802.11ac Migration

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.

Hans-Dieter Wahl: WLAN Business Line Manager

Beyond Gigabit Ethernet on the LAN

Global communicationThe coming generation of enterprise Wi-Fi Access Points will allow higher than 1 Gbps sustained payload data rates between the radio interface and the wired network to which they are connected. For this reason, current LAN infrastructure, that is mostly Gigabit Ethernet over CAT5e cabling, will become the bottleneck on the LAN communications.

The alternatives to overcome this bottleneck are various, each one with its own advantages and pitfalls.

A first approach could be to move to 10 Gbps technology (10GBASE-T). This would solve today’s problem and would leave a guard gap for a mid-term increase of bandwidth needs. The problems of this approach are not only a higher cost of the infrastructure (Access Points and Switches) but mostly the need to replace current local cabling. Today over 85% of installations use CAT5e and CAT6 cables, (a classification of the LAN cables based on their quality or capacity for transmitting higher data rates), which are not able to support 10G speeds. To be more precise, CAT5e cables do not support 10G at all and CAT6 cables do support it, but only for cables up to 55 meters long, which are not enough for the majority of the cases.

Another alternative consists on the aggregation of two connections (cables) between the Access Point and the local switch. This option allows the use of today’s cheap Gigabit Ethernet switches but poses various drawbacks. That is, it requires to provision a second LAN cable to the Access Point (normally placed on hard-to-reach ceiling or wall locations), it also obliges to double the switch ports dedicated to the wireless infrastructure, and it requires to configure some level of “traffic aggregation” on the two connections between the access point and the local switch.

Ethernet at speed higher than 1 Gbps ?

Due to the limitations of the two previous approaches, a new alternative is emerging in the industry to eliminate the bottleneck. It consists on the use of Ethernet over a new physical layer, using the existing CAT5e and CAT6 cabling, that enables higher than 1 Gbps speeds.

This means that the current LAN cabling can be used to transmit Ethernet at speeds higher than 1 Gbps thanks to the use of a better physical-level transmission technology. In particular, 2.5 and 5 Gbps speeds are being considered. Besides the key objective of exceeding 1 Gbps, the new technology should also be backward compatible with 10/100/1000 remote peers (when one of the two sides of the connection still does not support the new technology) and should also support the different POE standards, to power the access point from the switch using the LAN cable.

NBASE-T ó MGBASE-T?

The main advantage of this new technology is that it does not require replacing existing LAN cables, although on the negative side, new switches or switch cards supporting the new technology are needed and also the cost of such switches and the access points will be more expensive on the first wave of products, due to the “early adoption” stage.

The industry is heavily pushing towards this solution, but the lack of previous standards and technology has fragmented the market into two different and incompatible “pre-standard” technologies. NBASE-T and MGBASE-T, backed by their corresponding non-profit organizations industry alliances, are fighting for market share and adoption. Technology (silicon) vendors and end–system vendors are aligning themselves into one or the other (or the two) groups.

As the saying goes, “prediction is very difficult, especially about the future” but eventually one of the two technologies will prevail or they will both merge into a single unified standard, although until then, interoperability is just not possible.

Eduardo Tejedor: