Supporting VoIP in IEEE802.11 Distributed WLANs

Supporting VoIP in IEEE802.11 Distributed WLANs Zuo Liu Supervisor: Dr. Nick Filer July 2012 1

Voice VoIP Applications Constant Streaming Traffic Packetize interval usually 10-30 ms 8 160 bytes each packet RTP/UDP Voice Voice Voice Voice Voice Voice Voice Voice Voice Time Sensitive Interactive voice service If round-trip delay is high (e.g. >300 ms), users may suffer in conversation Tolerate to Some Packet Losses Conversation can go on even when some packets are not delivered in time (e.g. 10%) Packet lost concealment techniques 2

Existing Research Infrastructure Unbalanced uplink/downlink traffic My Research Fully distributed Contentions for transmission opportunity VoWLAN Scenarios Real World Mixed Internet 3

Issues for VoIP in IEEE802.11 WLAN 1 Shared Wireless Channel Overhead by contending for transmission opportunity (CSMA/CA) More contentions for VoIP traffic Delay when lost in contention Slot BUSY DIFS Frame SIFS ACK Contention Window Time Traffic Demands 4 Normal (Bursty) Traffic VoIP Traffic Time

Issues for VoIP in IEEE802.11 WLAN 2 Very Low Efficiency over Wireless Channel Control data overhead is too large Payload is tiny for each voice packet Preamble PLCP Header MAC Header Payload CRC IP+UDP+RTP Headers Data 5

micro-seconds (µsec) 2500 2250 2000 1750 1500 1250 1000 750 500 250 0 1363.6 222.22 Estimations 145.5 29.6 18.2 3.7 818 818 818 818 818 818 1500 bytes @ 11Mb/s 1500 bytes @ 54Mb/s 160 bytes @ 11Mb/s Payload 160 bytes @ 54Mb/s Overhead 20 bytes @ 11Mb/s 20 bytes @ 54Mb/s 6 802.11b/g (G.711)160 bytes @ 11Mb/s (G.711)160 bytes @ 54Mb/s (G.729)20 bytes @ 11Mb/s (G.729)20 bytes @ 54Mb/s VoIP Call Capacity 10.37883 11.79802 11.95886 12.16989

Buffer Accumulation Traffic Demands VoIP Traffic Time Outgoing Buffer Load tx tx tx tx tx Time 7

8 2500 2000 1500 1000 500 0 Delay Accumulation Delay Accumulation Observed from Round-Trip Time Measured in a Real Congested IEEE802.11 Distributed WLAN with 12 G.711 calls G.711@54Mb/s Milliseconds 1 38 75 112 149 186 223 260 297 334 371 408 445 482 519 556 593 630 667 704 741 778 815 852 889 926 963 1000 1037 1074 1111 1148 1185 1222 Pakcet IDs

Round Trip Time in Real 802.11 WLAN Milliseconds 9000 8000 7000 6000 5000 4000 3000 Average RTT Measured by VoIP-RTT-Emulator in Real IEEE802.11b/g Distributed WLAN G.711@11Mb/s G.711@54Mb/s G.729@11Mb/s G.729@54Mb/s 2000 1000 0 2 Calls 4 Calls 6 Calls 8 Calls 10 Calls 12 Calls 14 Calls Number of Simultaneous VoIP Calls 9

Packet Delivery Rate within 150 ms 10 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Simulated Congestion Test Normalised Packet Delivery Rate within 150 ms Delay Budget after Network Congestion Happens in Simulated IEEE802.11Distributed WLAN 10 Calls 12 Calls 14 Calls 16 Calls 0 5 10 15 20 25 Time in Seconds After Network Congestion

Auto Cleaning Queue (ACQ) Stale Voice Packets in Outgoing Buffer Not possible being delivered in time Receiver end already played a pseudo sample Wasted transmission opportunity Related Work Dynamic buffer size Drop front/random drop (mainly for TCP) ACQ Actively dropping voice packets older than Giving transmission opportunity to fresh voice packets Compatible with IEEE802.11e Voice (AC_VO) queue Fresh Packet Fresh Packet Fresh Packet Stale Packet Stale Packet 11

ACQ Evaluation 1 Milliseconds 1400 1200 1000 800 600 400 Average Transmission Latency for VoIP Traffic over Simulated IEEE802.11 WLAN G.711@54Mb/s G.729@54Mb/s G.711@54Mb/s + ACQ@100ms budget G.729@54Mb/s + ACQ@100ms budget G.711@54Mb/s + ACQ@150ms budget G.729@54Mb/s + ACQ@150ms budget G.711@54Mb/s + ACQ@200ms budget G.729@54Mb/s + ACQ@200ms budget 200 0 2 Calls 4 Calls 6 Calls 8 Calls 10 Calls 12 Calls 14 Calls 16 Calls Number of Simultaneous VoIP Calls 12

ACQ Evaluation 2 Packet Delivery Ratio within 150 ms 13 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Normalised Packet Delivery Ratio within 150 Milliseconds Delay Budget for VoIP Calls in Simulated IEEE802.11 Distributed WLAN G.711@54Mb/s G.729@54Mb/s G.711@54Mb/s + ACQ@100ms budget G.729@54Mb/s + ACQ@100ms budget G.711@54Mb/s + ACQ@150ms budget G.729@54Mb/s + ACQ@150ms budget G.711@54Mb/s + ACQ@200ms budget G.729@54Mb/s + ACQ@200ms budget 2 Calls 4 Calls 6 Calls 8 Calls 10 Calls 12 Calls 14 Calls 16 Calls Number of Simultaneous VoIP Calls

Small Packet Aggregation for Wireless Networks Routing Protocols NET De-aggregator Aggregator Out-going Buffer LLC IEEE802.11 MAC MAC PHY IEEE802.11 PHY 14

SPAWN Packet En-queue Process Packet In Check rx Address Block for rx Exists in Queue? N Y Check Block Size Create New Block Y Over Max Payload? N Add to Existing Block 15

SPAWN Outgoing Buffer Structure In Out Block3 Block2 Block1 Node B pkt 6 Node B pkt 2 Node A pkt 1 pkt 3 pkt 4 pkt 5 16

SPAWN Block Structure Compatible with IEEE802.11 No modification on frame header and structure No extra operations required below LLC layer IEEE802.11n aggregation (A- MPDU) resulting in new MAC protocol Flexible for Efficiency Variable number of packets Not forced to reach the maximum payload size MAC Packet Payload MAC Header Block Offset 2 Bytes IP Packet 1 Block Offset 2 Bytes IP Packet 2 CRC 4 Bytes 17

SPAWN Evaluation 1 Avg Transmission Latency (Sec) 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Average Transmission Latency for VoIP Traffic over Simulated IEEE802.11 WLAN G.711 using Normal IEEE802.11 G.711 using IEEE802.11 + aggregation G.729 using Normal IEEE802.11 G.729 using IEEE802.11 + aggregation 2 4 6 8 10 12 14 16 18 20 24 26 Number of VoIP Conversations 18

SPAWN Evaluation 2 1 Normalised Packet Delivery Ratio within 150 Milliseconds Delay Budget for VoIP Calls in Simulated IEEE802.11 Distributed WLAN Delivery Rate in 150 ms 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 G.711 using Normal IEEE802.11 G.711 using IEEE802.11 + aggregation G.729 using Normal IEEE802.11 G.729 using IEEE802.11 + aggregation 19 0 2 4 6 8 10 12 14 16 18 20 24 26 Number of VoIP Conversations

Outcomes Conclusions Similar behaviour for VoIP over distributed and infrastructure WLANs Delay accumulation after congestion ACQ resolves the delay accumulation SPAWN effectively increases the network efficiency Compatible with IEEE802.11a/b/g MAC and IEEE802.11e Future Work ACQ and SPAWN in real devices (seeking partners) Dynamic for ACQ Multicasting SPAWN Multi hops, multi flows, multi traffic types, etc. 20

Thank you! & Questions? liuza@cs.man.ac.uk 21