VoIP via IEEE 802.11 “VoWLAN” - folk.uio.nofolk.uio.no/paalee/referencing_publications/ref-wlan-alshuwair-smu... · –PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps

©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



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



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]



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]



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]



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]



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]



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]



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]



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



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]



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]



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



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



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”



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

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326 April 2008

Pre

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PLC

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Preamble + PLCP headers + SIFS will be savedSome overhead will be induced to identify each MPDU

Documents

VoIP via IEEE 802.11 “VoWLAN” - folk.uio.nofolk.uio.no/paalee/referencing_publications/ref-wlan-alshuwair-smu... · –PPS = (8 Kbps codec bit rate) / (160 bits) = 50 pps