One of the key aspects when calculating network capacity for 802.11b networks is that it is a shared medium. Because of this, consideration must be given for radio contention among the various devices. This means that the back−off algorithms in 802.11b, that allow multiple devices to access the medium, affect the overall throughput.

For the VoIP calculations below, a VoIP call has the following characteristics:

1.The packets are made up of a 20 byte IP header, an 8 byte UDP header, a 12 byte RTP header, and the RTP data.

2.The RTP data is a 20ms voice sample. For G.729, this is 20 bytes. For G.711, this is 160 bytes.

3.The total VoIP packet is 200 bytes of (IP+UDP+RTP) headers + RTP data. The 802.11 header (Layer 2 MAC) is 24 bytes long, so the total packet is 224 bytes.

4.RTP data is transmitted at 50 packets per second (pps) in each direction, or 100pps for a full−duplex conversation.

Looking at the 11Mb column of the chart, we can make the following calculations for G.711:

∙256 byte packet size = 2,596,588 bits per second = 324,573 bytes per second (Theoretical packet rate)

∙100 packets per second * 224 bytes per packet = 22,400 bytes per second (Bandwidth of a G.711 VoIP call)

∙324,573 / 22,400 = 14.489 calls (Theoretical maximum VoIP capacity per 802.11b channel)

∙14.489 * .6 = 8.69 calls (Theoretical maximum number of VoIP calls * 60 percent of the bandwidth)

Note: Sixty percent of the bandwidth is used to calculate the number of VoIP calls, which allows for the following:

♦It allows bandwidth to be available for data traffic.

♦It provides bandwidth consideration for 802.11b management traffic and acknowledgements.

The design consideration for G.711 calls is not to exceed seven concurrent VoIP calls per AP. This number has been proven in lab testing to provide acceptable voice quality.

The design consideration for G.729 calls is not to exceed eight concurrent VoIP calls per AP. This number has been proven in lab testing to provide acceptable voice quality.

Note: The following information affects Voice Activity Detection (VAD) configuration:

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

Page 7 Page 9
Page 8
Image 8
Cisco Systems 7920 IP manual
Page 7 Page 9

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.
Top Page Image Contents