Cisco Systems 7920 IP manual Numbers of 802.11b Phones per Layer 2 Subnet or Vlan

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All of the above calculations and design recommendations are based on VAD being disabled on the Cisco 7920 IP Phones. VAD is a mechanism in VoIP where no RTP packets are sent if no speech is occurring during the conversation.

VAD can be enabled on the Cisco 7920 phones and provides some bandwidth conservation, typically around 30 percent. With VAD enabled on the Cisco 7920, it does not use VAD for transmit (Tx) packets, but it understands what to do on the receive (Rx)−side if VAD is being used by the remote device (such as understanding the Service ID (SID) bit).

VAD is a global parameter on Cisco CallManager for all phones registered with a specific server or cluster. And the general design guidance for wired AVVID networks is to disable VAD because it can provide better overall voice quality. This means that unless the Cisco 7920 phones are going to register to a separate Cisco CallManager server than wired Cisco 79xx IP Phones, the VAD setting must be the same for all Cisco 79xx phones.

Beyond determining how much bandwidth is needed for an 802.11b VoIP call, consideration must also be made for the overall radio contention for a particular RF channel. The general rule is that no more than 15 to 25 802.11b end−points should be deployed per AP. As more end−points are added to an AP, the amount of overall bandwidth is reduced and transmission delays potentially increase.

The number of phones per AP is dependent on calling patterns of individual customers (Erlang ratios). Cisco Enterprise Solutions Engineering (ESE) recommends no more than seven calls (concurrent) using G.711, or eight calls (concurrent) using G.729. Beyond that number of calls, when background data is present, the voice quality of all calls becomes unacceptable.

Packetization rates for this testing were done with 20ms sample rates. This generates 50pps in each direction. VAD was disabled during the testing. Using large sample sizes (such as 40ms) could result in a larger number of simultaneous calls, but it also increases the end−to−end delay of the VoIP calls.

These testing results come from the creation of traffic simulating normal desktop traffic for 15 to 20 users (such as HTTP, FTP, Simple Mail Transfer Protocol (SMTP), Point of Presence (POP), Telnet 3270 (TN3270)), and then adding incremental Cisco 7920 phones. The number of Cisco 7920s phones added (with active calls) stopped when the Mean Opinion Scores (MOSs) dropped below the average MOS for G.711 or G.729 calls on the wired network.

Numbers of 802.11b Phones per Layer 2 Subnet or VLAN

The number of 802.11b phones that should be deployed per Layer 2 subnet or VLAN is dependent on the following factors:

∙No more than 30 APs should be deployed per Layer 2 subnet or VLAN. This is the recommendation to optimize memory and performance on the APs.

∙No more than seven (G.711) or eight (G.729) active calls should be deployed per AP.

∙The calling ratio used to determine active versus non−active calls. This is often determined using Erlang calculators.

Based on these factors, and normal business−class Erlang ratios (3:1 through 5:1), it is recommended not to exceed 450 to 600 Cisco 7920s per Layer 2 subnet or VLAN.

Note: The limitation of 30 APs per subnet or VLAN is introduced due to new functionality added to Cisco WLAN clients (such as PCs) and Cisco APs. The functionality is called Secure Fast Roaming, and introduces a new WLAN architecture that reduces the amount of time it takes a WLAN client to roam between APs. The

Cisco − Wireless IPT Design Guide for the Cisco 7920 IP Phone

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Contents Table of Contents Introduction PrerequisitesRequirements Wlan Overview Cisco 7920 IP Phone OverviewRF Overview Site Surveys and Design Recommendations Components UsedRssi VoIP QoS∙ Delay Variation Jitter Not to exceed 30ms Security for the Cisco 7920 and Wlan Networks Network Sizing Number of 802.11b Devices per APNumber of 802.11b IP Phones per AP Page Numbers of 802.11b Phones per Layer 2 Subnet or Vlan Understanding Roaming Terminology Understanding Layer 2 and Layer 3 RoamingLayer 2 Roaming Page Layer 3 Roaming VLANs Wlan QoS for VoIP Page Page Page Interconnecting WLANs to Cisco Campus Infrastructure Connecting APs to the Catalyst 3550 SMI or EMI Connecting APs to the Catalyst 2950 SI Connecting APs to the Catalyst 2950 EICaveats and Limitations Call Admission Control Designing Around the Lack of Layer 3 RoamingOther Caveats and Limitations Related Information

7920 IP specifications

The Cisco Systems 7920 IP phone represents a significant advancement in wireless communication technology, designed specifically for enterprises that require mobility and efficiency in their communication systems. This versatile device integrates seamlessly into a Cisco IP telephony network, allowing users to maintain connectivity while on the move, which is essential in fast-paced business environments.

One of the key features of the Cisco 7920 is its robust wireless capabilities. Operating on the IEEE 802.11b/g Wi-Fi standards, it provides a reliable connection to corporate networks, ensuring that users can access voice, data, and video services without being tethered to a desk. The phone supports dynamic call handling and features a responsive LCD display that enhances user interaction, making it easier to navigate menus and manage calls.

The Cisco 7920 also offers exceptional sound quality, thanks to its advanced audio technology. With Wideband audio support, users can experience clarity in conversations, which is particularly important in environments where clear communication is vital. The phone is equipped with noise-canceling capabilities that reduce background noise, allowing users to focus on their conversations without distractions.

Security is another critical aspect of the Cisco 7920. The device supports several security protocols, including WPA and WPA2, ensuring that all communications are encrypted and secure. This is crucial for organizations that handle sensitive information and need to comply with industry regulations.

Additionally, the Cisco 7920 features an extended battery life, enabling users to make calls throughout the day without frequent recharging. Its lightweight design and ergonomic build make it comfortable to use for extended periods.

In terms of integration, the Cisco 7920 IP phone is compatible with various Cisco Unified Communications Manager software versions, allowing for easy configuration and management within existing network infrastructures. Its support for multiple languages also makes it a suitable choice for international organizations, accommodating diverse user groups.

Overall, the Cisco Systems 7920 IP phone combines the necessary features, technologies, and characteristics to meet the demands of modern enterprise communication. Its blend of wireless capability, superior audio quality, security measures, and integration versatility makes it an excellent choice for organizations seeking efficient and reliable communication solutions.
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