August 3, 2009 Page 1 of 6 VOICE INTEROPERABILITY TEST RESULTS FOR NEC UNIVERGE MH240 MOBILE HANDSET AND CISCO AP WITH WCS Table of Contents Test Results- Summary 2 Product Summary 2 MH240 Mobile Handset Design with 3 rd Party Access Points 3 Network Configuration 3 WLAN Coverage 3 Data Rates 3 Impact of WLAN retransmissions 3 Dynamic Channel Assignment 3 Voice Call Admission Control 3 Handover times 3 Battery Life Considerations 4 DTIM Timer 4 Impact of Multicast Traffic 4 AP Configuration 4 Configuration Options and features 5
Page 2 of 6 Test Results- Summary This application note describes the configuration of CISCO wireless controller with the NEC MH240 Mobile Handsets. Product Summary: Manufacturer Model Name AP Radio(s): Security: Handset model tested Handset software tested: Radio mode: CISCO 2006/4400 wireless controllers using LWAPP 2.4 GHz (802.11b/g) WEP, WPA-PSK, WPA2-PSK, MH240 01.02.00 (NA) 2.4 GHz (802.11b/g) Known Service Conditions and/or Limitations Service Conditions/Limitations that may affect voice quality: 1. CISCO does not support standard based CAC, a method to limit the maximum number of clients (MH240 handsets) per radio. This could cause issues such as degradation to voice quality if there are over subscriptions on a particular access point 2. CISCO does not support fast handover, as defined by 802.11f. Handover time between AP ranged from ~ 120-150ms during our test. A brief quiet may be experienced during handover.
Page 3 of 6 MH240 MOBILE HANDSET DESIGN WITH 3 RD PARTY ACCESS POINTS When designing and implementing the NEC MH240 handset on 3 rd party Wireless LAN Controller configuration and/or autonomous access point s specific configuration settings may or may not be supported and thus may have impact on battery life and/or voice quality. There are certain key wireless configuration considerations that directly affect the overall NEC MH240 VoWLAN design and implementations. NETWORK CONFIGURATION WLAN COVERAGE RF design is critical. The MH240 handset design and implementation best practices require that each AP support 2500 square feet. This is true regardless of which 3 rd party AP is used In this design it is recommended that the RSSI value between access points be no more than -55Dbm. It is also recommended that the access point be set to half power (50db) to better align with the transmit power of the MH240 and thus reduce the near/far affect DATA RATES The goal in setting the data rates for the VoWLAN network is to match the data rates of MH240 handsets as closely as possible. 802.11 1Mbps and 2Mbps should not be supported. Any lowering of the data-rate below 5.5Mbps, extends the AP cell size, increases co-channel interference, and reduces call capacity. The best practices for data rates for the MH240 handset are to enable all data rates except 1 and 2 Mbps. Both 1 and 2 Mbps must be disabled to dramatically reduce retransmissions: IMPACT OF WLAN RETRANSMISSIONS Voice is a real time application and unlike other data traffic, too many retransmissions can deteriorate voice quality. NEC recommends the Tx Retry settings be set to no more than 5 DYNAMIC CHANNEL ASSIGNMENT Radio Resource Management (RRM) can adjust AP channels (dynamic channel assignment) and power (dynamic transmit power control) to maintain the RF coverage and quality: The radio configuration of each AP, both Auto-RF and dynamic channel assignment, must be disabled VOICE CALL ADMISSION CONTROL VoWLAN Voice Call Admission Control (CAC) prevents rejection of calls when suitable capacity is available. A standards based solution is not available and as a result all 3 rd party access points will not support this feature and high simultaneous calls must be considered carefully HANDOVER TIMES When working with any 3 rd party access point vendor, fast handover, as defined by the 802.11f is not supported. Therefore, depending on the particular 3 rd party AP vendor handover times between AP ranged from ~ 100-200ms. During that time a brief quiet may be experienced.
Page 4 of 6 BATTERY LIFE CONSIDERATIONS DTIM TIMER Some VoWLAN handsets might require the delivery traffic indication Map (DTIM) to be increased to maximize battery life, but this change should only be done based on design recommendation specific to the handset. The DTIM period sets the number of beacon intervals that a WLAN client will sleep before waking up to see whether any traffic has been buffered for it (when in power save mode). IMPACT OF MULTICAST TRAFFIC Multicast and broadcast traffic must be buffered as well as any unicast traffic when destined for power saving clients. This can affect application performance, so DTIM should only be adjusted to the levels recommend by NEC. DTIM settings are usually global for the band and are not changed on a per WLAN basis; therefore, changing the DTIM value will affect each WLAN on a given AP radio. Given that the multicast traffic on a WLAN is sent out to every AP radio with clients associated to that WLAN regardless of that client(s) requirements, every effort should be made to minimize the multicast traffic on every WLAN interface. You can minimize the potential effects of multicast traffic by disabling IGMP on interfaces not requiring multicast and filtering multicast traffic on interfaces that have IGMP enabled. Some access point vendors use Proxy ARP, or the address resolution protocol This process is called Proxy ARP because on network system (wireless controller) is providing the proxy for the MH240 handsets. This provides controller based APs another method to filter unwanted multicast/unicast messages to the MH240 handsets When this is an option for the AP vendor, NEC highly recommends this solution for saving batteries life on the MH240 handsets
Page 5 of 6 AP Configuration Configuration Options and features The following is a list of AP configuration options or features that have a potential impact on the operation or performance of the MH240 Mobile Handsets. Recommended or required value noted below should be used. Please record the value or setting that was used in your testing. AP Option/Feature DHCP IP Static IP Recommended Configuration Settings Recommend DHCP Results from Testing 802.11b/g Recommended: 802.11g SSID Security QoS settings / WMM VoWLAN Call Admission Control Packet Filter and Proxy ARP Broadcast ESSID Dynamic Radio Channel Control Recommended: Setup a separate voice SSID for MH240 only Recommended: WPA2- PSK Recommended: Platinum COS Specify if there is any supported Recommended: Enable or Disable Required: Disable The CISCO AP used in this test do not support standards based Call Admission Control The CISCO 4400 wireless controller supports theses features as default Power-Save mode Set to 5 Tx Retry settings Recommended: 5 retries Tx power level Recommended 50 mw Beacon interval Required: 100ms DTIM Required: 5
Page 6 of 6 AP Configuration, continued Configuration Options and features AP Option/Feature Data rates (basic and supported rates) 54 48 36 24-18 - 11-9 6 5.5 2 - Disabled 1 - Disabled Recommended Configuration Settings Data rates (basic and supported rates) 54 48 36 24-18 - 11-9 6 5.5 2 - Disabled 1 - Disabled Required: 1Mbps and 2Mbps must be disabled. Results from Testing Data rates (basic and supported rates) 54 48 36 24-18 - 11-9 6 5.5 2 - Disabled 1 - Disabled