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manual abstract
Technology Overview | HP Velocity
LiveWiFi
Wi-Fi is constrained for a number of technical reasons and, as a result, delivers a much lower network performance
experience than wired networks. High-end, consumer-grade Wi-Fi access points (APs) advertise that they are capable of
speeds of 300 to 450 Mb/s. In reality, Wi-Fi capacity is much lower than advertised.
• Distance (signal strength): The further away a Wi-Fi-enabled device is from the AP, the lower the signal strength,
which in turn lowers the effective available throughput.
• Noise from other devices: The most common frequency used for Wi-Fi is the 2.4 GHz band, which is also used for
household devices, such as cordless phones, baby monitors, and microwave ovens. Throughput is degraded if any of
these devices are used within range of a Wi-Fi network.
• Noise from other APs: There are only three non-overlapping channels that can be used by 2.4 GHz Wi-Fi. In areas with
a high density of APs, such as a city neighborhood or an office tower, it is likely that there are several other networks
using the same channel, leading to speed degradation.
• Older devices: If an 802.11n-enabled AP tries to connect to an older device that supports only 802.11b, the AP must
drop the supported speeds for everyone while the 802.11b device is operating. This significantly reduces the
throughput that 802.11n devices can achieve.
• Management overhead: Wi-Fi networks carry a significant amount of management overhead. As APs advertise their
presence, wireless clients must regularly probe the AP to notify it that they are still there. When there are a large
number of Wi-Fi devices present in a single location, the management overhead becomes excessive and the capacity
of the Wi-Fi network is reduced.
• Acknowledgments: All Wi-Fi packets must be acknowledged by the receiver to ensure successful delivery. These
acknowledgment packets are sent by a Wi-Fi device every time it receives a packet. When combined with the overhead
of protocols like TCP, this can result in three out of every four Wi-Fi packets becoming overhead packets, with only one
out of four packets containing useful data.
Figure 4: Wi-Fi overhead in a non-optimized flow
• Half duplex technology: A wired Ethernet network is full duplex, meaning that a device can send and receive, or upload
and download, simultaneously. Wi-Fi is half duplex; thus, if a client sends data to the AP, the AP cannot send data to
the same or any other client at the same time. For two-way communication, which includes most applications used
over the Internet, such as video or voice chat, this essentially halves throughput when compared to a full-duplex
technology.
• Retransmissions: Not all Wi-Fi packets are successfully received the first time they are sent. A client might not receive
a packet because of collisions or insufficient signal strength. A single bit error in a packet results in the retransmission
of the entire Wi-Fi packet, which might happen repeatedly for the same Wi-Fi packet.
• Wireless contention: When a client wants to send data and the channel is occupied, the client must wait, otherwise
collisions will occur and the data will be corrupted. Once the channel clears, the client must wait even longer before it
can attempt to send. Similar to trying to cross a single-lane bridge, if there are cars wanting to cross from both
directions, everyone must wait their turn and there is uncertainty about whose turn is next.
If a user on a wireless network is using large amounts of bandwidth through activities such streaming a video or
downloading a file, it is more difficult and takes longer for another device to send, even when performing a task that
requires very little data, such as checking email.
LiveWiFi addresses these issues using Wi-Fi prioritization and TCP over Wi-Fi.
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