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www.ict.csiro .au End-2-End QoS Internet Presented by: Zvi Rosberg 3 Dec, 2007 Caltech Seminar
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End-2-End QoS Internet

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End-2-End QoS Internet. Presented by: Zvi Rosberg 3 Dec, 2007 Caltech Seminar. What is this talk about. The shortcoming of QoS support in current Internet A novel holistic Rate Management Protocol A new scalable QoS guarantee architecture - PowerPoint PPT Presentation
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Page 1: End-2-End QoS Internet

www.ict.csiro.au

End-2-End QoS Internet

Presented by: Zvi Rosberg3 Dec, 2007

Caltech Seminar

Page 2: End-2-End QoS Internet

www.ict.csiro.auWhat is this talk about

The shortcoming of QoS support in current Internet

A novel holistic Rate Management Protocol A new scalable QoS guarantee architecture The theoretical foundation of our architecture How TCP window flow control may adapt in

the presence of our network layer RMP Another E-2-E prioritized Delay/Loss RMP

Page 3: End-2-End QoS Internet

www.ict.csiro.auMotivation

Shortcoming of current QoS architecture Beside being immature and requiring

horrendous configuration, current QoS also has…

Fundamental inhibitors:

1. Scalability for real QoS guarantee (IntServ and Cisco’s “IntServ over DiffServ”)

2. No bandwidth nor E2E delay guarantee when using a scalable configuration of DiffServ

Page 4: End-2-End QoS Internet

www.ict.csiro.auSo what are we doing about it ?

We are implementing a prototype on Network Processors (NPU) addressing the current QoS issues - The architecture is

1. Scalable and has bandwidth, loss and E2E delay guarantee

2. Adaptive - so configuration is minimized

3. Allocates the residual bandwidth fairly

The NPUs execute a new IP layer protocol that router’s should run in the future

Page 5: End-2-End QoS Internet

www.ict.csiro.au

The Architecture

Page 6: End-2-End QoS Internet

www.ict.csiro.auThe Key Elements of our solution

Runs in Edge & Core Routers at IP

layer

EdgeRouter

10Eth

erne

t

CoreRouter

11

CoreRouter

12

EdgeRouter

20

CoreRouter

13

CoreRouter

14

CoreRouter

15

EdgeRouter

30

Ethernet

Ethernet

UserDevices

UserDevices

UserDevices

1

2

3

51

52

53

3

4

RMP

RMP

RMP

Novel Rate Management

Protocol (RMP) for Multi-Service Flows

RMP

RMP

RMP

RMP

RMP

Provides Services to Management

functions in the Edge Routers

Services

Services

Services

Page 7: End-2-End QoS Internet

www.ict.csiro.auArchitectural Components

QoS Fair Rate

Calculation

RMP

Link Penalties Gathering

Performance Probing

Admission Control

Scalable Bandwidth Reservation Protocol

Classification/Marking at Edge Routers

Rate Policing

in the Edge

Priority Packet

Scheduling in Routers

Control PlaneData Plane

Page 8: End-2-End QoS Internet

www.ict.csiro.au

Theoretical Foundation

Page 9: End-2-End QoS Internet

www.ict.csiro.auOur Theoretical Contribution

Extending Fairness beyond “best-effort” service Extending the primal-dual iterative distributed

algorithm (used by Kelly) for rate allocation with

1. Rate and delay constraints

2. Priority packet scheduling Revisit TCP flow control when rate is controlled

by the network layer An aside question is: Why priority scheduling?

It improves link utilization – delay-sensitive packets will not have to wait for delay-insensitive packets, so we can have more from the delay-insensitive packets

Page 10: End-2-End QoS Internet

www.ict.csiro.auFairness with Best-effort

- proportional fairness is equivalent to the solution of:

as long as X is convex

Page 11: End-2-End QoS Internet

www.ict.csiro.auFairness with QoS

A natural way to extend the best effort fairness is to add the QoS requirements to the constraints and …

… optimize on the residual link capacities

Page 12: End-2-End QoS Internet

www.ict.csiro.au

Since X is convex – proportional fairness follows

Flow rates of prio 1,2…,m traversing

each link

maximum loss and delay constraints

minimum bandwidth constraints

Fairness with QoS (Cont.)

Page 13: End-2-End QoS Internet

www.ict.csiro.au

The delay/loss constraints are NOT EXPLICIT – they are attained by an outer-loop control of

Fairness with QoS (Cont.)

Page 14: End-2-End QoS Internet

www.ict.csiro.au

Primal-dual iterative distributed algorithm extension

The fair residual rates, , are computed iteratively after a reduction to residual link capacities, , given by

… which is made possible by our scalable reservation protocol

The policed rate of flow is then

Page 15: End-2-End QoS Internet

www.ict.csiro.auThe Rate Management Protocol (RMP)

• In each router output link n and priority m :

• Total rate of flows from priorities 1,..,m on link n on unreserved link capacity

• Link capacity reduced by utilization upper bound per priority class m

• Adaptively set from sources based on RTT and Loss probing

• Route penalty of flow i

Page 16: End-2-End QoS Internet

www.ict.csiro.auStability Proof

To prove stability with fixed We redefine the routing matrix, , to include one virtual link for each priority

classFlows with priority m use all virtual links having priorities m along their

original path

The redefined problem is a single class problem equivalent to the priority problem

After this reduction, stability follows by Kelly’s results

Page 17: End-2-End QoS Internet

www.ict.csiro.auStability Proof (cont.)

To prove stability with adaptive “Unhappy” flow sources (having excessive delay/losses) signal it in their

RMP packets Congested links decrease the respective

To prove convergence, we allow only to decrease In practice, convergence is observed also when are also

increased when flow sources are “too-happy”

Page 18: End-2-End QoS Internet

www.ict.csiro.au

TCP Flow Control - Revisited

Page 19: End-2-End QoS Internet

www.ict.csiro.auTCP Flow Control Revaluation

Once RMP is in place, TCP flow control needs a revaluation The RMP of the core network will take care of fair rate calculation

and congestion avoidance RMP will also signal end applications about their current target

rates, and then…TCP could be extended beyond “best-effort”

Given rate, , TCP can achieve it with a window update of the form:

Page 20: End-2-End QoS Internet

www.ict.csiro.auPerformance Evaluation

We showed that assuming linear scalability, the window flow control converges to a unique stable state under totally asynchronous updates

linear scalability: Total number of bytes queued in each link scales up linearly with the window size

It is an average flow property of the flows crossing a given link, rather a per-flow property

Plausible for large networks

Stability was also verified by simulation In the fluid model of [Mo & Walrand] used to relate

rate and windows, linear scalability is implied

Page 21: End-2-End QoS Internet

www.ict.csiro.auTCP Flow Control Comparison

Epoch ISP Network, USA# core links: 74 (37 full-duplex)# flows: 512# access links: 512core link capa: 1 Gb/saccess link capa: 0.1 Gb/s

Page 22: End-2-End QoS Internet

www.ict.csiro.auSimulation Method

2-way TCP flows using fixed shortest paths ACKs are either piggybacked or pure (statistically) RTO is estimated according to RFC 2988 (Jacobson Alg) Duplicate ACKs are triggered if All TCP flow controls half their window size upon 3-

duplicate ACKs and reduce it to 2 MSS upon RTO Otherwise - Fast TCP adapts its window sizes according

Page 23: End-2-End QoS Internet

www.ict.csiro.auSimulation Method (cont.)

Simulation time is about 3.5 real operational minutes In every step - window packets are processed in one batch First, they are arbitrarily distributed between forward and

backward paths Then, the packets that can “fill” the links are in transit The rest, are distributed between the bottleneck links in

proportion to the bottleneck queueing time Async operation is modelled by i.i.d Bernoulli r.v's

determining which of the flows receive an ACK

Page 24: End-2-End QoS Internet

www.ict.csiro.auTCP Flow Control Comparison

Our TCP Flow Control (9 typical flows windows)

Page 25: End-2-End QoS Internet

www.ict.csiro.auTCP Flow Control Comparison

Fast TCP Flow Control

Page 26: End-2-End QoS Internet

www.ict.csiro.auTCP Flow Control Comparison

TCP Vegas Flow Control

Page 27: End-2-End QoS Internet

www.ict.csiro.auTCP Flow Control Comparison

TCP Reno Flow Control (“Sawtooth”)

Page 28: End-2-End QoS Internet

www.ict.csiro.auComparison Summary

Avg

Rate

Avg RTT Avg Win Fairness Dev

Max Fair Dev

Ours 492 P 191 ms 28 P 3% 20%

Fast 479 P 231 ms 28 P 5% 25%

Vegas 449 P 248 ms 29 P 4% 44%

Reno 451 P 548 ms 59 P 12% 91%

Page 29: End-2-End QoS Internet

www.ict.csiro.auFlow Control with QoS Support

Avg Rate Avg RTT Avg Win

Priority 1 43.8 P 50 ms 1 P

Priority 2 224 P 56 ms 5.12 P

Priority 3 225 P 81 ms 7 P

3 x 256 2-way TCP connections with 3 priorities

Utilization upper bounds: (0.1, 0.75, 1.0)

Avg total fair rate: 164.30 packets (compared with 492)

Avg Fairness deviation: 5.5%

Page 30: End-2-End QoS Internet

www.ict.csiro.auSimulation with Link Utilization Adaptation

When are adapted based on flow source experienced RTT and Losses

(i.e., RTT > RTO), then all QoS requirements are met

Page 31: End-2-End QoS Internet

www.ict.csiro.au

Another E2E Delay-Loss Control

Page 32: End-2-End QoS Internet

www.ict.csiro.auRate Time Derivative in the Fluid Model

clearance time of bits from flows

with prio higher/equal p in link l at time t delay prices for flow i at time t

We study the following prioritized combined Rate-Delay control problem

Page 33: End-2-End QoS Internet

www.ict.csiro.auDelay Time Derivative in the Fluid Model

total rate of flows with priorities

less/equal p in link l at time t

The rate control is the gradient search of

Page 34: End-2-End QoS Internet

www.ict.csiro.auDelay Prices Adapting

is learned by the flow source from the RMP packets

… and is adapted if Adaptation signals must also be

disseminated to other relevant sources …. which is done again with RMP signalling

packets

Page 35: End-2-End QoS Internet

www.ict.csiro.auResult Summary

If the routing matrix is full-rank, then

For any e2e delay requirement, there is a unique equilibrium point

The adaptive rate control converges to the stable point from any initial condition

Synchronous Fluid Model

Time Lag Fluid Model (Rate and Delay effects)

For a single bottleneck case – global stability holds true only if time lag is limited (e.g., ~650 ms)

Emulation – holds true for multiple bottlenecks

Page 36: End-2-End QoS Internet

www.ict.csiro.au

Thank You