©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 1
VoIP via IEEE 802.11 “VoWLAN”
EETS 8313: Internet TelephonySami Alshuwair
Agenda
Evolution of Enterprise Telephony
Why Deploy Vice over Wireless LAN
VoWLAN Market Trends
VoIP Challenges and Solution
VoWLAN Challenges and Solution
WLAN System Architectures Considerations
26 April 2008
WLAN System Architectures Considerations
VoWLAN Alternatives
Recommendations
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 2
Evolution of Enterprise Telephony From circuit-switched to packet-switched
Traditionally private branch exchange (PBX)–Analog/digital phones, proprietaryg g p p p y
Internet Protocol PBX began a new era–Converge voice/data, IP-based enterprise network
Session Initiation Protocol (SIP) emerges
VoIP extends coverage to include WLANs
36 April 2008
g–SIP-based, VoWLAN phones provide comm.
Fixed mobile convergence solution emerging–Seamless handoff between mobile cellular and Wi-Fi
networks
Why Deploy VoWLAN? Clearly understand your needs
Reduce mobile cellular minutes– VoWLAN conversations are “free” calls
Improve in-building voice coverage– Deploy more access points to improve coverage
Integrate mobile & enterprise telephony systems
When cellular phones are not an option
46 April 2008
p p– VoWLAN signals use 2.4 GHz or 5 GHz bands
Provide wireless foundation for unified comm. – Voice, video, IM, all over common IP network
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 3
VoWLAN Market Trends Growing becoming pervasive
WLAN phone market reach $3.7B by 2009$ .7 by 9
Integrate enterprise Telephony + mobility
Vendors integrate their voice solutions
Source: Infonetics Research
56 April 2008
Vendor consolidation
IEEE 802.11 tech. improving
Mobile cellular tech. improving Source: Gartner (November 2007)
[1] [2]
How VoWLAN Solutions Can Reduce Cost and Improve Productivity Dual-mode “Smart Phones”
Enterprise: TOC Comparison of Cell Phones and Dual-Modes
–Market forces employees to be more productive
Healthcare:–Critical to reach the
Source: Cisco 2006
Cisco ROI Model Assumption:
Si i d
66 April 2008
right person immediate
Warehouse/retail:–Effective customer
services
Six-year period
1000 users; 40% mobile users
US tariff rates
Deploy Cisco Unifies wireless Solution
Cisco Dual Mode net price $290[3]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 4
VoIP Protocol Stack Header Overhead
Vocoder Frame
Vocoder FrameRTP
Vocoder FrameRTPUDP
Vocoder FrameRTPUDPIP
1220IPv4
8
Vocoder FrameRTPUDPIPMAC
Vocoder FrameRTPUDPIPMACPHYVariable based on
coder used34
802.1115 – 24802.11b
Codec Information Bandwidth Calculations
Codec & Bit Rate (Kbps)
Codec Sample Size
(Bytes)
Codec Sample
Interval (ms)
Mean Opinion
Score (MOS)
Voice Payload Size
(Bytes)
Voice Payload Size
“Pctz D” (ms)
Packets Per Second (PPS)
Bandwidth MP or FRF.12 (Kbps)
Bandwidth w/cRTP MP or FRF.12 (Kbps)
Bandwidth Ethernet (Kbps)
G.711 (64 ) 80 Bytes 10 ms 4.1 160 Bytes 20 ms 50 82.8 Kbps 67.6 Kbps 87.2 Kbps
Codec Comparison
76 April 2008
•Compressed Real-Time Protocol (cRTP) reduces the IP/UDP/RTP headers to 2 or 4bytes (cRTP is not available over Ethernet). •6 bytes for Multilink Point-to-Point Protocol (MP) or Frame Relay Forum (FRF).12 Layer 2 (L2) header.•G.711 (64) = 80 bytes * 8 bit * 10ms = 64kbps
G.729 (8) 10 Bytes 10 ms 3.92 20 Bytes 20 ms 50 26.8 Kbps 11.6 Kbps 31.2 KbpsG.723.1 (6.3) 24 Bytes 30 ms 3.9 24 Bytes 30 ms 34 18.9 Kbps 8.8 Kbps 21.9 KbpsG.723.1 (5.3) 20 Bytes 30 ms 3.8 20 Bytes 30 ms 34 17.9 Kbps 7.7 Kbps 20.8 KbpsG.726 (32) 20 Bytes 5 ms 3.85 80 Bytes 20 ms 50 50.8 Kbps 35.6 Kbps 55.2 KbpsG.726 (24) 15 Bytes 5 ms 60 Bytes 20 ms 50 42.8 Kbps 27.6 Kbps 47.2 KbpsG.728 (16) 10 Bytes 5 ms 3.61 60 Bytes 30 ms 34 28.5 Kbps 18.4 Kbps 31.5 Kbps
http://www.cisco.com/warp/public/788/pkt-voice-general/bwidth_consume.html
[4]
VoIP Bandwidth Calculation per CallFor example, the required bandwidth for a G.729 call (8 Kbps codec bit rate) with cRTP, MP and the default 20 bytes of voice payload is:–Codec bit rate = codec sample size / codec sample Codec b e codec s p e s e / codec s p e
interval–Total packet size (bytes) = (MP header of 6 bytes) +
(compressed IP/UDP/RTP header of 2 bytes) + (voice payload of 20 bytes) = 28 bytes
–Total packet size (bits) = (28 bytes) * 8 bits per byte = 224 bits
86 April 2008
–Voice payload size = 20 bytes (default voice payload) * 8 bits per byte = 160 bits
–PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps –Bandwidth per call = voice packet size (224 bits)
* 50 pps = 11.2 Kbps[4]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 5
VoIP Challenges and SolutionsBandwidth Management:–Challenge: loaded network/SW with adv. encoding –Solution: load balancing, call admiss. control
Packet Loss:–Challenge: RTP: packet loss < 3%–Solution: Packet loss concealment & redund. algor.
Latency: –Challenge: One way latency “G.113” <= 150 mSec
96 April 2008
g y y–Solution: 802.11e/WMM + wired QoS mechanism
Jitter:–Challenge: Packet arrival time <= 30 mSec–Solution: Jitter butter, 802.11e/WMM + wired QoS
802.11 WLAN “de facto” Standards
Standard Op. Frequency
PHY MAC Throughput (Typ)
Max Raw Rate
Service Interference
IEEE 802.11a 5 GHz OFDM CSMA/CA 23 Mbit/s 54 Mbps-Cordless phone -Amateur Radio -Aeronautical Radio -Navigation
106 April 2008
IEEE 802.11b 2.4 GHzDSSS, CCK CSMA/CA 4.3 Mbit/s 11 Mbps
-MW Oven -Bluetooth Device -Amateur Radio
IEEE 802.11g 2.4 GHz OFDM, CCK
CSMA/CA 19 Mbit/s 54 Mbps -Same as 802.11b
IEEE 802.11n (Draft 2.0)
2.4 GHz & 5 GHz
OFDM, CCK
CSMA/CA 74 Mbit/s 248 Mbps -Same as 802.11b/11a
[5] [6]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 6
802.11 Medium AccessMAC Frame Types:–Data–Control: RTS, CTS & ACK–Management: Beacon
Distrib. Coord. Func. (DCF)–Uses a CSMA/CA algorithm –Senses the medium first–If it is idle for DIFS amount of
DCF Method Signal Flow
116 April 2008
If it is idle for DIFS amount of time, the frame transmitted
–Otherwise a backoff time B is randomly in the interval [0, CW]
–Has no priory “best effort”
SIFS = Short Interframe Space. 16us for .11a and 10us for .11b/gDIFS = DCF Interframe Space = SFIS + 2 x Slot Time
PIFS = PCF Interframe Space = SIFS + Slot Time
Slot Time = 20us for .11b & 9us for .11a , .11g is 9us when all STA high-speed otherwise 20us Backoff = Random * Slot Time
[7]
802.11 Medium Access Cont.
Point Coordination Function (PCF)–Contention-free frame transfer–Single Point Coordinator (PC) controls access to the g ( )
medium. AP acts as PC.–PC transmits beacon packet when medium is free for
PIFS time period. PCF has higher priority than DCF (PIFS < DIFS)
–PCF not used b/c not ideal for real-time traffic:U hi d f h ffi l d i
126 April 2008
Unachieved performance when traffic load increas. Polling schemes prolong the delay in WLAN
PCF Method Signal Flow
[7]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 7
IEEE 802.11e “QoS” Overview
Hybrid Coordination Function (HCF) combines polled and CSMA/CA
AC0 AC1 AC2 AC3Single Queue
High Priority Low Priority
802.11e WLAN Station
Legacy 802.11
Legacy Station
802.11e EDCA
1 2 0 BE
BKBK
BE
BKBK
BE
BKBK
BE
BKBK
channel access
Enhanced DCF Channel Access (EDCA)–Contention based–DiffServ-Service like
SchedulerVirtual Collision Handler
Backo
ffAIF
S[0
]BO[0
]
Backo
ffAIF
S[1
]BO[1
]
Backo
ffAIF
S[2
]BO[2
]
Backo
ffAIF
S[3
]BO[3
]
Transmission attempts
Backo
ffSIF
S
03 4 5 6 7 Voice
VoiceVideo
BE
Video
VoiceVoiceVideo
BE
Video
BE
VoiceVoiceVideo
BE
Video
BE
VoiceVoiceVideo
BE
Video
BE
136 April 2008
–DiffServ-Service like–Traffic can be classified
into 8 different classes –Each station has 4 Access
Categories (AC)
p
DIFS/AIFS
Next Frame
Contention Window
Backoff SlotsDefer Access
BusyMedium
AIFS (2)
AIFS (1)
AIFS (0) = DIFS
PIFS
SIFS
AIFS: ArbitrationInterframeSpacing
DIFS: DistributedInterfame Spacing
PIFS: PointInterframeSpacing
SIFS: ShortInterfame Spacing
VoWLAN
[8] [9]
IEEE 802.11e “QoS” Overview Cont.
• HCF Controlled Channel Access (HCCA)–“InServ-service like”–Specify time interval for STA “TDM-service like”Specify time interval for STA TDM service like–Can start polling period at any time
Automatic Power Save Delivery (APSD)–Reduces power consumption 50% to 80% in active
mode.
146 April 2008[10] [11]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 8
VoWLAN Security
Wired Equivalent Privacy (WEP) –40 bit – 128 bits key–Authentication easy to break
L2 & L3 Handover Procedure for VoWLAN
y802.11i:–802.1x: “authentication”
Varies; vendors preference –TKIP known as WPA–CCMP known as WPA2
156 April 2008
–CCMP known as WPA2 Increased overheadMore processing time/delay
–Hard to implement in inter-domain handover
TKIP = Temporal Key Integrity Protocol WPA = WiFi Protected Access CCMP = Counter Mode with Cipher Block Chaining
Message Authentication Code ProtocolPMK = Pairwise Master KeyPTK= Pairwise Transient Key
[7] [8] [10]
VoWLAN Security Cont. VLANs:
SSID: DataSecurity:
AP Channel:SSID “Data” = VLAN 1
802.1Q WiredNetwork w/VLANsVLAN Prevent:VLAN Prevent:
--Toll fraudToll fraud--Denial of Service (DoF) attacksDenial of Service (DoF) attacks--Eavesdropping & InterceptionEavesdropping & Interception
Security: PEAP + AES
SSID Data = VLAN 1
SSID: VoiceSecurity: LEAP + WPA
SSID “Voice” = VLAN 2SSID “Visitor” = VLAN 3
166 April 2008
SSID: VisitorSecurity: Open
SSID = Service Set ID, PEAP = Protected Extensible Authentication Protocol, AES= Advanced Encryption Standard,LEAP= Lightweight Extensible Authentication Protocol
[13] [14]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 9
VoWLAN Handover/Roaming WLAN AP covers 50m2 to 300m2 freq. handover
< 50ms recommended, but >200ms packet lost
L 2 “V” h d f AP t AP / IPLayer 2 “V” handover: from AP to AP w/same IP
Layer 3 “H” handover: from AP to AP w/new IP– SIP or MIP used to resume voice session
With 802.1x & .11i association takes 300-500msInclude scan joining new ch authen & associat
176 April 2008
–Include scan. joining new ch, authen. & associat.–Passive scan during active VoIP to reduce scan time–Establish secure key introd. delay “four handshake”
802.11r fast handover: cache context “neighbor graph” [7] [8] [12]
VoWLAN Fast Secure Roaming Layer 2 “Vertical”- Same IP Subnet
CentralAuthentication
ServerSiSi
WAN LinkWAN Link*WDS
186 April 2008
*WDS = Wireless Domain Server (Local Authentication Server + Access Point)[13] [14]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 10
Subnet A
1. Client associates with AP and receives an IP address, optionally using WPA (802.1x) or VPN for security 3 4 5
VoWALN Fast Secure Roaming Layer 3 “Vertical”-Different IP Subnet
y
3. Client roams to new subnet or roams out of radio coverage and returns
4. Client associate with new AP
3 4
GR
E Tu
nnel
168.1.1.1
Corporate Network
2. Control “B” create client database: MAC & IP, security context & association, QoS, etc.
5
196 April 2008
Radius, LDAP,Active Directory,
NT Domain Server
CorporateServersSubnet B
4. Client associate with new AP & controller. Client database is copied to new controller
168.1.1.1 1 25. New controller recognizes roaming event and provides client with the same initial IP address
GRE = Generic Routing Encapsulation is a tunneling protocol [13] [14]
VoWALN Capacity
What is the max. number of voice call AP can support?–Ask your vendor
Transmission rate “throughput”
Voice packet payload length depended on encoding
Capacity enhancement solutions: –Enhanced air access MAC “HCF”
i l ll k i
206 April 2008
–Virtual cells “Meru Network propriety”–Header compression –Frame aggregation
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 11
VoWALN Capacity Cont.Throughput Effect:80.11b is around 6Mbps & 802.11a/g around 26/17Mbps
802.11b WLAN UDP-based Throughput measurement by Arranz et al
VoIP capacity can not be estimated based on raw data throughput:–Assuming 10Kb/s voice source, theoretical capacity
of 802.11b is 11Mbps/10Kbps =1100 → 550 two-way VoIP sessions.
216 April 2008
way VoIP sessions.–In practice only a few VoIP users can be supported in
802.11b!–Low payload to overhead ratio for short VoIP packets and inherent inefficiency in 802.11 MAC
[7]
VoWALN Capacity Cont.
Packet Interval & Vocoder Effect:
M d l 30
Max Number of VoIP Connection using 802.11b and Different Packet Intervals
Many vendor select 30ms
Voice call increase w/packet interval increase
VoWLAN 802.11a 5x than VoWLAN 802.11b
Max Number of VoIP Connection using 802.11a and Different Packet Intervals
226 April 2008
Larger packatization interval more end-to-end delay
[7]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 12
VoWALN Capacity Enhancement No over-the-air QoS
“CSMA/CA”
81012
Channel Access with Meru AP for QoS
Over-the-air QoS “TDMA-like HCF”
Channel Access with Today’s 802.11 APChannel Access with Today’s 802.11 AP
81012
HCF “802.11e”doesn’t reduce overhead rather improves air traffic control “QoS”; contention loss is reduced and jitter is predictable/low
5.56
AP
64
8
5.36 5.38 5.4 5.445.46 5.48 5.5 5.52 5.545.42Time (Sec)
5.46 5.48 5.5 5.52 5.54 5.56Time (Sec)
AP
64
5.36 5.38 5.4 5.445.42
236 April 2008
Reduce AP spacing: data
Further AP spacing: voice
802.11n/abg virtual cells [12] [15] [16]
VoWALN Capacity Enhancement Timing Overhead of single Voice Frame over 802.11b
Aggregated Vocoder Frame
Frame ' 1 ' Frame ' 2 ' Frame ' n '
Frame Aggregation into RTP Frame by Voice Source
gg g
Aggregated Vocoder FrameRTPBulk overhead lies on L2 & L1Header compression for IP layer and above would be insignificant Packet delay increases
Inter-Call Frame Aggregation: Multicast. Multiplexing “M-M” Frame Aggregation “Intra-Call”
246 April 2008
• Capacity 80%-90% higher than VoIP • Security & Delay (collision & PSM)
Requires changes in the MAC layer implement. of the interface queue
PSM = Power Saving Mode[17] [18]
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 13
VoWLAN Challenges and SolutionsLocation Tracking–Challenge: meet E911 and E112 requirements –Solution: WLAN appliance, GSM/CDMA tracking
Handset Battery Life–Challenge: improve talk/standby time to 4+/100+–Solution: U-ASPD, propriety
Coverage & Capacity
256 April 2008
Cove age & Capac y–Challenge: Pervasive coverage, no dropped call, etc.–Solution: HCF, propriety, frame aggregation
VoWLAN Challenges and Solutions Cont.
Roaming–Challenge: Maintain connection/quality <50 ms–Solution: 802.11r, propriety, 802.11k/.11v (future)
Security–Challenge: avoid eavesdropping, maintain access
control–Solution: WAP2 (wireless) + VLAN (wired), 802.1x
266 April 2008
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 14
WLAN System Architectures Consideration
Centralized versus distributed
Definition –Centralized (C) – controller-based data forwardingCentralized (C) controller-based data forwarding–Distributed (D) –AP-based forwarding
Impact on wired network– C – may switch packets twice– D – switch packets only once
276 April 2008
D switch packets only once
Impact on WLAN controller– C – controller touches packets from every AP– D – AP – touches packets from associated stations
[19]
WLAN System Architectures Consideration cont.
Impact on VoWLAN jitter/latency– C – controller processes every VoWLAN call/packet– D – AP processes packets for associated stations
Other factors–Emergence of 802.11n
802.11n will increase traffic by 5x
286 April 2008
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 15
VoWLAN Alternatives; Pros and Cons
Mobile Cellular Phones–Example: Nokia E60, iPhone, etc.–Pro: Widely available, good outdoor coverage–Con: Costly, limited in building coverage, not
integrated with enterprise telephony system (FMC)
Cordless PBX HandsetsExample: Avaya TransTalk 9040 Philips 5111
296 April 2008
–Example: Avaya TransTalk 9040, Philips 5111 –Pro: Excellent range, good voice quality, no WLAN
security issues–Con: Requires an additional wireless network, no
high-speed data, limited capacity
Recommendations
Determine the need for VoWLAN
Make sure that WLAN coverage is sufficient g
Verify WLAN is ready for VoWLAN
Ensure VoWLAN compatibility with emprise WLAN
Gain e perience ith single mode phones
306 April 2008
Gain experience with single-mode phones before introducing dual-mode “smart phones”
©2008, Sami Alshuwair
EETS 8313: VoIP over IEEE 802.11 16
References[1] http://www.gizmag.com/go/7258/[2] http://mediaproducts.gartner.com/reprints/merunetworks/153883.html[3] How Cisco Mobility Solutions Can Reduce Costs and Improve Productivity for Today's Enterprise, Cisco, 2006 [4] Voice Over IP - Per Call Bandwidth Consumption, Cisco, 2006[5] Fundamentals of Wireless LANs, Ciscopress, 2004[6] IEEE 802.11n, http://en.wikipedia.org/wiki/802.11n[7] Trond Ulseth and Paal Engelstad, “Voice over WLAN (VoWLAN)- A Wireless voice alternative?,”Telenor R&D, 2006[8] Jean-Michel Lauriol, Luc Brignol, Philippe Laine, Philippe Dauchy and Alberto Conte “WLAN, a Converged Data and Voice
Mobility Solution for Enterprise,” Alcatel-Lucent, 2004[9] Lin Cai1,Yang Xiao2, Xuemin (Sherman) Shen, Lin Cai3,and Jon W. Mark, “VoIP over WLAN Voice capacity, admission
control, QoS, and MAC,” International Journal of Communication System, 2006[10] Shiao-Li Tsao,“Research Challenges and Perspectives of Voice over Wireless LAN,” Dept. of Computer Science and
Information Engineering, National Chiao Tung University, Hsinchu, Taiwan, R.O.C., 2005[11] WMM Power Save for Mobile and Portable Wi-Fi Certifid Devices, Wi-Fi Alliance, December 2005[12] Is It the Network? Solving VoIP Problems on a Wireless LAN, Global Knowledge Training LLC, 2007[13] Is Your WLAN Ready for Voice, Cisco, 2007[14] Design Principles for Voice over WLAN, Cisco, 2007
316 April 2008
[ ] g p , ,[15] The enterprise is ready for wireless VoIP. Is wireless VoIP ready for the enterprise, Meru Networks, 2005[16] Fulfilling the promise of 802.11n in the Enterprise without compromise, Meru Networks, 2007[17] Wei Wang and Soung Chang Liew,” Solutions to Performance Problems in VoIP Over a 802.11 Wireless LAN,” IEEE Journal,
2005[18] Sangki Yun, Hyogon Kim, Heejo Lee, and Inhye Kang,“100+ VoIP Calls on 802.11b The Power of Combining Voice Frame
Aggregation and Uplink-Downlink Bandwidth Control in Wireless LANs,” IEEE Journal, 2007[19] Adding Voice to the Wireless LAN - Developing an Implementation Strategy, TechTarget, 2007
Legacy BurstPSDU1 PSDU2 PSDU3
Frame Aggregation “Intra-Call”
Perform aggregation
Pre
ambl
ePL
CP
head
er
MP
DU
Hea
der
MP
DU
Payl
oad
FCS
Pre
ambl
ePL
CP
head
er
MP
DU
Hea
der
MP
DU
Payl
oad
FCS
Pre
ambl
ePL
CP
head
er
MP
DU
Hea
der
MP
DU
Payl
oad
FCS
SIFS SIFS
326 April 2008
Pre
ambl
e+
PLC
P H
eade
r
A-PSDU
Preamble + PLCP headers + SIFS will be savedSome overhead will be induced to identify each MPDU