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JSIIntroduction to WINDECT Project

Marjan Spegel1, Barry Cheetham,2

1 Josef Stefan Institute, Ljubljana, Slovenia2. Computer Science, Manchester University, M13 9PL, UK

‘Specific targeted research & innovation’ project

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JSIAgenda of Presentation

• Motivation• Overview• Research issues and results• Technology development• Testbed, testing• Conclusions

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JSIMotivation

• Contribute to fulfilment of a major EU target for optimized access to IP-based services in “Broadband for all”

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JSIAim of WINDECT:To advance 'state of the art' of voice telephony overwireless LAN & propose extensions to existing standards as applied to converged voice/data enterprise networks.

Objectives:• Extend the DECT standard for cordless telephony to include communication over IEEE802.11 WLAN.

• Provide high quality of voice, maintained during hand-over, good coverage with error correction & concealment and low power consumption.

• Prototype and test a ‘WINDECT’ demonstrator.

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JSIWINDECT Approach

• Graft upper layers of DECT stack onto lower layers of WLAN stack to support• isochronous comm of voice packets during CFP• make-before-break handover.

• Optimize voice quality, coverage, and power autonomy.• Rely on WLAN standards, propose extensions.• Develop & prototype components (ICs, boards, mobile

phone, access points).• Build voice-quality test-bed and demonstrator.• Test and field-try the demonstrator.

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JSI

• Well-proven DECT protocols for voice services

• Voice&data transmitted over 802.11a WLAN

• Use of WLAN 'QoS' standard (HCCA of 802.11e)

• Promise of DECT-grade QoS

• Efficient use of network resources

• use of voice processing to enhance services

• Seamless hand-over & load balancing.

WINDECT Advantages

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JSIProblems

• How to implement WINDECT solution?• How to prototype and test the demonstrator?• How to optimise its performance ?• How to reconcile with standards?

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JSIHandover

• True seamless - make before break – handoverwith zero packet loss and load balancing isessential for professional voice services.

• WINDECT phone must be able to talk to two APsat the same time yet WLAN QoS standards stick to break-before-make.

• More on WINDECT solution to this problem in the presentation following this one.

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JSIVoice Quality

• How is voice quality perceived and defined?• Voice quality depends mainly on packet loss,

delay and jitter.• Voice quality optimization• Coding for forward error correction• Packet loss concealment• Use of damaged packets

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JSIEffect of packet loss

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0 1 2 3 4 5% loss (20 ms packets)

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Effect of packet loss on MOS scores

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JSIVoice Optimisation• Wired IP networks are designed for rare package damages.

• Packet loss concealment (PLC) employed for wired VoIP.

• WLAN standards seem to obey same principles.

• In VoWLANs, damaged packets are common (after FEC).

• Yet WLAN standards prohibit use of damaged packets!

• Can use of damaged packets raise voice quality more than PLC?

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JSI(a) Without modifying standard

Ignore FCS and put CRC over control bits in body only.

• If also CRC over body fails, discard the packet else use 'body‘ for voice processing.

• Apply majority voting for CRCs for retransmissions.

(b) With modifying standard

• Replace half-rate convolutional coder & Viterbi decoderand use selective bit-error protection & detection.

• Saves power also

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JSI

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

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Eb/N0 = 3.000000 dB

G711 with zero-insertion PLC

Effect of 20ms Packet Loss on Waveform

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JSI

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

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G711 with interpolation PLC

Packet Loss Concealment with Interpolation

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JSICoverage

• Good RF signal coverage is a very critical issue for professional mobile voice services

• More in a subsequent presentation

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JSIPower Saving

• Bringing power consumption of present VoWLAN phones down to DECT standards is vital for the success of WINDECT.

• Need standby time of about 200 h & talk time of about 20 h, i.e. improvement by almost an order of magnitude.

• More on this later

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JSIMAC/PHY Chipset

Full IEEE802.11a functions• Ad-hoc and infrastructure

modes• DCF, PCF, and RTS/CTS• Fragmentation, Encryption

and Authentication• Prioritized contention and

contention-free modes• Strictly-ordered and

reorderable multicastservice classes

• Power management

WLAN components:• MAC processor MIPS

with HW accelerator• Flash 8MB, RAM 1 MB• Cardbus or PCMCIA i/f• UART and JTAG for

programming• Baseband Processor• 5GHz analog frontend• Now also single-chip

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JSIWINDECT-Enabled WLAN Modules

• RF link emulator MAC module board version designedfirst to replace PHY layer and RF i/f with digital link for stable PHY parameters and repeatable H/O conditions for controlled SW development and testing.

• WLAN modem modules with PCMCIA i/f designed forWINDECT phones

• WLAN modem modules with MiniPCI/CardBus interface designed for WINDECT APs

• Improved run of ICs and modules in progress now• WINDECT MAC Protocol + Linux firmware (dual-

channel) driver provided

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JSIWLAN MAC/PHY link emulator

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JSIWINDECT WLAN module

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JSIWINDECT Mobile Phone

• No COTS WLAN 802.11a mobile phone yet• PDA-based WINDECT phone emulation• WINDECT WLAN module• iPAQ HP5550 PDA with Linux• Voice Processing SW• HCI for basic soft-phone functions

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JSITesting the demonstrator

• WLAN testing hard, VoWLAN in particular. • Lack of standardized methods and tools• IEEE802.11t for test methodology under development• Metrics-based testing limited to VQT / ITU-T• MOS, R, delay, jitter, packet loss measured• Roaming emulated by RF attenuation• SW-only tools for WINDECT test-bed• Test-bed built and undergoing improvements• Limited field-trial demonstrator in a hospital.

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JSITest-Bed Configuration

• Voice quality analysis by Opera SW• 4 HW VoIP phones (2 SIP, 2 H.323)• Several VoIP soft-phones• 1 notebook soft-phone (+2 WINDECT phones)• 4 WLAN802.11a APs (+2 WINDECT APs)• Several PCs (for voice signal play/rec, test management,

VQT, traffic generation)• RF signal attenuation equipment• Dedicated test-setup LAN backbone• Connection to enterprise LAN backbone&Internet

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JSIAd-Hoc VoWLAN VQ Test-Bed

RF isolation RF isolation

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JSIBackground Traffic Generation

RF isolation RF isolation

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JSIVQT Parameter Space

• VoIP phones (HW, SW) and APs• Signalling protocol (SIP, H.323)• Media selection (LAN, WLAN, LAN/WLAN)• Data rate selection (54MHz, 6MHz)• QoS settings (on AP, switch/router)• Voice traffic loading (1 to 20 channels)• Burst traffic loading• Handover execution• RF signal strength variation• Programmed test scenarios

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JSITesting QoS Off/On at 1-20 VoIPStreams and 1 Bkgr. Data Stream

PESQ Results w ith QoS Disabled and QoS Enabled

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PESQ MOS G.107 Rating Delay Avg [ms]

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JSISummary of Test Results

• HW VOIP SIP phones have automatic buffer length adjustments• VQ good until consecutive lost packets occur• VQ drops fast when no free bandwidth left (multiple errors)• Delays:

• increase with RF interferences (delayed or missing RTP packets)• increase stepwise after end of detected silence period, decrease

gradually during error free RTP transfer• slowly periodic variation when available bandwidth falling to

minimum required bandwidth (due to asynchronous clocks in VoIPphones)

• decrease sharply when remaining bandwidth drops close to or below required bandwidth (terminal buffers never fill up)

• QoS makes difference has greater influence when also many low priority data streams

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JSITests for 0-20 RTP Streams

PESQ Results for 20 Repetitions with 0 to 20 Background VoIP Streams

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Sequence No. of PESQ Measurement

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JSITests With RTP and Burst Traffic

80 Repetitions for 0 to 20 RTPs and Burst Traffic (1 stream), no QoS

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PESQ MOS Delay Avg [ms] Linear (PESQ MOS)

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JSITesting with QoS Enabled

20 Repetitions for 0 to 20 backround VoIP streams and Burst Traffic (1 stream), QoS enabled

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PESQ MOS Delay Avg [ms] Linear (PESQ MOS)

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JSISpread of Results

• HW Phones, SIP, no QoS, 1-20 voice ch., 6Mb, FTP traffic, 4 streams avg.1,5Mb

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PESQ MOSPESQ MOS SPEECHPESQ MOS BACKGROUNDG,107 RatingDelay Avg [ms]

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JSITesting Problems

• Results for given VoWLAN configuration• For ideal traffic conditions MOS above 4.0 but

delays bad• Widening spread of results with load increase• Oscillations of VQ of increasing period and

amplitude• Only few handover test made so far, delays in

seconds• Timing control, repeatability of H/O conditions • Test-bed undergoing improvements.

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JSIConclusions

• DECT-grade voice service on WLAN realistic• WINDECT HCCA mode of IEEE802.11e worldwide first?• Seamless make-before-break handover on WLAN solved• Power consumption reduced significantly• Voice quality improved at edges of ideal conditions by

• packet loss concealment by extrapolation. • processing and use of damaged voice packets.

• Extensions to DECT and WLAN standards in preparation• Test-bed for VoWLAN and WINDEC voice quality testing

integrated, but needs improvement.

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JSIAcknowledgementsThe partners on WINDECT gratefully acknowledge the project would not have been possible without the supportof:

• European Commission,

• Swiss Federal Office for Education and Science,

• Slovenian Ministry of Science

• Prevent Global Corporation, Slovenj Gradec, Slovenia

Reference:http://www.windect.ethz