September 05, 2005
The planning required for implementing a wireless LAN service
Voice over wireless LAN (VoWLAN) is finding increased acceptance across vertical markets in the healthcare, retail, and warehousing industry. Deploying VoWLAN presents its own set of challenges, distinct from those presented by wired VoIP requirements. Low latency with minimum jitter, smooth hand-offs, coverage, and mobility are some of the requirements that need to be fulfilled. In a WLAN setup, the bandwidth is lower as compared to wired networks and there are several devices that compete for the same bandwidth. Consequently, radio frequency (RF) has to be used intelligently in order to minimize latency. This can be achieved by implementing a mechanism that regulates traffic and prioritizes voice traffic over data traffic, thereby ensuring QoS. Wireless multimedia extensions (WME) and Wi-Fi scheduled multimedia (WSM) are standards compliant protocols for prioritizing voice traffic. The prioritization has to work with IP-based prioritizations like DiffServ code point and 802.1p. Since wireless phones have to fulfill cost, mobility, and power consumption criteria, they do not have a very robust security and authentication system. In fact, a robust authentication system can lead to increased latency and hamper seamless roaming while shifting from one access point to another. By working in a virtual network, wireless phones can work in a secure domain without connecting to a voice gateway. VoWLANs work with 802.11b that offers a bandwidth of 11 Mbps; however, to utilize the bandwidth in optimum fashion it is important that the LAN be designed correctly. Factors such as location, risk of network failure, operational loads, etc affect the performance of the radios in a WLAN. RF management and load balancing should be used to control the interference with other radios in the vicinity and to handle the calls in busy areas more effectively. VoWLAN requires sufficient coverage in order to avoid dropped calls and therefore the installations should be used only for voice traffic and not for storing data. RF management should be able to plug any coverage gaps in case of AP malfunctions or redundant WLAN resources should be provided. VoWLANs should enable seamless connectivity to enable people to use their cell phones as well. A Layer 2 (VLAN) and a Layer 3 (IP) infrastructure support roaming. Roaming with Layer 2 is easy to execute but restricts the users whereas a Layer 3 service is non-restrictive but is not very easy to implement. Since VoWLAN roaming is effected with an IP infrastructure, a Layer 3 roaming is preferred. The performance of a VoWLAN with respect to roaming can be measured in terms of the scalability of roaming, amount of jitter at an access point coupled with a different controller, etc. Finally, it can be concluded that the success of VoWLAN depends upon the architecture of the WLAN and factors such as mobility, security, and coverage.
--
Did you enjoy this post?
« Know your wireless standards | Main | Wireless VoIP and savings in the office »
