The Cisco Wireless IP Phone 8821 and 8821-EX supports several industry-standard and Cisco network protocols required for voice communication. The following table provides an overview of the network protocols that the phones support.

The Cisco Wireless IP Phone 882x Deployment Guide contains useful information about the wireless phone in the Wi-Fi environment. You can find the deployment guide at this location:

https://www.cisco.com/c/en/us/support/collaboration-endpoints/unified-ip-phone-8800-series/products-implementation-design-guides-list.html

Access points (APs) transmit and receive RF signals over channels within the 2.4GHz or 5GHz 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 "Designing the Wireless LAN for Voice" section in the Cisco Wireless IP Phone 8821 Series Deployment Guide.

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.

Note	Packet loss occurs during roaming; however, the security mode and the presence of fast roaming determines how many packets are lost during transmission. Cisco recommends implementation of Cisco Centralized Key Management (CCKM) to enable fast roaming.

For more information about Voice QoS in a wireless network, see the Cisco Wireless IP Phone 8821 Series Deployment Guide.

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.

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

Note	The device marks the SIP signaling packets with a DSCP value of 24 (CS3) and RTP packets with DSCP value of 46 (EF).

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 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.

To help address issues with call quality, 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 limiting the number of active voice calls so as not to exceed the configured limits on the AP. During times of network congestion, the system maintains a small bandwidth reserve so wireless device clients can roam into a neighboring AP, even when the AP is at "full capacity." After the voice bandwidth limit is reached, the next call is load-balanced to a neighboring AP so as not to affect the quality of the existing calls on the channel.

The phones use TCP for SIP communications, and call control system registrations can potentially be lost if an AP is at full capacity. Frames to or from a client that has not been "authorized" through the CAC can be dropped, leading to call control system deregistration. Therefore, we recommend that you disable SIP CAC.

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.

Note	Enablement of World mode (802.11d) may not be necessary if the frequency is 2.4 GHz and the current access point is transmitting on a channel from 1 to 11.

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 IP Phone 8821 Series Deployment 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.

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.

The Cisco Wireless IP Telephony solution provides wireless network security that prevents unauthorized sign-ins and compromised communications through use of the following authentication methods that wireless phones support:

• WLAN Authentication

  • WPA (802.1x authentication + TKIP or AES encryption)

  • WPA2 (802.1x authentication + AES or TKIP encryption)

  • WPA-PSK (Pre-Shared key + TKIP encryption)

  • WPA2-PSK (Pre-Shared key + AES encryption)

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

  • EAP-TLS (Extensible Authentication Protocol – Transport Layer Security)

  • PEAP (Protected Extensible Authentication Protocol) MS-CHAPv2 and GTC

  • CCKM (Cisco Centralized Key Management)

  • Open (None)

• WLAN Encryption

  • AES (Advanced Encryption Scheme)

  • TKIP / MIC (Temporal Key Integrity Protocol / Message Integrity Check)

  • WEP (Wired Equivalent Protocol) 40/64 and 104/128 bit

Note	Dynamic WEP with 802.1x authentication and Shared Key authentication are not supported.

For more information about authentication methods, see the "Wireless Security" section in the Cisco Wireless IP Phone 8821 Series Deployment Guide.

The phones support the following certificates.

• X.509 digital certificate for EAP-TLS or to enable PEAP + Server Validation for WLAN authentication

• Simple Certificate Enrollment Protocol (SCEP) for certificate enrollment and auto-renewal

• 1024, 2048, 4096 bit keys

• SHA-1 and SHA-256 signature types

• DER and Base-64 (PEM) encoding types

• User Installed Certificate in PKCS #12 format (.p12 or .pfx extension), which also contains the private key

• Server (Root CA) Certificate with .crt or .cer extension

You install certificates on the phones in one of these ways:

• Use the Administration web page. For more information, see Cisco IP Phone Administration Page.

• Use an SCEP server to manage and install the certificates. For more information, see SCEP Setup

If your users set up their phones themselves and their phones need certificates, you need to give them the type of certificate when you give them the other configuration settings. If you don't use SCEP for certificate installation, then you need to install the certificates yourself.