qos-aware traffic protection for access rings srivas chennu kai habel klaus-dieter langer

QoS-aware Traffic Protection for Access Rings

Srivas Chennu

Kai Habel

Klaus-Dieter Langer

S. Chennu, K. Habel, K.-D. Langer

A Brief Outline

> Link layer architecture for protected access rings

> The Fast Access Ring Protection Protocol (FARPP)

> QoS-awareness in the access ring

> Simulative evaluation of FARPP

> Conclusions


Access Ring Protection Architecture

> Design philosophy: Centralized network management • Operates at the link layer• Exploits uneven breakup of responsibilities• Simplifies design• Leads to lower cost devices (reduced investment) in the field• Provides for reduced latency times for reconfiguration• Affords better control over traffic distribution in ring• Borrows ideas from existing standards and protocols

> Two dissimilar protocol entities• Relatively complex HUB entity at the CO• Simple ONU entity at end user


The HUB Entity

> ‘Intelligent' component in control of network operator

> Responsible for key network management tasks

> Has 2 ring ports and an external MAN/WAN port

> Lookup table stores topology view

HUB

MAN/WAN port

Ring port 2Ring port 1

Ring section 1 Ring section 2

> Records ring port providing least-cost path to ONU in table

> This port is used for forwarding data to ONU

> HUB regularly checks connectivity status of ring

> Reacts to faults reported by ONUs by updating lookup table

> Uses alternate path to ONUs to route around faults


The ONU Entity

> Designed to be a simple, low-cost device

> Two ring ports and one LAN port

> Each ring port assigned a cost

> Has a unique ID used for addressing it within the ring

ONU

End user/LAN port

Ring port 2Ring port 1

> Registers itself with the HUB on initialization

> Labels its ring ports as PRIMARY and SECONDARY

> PRIMARY port provides least-cost default path to HUB

> Periodically pings HUB to report status and notify detected faults

> ONUs affected by a fault switch to using their SECONDARY port

> Failed ONUs are eventually removed from the HUB lookup table


A Brief Outline





> Conclusions


ONU Registration

> ONU sends out JOIN messages on both ports on initialization

> Path cost stored in messages incremented by each downstream ONU

> HUB computes least-cost path to ONU using received JOINs

> Registers ONU in lookup table and replies with JOIN ACK on least-cost path

> ONU registers port providing least-cost path as PRIMARY

HUB

1

2

3

45

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8PRI

SEC

SEC

PRI

SECSEC

SEC

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PRI

PRI

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PRIPRI

PRI

SEC

PRI

JOIN

JOIN

JOINJOINJOIN ACK

JOIN ACK


Event-based Fault Detection

> Link layer receives interrupts from physical layer

> Affected ONU reconfigures itself

> Sends out FAULT frames on working port

> FAULT frames trigger reconfiguration at ONUs along downstream path

> HUB updates its topology on reception of FAULT frames

> Secondary Timers-based mechanism as fallback

> Configurable number of timer expiries control fault detection latency

HUB

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8PRI

SEC

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PRI

SECSEC

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PRI

PRI

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PRIPRI

PRI

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PRI

FAULT

FAULT FAULT

FAULT


Frame reflection

> ONUs neighboring a fault reflect frames instead of forwarding

> Such frames are marked as REFLECTED_FRAME

> And returned to the HUB

> HUB marks them as DATA_FRAME and forwards them on alternate path

> Frames reach recipient out of sequence and delayed

> QoS-aware reflection reduces frame loss for high priority traffic during fault recovery

HUB

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PRI

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PRI

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PRI

DATA REFLECTED

REFLECTEDDATA


A Brief Outline





> Conclusions


Background: QoS classes in MUSE

> Borrows from recommendations by ITU and 3GPP

> 4 QoS classes proposed

> Classifies data streams based on two primary differentiators• Elasticity• Interactivity

> Further differentiators (Symmetry, Bandwidth requirement) can be used to construct complete QoS class tree

Elasticity Interactivity Traffic Class App Example

ElasticNon-interactive Background (BKG) File Download

Interactive Interactive (INT) Web browsing

InelasticNon-interactive Streaming (STR) VoD, Radio

Interactive Conversational (CON) VoIP, Gaming


QoS Awareness

> VLAN ID (IEEE 802.1Q) and Priority bits (IEEE 802.1p) encode QoS information in data frames

> ONU has to efficiently multiplex transit data with incoming and outgoing data

> Ring interface queue at ONU classifies and queues frames according to traffic class

> Queuing policy determines scheduling order

> Priority queuing (Non-preemptive) has been adopted

> Has been shown to be a simple and cost-effective solution

> During faults, in case of background class traffic is preferentially dropped in favor of higher priority traffic


A Brief Outline





> Conclusions


Simulation Setup

> Uses NS-2 to simulate network stack using modular components

> Simulation scenarios create worst-case conditions for 100 Mbps links

> Bandwidth allocated per ONU and per traffic class

> Queues dimensioned using estimates from Queuing Theory


Path Restoration Time (PRT) Scaling

> PRT is end-to-end restoration delay

> Plotted against increasing ring size

> Measured with 10-20-40-30 traffic distribution between traffic classes

> In 100-ONU Ring:

• ~20 ms for CON and STR classes

• ~ 32 ms for INT class

• ~60 ms for BKG class


Per-ONU Queuing Delay

> Queuing delay at most heavily-loaded link in a 50-ONU ring

> Measured during normal operation and faults

> Probability distribution for each traffic class plotted

> Only BKG traffic class sees big increase during faults


A Brief Outline





> Conclusions


Conclusions and Future Work

> A QoS-aware link layer protection scheme for access rings outlined

> Centralized network management model exploits natural breakdown of responsibilities between HUB and ONU

> Performance of FARPP in mediating low-latency fault detection and recovery demonstrated

To Do

> Detailed study of operational and dimensioning parameters to optimize operation of FARPP in a real access network

> Translation of user-level fairness into bandwidth allocation scheme at ONUs

Thank You


Existing Protection Schemes and FARPP

Feature ►

Scheme

▼

Cost Speed

Suitability

for

Bursty Traffic

Flexibility Complexity Inter-operability

Optimality for

Access Rings

SDH – <50 ms – – o + –

RSTP + 2 – 30 s + + + + –

RPR – <50 ms + + – + –

EAPS

RFER

T-Metro

o <50 ms + + + o –

FARPP + 20 - 60 ms + + + o +


Fault reporting

> ONUs encode link state information in HELLO and FAULT frames

> Sent out at regular intervals and in response to faults

> HUB can collate reported status to build a complete picture of ring topology

> Topology view and changes can be reported to suitable management layer

HUB

1

2

3

45

6

7

8PRI

SEC

SEC

PRI

SECSEC

SEC

SEC

PRI

PRI

SEC

PRIPRI

PRI

SEC

PRI

FAULT(DOWN:UP)

FAULT(UP:DOWN)

HELLO(UP:UP)

FAULT(UP:UP)


FARPP Message Passing

> FARPP frames carry administrative messages in the ring

> Header format follows Ethernet compliant structure

> Maintains interoperability and minimizes protocol overhead

> VLAN ID (IEEE 802.1Q) and Priority bits (IEEE 802.1p) encode QoS information in data frames

> Header inserted/removed into/from data frames at entry/exit points to/from ring

Dest MAC Addr (48)

Source MAC Addr (48)

FARPP Type (3)

ONU ID (32)

FARPP Protocol Specific Information (32)

Reflected Bit (1) Unused (12)Ethernet Type (16)

Timestamp (64)

qos-aware traffic protection for access rings srivas chennu kai habel klaus-dieter langer

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