) for real-time applications (e.g., interactive communication)
    • Trust issue  how can you trust users that will react properly in case of congestion?
slide4
Two Approaches for Providing

QoS on the Internet

  • “Freeway model” -- integrated services Internet (intserv)
    • Build a dedicated highway or “circuit” between communicating points (VIP)
  • “Doctor’s model” -- differentiated services (diffserv)
    • Mark a doctor’s vehicle (e. g.,ambulance) or “packet” to get priority the road and limit the percentage of such high- priority vehicles in the total traffic mix (fire-engine, policeman)
a solution integrated services
A Solution: Integrated Services
  • Enhance IP’s service model
    • old model: single best-effort service class
    • new model: multiple service classes, including best-effort and QoS classes
  • Create protocols and algorithms to support new serv models
    • old model: no resource management at IP level
    • new model: explicit resource management at IP level
  • Key architecture difference
    • old model: stateless
    • new model: per flow state maintained at routers
      • used for admission control and scheduling
      • set up by signaling protocol
integrated services network
Integrated Services Network
  • Flow or session as QoS abstractions
  • Each flow has a fixed or stable path
  • Routers along the path maintain the state of the flow
ietf service classes
IETF Service Classes
  • Service can be viewed as a contract between network and communication client
  • Three common services
    • Best-effort (“elastic” applications)
    • Hard real-time (“real-time” applications)
      • Guaranteed service (RFC)
        • Intolerant GS
        • guaranteed QoS control service
      • equivalent to CBR+VBR-rt in ATM
    • Soft real-time (“tolerant” applications)
      • Controlled-load service (RFC2000)
        • Tolerant GS
        • controlled link sharing
        • predictive service - RFC1994
      • similar to VBR-nrt
guaranteed service intolerant gs hard real time
Guaranteed Service- Intolerant GS (hard real-time)
  • Service contract
  • absolute, strict
  • network to client: guarantee a deterministic upper bound on delay for each packet in a session di ≤Di
  • client to network: the session does not send more than it specifies
  • Algorithm support
  • admission control based on worst-case analysis
  • per flow classification/scheduling at routers
controlled load service tolerant gs soft real time
Controlled-load Service - Tolerant GS (soft real-time)
  • Service contract
  • statistical, approximate
  • network to client: similar performance as an unloaded best-effort network
    • nominal mean delay, but can tolerate “occasional” variation
  • client to network: the session does not send more than it specifies
  • Algorithm support
  • admission control based on measurement of aggregates
  • scheduling for aggregate possible
implementation framework 1
Implementation Framework (1)
  • Four components:

-- packet classifier, scheduler, admission control routine, reservation setup (signaling) protocol

  • Classifier

-- each incoming packet must be mapped into some class; all packets in the same class get the same treatment from the packet scheduler

  • Scheduler

-- manages the forwarding of different packet streams using a set of queues and other mechanisms like timers

implementation framework 2
Implementation Framework (2)
  • Admission control

-- implements the decision algorithm that a router or host uses to determine whether a new flow can be granted the requested QoS

-- admission control is sometimes confused with policing or enforcement, which is a packet-by-packet function at the “edge” of the network to ensure that a host does not violate its promised traffic characteristics. We consider policing to be one of the functions of the packet scheduler.

  • Reservation setup protocol (RSVP)

-- create and maintain flow-specific state in the endpoint hosts and in routers along the path of a flow

role of rsvp in the architecture
Role of RSVP in the Architecture
  • RSVP is a signaling protocol that applications may separate with Intserv
  • Intserv/RSVP architecture is current prevailing model
  • Signaling protocol for establishing per flow state
  • Carry resource requests from hosts to routers
  • Collect needed information from routers to hosts
  • At each hop
    • consults admission control and policy module
    • sets up admission state or informs the requester of the failure
implementation framework 3 implementation reference model for routers
Implementation Framework (3)---- Implementation Reference Model for Routers

Routing

Messages

Routing

RSVP

RSVP

messages

Control Plane

Admission

Control

Data Plane

Forwarding Table

Per Flow QoS Table

Data In

Route Lookup

Classifier

Scheduler

Data Out

outline1

Outline

Integrated Services in the Internet

service definitions, protocol support

architecture framework

algorithms support

Differentiated service

Intserv over Diffserv

Engineering for QoS

what is still missing
What Is Still Missing?
  • Classification algorithm
  • Scheduling algorithm
  • Admission control algorithm
  • QoS Routing algorithm
measurement based admission control
Measurement-based admission control
  • Predictive service offers a fairly, but not absolutely, reliable bound on packet delivery times
  • MBAC relies on measurements of the delay and bandwidth
mpeg trace statistical parameters
MPEG Trace Statistical Parameters
  • Trace name Mean-bit St.variance Peak/Mean Delay Bound
  • Fuss 27129 25969 6.9 0.0416
  • News 15358 19506 12.4 0.0422
  • Lambs 7312 11196 18.4 0.0298
  • Figure 1. The one-link topology
single hop simulation results
Single-Hop Simulation Results
  • Trace name Guaranteed Predictive
  • %Util #Actv %Util #Actv
  • Fuss 15 10 53 36
  • News 8 10 48 58
  • Lambs 5 14 40 102
  • EXP1 46 144 80 250
  • EXP2 28 28 76 75
  • EXP3 2 18 62 466
  • POO1 7 144 74 1637
  • POO2 3 38 64 951
why did intserv fail
Why did IntServ fail?
  • Economic factors
    • Deployment cost vs Benefit
  • Is reservation, the right approach?
    • Multicast centric view
  • Is per-flow state maintenance an issue?
  • What about QoS in general?
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