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Voice Over Wireless Lans and Fixed Mobile Convergence Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence Voice over Wireless LANs and Fixed Mobile Convergence Michael F. Finneran dBrn Associates, Inc. (516) 569-4557 [email protected] Program Objectives • Quickly review the standards and technologies used for WLANs and the major applications to be served • Introduce the major quality issues and performance objectives for VoIP • Describe WLAN radio links and protocols and how they will impact WLAN voice quality • Review the major issues in supporting WLAN voice including QoS, battery life, hand-offs, and security • Introduce and define fixed mobile convergence and mobile unified communications • Describe the range of solutions that are being proposed • Provide some general guidelines for pursuing VoWLAN implementations 2 © dBrn Associates, Inc. 1 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence Program Outline Section 1: WLAN Fundamentals Review Section 2: Voice over Wireless LANs – VoIP Quality Issues and Performance Objectives – Protocol issues and QoS Options – Security, Handoffs, Battery Life, Call Capacity Section 3: Fixed Mobile Convergence – Carrier Controlled versus Enterprise Controlled FMC Section 4: Conclusion 3 My background… • Independent consultant, writer, and industry analyst specializing in wireless and mobility with over 30-years experience • Wrote: Voice over Wireless LANs- The Complete Guide (Elsevier, 2007) • Spoken at numerous industry conferences including InterOp, Mobile Business Expo, VoiceCon, ComNet, Wall Street Tech Assn. • Chair the Wireless and Mobility Track at VoiceCon • Partner in Telecom+UC Training: Presented over 2000 training programs in the US, Europe, Asia, Africa, and Latin America • Published over 200 columns and articles in Business Communications Review, Computerworld, ACUTA Journal… • Blog regularly on mobility topics for NoJitter.com and UCStrategies.com 4 © dBrn Associates, Inc. 2 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence Section 1 WLAN Fundamentals 5 Wireless LAN Organizations • IEEE 802.11 • Wi-Fi Alliance (www.ieee802.org/11/ ) (www.wi-fi.org) – Defines implementation of – Develop Wireless IEEE 802.11 standards LAN Standards – Develops test suites to – Multiple Elements insure multi-vendor compatibility – Ongoing activity – Certifies products – Develops interim “standards” (WPA, WMM, Draft N) 6 © dBrn Associates, Inc. 3 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence Typical WLAN Configuration 1. Basic Service Set (Also called “Infrastructure Mode”) Enterprise Configuration Residence Configuration (Indoor Cellular Network) Wireless Router LAN Switch Access Point ADSL/Cable Modem 50 Packets per second in and out per voice connection Wired Users Access Point Extended Service Set (ESS) Multiple APs, Same Network Name 7 Basic Characteristics of WLANs • Maximum Range: Nominal 100 meters (100 feet is more typical) • Operates in Unlicensed Radio Spectrum – No protection from interference (Other WLANs, Bluetooth, Cordless phones) – Interference causes stations to reduce transmission rate! • Maximum Network Capacity: 11 M or 54 Mbps • Capacity/Range Relationship: – Actual bit rate depends on distance, obstructions, and interference • Half Duplex/Shared Media : – Several users sharing one channel. Slower users effect the performance of higher speed users! • Transmission Acknowledgements – Receiving station returns an ACK message to confirm receipt • Overhead: – Reduces throughput to 50% of line rate 8 © dBrn Associates, Inc. 4 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence WLAN Voice Applications • WLAN Voice Only: Task Workers – Health Care, Big Box Retail, Warehousing • WLAN/Cellular Fixed Mobile Convergence • Carrier Provided UMA – T-Mobile’s Unlimited HotSpot Calling® • Remote Access Hot Spot Calling – Skype on the iPhone, BlackBerry 9 Comparison of Radio Links Channel Maximum Fallback Frequency Signal Standard Bandwidth Rate Rates Band Encoding 802.11 22 MHz 2 Mbps 1 Mbps 2.4 GHz Direct Sequence (1997) Spread Spectrum 802.11b 22 MHz 11 Mbps 5.5 M, 2 M, 1 Mbps 2.4 GHz Complementary (1999) Coded Keying 802.11a 20 MHz 54 Mbps 48M, 36M, 24M, 5 GHz OFDM (1999) 18M, 12M, 9M, (5 GHz Band) 6Mbps 802.11g 20 MHz 54 Mbps 48M, 36M, 24M, 2.4 GHz OFDM (2001) 18M, 12M, 9M, 6M, (2.4 GHz Band) 802.11b: 11M,5.5M, 2M, 1Mbps 802.11n 20 MHz/ 289 Mbps/ Multiple 2.4 GHz/ OFDM with (Draft 2.0) 40 MHz 600 Mbps 5 GHz 4-Chain MIMO 10 © dBrn Associates, Inc. 5 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence 802.11n For Voice • No 802.11n voice devices today, and none are expected for a few years to come • MIMO transmission requires multiple radio transmitters and a processor-intensive receiver; Battery Drain! • There is a plan to have a one-chain (i.e. one rather than multiple transmit radios) for 802.11n voice devices – Maximum transmission rate of 72 Mbps on a 20 MHz channel (versus 54 Mbps with 802.11a or g) – Apple is apparently considering it for the next generation iPhone – Vocera doesn’t even support 802.11a (5 GHz band) because of battery challenges 11 12 © dBrn Associates, Inc. 6 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence Section 2 Voice over Wireless LANs 13 Section Objectives • Describe the quality issues in packet voice • Overview the operation of the CSMA/CA protocol • Describe the QoS capabilities of 802.11e/WMM as well as the vendor proprietary alternatives • Describe the other issues to be addressed in WLAN voice: • Handoffs • Security • Battery Life • Define the voice call capacity of a WLAN 14 © dBrn Associates, Inc. 7 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence Quality Issues in VoIP 1. Voice Quality . Factor of voice coding and dropped/errored packets 2. Transit Delay . Maximum 150 msec one-way to maintain conversational flow . Uncongested WLAN adds 20- to 30-msec additional delay 3. Jitter (Variation in delay packet-to-packet) . Left untreated, renders voice unrecognizable . Real-time Transport Protocol (RTP) process used to treat jitter Comparison of Voice Coding Options Codec Bit Rate Bit Rate with Encoding Loss IP Headers Time Tolerance G.711 64 Kbps 80 Kbps .25 msec 10% G.726 32 Kbps 48 Kbps .25 msec 5% G.729A 8 Kbps 24 Kbps 25 msec 1% G.723.1 5.3 Kbps 21.3 Kbps 70 msec 1% 15 Real-time Transport Protocol (RTP) • Isochronous Transport – Transmission service that provides consistent delay • Real-time Transport Protocol (RTP) – Adds time stamps and sequence numbers to voice samples – Receiver buffers frames and reestablishes timing continuity • Trade-offs in Receive Buffering – Too Long: Adds to transit delay- Major complaint – Too Short: Packets received too late are dropped • Adaptive jitter buffers preferred- Adjust to compensate for actual jitter – QoS provides consistency (i.e. less jitter) minimizes buffering Time Stamped Packets Jitter (50 Packets per second) Packet Network Buffer Variable Delay Isochronous Isochronous Jitter 16 © dBrn Associates, Inc. 8 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence WLAN MAC Protocol: CSMA/CA • CSMA/CA Distributed Control Function (DCF) – Stations collaborate to avoid collisions • "Sending While Deaf" – WLAN stations cannot sense collisions, and transmissions require acknowledgements • Basic Definitions: – Inter-Frame Spacings: Waiting interval before sending once the channel is idle. • DIFS: Waiting interval to send a frame or restart a back-off timer • SIFS: Waiting interval to send an ACK, CTS, or Subsequent Fragment • PIFS: Waiting interval to seize the channel for PCF mode (rarely used) • AIFS: Different waiting intervals for different traffic priorities (802.11e/WMM) – Transmissions with shorter waiting intervals have higher priority. 802.11 Inter-Frame Spacing Intervals Interval Computation 802.11b or b/g 802.11a or g SIFS -- 10 µsec 10 µsec PIFS SIFS + 1 Time Slot 30 µsec 19 µsec DIFS SIFS + 3 Time Slots 70 µsec 37 µsec 17 CSMA/CA Definitions • Contention Window (CW)/Back-off Window – The randomizing element in the DCF Inter-Frame Spacing – The contention window comes into play in two instances: • If the channel is busy when a station tries to access it • If a station has tried unsuccessfully to send a frame – Counter increases with each unsuccessful attempt (Next 2n-1 step) Contention Window Ranges 802.11b or b/g 802.11a or g CWMIN CWMAX CWMIN CWMAX 31 1023 15 1023 • Network Allocation Vector (NAV): – A timer in each station during which it will not send (i.e. virtual carrier sense). Used to reserve transmission time on the channel. 18 © dBrn Associates, Inc. 9 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence CSMA/CA Operation AIFS Time Periods in 802.11 Access DIFS Contention PIFS SIFS DIFS Window SIFS Data ACK Data ≤2730-octets 16-octets ≤2730-octets Back-off Time Slots Waiting Intervals: (802.11b- 20µsec 802.11a/g- 9 µsec) DIFS- DCF Inter-Frame Spacing (Sending Frames) SIFS- Short Inter-Frame Spacing (Sending ACKs, CTS messages, or Fragments) PIFS- PCF Inter-Frame Spacing (Enter PCF Mode) AIFS- Arbitrated Inter-Frame Spacing: Defined in IEEE 802.11e EDCA- Four different values for different priority levels (Access Categories). 19 IEEE 802.11 Message Format Frame W F PLCP M Frame Body C Header M S Physical Layer Frame Header WMMHeader Frame Body Frame Check Convergence Part (≤30-octets) (2-octets) (0 to 2312-octets) Sequence (24-octets) (4-octets) G.711 (PCM) Voice: 200-octets Sent at the lowest bit rate G.729a Voice: 60-octets Physical Layer Convergence Part (PLCP) Header (Part of Layer 1): o Synchronization (128-bits): 1/0 Pattern o Start Frame Delimiter (16-bits): Hex F3 A0 o Signal (8-bits): Data rate in 100 Kbps increments o Service (8-bits): Unused o Length (16-bits): Time required to transmit in microseconds o Frame Check Sequence (16-bits): Error check 20 © dBrn Associates, Inc. 10 Voice over Wireless LANs and May 18, 2009 Fixed Mobile Convergence DCF Operation- Idle Channel 1. Station determines the channel is idle – Senses no activity on the radio channel – Network Allocation Vector = 0 2.
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