When Priority Resolution Goes Way Too Far: An Experimental - - PowerPoint PPT Presentation

When Priority Resolution Goes Way Too Far: An Experimental Evaluation in PLC Networks

Cristina Cano and David Malone 09/06/2015

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Motivation

In-house Power Line Communications Standards: Homeplug/Homeplug AV/IEEE 1901 Qualcomm Atheros reports 100M PLC devices shipped Research efforts focused on the physical layer PLC MAC is relatively unexplored MAC like IEEE 802.11, but:

Deferral counter Strict priority resolution scheme Negotiated tone map Large aggregated frames

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Priority Resolution

Definition of 4 CAs CA3/CA2 and CA1/CA0 share Wi (BO) and Mi (DC) values Strict prioritisation through Priority Resolution Slots (PRS)

TRANSMISSION FRAME FRAME TRANSMISSION BACKOFF PRS1 PRS0 ACK CIFS RIFS t

...

But, only present after successful transmissions!

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Testbed Setup

Devices

Zyxel PLA4215 PLC adapters with INT7400 chipset Connected via an UPS unit Attached to the Gigabit Ethernet port of Soekris boxes

Tools:

Iperf:

Generate traffic/measure per-second throughput

Faifa

Count channel accesses (Jain’s Fairness Index)

Spectrum Analyser

Get more insight on the transmissions on the channel

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PRS?

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Lower Priority Starvation

Two saturated stations in different CAs. How strict is the prioritisation?

20 40 60 80 100 120 140 160 180 200 50 100 150 200 250

CA3

• av. 179.3564
• min. 0
• max. 203.0952

SCA3 [Mbits/s] Frequency 20 40 60 80 100 120 140 160 180 200 500 1000 1500 2000 2500

CA2

• av. 1.2075
• min. 0
• max. 181.5979

SCA2 [Mbits/s] Frequency

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Higher Priority Contention

3 CA3 Stations. What???!!!

20 40 60 80 100 120 140 160 180 200 500 1000

CA3

• av. 58.4822
• min. 0
• max. 197.1211

SCA3 [Mbits/s] Frequency 20 40 60 80 100 120 140 160 180 200 500 1000

CA3

• av. 44.3043
• min. 0
• max. 200.4139

SCA3 [Mbits/s] Frequency 20 40 60 80 100 120 140 160 180 200 500 1000

CA3

• av. 48.2669
• min. 0
• max. 199.2262

SCA3 [Mbits/s] Frequency

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Higher Priority Contention

Oscillatory Behaviour!

50 100 150 200 250 300 20 40 60 80 100 120 140 160 180 200 t Throughput [Mbits/s]

Tone map information is sent at CA2!

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Conclusions

Outcomes

Lower-CA traffic

Suffers from starvation High variability (aggregation and buffer management)

Higher-CA flows

Oscillatory behaviour

Some plausible solutions

Reserved priority for control messages Police/Shape higher classes Limit variability of aggregation

JSAC Issue on PLC in Networking Ecosystem: Submission 1 July 2015.