TD 92408EN System Planning Ascom VoWiFi System 9 December 2011 / Ver.
System Planning Ascom VoWiFi System TD 92408EN Contents 1 Introduction .................................................................................................................... 1 1.1 Abbreviations and Glossary................................................................................................... 1 2 General ............................................................................................................................ 4 2.1 Introduction to Wireless Planning .............
System Planning Ascom VoWiFi System TD 92408EN 8.1 Automatic RF Adaptations in WLAN Systems ............................................................... 27 8.2 Load Balancing....................................................................................................................... 27 9 Tools in the VoWiFi Handset ....................................................................................... 28 10 AP Configuration .....................................................................
System Planning Ascom VoWiFi System 1 TD 92408EN Introduction This document is intended as a guide for considerations on WLAN infrastructure planning and installation to obtain maximum performance with respect to voice quality. The document handles the RF aspects in the 2.4 GHz and 5 GHz band of a multi-cell WLAN system with a focus on Access Point (AP) placement.
System Planning Ascom VoWiFi System TD 92408EN DiffServ Differented Services (TOS field) dBm Power ratio in decibels (dB) referenced to one milliwatt (mW). DFS Dynamic Frequency Selection DSCP Differentiated Services Code Point DTIM Delivery Traffic Indication Message EAP Extensible Authentication Protocol. EAP-FAST EAP-Flexible Authentication via Secured Tunnel. EAP-TLS EAP-Transport Layer Security. EDCF 802.11e Enhanced Distributed Coordination Function.
System Planning Ascom VoWiFi System TD 92408EN STA Station: a mobile device in an IEEE802.11 WLAN system. TCP Transport Control Protocol TLS Transport Layer Security TOS Type of Service TSpec Traffic Specification. UniteCM The Ascom UniteCM (Unite Connectivity Manager) is a web-based tool used for messaging and alarm handling in the system. It also includes the Device Manager. UDP User Datagram Protocol. UP User Priority. VLAN Virtual Local Area Network.
System Planning Ascom VoWiFi System 2 TD 92408EN General 2.1 Introduction to Wireless Planning 2.1.1 Adding Voice to a Wireless LAN Data and voice traffic has different characteristics and thus put different requirements on the design of the WLAN network. Data clients, like a laptop set up to use its wireless card for browsing the Internet, tries to use the max packet size that is allowed to transport the relative high amount of data that modern web pages contain.
System Planning Ascom VoWiFi System TD 92408EN Physical separation A WLAN network can either operate on the IEEE 802.11 2.4 GHz (b/g) or a 5 GHz (a) band. Depending on the WLAN APs used, a network may support either one of those bands or both if the AP is equipped with dual radios. In such a case, the WLAN network can be thought of as two independent WLANs which are physically separated by the usage of different frequencies.
System Planning Ascom VoWiFi System • • • • TD 92408EN Protecting devices from access by unauthorized personnel. Give priority in the network for some kind of traffic. Using role-based access rights and access to a VLANs depending on users group membership. Create security rules and allow the use of internal firewalls.
System Planning Ascom VoWiFi System 2.2.1 TD 92408EN Legacy Network Not Using Any 802.11n APs b/g a Comment Customer is running single radio APs. Most vendors single radio APs are using the b/g band. Data/Voice - Due to the limited amount of channels available, any WiFi device must share the airtime. Since voice requires a steady access to the media, it is important to minimize the impact of the other devices in the WLAN by changing the randomness of getting access to the channel. Standard 802.
System Planning Ascom VoWiFi System TD 92408EN b/g a Comment Voice (g) Data This allows the 2.4 GHz band to be dedicated to voice and all data clients, if possible, are moved to the a-band. 2.2.3 Customer Is Adding 802.11n APs and Is Also Keeping Old APs It is not uncommon that, when upgrading a b/g WLAN with a second radio for 5.0 GHz, new APs have to be installed (if there is no slot reserved in the AP for a second radio). Most modern APs include support for the 802.11n standard.
System Planning Ascom VoWiFi System TD 92408EN Customer buys new APs for the n-radio and keeps the old a/b/g dual radio APs intact. The customer adds n-supported APs across the complete site. b/g old AP a old+new AP Comment Voice + data (legacy) Data(HT) 20 MHz only Turn off the a-radio in the a/b/g APs. This leaves the old AP to support only b/g clients. 40 GHz only DFS+non DFS New APs set to use only the a-radio. HT only Greenfield mode.
System Planning Ascom VoWiFi System TD 92408EN b/g/n a/n Legacy data Voice 20 MHz + Voice and data are both on the a/n radio. Data (HT) Using 40 MHZ channels for data will reduce the amount of channels possible by half for the VoWiFi Handset. 40 MHz non-DFS Mixed mode Comment or Voice 20 MHz + Best combination is to move voice over to a/n. Data (HT) 20 MHz Mixed mode Legacy data Voice 20 MHz Data 20 MHz Note: Greenfield mode is not supported in the VoWiFi Handset. or 40 MHz Greenfield mode 2.
System Planning Ascom VoWiFi System TD 92408EN The following table lists the DFS and non-DFS channels on the 5 GHz band: Band Channel ETSI (EU/EFTA etc) FCC (US etc) UNII-1 36,40,44,48 Non-DFS Non-DFS UNII-2 52,56,60,64 DFS DFS UNII-2e 100,104,108,112, DFS 116,120,124,128, 132,136,140 DFS Note: 120, 124, 128 excluded.a UNII-3 149,153,157,161 Non-DFS ISM 165 a.
System Planning Ascom VoWiFi System TD 92408EN The 802.11n builds on the same frequency bands as the 802.11b/g and 802.11a radios and is designed to coexist with older clients. Legacy clients will use lower speeds than the 802.11n clients. To really benefit from 802.11n, a WLAN that utilizes the 802.11n enhanced standards should be configured for Greenfield mode. This means that no non-802.11n devices should be present in the coverage area.
System Planning Ascom VoWiFi System 2.5 TD 92408EN Battery Considerations 2.5.1 Speech Time and Standby Time Both the speech time and the standby time is greatly affected by the configuration of the network and the power save mode used. The standby time can be increased several times by following the instructions in chapter 10.4 Beacon Period on page 30 and 10.5 DTIM Interval on page 30. During a call, the power savings are significant with the VoWiFi Handset in U-APSD mode compared to Active mode.
System Planning Ascom VoWiFi System 3 TD 92408EN Wired LAN/Backbone Requirements There are several things to consider when designing a network for VoWiFi: In order to achieve optimal performance for VoWiFi, the wireless infrastructure should be connected to a switched network (that is, there are no hubs or repeaters). In a switched network the transmission delay should not be an issue, but if voice traffic is routed, a significant transmission delay could be added.
System Planning Ascom VoWiFi System 3.1.2 TD 92408EN IEEE 802.1q Priority Field The structure of the VLAN Tag defined in 802.1Q is illustrated in figure 1. Figure 2. VLAN Identifier (VID) Prirority Mark 8 7 6 5 4 3 2 Octets 1 1 8 7 6 5 4 3 2 1 2 002 = 1 Bit Figure 1. Structure of a VLAN Tag. Note: The use of the 802.1Q VLAN tag does not require an implementation of a full-blown VLAN system since by default all devices belong to the same VLAN and thus can communicate with each other.
System Planning Ascom VoWiFi System TD 92408EN Note: The 802.1p priority tag is likely not preserved if VLANs are not configured throughout the wired network. If the packets will travel across different subnets, the router configuration needs to cope with preservation of the 802.1p priority tag. Note: Any device that assigns QoS information to a data frame must be connected to a port in the LAN switch which is defined as a trunk port.
System Planning Ascom VoWiFi System 4 TD 92408EN Security Considerations The VoWiFi Handset can be configured to use various encryption and/or authentication schemes. The use of extensive encryption/authentication schemes can cause incidents of dropped speech during handover due to the time to process the authentication. No speech frames will be delivered to/from the VoWiFi Handset until the authentication is successfully completed. It is recommended to use WPA2.
System Planning Ascom VoWiFi System 5 TD 92408EN Basic Cell Planning Cell planning for traditional cordless telephony systems (DECT) deals with coverage and additional capacity reinforcement. Normally, a sufficient number of channels are available to plan the cells for frequency reuse at a distance large enough to limit the effects of cochannel interference. 2.4 GHz-radio b/g/n, VoWiFi Handsets IEEE 802.11 operation in the 2.
System Planning Ascom VoWiFi System TD 92408EN the cells, see figure 3. 4. Figure Figure 3. Cell overlap between adjacent cells The distance between the APs is often a trade-off between the amount of APs and coverage. To make up for fading effects in an indoor office environment it is recommended that the radio signal strength at the cell coverage boundary does not drop below -70 dBm. The APs should be placed to overlap their boundaries by approximately 6–10 dB.
System Planning Ascom VoWiFi System • TD 92408EN The lower the transmission rate, the more energy per bit is available at the receiver's detector. Thereby the transmission range is increased by lowering the transmission rate and thus the transmission will take longer. As an 802.11 STA moves away from an AP, the Tx rate is lowered in order to increase the range. This has effects on the capacity in the cell.
System Planning Ascom VoWiFi System TD 92408EN The VoWiFi network has to be designed in such a way that the adverse effect of these reflections is minimized. The MIMO feature used in the 802.11n standard utilizes more than one radio and one antenna at the same time. This allows the AP and STA to use multiple streams of data which are separated in the air by their phase because they have travelled different paths.
System Planning Ascom VoWiFi System 6 TD 92408EN Co-Channel Interference There are only three non-overlapping channels available in the 2.4 GHz band at 20 MHz which results in a high probability of channel re-use within a close proximity. In b/g/n 40MHz channels should be avoided in the 2.4 GHz band. With 40 MHz channel width, only one or two channels can be used in the WLAN system (depending on country regulations). Further, interference with neighboring WLANs is more likely due to increased coverage.
System Planning Ascom VoWiFi System TD 92408EN Even if APs that use the same channel are placed far away, there can be STAs present in the cells that are closer and thereby causing transmission interruptions, see figure 4 on page 23. 6. Figure Figure 4. CCA might cause problems even for far away STAs VoWiFi Handset a/b/g If the VoWiFi Handset detects an energy level that is stronger then -70 dBm or confirmed 802.11 traffic it will consider the air as occupied and not transmit.
System Planning Ascom VoWiFi System TD 92408EN transmissions. Therefore if they transmit at the same time, collision is likely to occur at the AP which will not be able to receive an error free frame from any of the two STAs. 7. Figure Figure 5. 2 STAs and an AP showing simultaneous transmission and collision The hidden node problem is accentuated when adjacent cells use the same channel. One common solution to this problem is to use Request-To-Send/Clear-To-Send (RTS/CTS).
System Planning Ascom VoWiFi System 7 TD 92408EN AP Placement for Optimal Performance There is a contradiction between the two essential requirements for optimal AP placement. Good performance requires good coverage, but “over-coverage” will reduce the performance. As described in 5 Basic Cell Planning on page 18, enough overlap between adjacent cells is needed in order to have sufficient radio signal strength at all places and enough margin when roaming between cells.
System Planning Ascom VoWiFi System TD 92408EN In a building with thick walls APs may be needed to be placed inside the rooms for optimal coverage. Then a placement of an AP in the walking path outside these rooms is recommended to minimize the amount of roamings, see figure 7 below. Note that if too many APs are placed in the corridor, the roaming problem is just moved to the corridor APs. 9. Figure Figure 7.
System Planning Ascom VoWiFi System 8 TD 92408EN Infrastructure Dependant Features 8.1 Automatic RF Adaptations in WLAN Systems Many WLAN infrastructures make use of an internal tool that is changing the AP channels and/or transmit power level in a dynamic way. The intention of the tool is to compensate for changes in the RF environments due to layout changes of furnishings and/or AP failure.
System Planning Ascom VoWiFi System 9 TD 92408EN Tools in the VoWiFi Handset There are a number of tools present in the VoWiFi Handset to assist in verification of a WLAN system deployment. For information on how to use the tools, see User Manual, Ascom i62 VoWiFi Handset, TD 92599EN. The basic set of tools includes: • • View with all APs and their corresponding RSSI. Possibility to filter APs based on SSID and/or channel Configurable range beep level 9 December 2011 / Ver.
System Planning Ascom VoWiFi System 10 TD 92408EN AP Configuration 10.1 Regulatory Domains - 802.11d IEEE 802.11d was developed to support the use of equipment across regulatory domains around the world without violation of local frequency rules.The 802.11d regulatory domain information is broadcasted in beacons and contains information on which channels and power levels that are allowed. Since this capability is broadcasted, no regulatory domain configuration is needed at the client side.
System Planning Ascom VoWiFi System TD 92408EN 10.4 Beacon Period A beacon is a periodic broadcast transmission from the AP to all STAs in the BSS.
System Planning Ascom VoWiFi System TD 92408EN 10.7 Recommended Settings 10.7.1 Basic Configuration b/g/n Item Recommended Settings Description Radio 802.11g With a g only network the stations do not need to use protection against b only stations. The transmission rate will be up to 54 Mbps. 802.11b/g Mixed mode where b only and g stations coexist will affect the g stations to use protection and the throughput will be decreased.
System Planning Ascom VoWiFi System TD 92408EN a/n Item Recommended Settings Transmitting power Set to match desired If the output power is reduced make sure the cell size. APs and clients are configured to use the same output power to avoid asymmetric communication link budgets. Refer to 10.6 Transmission Power on page 30. Radio channel UNII-1, UNII-3 Regulatory domain Enabled (802.
System Planning Ascom VoWiFi System TD 92408EN 10.7.3 Quality of Service Item Recommended Settings Description WMM Enablea Disabled QoS may work but there will be no guarantee for high voice quality. a. For the specific infrastructure, see the Interoperability Report. 10.7.4 Identifier Item Recommended Settings Description SSID Max. 32 char A unique identifier which stations use to associate with the AP.
System Planning Ascom VoWiFi System 11 TD 92408EN Known Problems b/g/n 802.11 operates in the 2.4GHz Industrial Scientific Medical (ISM) band. This band is unlicensed and many different wireless equipment uses this band with various radio techniques. As described in 6.1 Clear Channel Assessment, CCA on page 22, the CCA makes 802.11 equipment sensitive to other transmissions. This applies to all RF signals, not only other 802.11 equipment.
System Planning Ascom VoWiFi System 12 TD 92408EN Related Documents System Description, Ascom VoWiFi System TD 92313EN Function Description, Ascom VoWiFi System TD 92314EN Configuration Manual, Ascom i62 VoWiFi Handset TD 92675EN Data Sheet, Ascom i62 VoWiFi Handset TD 92587EN User Manual, Ascom i62 VoWiFi Handset TD 92599EN 9 December 2011 / Ver.
System Planning Ascom VoWiFi System 13 TD 92408EN Document History For details in the latest version, see change bars in the document. Version Date Description A 2006-05-24 First version B 2006-11-01 AP Configuration added C 2007-08-27 • Proactive key caching (opportunistic key caching) added to chapter 4 Security Considerations on page 17. • New information in chapter 10.6 Transmission Power on page 30.
System Planning Ascom VoWiFi System TD 92408EN Appendix A: Migration from i75 to i62 A.1 General When migrating from i75 to i62 VoWiFi Handsets, or having a site with mixed population of VoWiFi Handsets, there are certain SW versions that need to be compatible for a working installation. Below follows information of the needed SW versions for i62 and i75 VoWiFi Handsets. i62 VoWiFi Handset: i62 SW VoIP Gateway IMS3 UPAC Unite CM (Elise3) PDM 2.1.20 v.7HF15 2.
System Planning Ascom VoWiFi System A.5 TD 92408EN Interoperability i62 A.5.1 WLAN For information about the supported WLAN infrastructures for i62 please see the interoperability site on the Extranet; https://www.ascom-ws.com/AscomPartnerWeb/en/ startpage/Sales-tools/Interoperability/Verified-Products/ A.5.2 SIP On the IP-PBX side we will re-use our thoroughly tested and stable SIP/H.323-stack on i62 as we do on IP-DECT and i75.
System Planning Ascom VoWiFi System TD 92408EN This experience can be gained from installations performed, and from practical measurements done in different typical environments either in situ or in the lab, and should concentrate on the radio performance of a handset or laptop. The technician should also gain this knowledge by using different brands of the same client type in different environments.
System Planning Ascom VoWiFi System TD 92408EN The two handsets from Ascom are not to be considered as clients with the same performance profile. Both are branded with the Ascom logo but must be considered as two cousins in the Ascom family or as if they were phones from different vendors. A.6.
System Planning Ascom VoWiFi System TD 92408EN Due to the different characteristics of the handsets a complementary site survey and quality assessment must be done for the i62s, if the i75s and the i62s will be running on the same band using the same Voice SSID. This may lead to the need to change power levels of APs, add more APs and/or change the location of the APs placement. If the i62s will run in the 5GHz band, the WLAN needs two SSIDs.
