2.After the IFS expires, the end point selects a value between 0 and aCWmin. The end point waits the length of this value and determines if the medium is available to transmit.

3.If the medium is available, the end point transmits the packets.

4.If the medium is unavailable (such as if another device sent a packet), the end point waits until the end of the packet transmission (from another device) and the IFS period. In addition, it doubles the value chosen in Step 2 and then attempts to transmit.

5.The end point continues to double the value from ￿b￿ until it either reached aCWmax or the packet is transmitted.

The following shows the growth in the random backoff range with retries:

For WLAN QoS, Cisco APs and Cisco 7920 phones use a technique similar to IEEE 802.11e, called Enhanced DCF (EDCF). EDCF is a model that allows end devices that have delay sensitive multimedia traffic to modify their aCWmin and aCWmax values to allow for statically greater (and more frequent) access to the medium. The following is an example of how EDCF works on Cisco WLAN devices:

By default, end points usually have aCWmin and aCWmax values of 31 and 255, respectively, for all data traffic. For VoIP traffic, Cisco APs and Cisco 7920s set the aCWmin and aCWmax to values of 3 and 31, respectively. This is equivalent to CoS of 6. Cisco IOS Software based APs can also vary the IFS (in addition to the aCWmin and aCWmax).

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

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Cisco Systems 7920 IP manual
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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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