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For the phone to successfully operate as an endpoint in your network, your network must meet the following requirements:

• VoIP Network

  • VoIP is configured on your Cisco routers and gateways.

  • Cisco Unified Communications Manager (Unified CM) is installed in your network and is configured to handle call processing.

• IP network that supports DHCP or manual assignment of IP address, gateway, and subnet mask.

Devices with wireless capability can provide voice communication within the corporate WLAN. The device depends on and interacts with wireless access points (AP) and key Cisco IP Telephony components, including Cisco Unified Communications Manager (Unified CM) administration, to provide wireless voice communication.

The wireless phones exhibit Wi-Fi capabilities that can use 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, and 802.11ax Wi-Fi.

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

When a phone powers on, it searches for and associates with an AP if the device wireless access is set to On. If remembered networks are not within range, you can select a broadcasted network or manually add a network.

The AP uses the connection to the wired network to transmit data and voice packets to and from the switches and routers. Voice signaling is transmitted to the call control 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. In some WLANs, each AP has a wired connection to an Ethernet switch, such as a Cisco Catalyst 3750, that is configured on a LAN. The switch provides access to gateways and the call control server to support wireless IP telephony.

Some networks contain 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 https://www.cisco.com/c/en/us/products/wireless/index.html.

The phone must interact with several network components in the WLAN to successfully place and receive calls.

AP channel and domain relationships

Access points (APs) transmit and receive RF signals over channels within the 2.4 GHz, 5 GHz, or 6 GHz frequency band. To provide a stable wireless environment and reduce channel interference, you must specify nonoverlapping channels for each AP.

For more information about AP channel and domain relationships, see the Wireless LAN design section in the Cisco Wireless Phone 9821 deployment and connection guide.

AP interactions

Wireless phones use 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 can make the call inaudible. Packet errors can also cause blocky or frozen video.

Wireless phones users are mobile and often roam across a campus or between floors in a building while connected to a call. In contrast, data users remain in one place or occasionally move to another location. The ability to roam while maintaining a call is one of the advantages of wireless voice, so 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 settings that are suitable to wireless voice and assists in the design and layout of the WLAN; for example AP placement, power levels, and channel assignments.

After deploying and using wireless voice, you should 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.

For more information about Voice QoS in a wireless network, see the Cisco Wireless Phone 9821 deployment and connection guide.

AP association

At startup, the phone scans for APs with SSIDs and encryption types that it recognizes. The phone builds and maintains a list of eligible APs and selects the best AP, based on the current configuration.

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 end user, but can seriously impact a voice or video call. To ensure that voice and video traffic receives timely and reliable treatment with low delay and low jitter, you must use Quality of Service (QoS).

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

Unlike wired networks with dedicated bandwidths, wireless LANs consider traffic direction when implementing QoS. Traffic is classified as upstream or downstream relative to the AP as shown in the following figure.

The Enhanced Distributed Coordination Function (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:

• QoS or 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 up to eight queues on the AP can be set up, you should use only three queues for voice, video, and signaling traffic to ensure the best possible QoS. Place voice in the Voice queue (UP6), video in the Video queue (UP5), signaling (SIP) traffic in the Video queue (UP4), and place data traffic in a best-effort queue (UP0). Although 802.11b/g EDCF does not guarantee that voice traffic is protected from data traffic, you should 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

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

To improve reliability of voice transmissions in a nondeterministic environment, the device 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. 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.

Set up flexible DSCP

1. In Cisco Unified Communications Manager Administration, go to System > Service Parameters.
2. In Clusterwide Parameters (System - Location and Region), set Use Video BandwidthPool for Immersive Video Calls to False.
3. In Clusterwide Parameters (Call Admission Control), set Video Call QoS Marking Policy to Promote to Immersive.
4. Save your changes.

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. The wireless phones support the following standards:

• 802.11a: Uses the 5 GHz band that provides more channels and improved data rates by using 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 transmission and receipt of 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 the channels and powers to use. The phone requires World mode (802.11d) to determine which channels are legally allowed for any given country. For supported channels, see the table that follows. Ensure that 802.11d is properly configured on the Cisco IOS Access Points or Cisco Unified Wireless LAN Controller.

• 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 Orthogonal Frequency Division Multiplexing (OFDM) technology. OFDM is a physical-layer encoding technology for transmission of signals through use of RF.

• 802.11h: Supports 5 GHz spectrum and transmit power management. 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 transmission and receipt of data with speeds up to 150 Mbps, and enhances data transfer through the use of multiple input, multiple output (MIMO) technology, channel bonding, and payload optimization.

• 802.11r: Specifies requirements for fast secure roaming.

• 802.11ac: Uses the radio frequency of 5 GHz for both transmission and receipt of data with speeds up to 433 Mbps.

• 802.11ax: Capable of Wi-Fi 6 and 6E standard, supports HE0 to HE11 with data bitrate up to 600 Mbps.

For information about supported data rates, Tx power and Rx sensitivity for WLANs, see the Cisco Wireless Phone 9821 deployment and connection guide.

World mode (802.11d)

The wireless phones use 802.11d to determine the channels and transmit power levels to use. The phone inherits its client configuration from the associated AP. Enable World mode (802.11d) on the AP to use the phone in World mode.

Because all countries support these frequencies, you can attempt to scan these channels regardless of World mode (802.11d) support.

For more information on enabling World mode and 2.4 GHz support, see the Cisco Wireless Phone 9821 deployment and connection guide.

Enable World mode (802.11d) for the corresponding country where the access point is located. World mode is enabled automatically for the Cisco Unified Wireless LAN Controller.

Radio frequency ranges

WLAN communications use the following radio frequency (RF) ranges:

• 2.4 GHz—Many devices that use 2.4 GHz can potentially interfere with the 802.11b/g connection. Interference can produce a Denial of Service (DoS) scenario, which may prevent successful 802.11 transmissions.
• 5 GHz—This range divides into several sections called Unlicensed National Information Infrastructure (UNII) bands, each of which has four channels. The channels are spaced at 20 MHz to provide nonoverlapping channels and more channels than 2.4 GHz provides.
• 6 GHz—More available channels in 6G bands to deliver significantly lower latency and higher network capacity in dense, high-traffic environments. The bandwidth can be 20 M, 40 M, and 80 M. 80 M is highly reconmmended.

Because all WLAN devices that are within range can receive all other WLAN traffic, security of voice communications is critical in WLANs. To ensure that intruders do not manipulate or intercept voice traffic, the Cisco SAFE Security Architecture supports wireless phones and Cisco Aironet APs. For more information about security in networks, see https://www.cisco.com/c/en/us/solutions/enterprise/design-zone-security/index.html.

Cisco Wireless Phone 9821 supports three frequency bands—6 GHz, 5 GHz, and 2.4 GHz—enabling it to connect across these bands and providing interband roaming support. Cisco Wireless Phone 9821 support fast roaming 802.11k, 802.11v, 802.11r and legacy roaming.

For more information, see the Cisco Wireless Phone 9821 deployment and connection guide.

Cisco Unified Communications Manager (Unified CM) lets you integrate with different voice messaging systems, including the Cisco Unity Connection voice messaging system. Since you can integrate with various systems, you must provide users with information about how to use your specific system.

To enable the ability for a user to transfer to voicemail, set up a *xxxxx dialing pattern and configure it as Call Forward All to Voicemail. For more information, see Feature Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs or later.

Provide the following information to each user:

• How to access the voice messaging system account.

• Initial password for accessing the voice messaging system.

  Configure a default voice messaging system password for all users.

• How the phone indicates that voice messages are waiting.

  Use Cisco Unified CM to set up a message waiting indicator (MWI) method.