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Understanding the VoIP Wireless Network
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Contents

Understanding the VoIP Wireless Network

This chapter provides an overview of the interaction between Cisco Cius and other key components of a VoIP network in a wireless local area network (WLAN) environment.

This chapter comprises the following topics:

Understanding the Wireless LAN

With the introduction of wireless communication, Cisco Cius can provide voice and video communication within the corporate WLAN. Cisco Cius depends on and interacts with wireless access points (APs) and key Cisco IP telephony components, including Cisco Unified Communications Manager, to provide wireless voice communication. Cisco APs can run in standalone or unified mode. Unified mode requires the Cisco Unified Wireless LAN Controller.

Cisco Cius exhibits Wi-Fi capabilities that can use 802.11a, 802.11b, 802.11g, and 802.11n Wi-Fi.

The following illustration shows a typical WLAN topology that enables the wireless transmission of voice for wireless IP telephony.

Figure 1. WLAN with Cisco Cius

When Cisco Cius powers up, it attempts to associate with remembered networks if it is in range of those networks. If remembered networks are not within range, you can select a broadcasted network or manually add a network. For more information, see Configuring Wireless LAN.

The AP uses its connection to the wired network to transmit data and voice packets to and from the switches and routers. Voice signaling is transmitted to the Cisco Unified Communications Manager server for call processing and routing.

APs are critical components in a WLAN because they provide the wireless links or hot spots to the network. Cisco requires that APs supporting voice communications use Cisco IOS Release 12.4(21a)JY. For more information about APs, see the Cisco Cius Wireless LAN Deployment Guide.

Each AP has a wired connection to an Ethernet switch, such as a Cisco 3750 Series, that is configured on a LAN. The switch provides access to gateways and the Cisco Unified Communications Manager server to support wireless IP telephony.

Some networks have wired components that support wireless components. The wired components can comprise switches, routers, and bridges with special modules to enable wireless capability.

For more information about Cisco Unified Wireless Networks, see http://www.cisco.com/en/US/products/hw/wireless/index.html.

Understanding WLAN Standards and Technologies

802.11 Standards for WLAN Communications

Wireless LANs must follow the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards that define the protocols that govern all Ethernet-based wireless traffic. Cisco Cius supports the following standards:

  • 802.11a - Uses the 5 GHz band that provides more channels and improved data rates by using Orthogonal Frequency Division Multiplexing (OFDM) technology. Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) support this standard.
  • 802.11b - Specifies the radio frequency (RF) of 2.4 GHz for both transmitting and receiving data at lower data rates (1,2,5.5, 11 Mbps).
  • 802.11d - Enables access points to advertise their currently supported radio channels and transmit power levels. The 802.11d-enabled client then uses that information to determine which channels and power levels to use. Cisco Cius requires World Mode (802.11d) to determine which channels are legally allowed for any given country. For supported channels, see Table 1. Make sure that 802.11d is properly configured on the Cisco IOS Access Points or Cisco Unified Wireless LAN Controller. For more information, see the World Mode (802.11.d) and theCisco Cius Wireless LAN Deployment Guide.
  • 802.11e - Defines a set of Quality of Service (QoS) enhancements for Wireless LAN applications.
  • 802.11g - Uses the same unlicensed 2.4 GHz band as 802.11b, but extends the data rates to provide greater performance by using OFDM technology. OFDM is a physical-layer encoding technology for transmitting signals by using RF.
  • 802.11h - Provides DFS and TPC to the 802.11a Media Access Control (MAC).
  • 802.11i - Specifies security mechanisms for wireless networks.
  • 802.11n - Uses the radio frequency of 2.4 GHz or 5 GHz for both transmitting and receiving data, and enhances data transfer through the use of multiple input, multiple output (MIMO) technology, channel bonding, and payload optimization.

    Note

    Cisco Cius has a single antenna and uses the Single Input Single Output (SISO) system, which supports MCS 0 to MCS 7 data rates only (72 Mbps with 20 MHz channels and 150 Mbps 40 MHz channels). MCS 8 to MCS 15 can optionally be enabled if there are 802.11n clients utilizing MIMO technology which can take advantage of those higher data rates.

The following table lists the supported channels for Cisco Cius.

Table 1 Supported Channels for Cisco Cius

Part number

Band range

Available channels

Channel Set

-

2.412 - 2.472 GHz

13

1 - 13

5.180 - 5.240 GHz

4

36, 40, 44, 48

5.260 - 5.320 GHz

4

52, 56, 60, 64

5. 500 - 5.700 GHz

11

100 - 140

5.745 - 5.825 GHz

5

149, 153, 157, 161, 165


Note

802.11j (channels 34, 38, 42, 46) are not supported.

World Mode (802.11.d)

Cisco Cius uses 802.11d to determine which channels and transmit power levels to use and inherits its client configuration from the associated AP. Enable World Mode (802.11d) on the AP to use Cisco Cius in World Mode.

The following table lists countries and their 802.11d codes that Cisco Cius supports. For more information, see the Cisco Cius Wireless LAN Deployment Guide.

List of Countries and 802.11d Codes

Argentina (AR)

India (IN)

Poland (PL)

Australia (AU)

Indonesia (ID)

Portugal (PT)

Austria (AT)

Ireland (IE)

Puerto Rico (PR)

Belgium (BE)

Israel (IL)

Romania (RO)

Brazil (BR)

Italy (IT)

Russian Federation (RU)

Bulgaria (BG)

Japan (JP)

Saudi Arabia (SA)

Canada (CA)

Korea (KR / KP)

Singapore (SG)

Chile (CL)

Latvia (LV)

Slovakia (SK)

Colombia (CO)

Liechtenstein (LI)

Slovenia (SI)

Costa Rica (CR)

Lithuania (LT)

South Africa (ZA)

Cyprus (CY)

Luxembourg (LU)

Spain (ES)

Czech Republic (CZ)

Malaysia (MY)

Sweden (SE)

Denmark (DK)

Malta (MT)

Switzerland (CH)

Estonia (EE)

Mexico (MX)

Taiwan (TW)

Finland (FI)

Monaco (MC)

Thailand (TH)

France (FR)

Netherlands (NL)

Turkey (TR)

Germany (DE)

New Zealand (NZ)

Ukraine (UA)

Gibraltar (GI)

Norway (NO)

United Arab Emirates (AE)

Greece (GR)

Oman (OM)

United Kingdom (GB)

Hong Kong (HK)

Panama (PA)

United States (US)

Hungary (HU)

Peru (PE)

Venezuela (VE)

Iceland (IS)

Philippines (PH)

Vietnam (VN)

For the Cisco Unified Wireless LAN Controller, World Mode is enabled automatically when a country code is entered. See the 802.11d section in Cisco Cius Wireless LAN Deployment Guide for the proper country code. For Cisco Autonomous Access Points, World Mode must be enabled manually. Use the following commands: 

Interface dot11radio X
world-mode dot11d countryUS both

Note

For 2.4 GHz radio, enter 0 for X in the Interface Command field. For 5 GHz radio, enter 1 for X.

For more information, see the Models and Localization section in Cisco Cius Wireless LAN Deployment Guide.

Radio Frequency Ranges

WLAN communications use the following radio frequency ranges:

  • 2.4 GHz - Many devices that use 2.4 GHz can potentially interfere with the 802.11b/g connection. An interferer can produce a Denial of Service (DoS) scenario, possibly preventing successful 802.11 transmissions.
  • 5 GHz - The 5 GHz frequency provides more channels and has less interferers than the 2.4 GHz frequency. It is divided into several sections called Unlicensed National Information Infrastructure (UNII) bands, each with four channels. The channels are spaced at 20 MHz.

802.11 Data Rates Transmit Power Ranges and Decibel Tolerances

See the Radio Characteristics section in the Cisco Cius Wireless LAN Deployment Guide for Transmit (Tx) power capacities, data rates, ranges in feet and meters, and decibels tolerated by the receiver by 801.11 standard.

Wireless Modulation Technologies

Wireless communications use the following modulation technologies for signaling:

  • Direct-Sequence Spread Spectrum (DSSS) - Prevents interference by spreading the signal over the frequency range or bandwidth. DSSS technology multiplexes chunks of data over several frequencies so that multiple devices can communicate without interference. Each device has a special code that identifies its data packets and all others are ignored. Cisco wireless 802.11b/g products use DSSS technology to support multiple devices on the WLAN.
  • Orthogonal Frequency Division Multiplexing (OFDM) - Transmits signals by using RF. OFDM is a physical-layer encoding technology that breaks one high-speed data carrier into several lower-speed carriers to transmit in parallel across the RF spectrum. OFDM, when used with 802.11g and 802.11a, can support data rates as high as 54 Mbps.

The following table provides a comparison of data rates, number of channels, and modulation technologies by IEEE standard.

Table 2 Data Rates, Number of Channels, and Modulation Technologies by IEEE Standard

Item

802.11b

802.11g

802.11a

802.11n

Data rates

1, 2, 5.5, 11 Mbps

6, 9, 12, 18, 24, 36, 48, 54 Mbps

6, 9, 12, 18, 24, 36, 48, 54 Mbps

  • 20 MHz Channels: 7 - 72 Mbps
  • 40 MHz Channels: 15 - 150 Mbps

Channels

13

13

24

13 or 24

Wireless modulation

DSSS

OFDM

OFDM

OFDM

AP Channel and Domain Relationships

APs transmit and receive RF signals over channels within the 2.4 GHz or 5 GHz frequency band. To provide a stable wireless environment and reduce channel interference, you must specify nonoverlapping channels for each AP. The recommended channels for 802.11b and 802.11g in North America are 1, 6, and 11.


Note

In a noncontroller-based wireless network, Cisco recommends that you statically configure channels for each AP. Some channels may need to be statically configured if there is an intermittent interferer to avoid disruptions in that area. If your wireless network uses a controller, use the Auto-RF feature with minimal voice disruption.

For more information about APs, see the Configuring VoIP WLAN.

For more information about AP, channel, and domain relationships, see the Designing the Wireless LAN for Voice section in the Cisco Cius Wireless LAN Deployment Guide.

WLANs and Roaming

For information about WLANs and roaming for Cisco Cius, see Cisco Fast Roaming Application Note at: http://www.cisco.com/en/US/products/hw/wireless/ps4570/prod_technical_reference09186a00801c5223.html and the Roaming section of the Cisco Cius Wireless LAN Deployment Guide.

Related Information

Bluetooth Wireless Technology

Bluetooth enables low-bandwidth wireless connections within a range of 30 feet (10 meters). The best performance is in the 3-to 6-foot (1- to 2-meter) range. Bluetooth wireless technology operates in the 2.4 GHz band which is the same as the 802.11b/g/n band. There can be a potential interference issues with Bluetooth devices, microwave ovens, cordless phones, and large metal objects; therefore, Cisco recommends that you use 802.11a or 802.11.n that operates in the 5 GHz band.

For more information about configuring Bluetooth on Cisco Cius, see the Bluetooth Settings Menu Options. For more information about using Bluetooth headsets with your Cisco Cius, see Hands-Free Profile and the Bluetooth Configuration section of the Cisco Cius Wireless LAN Deployment Guide.

Components of the VoIP Wireless Network

Cisco Cius must interact with several network components in the WLAN to place and receive calls successfully. The following topics describe network components:

Interacting with Cisco Unified Wireless APs

Cisco Cius uses the same APs as wireless data devices. However, voice traffic over a WLAN requires different equipment configurations and layouts than a WLAN that is used exclusively for data traffic. Data transmission can tolerate a higher level of RF noise, packet loss, and channel contention than voice transmission. Packet loss during voice transmission can cause choppy or broken audio and make the phone call inaudible. Packet errors can also cause blocky or frozen video.

Because Cisco Cius users move from location to location, RF coverage needs to include stairwells, elevators, quiet corners, outside conference rooms, and passageways. To ensure good voice quality and optimal RF signal coverage, you must perform a site survey. The site survey determines what AP platform, antenna type, AP placement, Tx power levels, channel, and data rates are best for this environment. Ensure that all required areas are surveyed so adequate coverage is provided.

After deploying and using wireless voice, continue to perform postinstallation site surveys. When you add a group of new users, install more equipment, or stack large amounts of inventory, you are changing the wireless environment. A postinstallation survey verifies that the AP coverage is still adequate for optimal voice communications.


Note

Packet loss can occur during roaming; however, the security mode and the presence of fast roaming depicts how much packet loss occurs during transmission. Cisco recommends implementing Cisco Centralized Key Management (CCKM) to enable fast roaming.

For more information about Voice QoS in a wireless network, see the Voice QoS in a Wireless Network and the Quality of Service (QoS) section of Cisco Cius Wireless LAN Deployment Guide.

Associating to APs

At startup, Cisco Cius scans the channels for remembered profiles. Cisco Cius performs active scans (for remembered profiles) and passive scans (for broadcasted WLANs). Cisco Cius uses the Received Signal Strength Indicator (RSSI) variable to determine the best AP. RSSI measures the signal strength of available APs within the RF coverage area. Cisco Cius attempts authentication to a frequency band based on the 802.11 mode configuration for the discovered WLAN:

  • Auto - Cisco Cius connects to the AP with the highest RSSI value
  • 5 GHz - Cisco Cius associates with 5 GHz channels
  • 2.4 GHz - Cisco Cius associates with 2.4GHz channels

Cisco Cius associates with the AP with the highest RSSI that has matching SSID and encryption types. To ensure that voice traffic is handled properly, you must configure the correct QoS in the AP.

Related Information

Voice QoS in a Wireless Network

Voice and video traffic on the Wireless LAN, like data traffic, is susceptible to delay, jitter, and packet loss. These issues do not impact the data user, but have serious implications for a voice call. To ensure that voice traffic receives timely and reliable treatment with low delay and low jitter, you must implement QoS and use separate virtual LANs (VLANs) for voice/video and data. By isolating the voice and video traffic onto a separate VLAN, you can use QoS to provide priority treatment for voice and video packets when they travel across the network. Also, use a separate VLAN for data traffic, not the default native VLAN, which is typically used for all network devices.

Cisco recommends the following VLANs on the network switches and the APs that support voice and video connections on the WLAN:

  • Voice/Video VLAN - Voice traffic to and from Cisco Cius
  • Data VLAN - Data traffic to and from other wireless devices
  • Native VLAN - AP management

Assign separate SSIDs to the voice/video and to the data VLANs. If you configure a separate management VLAN in the WLAN, do not associate an SSID with the management VLAN.

By separating Cisco Cius devices into a voice VLAN and marking voice packets with higher QoS, you can ensure that voice traffic gets priority treatment over data traffic, resulting in lower packet delay and fewer lost packets.

Unlike wired networks with dedicated bandwidths, traffic direction is important for wireless LANs when implementing QoS. Traffic is classified as upstream or downstream from the AP as shown in the following illustration.

Figure 2. Voice traffic in a wireless network

Beginning with Cisco IOS release 12.2(11)JA, Cisco Aironet APs support the contention-based channel access mechanism called Enhanced Distributed Coordination Function (EDCF). The EDCF type of QoS has up to eight queues for downstream (toward the 802.11b/g clients) QoS. You can allocate the queues based on these options:

  • Differentiated Services Code Point (DSCP) settings for the packets
  • Layer 2 or Layer 3 access lists
  • VLANs for specific traffic
  • Dynamic registration of devices

Although you can have up to eight queues on the AP, Cisco recommends that you use only two queues for voice traffic to ensure the best possible voice QoS. Place voice (RTP) and signaling (SIP) traffic in the highest-priority queue, and place data traffic in a best-effort queue. Although 802.11b/g EDCF does not guarantee that voice traffic is protected from data traffic, you get the best statistical results by using this queuing model. The queues are:

  • Best Effort (BE) - 0, 3
  • Background (BK) - 1, 2
  • Video (VI) - 4, 5
  • Voice (VO) - 6, 7

Note

Call Control (SIP) is sent as UP4 (VI). Video is sent as UP5 (VI) when Admission Control Mandatory (ACM) is disabled for video (Traffic Specification [TSpec] disabled). Voice is sent as UP6 (VO) when ACM is disabled for voice (TSpec disabled).

The following table provides a QoS profile on the AP giving priority to voice, video, and call control (SIP) traffic.

Table 3 QoS Profile and Interface Settings

Traffic type

DSCP

802.1p

WMM UP

Port range

Voice

EF (46)

5

6

UDP 16384–32677

Interactive Video

AF41 (34)

4

5

UDP 16384–32677

Call Control

CS3 (24)

3

4

TCP/UDP 5060–5061

To improve reliability of voice transmissions, Cisco Cius supports the IEEE 802.11e industry standard and is Wi-Fi Multimedia (WMM) capable. WMM enables differentiated services for voice, video, best-effort data, and other traffic. However, in order for these differentiated services to provide sufficient QoS for voice packets, only a certain amount of voice bandwidth can be serviced or admitted on a channel at one time. If the network can handle N voice calls with reserved bandwidth, when the amount of voice traffic is increased beyond this limit (to N+1 calls), the quality of all calls suffers.

To help address the problems of VoIP stability and roaming, an initial Call Admission Control (CAC) scheme is required. With SIP CAC enabled on the WLAN, QoS is maintained in a network overload scenario by ensuring that the number of active voice calls does not exceed the configured limits on the AP. During times of network congestion, the system maintains a small bandwidth reserve so wireless phone clients can roam into a neighboring AP, even when the AP is at "full capacity." After reaching the voice bandwidth limit, the next call is load-balanced to a neighboring AP without affecting the quality of the existing calls on the channel.

Implementing QoS in the connected Ethernet switch is highly desirable to maintain good voice quality. The Class of Service (COS) and DSCP values that Cisco Cius sets do not need to be modified.


Note

The DSCP, COS and WMM UP markings correctly display for the optimum transmission of video frames. Cisco Cius does not support Voice and Video CAC; Cisco recommends that you implement SOP CAC.

Related Information

Interacting with Cisco Unified Communications Manager

Cisco Unified Communications Manager is the call control component in the network that handles and routes calls for the wireless IP phones, including Cisco Cius. Cisco Unified Communications Manager manages the components of the IP telephony system - Cisco Cius devices, access gateways, and the resources - for such features as call conferencing and route planning. When deploying Cisco Cius on a wireless LAN, you must use Cisco Unified Communications Manager Release 8.5 or later and the SIP protocol.

Before Cisco Unified Communications Manager can recognize a Cisco Cius device, it must register with Cisco Unified Communications Manager and be configured in the database. For information about setting up Cisco Cius in Cisco Unified Communications Manager, see the Configuring Cisco Cius in Cisco Unified Communications Manager and the Configuring Product-Specific Options.

You can find more information about configuring Cisco Unified Communications Manager to work with Cisco Cius and IP devices in the Cisco Unified Communications Manager Administration Guide, Cisco Unified Communications Manager System Guide, and Cisco Cius Wireless LAN Deployment Guide.

Security for Voice Communications in WLANs

Because all WLAN devices that are within range can receive all other WLAN traffic, securing voice communications is critical in WLANs. To ensure that voice traffic is not manipulated or intercepted by intruders, Cisco Cius and Cisco Aironet APs are supported in the Cisco SAFE Security architecture. For more information about security in networks, See http://www.cisco.com/en/US/netsol/ns744/networking_solutions_program_home.html.

This section contains the following items:

Authentication Methods

The Cisco Wireless IP telephony solution provides wireless network security that prevents unauthorized sign-in and compromised communications by using the following authentication methods:

  • WPA (Wi-Fi Protected Access)
  • WPA2 (Wi-Fi Protected Access 2)
  • WPA-PSK (Wi-Fi Protected Access-Pre-Shared Key)
  • WPA2-PSK (Wi-Fi Protected Access 2-Pre-Shared Key)

    Note

    WPA2-PSK appears as WPA/WPA2-PSK on Cisco Cius.

  • EAP-FAST (Extensible Authentication Protocol–Flexible Authentication via Secure Tunneling)
  • PEAP (Protected Extensible Authentication Protocol)

    Note

    EAP-FAST and PEAP are the 802.x options when choosing WPA/WPA2 via 802.1x EAP selection.

  • EAP-TLS (Extensible Authentication Protocol–Transport Layer Security)
  • PEAP-GTC/MSCHAPV2 (Protected Extensible Authentication Protocol–Generic Token Card/Microsoft Challenge Handshake Authentication Protocol Version 2)
  • CCKM (Cisco Centralized Key Management)

  • Note

    CCKM can be optionally used with WPA/WPA2.

  • WEP (Wired Equivalent Protocol)
  • Open

For more information about authentication methods, see the Wireless Security section in the Cisco Cius Wireless LAN Deployment Guide.

Encryption Methods

To ensure that voice traffic is secure, Cisco Cius supports the following encryption methods:

  • AES (Advanced Encryption Scheme)
  • TKIP/MIC (Temporal Key Integral Protocol/Message Integrity Check)
  • WEP (Wired Equivalent Protocol) 40/64 and 104/128 bit

For more information about encryption methods, see the Wireless Security section in the Cisco Cius Wireless LAN Deployment Guide.

Choosing AP Authentication and Encryption Methods

See the Wireless Security section in the Cisco Cius Wireless LAN Deployment Guide for a list of authentication and encryption schemes that Cisco Cius supports.

Related Information

Configuring VoIP WLAN

This section provides configuration guidelines for deploying Cisco Cius in the WLAN and contains these topics:

Supported Access Points

Cisco Cius is supported on both the Cisco autonomous and unified solutions. Minimum and recommended versions are:

  • Cisco IOS Access Points (Autonomous)
    • Minimum = 12.4(21a)JY
    • Recommended = 12.4(25d)JA or later
  • Cisco Unified Wireless LAN Controller
    • Minimum = 6.0.202.0
    • Recommended = 7.0.116.0 or later

See the Wireless Security section in the Cisco Cius Wireless LAN Deployment Guide for current AP recommendations.

Supported APs and Modes

See the Wireless Security section in the Cisco Cius Wireless LAN Deployment Guide for current AP recommendations.


Note

Voice over the Wireless LAN (VoWLAN) via Outdoor MESH technology (Cisco 1500 Series) is not supported.

Third-party access points are not fully supported or certified because no testing is performed to guarantee interoperability. However, if the access point is Wi-Fi compliant, basic interoperability should be available. Some features, such as CCX, and other key features, such as WMM, Unscheduled Auto Power Save Delivery (U-APSD), Dynamic Transmit Power Control (DTPC), proxy ARP, 802.11d, 802.11e, 802.11i, 802.11h, and CCKM may not be available.

Supported Antennas

See the Supported Antennas section in the Cisco Cius Wireless LAN Deployment Guide for a list of supported antennas.

Configuring Wireless LAN

Ensure that the Wi-Fi coverage in the location where the wireless is deployed is suitable for transmitting video and voice packets. See the Cisco Cius Wireless LAN Deployment Guide, which includes the following configuration sections:

  • Configuring Cisco Unified Communications Manager
  • Configuring the Cisco Wireless LAN Controller and Access Points
  • Configuring Cisco Cius

Before Cisco Cius can connect to the WLAN, you must configure the network profile for Cisco Cius with the appropriate WLAN settings. You can use the Network Setup menu on Cisco Cius to access the WLAN Setup submenu and set up the WLAN configuration. For instructions, see the Wireless and Network Settings Menu.

For information regarding troubleshooting WLAN, see the Troubleshooting WLAN.