An Integrated IP Packet Shaper and An Integrated IP Packet Shaper and Scheduler for Edge RoutersScheduler for Edge Routers

MSEE Project Presentation

Student: Yuqing Deng

Advisor: Dr. Belle Wei

Spring 2002

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Yuqing Deng’s MSEE Project Presentation

Outline

• Introduction

• Design Consideration

• Integrated Traffic Shaper and Scheduler

• Conclusion

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Yuqing Deng’s MSEE Project Presentation

• IP Traffic Management Challenges

-- Quality of Service (QoS):End-to-end guarantees for delay, throughput and loss regulated in Service Level Agreement (SLA); Under the Differentiated Service (DS) scheme, this is expressed by varied priority levels for different data types ( video conferencing, ftp, email, etc);

-- Fairness:Happens when multiple packet flows contend for limited resource;

-- Traffic Shaping:To avoid potential congestion, bursty traffic has to be smoothed out.

Introduction

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Yuqing Deng’s MSEE Project Presentation

Introduction (cont’d)

• Implementation Algorithms:

-- Scheduler:Fair Queuing (Per Flow Queuing);

Weighted Round Robin (WRR);

Priority Queuing;

Timestamp;

-- Shaper:Token Bucket;

Leaky Bucket;

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Yuqing Deng’s MSEE Project Presentation

Design Consideration

• Fair Queuing: needed?Precise scheduling, but complex implementation;

• Timestamp Integration:Should reflect both QoS and shaping feature;

• Virtual Output Priority Queue (VOPQ):

Targeted queue for scheduled packets.

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Yuqing Deng’s MSEE Project Presentation

Integrated Traffic Shaper and Scheduler

Parser/Search Engine

TimestampGenerator

Packet Memory

Flow StatusLookup Table

Clock

Packets In

Scheduler

VOPQ

Inse

rtio

n n

Packets Out to Switch Fabric

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Yuqing Deng’s MSEE Project Presentation

Timestamp Generator/Flow Status LUT:

• Timestamp is calculated based on:

1) Token Bucket Algorithm for the shaping part;2) Virtual Finish Time for QoS part;

• Algorithm (per flow base):

TSk = TSk-1 + Lk/r + Sk;

Where Sk = max [0, (TAk-1 + Sk-1 + Lk-1/ρ – TAk)], with S0 = 0;

TAk/TSk: Arrival time/Timestamp for the current packet;

TAk-1/TSk-1: Arrival time/Timestamp for the previous packet;

Lk/ Lk-1 : Size of the current/previous packet; ρ: token generation rate; r: transmission rate for the flow;

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Yuqing Deng’s MSEE Project Presentation

Timestamp Generator/Flow Status LUT (cont’d):

• Flow status LUT keeps the following flow information:

- Transmission rate;

- Timestamp of previous packet;

- Shaping adjustment of previous packet;

- Arrival time of previous packet;

- Priority level of the flow;• Timestamp calculator updates flow status info when processing

a new packet;• Packet header info is sent to VOPQ along with its timestamp,

based on its priority level;

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Yuqing Deng’s MSEE Project Presentation

Timestamp Generator/Flow Status LUT: Block Diagram

Buffer

Flow Status Lookup Table

Timestamp Calculator

Packet header with timestamp

Packet header

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Yuqing Deng’s MSEE Project Presentation

Virtual Output Priority Queue (VOPQ)

• VOQ: has be extensively adopted for IP router, due to its better performance than normal Output Queue used in ATM switch;

• Priority Queue (PQ): used to implement Differentiated Service demand; a sorting/insertion technique is needed;

• VOPQ: a combination of VOQ and PQ; each output corresponds to a set of PQs in VOPQ;

• Implementation: Priority Content Addressable Memory (PCAM);

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Yuqing Deng’s MSEE Project Presentation

VOPQ: Block Diagram

PCAM Sorting

Flow Priority Info

Packet with TS

………………

………………

. .. .

. .

. .

. .Scheduler

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Yuqing Deng’s MSEE Project Presentation

Conclusion

• FQ not used but per flow status maintained: simplified design without sacrificing performance;

• Combined VOQ and PQ: further simplified design and increased speed;

• Integrated Timestamp: more function and flexibility;

• PCAM: fast sorting and scalable;