ThinkstockPhotos-509029432802.11ac is a new wireless LAN standard for meeting the demands of higher bandwidth. This new standard is an update of the .11n standard and downward compatible to wireless LAN clients operating with older standards such as 802.11a/b/g/n. The new standard uses exclusively the 5 GHz frequency. Access Points supporting .11ac should therefore always be dual radio access points for using both 2.4 and 5 GHz.

In general, 802.11ac access points have two radio modules. One radio module supports clients which only have 2.4 GHz 802.11bgn. The other one is a 5 GHz 802.11ac radio module. This enables a smooth migration to the new standard without excluding older clients. Furthermore, the 802.11ac radio module is also compatible to previous clients supporting 802.11a/h (4 Mbit/s) or 802.11an. A mixed operation between 802.11a/h, 802.11an and 802.11ac clients is also possible.

Migrating a network towards .11ac

The following aspects have to be taken into account when converting a network to the 802.11ac standard.

Ethernet cabling and switches

Cabling and switches should have Gigabit standard in the LAN. Earlier versions such as 100Mbit/s should be replaced as these switches are already a bottleneck in 802.11n systems. Professional access points use 1Gbit/s LAN ports with full performance. Two Ethernet cables and a complex bundle of the two Ethernets within the switch are usually not necessary. Whether a Gigabit interface as an uplink is sufficient or a 10 Gigabit interface is necessary has to be decided individually.

Power supply

Business access points with .11ac standard MIMO 2×2 are recommended because they need less than 12.4 watts and can therefore operate according to the common 802.3af standard via PoE. 802.11ac access points with 3×3 or 4×4 MIMO are not recommended because these need up to 21 watts requiring the mandatory conversion of the PoE infrastructure to work correctly. Access points with 3×3 or 4×4 MIMO can in theory be installed on PoE switches with a 12.4 watt capacity, however the performance of these devices drop, as they would switch to an “emergency program mode” which would only allow them to use 2×2 MIMO. Moreover, 3×3 and 4×4 MIMO access points have higher electricity costs of up to 25€ per year.

Site survey

If the customer wishes to take a network that has currently been operating on the 2.4 GHz band and convert it to an .11ac 5 GHz network, then a new site survey would be necessary.

Channel planning

First of all, the channel bandwidth has to be determined. Every administrator tries to achieve the best performance from hardware and tends therefore to set up the best possible channel bandwidth (e.g.80 MHz). Nevertheless, in wireless LAN infrastructure with several access points, it has to be taken into account that the same radio channel can be used by several access points but you have to ensure that the field strength of the reused channel at the installed site of the access point is already low enough. To put it more simply: The access points using the same channel have to be far apart from each other.

Conclusion

Teldat’s current access points can be integrated without any problems in already existing installations, and even without large investments. Compared to access points with MIMO 3×3 or MIMO 4×4, Teldat’s devices with MIMO 2×2 have technological advantages. At this time, an investment of MIMO3x3 or MIMO 4×4 access points do not make sense yet because only few terminal devices support this technology. In particular, caution should be taken with low cost devices from the consumer market because these devices very rarely support DFS channels in the 5 GHz area which is extremely important for an .11ac installation, due to the shortage of channels available in the 5GHz network.


About the author

Hans-Dieter Wahl
WLAN Business Line Manager

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