October 11, 2005
Wireless LAN management - part 1
The convergence of voice and data enabled by VoIP is allowing companies to realize savings in telecom and operations and also reap productivity benefits. Wireless LANs, also known as Wi-Fi networks, are based on IEEE 802.11 are moving out of their traditional applications in warehouses and healthcare institutions and are becoming a part of the corporate world.
According to the Synergy Research Group, the proliferation of wireless LANs will be driven the growth of VoIP over wireless LAN (VoWLAN). It is expected to grow at a CAGR of 36% for the next five years. In a wireless network, the VoIP signals can get delayed due to multipath. In a radio-frequency (RF) medium, the obstacles in the path of a signal can lead to the signals arriving at the receiving end from more than one path.
Delays in handoffs that take place between wireless access points also affect signal quality. In an enterprise environment where cabling is either difficult or costly, wireless mesh backbone nodes offer an alternative. The cable connections to the hops between the nodes and from the APs to the Ethernet switches lead to an increase in the latency. Interference and the lack of synchronization between the hops can lead to frame corruption at the nodes. In order to avoid corruption, the frame contents are validated for every frame by means of running a checksum. A corrupt frame is retransmitted after a brief backoff.
Retransmission and delay are the main reasons for jitter in a wireless network and these affect its reliability.
Emerging 802.11 standards should help in prioritizing real-time traffic. However, given the variability inherent in a Wi-Fi network, achieving a high QoS may be a difficult proposition. There is always a possibility of a dead coverage spot or an AP becoming overloaded temporarily leading to poor signal strength. It is important that the network managers embed VoIP monitoring software into the wireless LAN network elements.
In a wireless network, the components that make up the LAN traversed by VoIP packets include wireless VoIP handsets, APs, wireless LAN switches, wireless LAN gateways, 802.11 nodes and routers.
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