Delivering Lync Real-Time Communications Over Wi-Fi

Delivering Lync Real-Time Communications over Wi-Fi

Published:June 2012

Author: Peter Schmatz

Technical Reviewers:Amer Hassan, Pascal Menezes, Victoria Poncini

Abstract:This white paper describes how Lync 2010 communications software, and previous releases, Office Communications Server 2007 R2 and Office Communications Server 2007, can be successfully implemented over wireless local area networks (Wi-Fi), even though these workloads have not yet been validated with voice and video (real-time media) over wireless networks. This overview of issues and mitigations will help you to ensure a high-quality voice and video Lync experience for all users. To optimize the wireless infrastructure, particularly for real-time media traffic, you’ll find details regarding Wi-Fi (WLAN) technology, configuration settings, and optimization. In addition, this paper provides deployment recommendations and evaluates typical enterprise, public hotspot, and home Wi-Fi deployments for real-time bidirectional media quality.

This document is provided “as-is”. Information and views expressed in this document, including URL and other Internet Web site references, may change without notice.

Some examples depicted herein are provided for illustration only and are fictitious. No real association or connection is intended or should be inferred.

This document does not provide you with any legal rights to any intellectual property in any Microsoft product. You may copy and use this document for your internal, reference purposes.

Table of Contents

1Overview

2Introduction

2.1Glossary

3Usage Scenarios

3.1Enterprise Wi-Fi

3.1.1Enterprise voice/video mobility scenarios

3.1.2Personal devices and enterprise Wi-Fi

3.2Home Wi-Fi

3.3Public Wi-Fi hotspots

4Issues That Affect Wi-Fi Performance for Real-Time Application

4.1General issues

4.1.1Wireless NIC drivers

4.1.2Wireless NIC chipsets and hardware

4.1.3Legacy interoperability issues

4.2Issues in enterprise Wi-Fi deployments

4.3Issues in public Wi-Fi hotspots

4.4Issues in home Wi-Fi deployments

5. Wi-Fi Deployment Recommendations

5.1Enterprise Wi-Fi

5.1.1Mixed or Wi-Fi-only enterprise deployment

5.1.2Device types in enterprise Wi-Fi deployments

5.1.3Usage patterns in enterprise Wi-Fi

5.1.4Legacy devices in enterprise Wi-Fi

5.1.5WMM QoS and WMM-Power Save support

5.1.6Enterprise WLAN controller

5.1.7Recommended Wi-Fi feature support

5.1.8Recommended Wi-Fi configuration settings

5.1.9Wi-Fi policies

5.1.10Wireless network card (network adapter) recommendations

5.1.11Enterprise voice certifications

5.2Home Wi-Fi

5.2.1Home Wi-Fi deployment recommendations

5.3Public hotspot Wi-Fi

5.3.1Basic hotspot Wi-Fi configurations

1Appendix A: Wi-Fi Standards

1.1IEEE 802.11a/b/g/n Wi-Fi standards

1.2802.11a (legacy standards)

1.3802.11b (legacy standards)

1.4802.11g (current standards)

1.5802.11n (current standards)

1.5.1802.11n MIMO

1.5.2802.11n Spatial diversity

1.5.3Physical layer access by using a 40-MHz wide band

1.5.4Wi-Fi Certified 802.11 n devices

1.6802.22 and 802.11af Wireless Regional Network (future standards)

1.7802.11ac Gigabit Wi-Fi (future standards)

2Appendix B: Wi-Fi Frequencies

2.12.4-GHz band

2.1.1Coexistence of 11b/g/n in 2.4 GHz

2.25 GHz band

2.3Quality of Service and Wi-Fi Multimedia (WMM)

2.3.1WMM prerequisites

2.3.2WMM-Power Save (APSD)

3Appendix C: Wi-Fi Security

3.1Wi-Fi security and real-time media workloads

3.1.1Pairwise Master Key Security Association (PMKSA)

3.1.2Opportunistic Pairwise Master Key (PMK) Caching

3.1.3802.11r fast BSS transition

4Appendix D: Wi-Fi WAP Handover and Resource Management

4.1Background WAP scanning

4.2802.11k Radio resource management

4.3Other industry-standard fast handover solutions

4.4802.11v Wireless network management

4.5WMM-Power Save and DTIM interval

1Overview

Microsoft®Lync® 2010 communications software, and previous releases,Microsoft Office Communications Server 2007 R2 and Microsoft Office Communications Server 2007, have not been validated with voice and video (real-time media) workloads over wireless local area networks. However, many Lync 2010 deployments successfully implement these workloads over wireless local area networks.This deployment guideprovides an overview of issues and mitigations to help you ensure a high-quality voice and video Lync experience for all users. Lync 2010 continues to provide “best effort” support for real-time mediaover Wi-Fi.

To optimize the wireless infrastructure, in particular for real-time media traffic, this guide provides details regarding Wi-Fi (WLAN) technology, configuration settings, and optimization.

In addition, thisguide provides deployment recommendations and evaluates typical enterprise,public hotspot, and home Wi-Fi deployments for real-time bidirectional media quality.

2Introduction

Wi-Fi connectivity is ubiquitous, and users expect to find Wi-Fi access in the office, at home, in public hotspots, in hotels, and on the road. However, the Quality of Service (QoS)in Wi-Fi varies widely, ranging from the ability to support basic email sync and web traffic, to the ability to support of a full range of multimedia applications and real-time communications.

This deployment guide discusses different usage scenarios of wireless connected devices, coverage, capacity, and QoS aspects, specifically for delivering real-time communication workloads, such as audio, video, and application sharing.You’ll also find deployment recommendations for enterprise, hotspot, and home Wi-Fi deployments, and a full discussion of issues and mitigations. Finally, the extensive appendix provides a detailed overview of legacy, current, and future Wi-Fi standards, Wi-Fi frequencies, Wi-Fi security, and Wi-Fi WAP handover and resource management.

By successfully deploying Lync 2010 over wireless networks—optimizing your wireless infrastructure for real-time media traffic, prioritizing types of usage, preparing for specific scenarios, and applying appropriate mitigations—you can help to ensure the best possible experience Lync 2012 experience for all users.

2.1Glossary

WAP: Wireless access point that connects client devices (stations) to Wi-Fi.
BSS: Basic service set.The basic building block of an 802.11 wireless LAN; specifically, a single WAP with all associated stations.
BSSID: The basic service set identifier. Usually, the radio Mac address(s) of the WAP.
CCK: Complementary code keying. A modulation scheme used in wireless networks.
Contention ratio: The ratio of maximum potential demand to network bandwidth that is actually available.
DHCP: Dynamic Host Configuration Protocol. A networking configuration protocol that is used to automatically configure a device IP networking configuration.
DSSS: Direct-sequence spread spectrum.A modulation technique where the transmitted signal is distributed across thefrequency domain, resulting in asignalwith a widerbandwidth.
EAP: Extensible Authentication Protocol. Anauthentication framework used in wireless networks.
Guard interval: A time interval that ensure that separate transmissions of digital data do not interfere with one another. See also Short guard interval.
IEEE 802.11: A set of IEEE standards for the operation of wireless local area networks.
OKC (also OPC): Opportunistic Key Caching. A method that reduces the handoff latency for clients roaming between adjacent WAPs by providing preestablished authentication. Also known as Opportunistic Pairwise Master Key (PMK) Caching (OPC).
OPC. See OKC.
MIMO: Multiple-input multiple-output.
NAT: Network Address Translation. A process to reconfigure IP address information in IP packet headers in a routing device.
PMK: Pairwise Master Key.See also OKC and OPC.
QAM: Quadrature amplitude modulation.Ananalog and digital amplitudemodulation scheme that uses two streams.
Short guard interval: A shorter guard interval, which is possible in 802.11n. See also Guard interval.
SSID: Service Set Identifier. An association identifier between devices and Wi-Fi deployment.
Wi-Fi Alliance: A global nonprofit organization that provides product certification and other services.
UNII: Unlicensed National Information Infrastructure.
WMM: Wi-Fi Multimedia. A Wi-Fi Alliance specification that defines quality of service (QoS) settings for over the air (OTA) prioritization of 802.11 frames. Also known as Wireless Multimedia Extensions (WME).
WPA2 IEEE802.11i Wi-Fi protected access: security protocol and certification program developed by Wi-Fi alliance.
WEP: Wired Equivalent Privacy (WEP) is a security algorithm for IEEE 802.11 wireless networks.

3Usage Scenarios

For the purpose of this whitepaper, the Wi-Fi deployments are grouped into the following three main deployment types.

Enterprise
Public hotspot
Home

3.1Enterprise Wi-Fi

This deployment type is typically found in offices for professional usage of line-of-business (LOB) applications and other services provided to employees or guests. Attributes of an enterprise Wi-Fi implementation include the following:

Authentication and encryption are implemented,typically by using Wi-Fi Protected Access 2 (WPA2), enterprise wireless security software.
Multiple SSIDs are available that feature different levelsof service and access, such as employee LOB SSID or guest SSID.
Multiple “thin” access points are deployed, along with Wi-Fiinfrastructure controller managing WAPs.
Bandwidth and access policies may be in place.

Some small businesses may deploy a single consumer-grade WAP only, but will implement access control and security protocols. Such deployments can be considered similar to home deployments, as outlined later in this document.

3.1.1Enterprise voice/videomobility scenarios

Enterprise Wi-Fi real-time media usage can be further classified into two categories:

Fixed usage: The device typically remains stationary for the duration of a voice or video call, and maintains association with the same WAP.
Mobile usage: The user is actively moving during a call (for example, a Wi-Fi telephone device, smartphone, or tablet). The enterprise Wi-Fi and device must support a fast-handover between WAP points, with minimal impact to the audio quality, withno or only minor audio glitches.

Note that even in case of nomadic usage, devices may be redirected to a different WAP, which can occur due to active WAP load balance, or fluctuation of signal strength of adjacent WAPs.

3.1.2Personal devices and enterprise Wi-Fi

As a recent trend, enterprisesare starting to allow employees to connect personal devices, such as smartphones or tablets, to the corporate Wi-Fi network.

3.2Home Wi-Fi

In home Wi-Fi deployments,an ISP provides Internet access to a single dwelling (a house, for example, or an apartment). Devices that enablelocal Wi-Fi are typically multipurpose devices. Attributes of a home Wi-Fi implementation include the following:

A consumer-grade wireless router connected to a cable or DSL modem. This is typically a multipurpose device that features routing, NAT, firewall, and DHCP server functionality, in addition to the wireless access point in a single unit.
Authentication and encryption are enabled, but lower security settings and key length (WEP) may be used.
WPA/WPA2 security and authentication are typically supported by all recent generation,consumer-grade WAPs.
WPS (Wi-Fi Protected Setup) support to enable easy device hookup to secured Wi-Fi home deployments.
Single access point only. Typically, a single access point is deployedto provide coverage for all home devices.However, in selected cases, a wireless repeater is deployed to increase range.
Home ISP typically implements asymmetric upload/download configurations,which produces significantlylower upstream bandwidth than downstream bandwidth.
The home Wi-Fi router provides Internet access to a wide variety of devices, such as:
Smartphones
Tablet devices
Game consoles
Video streaming devices
Notebook and desktop systems

3.3Public Wi-Fihotspots

Public Wi-Fihotspots generally provide a free or a paid-per-useservice, and are typically located in the following areas:

Retail locations, coffee shops,airports
Hotels
Airplanes, trains, buses
Hospitals, public libraries

Typical attributes of public Wi-Fihotspots:

No authentication and encryption: Wi-Fiuses the Open setting.
Prior to granting Internet access, users are redirected to a Terms of Service and/or a billing page. Access to the Internet is then granted, based on the MAC address of the wireless network adapter.
Content filtering: Black-listing filtering based on HTTP URL, or plain text search (URL and keyword filtering).
Protocol or port filtering or throttling: Specific protocol or port ranges may be blocked or throttled after a certain usage amount. Typical examples: BitTorrent and other file-sharing application port ranges.
Primarilysupporting only IEEE802.11b and 802.11g, with only fewhotspots supporting IEEE802.11n access.
Internet traffic may be channeled through a proxy, which features content filtering and/or billing and other access control mechanisms. Thisproxy server may not be located on-premises with the Wi-Fi deployment, which adds overall latency and affects real-time media workloads.
Asymmetric upload/download speeds with significant throttling of upstream speed, which limits the workload capacity of applications such as video chat, which require symmetrical bandwidth.
Hotspots in vehicles or remote areas can be provided through an ISP connected via a satellite or cellular dataconnection (adding bandwidth and latency constraints).

Due to the wide diversity of public hotspotdeployments, it is difficult determine what level of service will be available. The typical goal of a public hotspot is to provide users with a basic Internet service that provides access to email, as well as web access (HTTP browser), and limits real-time or bandwidth-sensitiveworkloads. However, recent changes in usage patterns involvingcontent-rich multimedia and real-time media usagemake it necessary for public hotspots to provide more bandwidth and lower latency for all connected devices.

For details on Wi-Fi standards, see Appendix A: Wi-Fi Standards.

4IssuesThat Affect Wi-FiPerformance for Real-Time Application

4.1General issues

4.1.1Wireless NIC drivers

Inconsistent wireless NIC driver quality and performance. Drivers on consumer devices assume a single WAP home scenario and show poor performance in enterprise deployments with multiple WAPs.
Background scanning delays. Depending on a driver’s strategy for updating the WAP candidate list, implementation exhibit delays of up to 1 second or more can result, causing audible glitches in real-time media applications. Ideally, the delay caused by background scanning is less than 50 milliseconds.
Drivers do not consistently use the WAP candidate list available in the beacon request. Instead,theyfrequently try to rescan neighbor WAPs and compile a list by themselves.
Too high or too low roaming aggressiveness. Some driver implementations are too sticky to a WAP and attempt to roam only if the signal strength has already dropped significantly and much more suitable WAPs are nearby. Conversely,drivers sometimes jump between WAPs too aggressively even when the current WAP associate provides sufficient performance. Frequent WAP handover delays affect real-time media workloads (audio glitches). Good implementations roam to a different WAP when the receive signal strength (RSS) drops below 65dBm, and the signal-to-noise ratio (SNR) is below 30 dB.
Inconsistent TX (transmission rate) adaptation. Clients may drop too aggressively to a lower transmission rate, contributing to a congestive collapse on the WAP. Conversely, clients may stay too long at the high TX rate despite high packet loss, requiring a large number of packet retransmits.

4.1.2Wireless NIC chipsets and hardware

Inconsistent 2.4 GHz and 5 GHz support. Even in deployments with simultaneous dual-band WAP configuration (2.4/5 GHz), as well asthose that are dual-band capable, theclient may default to the congested 2.4-GHz band. Wireless NIC driver default settings prefer the 2.4 GHz, but typically also offer configuration options to prefer the 5GHz band.
Lack of antenna diversity and MIMO: Both 11g and 11n devices will benefit from multiple antennas (apart from the multistream ability of 11n), but antenna diversity is not implemented consistently andis typically not availablein smartphones, due to space constraints.
Form factor restriction: Smaller devices usually have lower performance Wi-Fi radios, and smaller (mostly single) built-in antennas, which provide less signal strengththan notebooks or tablet devices, which have a larger form factor. In addition, devices are held close to the body and are in motion while in use typically deliver a lower wireless performance overall.

4.1.3Legacy interoperability issues

In the 2.4 GHz band concurrent legacy IEEE 802.11b/g and802.11n operation may result in interoperability issues.The presence of legacy 11b/g devices with faster 11n may adversely affect the performance of each of the device groups, or may prefer either group in accessing the physical layer (inconsistent airtime fairness).Wi-Fi equipment vendors are providing nonstandardized solutions to improve airtime fairness, such as allocating airtime dynamically for each individual client by access type, traffic, and volume.

4.2Issues in enterprise Wi-Fideployments

Enterprise Wi-Fi deployments are usually fully managed, and if properly designed and configured,they can provide the best real-time media experience for mostly stationary clients.However, the following items may affect Wi-Fi performance in enterprise deployments:

Insufficient WAP density required to appropriately handle the bandwidth and number of concurrently connected clients.
Insufficient backhaul bandwidth WAPs.For example, a WAPthat supports 11n by running a single 100 Mbps backhaul connection, which caps the throughout below the achievable wireless bandwidth.
Adjacent WAPs interference.This may result in incorrect channel selection or reduced signal strength, specifically in the 2.4-GHz band.
Coverage gaps. Because WAP placement is typically designed for stationary use (desktop computers) or nomadicuse (notebook computers in meeting rooms), mobile users may experience coverage gaps—for example, a mobile user with a smartphone on a VoIP call in a hallway or stairwell.
A large meeting room with a significant number of devices that are using the same WAP may cause a high contention ratio on the physical layer and/or on the backhaul network.
Usage of “employee-sourced” devices. Some companies let employees connect devices that have lower-quality radios and antennas to the Wi-Fi deployment. This results in marginal signalsand a compromised performance overall.
Support of legacy devices (such as 11b) may significantly affect the overall throughput of faster 11g and 11n devices, resulting in air time contention.

4.3Issues in public Wi-Fi hotspots

Wi-Fi hotspots are available in public locations, such as airports or hospitals, retail shops, and coffee shops to offer users Internet access. Hotspots are available either for free or for a fee that is based on time or data volume used (payload data only). For most public hotspots, no security settings are implemented. Due to legal requirements, most public hotspots let users connect to the wireless network directlyonly if they launch a web browser to accept usage terms or provide billing information first. Some commercial hotspots provide the options of different access classes, such as (non-real-time) data only, or real-time media, which is usually charged at a higher rate.

Typical issues in publichotspots:

Depending on the coverage area, only a single WAP may be deployed, anddue to the high cost of enterprise-class WAPs, lower-grade or consumer-grade WAPs devices are typically used. The quality of the WAPand antenna configuration may negatively affect the performance.
In larger areas, such as airports or hospitals, there are typically no service-level agreements (SLAs) established, and the service provided is considered “best effort.” WAP density and coverage may be limited.
Backhaul network with limited upload speed: Most small-business Internet access packages provided by cable operators feature a relative fast download stream bandwidth, while providing only a fraction of upload bandwidth. For example, a typical package features 50 Mbps downstream and 10 Mbps upstream[i]. While this reasonable for typical Internet web traffic, real-time media traffic requires equal upstream and downstream performance, and so, in this scenario,only a limited number of concurrent voice/video conversations can be supported.

4.4Issues in home Wi-Fi deployments

Wi-Fi routers deployed at home (home WAP) often have the same issue of general radio frequency noise that is present in the 2.4 GHz band. This noise is caused by neighboring Wi-Fi routers that operate on the same channel and game consoles with wireless game controllers (Bluetooth), as well as cordless phones and household appliances such as microwave ovens. Additionally, residential walls may absorb radio frequency, resulting in suboptimal signal strength.