802.11n promises, and delivers, big bandwidth increases and significantly better coverage. For some organizations it is a must-have, but in many cases there is not a strong financial argument for a wholesale upgrade. While a few enterprises may actually be able to cost-justify a large investment in the technology, most will rely on qualitative measures to justify the investment. It is important to consider the costs and benefits of an 802.11n implementation.

The Hidden Costs and Challenges

Implementing 802.11n is not simply a matter of replacing Access Points (APs). Due to the increased bandwidth capacity and power requirements, it is possible that significant network upgrades will be necessary. With a theoretical maximum throughput of 300Mbps on most enterprise products, 10/100Mbps LAN infrastructure will not be sufficient to support the new APs. It will be necessary to upgrade at least some of the LAN infrastructure to support Gigabit Ethernet for the 802.11n APs.

In addition to the increased wired LAN prerequisite, powering the APs must be considered. The new APs draw more power than their 802.1a/b/g predecessors – in many cases more than the 15.4 Watt maximum delivered by the 802.3af Power over Ethernet (PoE) standard. The IEEE is working on the 802.3at standard – dubbed PoE Plus, with ratification expected in late 2008. As a result, 802.11n WLAN vendors have had to figure out ways around the power limitation. Vendors have taken different approaches to addressing the issue – Siemens HiPath and Aruba Networks have adapted APs to run on the existing 802.3af standard, while Cisco Systems has moved ahead with a proprietary solution called enhanced PoE (ePoE). Others have resorted to techniques such as dual-homed PoE connections to boost power.

Then there is the issue of a mixed client environment. Unless there is a plan to upgrade every client device to 802.11n, the WLAN will operate in a mixed client environment. This is not bad for 802.11a/g clients as these devices will reap the benefit of improved coverage, but will not experience speed enhancements. However, these devices will nominally reduce the overall speed of the network for 802.11n clients. On the other hand, 802.11b clients will kill the performance of any AP that sees them. Backward compatibility is a good thing, but when the practical throughput of an AP is reduced tenfold due to a legacy 802.11b client being connected, that can be a real problem. Disallowing 802.11b clients can be done, but if those 802.11b devices cannot be replaced and retired, there is absolutely no sense in upgrading to 802.11n.

The Benefits and Rewards

The theoretical throughput increase from 802.11a/g to 802.11n is almost six times (54Mbps to 300Mbps). In practice, the throughput increase will be approximately four times (20-25Mbps to 80-100Mbps). The speed improvement is realized by using a combination of techniques, including:

• Channel Bonding. By bonding the RF bandwidth of two channels together, throughput can be at least doubled. In the case of 802.11n, two 20MHz non-overlapping channels are bonded to create a single 40MHz channel, thus increasing throughput capabilities significantly.
• Multiple In Multiple Out (MIMO) Technology. Simply put, 802.11n APs and clients utilize multiple antennas to send and receive data. This allows for increased throughput at greater distances and more reliable connectivity.
• Packet Aggregation. This is a fairly complex technique, but the end result is reduced overhead and increased throughput.

In addition to increased throughput, 802.11n can cover a much larger footprint more reliably. In most cases, an 802.11n AP will cover an area 50% larger than an 802.11g AP (802.11a covers less area than 802.11g due to the higher frequency). This also makes the 5GHz frequency range much more viable than with 802.11a. There are a couple of benefits to using the 5GHz frequency – particularly the fact that it is much less crowded than the 2.4GHz frequency of 802.11b/g.

Recommendations

Upgrading the enterprise WLAN to 802.11n will make sense for some, but make sure the reasons for the upgrade are sound and the costs and benefits are weighted appropriately. Info-Tech recommends the following:

1. Assess the necessity. Determine if a significant bandwidth increase or better coverage is really necessary. For example, a hospital where doctors use the WLAN to access a PACS to view large images, or a school with a lot of users and a difficult campus to cover would be good candidates for an upgrade. For casual use in the enterprise, the existing WLAN is likely sufficient.

2. Consider all the costs. The cost of an enterprise grade 802.11n AP will be roughly $500. In addition, an upgraded central controller may be necessary. For a 100 AP 802.11n deployment, the cost will likely exceed $50,000. Adding in the potential costs of LAN infrastructure upgrades and additional PoE ports, the cost could escalate into six figures.

Bottom Line

With the IEEE 802.11n standard ratification date pushed out (again) to mid-2009, most enterprise WLAN vendors have decided to sell equipment based on the latest draft of the standard. The fact is that not every organization will benefit from an 802.11n implementation – carefully assess the benefits prior to investing in equipment based on the emerging standard.