Aruba Networks Version 3.3 manual Voice Functionality and Features, Traffic Prioritization

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call quality. Jitter buffers are used in VoIP networks to smooth out this effect, but they add delay and must be as small as possible. Aruba Mobility Controllers adjust network settings to minimize jitter and maximize voice quality.

Traffic Prioritization

Aruba Mobility Controllers use traffic prioritization as one method to address delay and jitter. Traffic prioritization assures that voice packets have preferential access to the media and are moved ahead of best-effort traffic in buffers during congestion.

Application-based prioritization requires stateful inspection; this capability is a crucial difference between an Aruba solution, and competing wireless solutions. Competing solutions prioritize based on a wireless SSID, meaning that all traffic transmitted on a particular SSID is treated the same. This precludes support for voice applications running on multi-function devices such as laptops or PDAs, since these devices use multiple protocols. Aruba Mobility Controllers contain a policy enforcement firewall that statefully identifies, tracks and dynamically prioritizes traffic based on the application flow, e.g., giving higher priority to a SIP session than an HTTP session, even from the same device.

Network Wide QoS

While the Aruba Mobility Controllers can handle much of the heavy lifting by identifying, properly tagging, and scheduling packets into the network, the rest of the components must also be ready to handle QoS. If the access, distribution, core, and data center switches and routers are only providing best effort delivery, voice quality will suffer. At each level in the network, devices that will be forwarding QoS tagged traffic must be configured to properly prioritize traffic above data and background traffic.

Voice Functionality and Features

Voice Service Module features provide deep visibility into the session, such as, viewing the call progression and voice quality of a SIP based VoIP call. Advanced voice-over-WLAN features such as Call Admission Control (CAC), voice-aware RF management, and voice-specific diagnostics allow the Mobility Controller to deliver enterprise class mobile VoIP capabilities.

Voice-Aware RF Management

As discussed in Chapter 7 on page 55, Aruba’s Adaptive Radio Management (ARM) is normally configured to adjust channel and transmit power levels of wireless APs based on nearby interference and other RF conditions. Client devices will react to a channel change by scanning for a new AP and then re-associating as though they were roaming. Most data applications will not be noticeably affected by this action. Voice is highly susceptible to packet loss, however, and a channel change during a voice call will very likely cause packet loss and audible disruption to the call.

Because Aruba Mobility Controllers statefully follow voice protocols, they will not allow a channel change while voice calls are taking place. If a channel change is required, the controller will wait until that AP is no longer handling active voice calls before initiating the channel change.

Call Admission Control

Typical voice codecs (Coder/Decoder) used in VoIP do not consume large amounts of bandwidth. Even with G.711, which uses 64Kbps per call, a typical 802.11b access point could theoretically support nearly fifty simultaneous calls based purely on bandwidth. In practice, the limiting factor is contention for the wireless medium because 802.11 uses a collision-avoidance algorithm that makes timely access to the wireless media a challenge for delay-sensitive devices. Due to this limitation, the number of

60 Voice over Wi-Fi

Campus Wireless Networks Validated Reference Design Version 3.3 Design Guide

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Contents Campus Wireless Networks Validated Reference Design Version Crossman Avenue Sunnyvale, California Phone Fax Contents Chapter RF Planning and Operation Aruba Reference Architectures Reference DocumentsContacting Aruba Networks IntroductionTelephone Support Understanding Centralized Wireless LAN Networks Aruba’s User-Centric Network ArchitectureIntroducing Aruba’s User-Centric Network Centralized Wlan ModelArubaOS and Mobility Controller ArubaOSMobility Controller Multi-function Thin Access Points Access PointAir Monitor Mesh Portal or Mesh Point Aruba’s Secure Enterprise Mesh NetworkMobility Management System Remote APMobility Management System PoC Network Physical Design Proof-of-Concept NetworkPoC Network Logical and RF Design VlanProof-of-Concept Network Proof-of-Concept Network Aruba Campus Wlan Physical Architecture Campus Wlan Validated Reference DesignAruba Campus Wlan Logical Architecture Data center ManagementMaster Campus Wlan Validated Reference Design Mobility Controller Access Point Deployment Understanding Master and Local OperationMobility Controller High Availability Master Controller Redundancy Local Controller Redundancy Second Local controller has an opposite configuration Vlan Design Do Not Make Aruba the Default Router Do Not Use Special VLANsVlan Pools VlanUser Mobility and Mobility Domains VLANs 10, 20, 30ArubaOS Mobility Domain MD1Mobility Controller Physical Placement and Connectivity Master Controller PlacementAP Placement, Power, and Connectivity Local Controller PlacementMobility Controller and Thin AP Communication AP Power and Connectivity AP Location and Density ConsiderationsOffice Deployment Voice Deployment Active Rfid Tag DeploymentConfiguration Profiles and AP Groups Mobility Controller ConfigurationConfiguration Profiles Required LicensesProfile Types AP groupSSIDs, VLANs and Role Derivation AP GroupsProfile Planning SSIDs VLANsSecure Authentication Methods Role DerivationAuthenticating with Corporate Authenticating with Captive Portal Authentication Methods for Legacy DevicesConfiguring Roles for Employee, Guest and Application Users Employee RoleGuest Role Create a bandwidth contract and apply it to an AP group Create the block-internal-access policy Modify the guest-logon role Device Role Wireless Intrusion Detection System Role Variation by Authentication MethodWireless Attacks Rogue APs Page Mobility Controller Configuration RF Plan Tool RF Planning and OperationAdaptive Radio Management Page Minimum Scan Time Sec Voice over Wi-Fi Quality of ServiceWMM and QoS Voice Functionality and Features Traffic PrioritizationNetwork Wide QoS Voice-Aware RF ManagementComprehensive Voice Management Voice over Wi-Fi Controller Clusters Mobility Management System LAN / WANMultiple Master/Local Clusters Page Multiple Master/Local Clusters Appendix a LicensesLicenses Appendix B Wlan Extension with Remote APWlan Extension with Remote AP Small Network Deployment Alternative Deployment ArchitecturesMedium Network Deployment Mobility Controller located in the network data centerBranch Office Deployment Corporate data center Pure Remote Access Deployment DMZ
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