Voice over Wireless LAN

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Voice over Wireless LAN

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Outline

„ Introduction to VoWLAN

„ Wireless LAN Technology

„ Why VoWLAN?

„ VoWLAN Requirement

„ VoWLAN Challenge

„ Summary

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Introduction to VoWLAN

„ VoWLAN or Voice over Wireless Local Area Network expands the capability of WLANs or Wireless LANs

„ VoWLAN is a natural extension of VolP

„ VoWLAN is the added feature that will enable you to make phone calls using this mobile Internet access

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VoWLAN Technology

„ VoIP + Wireless LAN

„ VoIP

„ SIP, RTP, H.323

„ Wireless LAN

„ WiFi : 802.11a/b/g

„ WiMAX : 802.16

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802.11 Overview

„ Infrastructure mode

Access Point

Access Point Wired Network

End Device

End Device End Device

End Device

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802.11 Overview

„ adhoc mode

End Device

End Device

End Device

End Device

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802.11 Overview

„ DCF : Distributed Coordination Function

„ Contention-based MAC function

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802.11 Overview

„ PCF : Point Coordination Function

„ Contention-free MAC function

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802.11 Overview

11/3 11/3

12/8 11/3

Channels/non- overlapping

PBCC OFDM

OFDM DSSS/CCK

Modulation Encoding

83.5MHz 83.5MHz

300MHz 83.5MHz

Available Spectrum

2.4GHz 2.4GHz

5GHz 2.4GHz

Frequency

6 Mbps 20~25Mbp

27Mbps s 4~5Mbps

Average Actual throughput

22/44Mbp s

54Mbps 54Mbps

11Mbps Raw Data Rates

802.11b 802.11g +

802.11a 802.11b

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WiFi Phone protocol stack

VoIP Application

Vocoder MMI

Application

Control Plane Data Plane Management Plane

SIP/SDP RTP/RTC

P RADIUS/DIAMETER

UDP/TCP IP

802.11 MAC

802.11 a/b/g/ RF/BB EAP/802.1x/…

802.11e/f/h/i/k …

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Why VoWLAN

„ Low cost

„ Free Charge of ISM Band

„ ISM band : free (2.4-2.4835 GHz)

„ 3G band : NTD 10 Billion

„ Inexpensive network deployment

„ Reuse of existing network, easy to setup

„ Low cost of Access Point VS. High cost of Base Station

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Why VoWLAN

„ Low complexity

„ Centralized architecture in cellular network

„ PBX contains most intelligence of the network

„ Typically hard to maintain the proprietary system

„ Decentralized architecture in VoIP network

„ Intelligence are implemented in User Agent

„ Easy for maintenance

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Why VoWLAN

„ Low transmission power

„ Small coverage of the AP, small transmission power needed

„ GSM: 500mW ~ 2W

„ WLAN: < 100mW

„ Easy for providing value-added service

„ Voice and data service is integrated into VoIP

„ Flexibility of SIP protocol

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Why VoWLAN

„ Market trend

„ VoWLAN market will reach $507 million (end user revenue) by 2007 (In Stat/MDR)

„ VoWLAN handset will grow by more than 89 percent annually until 2007 when there will be more than 653,000 (On world)

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VoWLAN Requirement

„ Performance

„ Voice quality must be as good as wired network

„ Delay >100 ms is typically sensible by human

„ Low latency : <50 ms latency is recommended

„ Reliable transmission over wireless channel

„ Low packet lost rate

„ User mobility management

„ Support roaming between wireless network

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VoWLAN Requirement

„ Capacity management

„ Heavy traffic load increase packet lost rate and latency

„ Number of Users must be controlled

„ Channel assignment

„ 11 channels in 802.11b

„ Manage operating channel among adjacent Access Point

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VoWLAN Requirement

„ Security

„ Data ciphering

„ Wireless channel is insecure

„ Data over wireless should be protected

„ AAA

„ Authentication : legal user identification

„ Authorization : service level differentiation

„ Accounting : statistics for billing

„ Location Tracking

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VoWLAN Challenge

„ Due to the requirements of VoWLAN, several issue should be solved

„ User Mobility Issue

„ Power Consumption Issue

„ Security Issue

„ QoS Issue

„ Capacity Issue

„ Other Related Issue

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User Mobility Issue

„ Supporting user mobility is an important feature of VoWLAN

„ Typically concern about two factors

„ Handoff latency

„ Packet lost rate

„ Seamless handoff

„ Fast handover : focus on reducing handoff latency

„ Smooth handover : focus on reducing packet loss during handoff

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Handoff Approach

„ Layer 2 approach

Access Point

End Device

Access Point

End Device 1

2 3

4

1 : reassociation

2 : auth (802.1x, EAP)

3 : auth (RADIUS/DIAMETER) 4 : packet send/recv

AAA Server

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Handoff Approach

„ MIP approach

Access Point Access Point

HA FA

CN

MN

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Handoff Approach

Access Point

MN

Access Point

SIP Proxy AAA Server

MN REINVITE

„ SIP Mobility approach

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Handoff Approach

„ Intra ESS

„ L2 approach with/without authentication

„ Inter ESS

„ DHCP + MIP

„ DHCP + SIP Mobility

„ Inter Domain

„ Same as Inter ESS, but business policy should be concerned

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Power Consumption Issue

„ Always be a problem since only limited battery power available at mobile

device

„ System

„ CPU, Memory, LCD, DSP/Codec

„ WLAN

„ Physical Layer: RF

„ MAC Layer: 802.11a/b/g

„ Network Layer: TCP/IP

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802.11 Power Saving Mode

„ Reduce power consumption of

transceiver when mobile device is idle

„ AP buffers data packet for the mobile device which is in PSM, and inform it to receive by sending beacon

„ Mobile device in PSM periodically wake up to receive data packet buffered in AP

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802.11 Power Saving Mode

PS data

AP

Client 1 1

1

1 1

1

Beacon

Interval Wait

Interval

beacon beacon with data PS poll

2

Client 2 2

2 2

2 sleep

sleep

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802.11h

„ Supplementary to 802.11a (5GHz)

„ TPC (Transmission Power Control)

„ Keeps signal strength efficient, using only enough power to reach active users rather than using a uniform power output

„ DFS (Dynamic Frequency Selection )

„ Selects the radio channel at the access point to minimize interference with other systems

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Security Issue

„ Data ciphering

„ WEP, 802.11i

„ AAA (Authentication, Authorization, Accounting)

„ 802.1x, RADIUS, DIAMETER

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WEP

„ WEP use RC4 to encrypt data which is dependent on the IV (Initialization

Vector) and Shared Key

Data ICV

IV Shared Key

CipherStream RC4

CipherText IV

XOR

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802.11i

„ Data transfer protection

„ TKIP : based on RC4

„ CCMP : import AES algorithm with better security

„ Authentication

„ 802.1x, EAP

EAP 802.1x

CCMP TKIP

Authentication

Data ciphering

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TKIP

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CCMP

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802.1x

„ General-purpose, port-based network access control mechanism for any 802 technology

„ Enables mutual authentication of devices

„ Provides service for exchange of 802.11 session keys

„ Leverages existing AAA infrastructure

„ Extensible protocol to support future authentication methods (RFC 2284)

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End Device

802.1x – EAP Authentication

Access Point Auth Server Request/Identity

Response/Identity Radius-Access-Request Radius-Access-Challenge EAP-Request

EAP-Response Radius-Access-Request Radius-Access-Challenge EAP-Success

802.1X RADIUS

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QoS Issue

„ Typically, voice quality is depend on the delay and loss rate of packets

„ No QoS guarantee in legacy 802.11 DCF, since each mobile device contends for

the channel by using CSMA/CA

„ There are some proprietary QoS

schemes proposed, but QoS is still an open issue

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802.11e

„ Promise to bring QoS capabilities WLAN system need for streaming applications

„ Introduce HCF (Hybrid Coordination

Function) to provide some QoS facilities

„ EDCA : Enhanced Distributed Cannel Access

„ HCCA : Hybrid coordination function Controlled Channel Access

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EDCA

„ Contention-based channel access

„ Four backoff entities within one station

„ Each backoff entities represents one

Access Category (AC) and has different contention window size

„ AC_VO (voice), AC_VI (video) , AC_BE (best effort) , AC_BK (background)

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EDCA

Mapping to Access Category

AC_VO Queue

AC_BK Queue AC_BE

Queue AC_VI

Queue

MSDU

Backoff Mechanism

Transmission Backoff

Mechanism

Backoff Mechanism

Backoff Mechanism

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HCCA

„ Controlled channel access

„ HC can allocate TXOP (Transmission Opportunity) during CFP or CP by

transmitting QoS CF-Poll frame

„ During CFP, this mechanism is the same as legacy 802.11

„ During CP, it will allocate the medium after detecting the channel being idle for PIFS

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HCCA

Contention Free Period Contention Period

Polled TXOP TXOP Polled TXOP

802.11e Superframe

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Capacity Issue

„ Voice quality is a key component of voice service (real-time, high throughput)

„ CSMA/CA mechanism limits the max # of subscribers under the AP

„ A VoIP streams typically requires less than 10Kbps

„ Ideally, the number of simultaneously VoWLAN sessions is

„ 11M / (10K * 2) = 550

„ However, the maximum number of VoIP sessions is about 12 if GSM 6.10 (13.2Kbps) is used

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Capacity Issue

„ An analysis result from “W. Wang et al, Solution to Performance Problems in

VoIP over 802.11 Wireless LAN”

11.4 G.729

10.8 G.726-32

17.2 G.732.1

10.2 G.711

11.2 GSM 6.10

Max # of user Codec

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Multiplex-Multicast Scheme

„ Multiplex : Combine several downlink data into one

„ Multicast : Multicast the packet to all destination

„ De-Multiplex : Retrieving the corresponding payload

DeviceEnd

Access

Point Voice

Gateway Access

Point Voice

Gateway

DeviceEnd

DeviceEnd End

Device Internet

MUX MUX

DEMUX DEMUX

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Other Related Issue

„ Codec Compression

„ The ability to maximize the wireless bandwidth for voice, intelligent use of compression codec is

important.

„ Often require hardware assist, the target device is hardware dependent and needs to be specially

designed

„ PBX Integration

„ Provide the PSTN access, often a gateway solution

„ SIP ENUM

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SIP ENUM

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Other Related Issue

„ Combine WLAN and Cellular

„ WLAN

„ High bandwidth, Low Cost, Multimedia Service, Video Phone

„ Cellular

„ Large Coverage, High Mobility, Mature Billing System, Popularity

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ServerAAA

WLAN + Cellular

Access Point Multimedia

Center

Access Point

HLR

PhoneWiFi WiFi Phone

ServerWeb

PhoneWiFi WiFi

Phone WiFi Phone PhoneWiFi

Internet

Cellular Sim-based AAA

Voice Session Multimedia Access

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Summary

„ The existing VoWLAN solutions may not be robust and reliable enough to support

deployment for a large base of users

„ QoS of VoWLAN is always an open issue

„ it may or may not have a good solution

„ Security and Capabilities for fast handoff between APs still needs some improvement

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Summary

„ RF management and MAC layer mechanism affect power consumption of mobile device

„ Voice over WLAN is a trend

„ Many cellular operators have devoted to the development of VoWLAN

„ Government promotes the combination of WLAN and Cellular network

„ VoWLAN may just be the next big thing in mobile telephony

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