What is IEEE 802.11n, what are the advantages and challenges for 802.11n in Wi-Fi networks
What is IEEE 802.11n in Wi-Fi networks?
This is the new standard (protocol) which would be supported fully by IEEE very soon (Meaning currently there is only a ‘Draft n’ standard which can be upgraded to full n, once it is ratified) to give a higher bandwidth per access point (About 300 Mbps currently), to support a greater distance than the earlier standards like 802.11 a,b,g and hence allow us to get an enhanced network performance in wireless.
This is possible by a technology employed by 802.11n access points called MIMO. MIMO stands for Multiple In and Multiple Out which means that there are multiple radios inside the AP, all of which work together to maximise the throughput. The main features of MIMO in 802.11n are:
¤ There are three antennas and two spatial streams.
¤ Provides optional 40 Mhz channel which provides twice the data rates of a 20 Mhz channel.
¤ Uses Orthogonal Frequency Division Multiplexing (OFDM).
¤ It supports MAC aggregation: Packs small packets in to a larger frame. This reduces the number of frames and hence the time lost to contention for the medium. So, the throughput is increased.
¤ It supports Block acknowledgement: One acknowledgement signal for many frames (as opposed to each frame) and hence making it better for real time applications like video, voice etc.
Advantages of IEEE 802.11n in Wi-Fi networks:
¤ It provides increased bandwidth per access point : Currently, the draft-n specification supports up to 300 Mbps per access point (This is in ideal conditions, and the actual bandwidth may vary between 100 to 200 Mbps). Still, it is a huge jump from the 54 Mbps (26 Mbps, practically) supported by the nearest 802.11 a, g standards. This feature alone might become the game changer in the industry – especially given the fact that they would be supporting 600 Mbps in the very near future when the n standard is ratified fully. Wireless networks could become the primary networks for the edge – then. Of course, the bandwidth per access point is shared by approximately 15-20 computers, but still there is enough for everyone, considering the current requirements/applications of networks.
¤ The Access Points that support 802.11n standard covers roughly 1.5 times more distance than the earlier standard – 802.11g , per Access Point (802.11g gave about 30 meters indoor coverage and 100 meters outdoor coverage in the open. But you don’t necessarily keep one access point every 30 meters as the positioning depends on the number of concurrent connections to the access point, assured bandwidth per user, site conditions etc.).
¤ This standard works better with NLOS circumstances as multiple antennas can collect information from reflections from surfaces better. So, not only they support more distances, they also support a more uniform bandwidth over such distances.
¤ 802.11n is totally backward compatible. It can support 802.11a, b and g standards for connecting the legacy clients too. And it can work both on 2.4 Ghz and 5 Ghz radios. The specifications for this goes something like: 802.11 a/n and 802.11b/g/n. Dual radio is supported.
¤ Many new laptops come with built in adaptors for 802.11n (draft n) and it can also be added via an interface like USB etc.
¤ The draft-n specifications is expected to be fully compatible with the final n and most devices might just need a software upgrade to support the final version, with some more advancements. The draft-n is being promoted by the Wi-Fi alliance, to ensure interoperability for different vendors.
¤ Most of the features of the earlier standards like Radio Management, Wireless Multi Media, WPA2 encryption, Intrusion Detection etc. would work with 802.11n too. Some are supposed to be better.
Challenges facing 802.11n Wi-Fi deployments:
¤ The cost of each 802.11n access point is two to three times that of b/g access points. This is however expected to come down soon.
¤ While the operation of 802.11n in 5 Ghz is good due to the availability of more non-overlapping channels, it remains a challenge on 2.4 Ghz as this has only three non-overlapping channels and would be highly used by the other radios and neighboring access points. If the signature feature of 40 Mhz spectrum is used here, there would be overlapping.
¤ Power for the 802.11n AP’s don’t follow the earlier 802.3af, which is the standard for POE. While newer POE injectors are available to support the minimum 17 Watts (for three radios and two spatial streams), all the switches (with POE) and power injectors may not support this. Some vendors also offer to operate their access points in the earlier standard by switching off one of the radios, for a slightly degraded performance instead of totally powering off the AP’s in that case.
¤ If the wired back-end networking doesn’t support 10/100/1000 Mbps (perhaps only supporting fast ethernet – 10/100), then all the components, including cables (cat 6 cables are required for 1GE), patch panels, fiber interfaces, edge/core switches need to be 1GE enabled to realize the enhanced performance of 802.11n as every access point can easily utilize more than 100 Mbps.
¤ The 802.11n adaptors are available only in the clients shipped recently. Most of the earlier ones don’t support. That means they should also be upgraded. It is better to upgrade the earlier ones as the presence of more 802.11 b/g/a adaptors in the network brings down the performance of 802.11 n clients, as they reduce the effective capacity of the cell.
¤ The network planning for 802.11n access points is different from the network planning for earlier standards. The biggest challenge is to accommodate the earlier access points in a few ‘non-critical’ places in the network or discard them completely. A lot of companies have made huge investments in the older access points, which most of the time is sufficient for their applications.
¤ Controller should be able to support the higher bandwidth provided by 802.11n access points. But how ever it is vendor and model specific. So, for some installations, new controllers might be required too.
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I read your article about the advantages and challenges of 802.11n. My understanding of the IEEE Standard for 802.11n is that if a piece of equipment has this standard listed by the manufacturer as, part of their marketing data and included in their Manufacturer specification then, it should conform to all aspects of that that standard.
I purchased a laptop with that standard listed. The laptop however does not recognize the 5ghz bandwidth. It works fine on 2.4 GHz but will not access a 5 GHz wireless bandwidth network. I spoke to the Tech support people at both the Retail outlet where purchased and also to the Manufacturer of the laptop. They both say it is performing to the 802.11n standard. I have asked for a replacement or a refund and they refused either. They say it is doing what it is supposed to.
I am no expert but I believe that if a piece of equipment that lists the standard, and then it should conform to it. I cannot believe a manufacturer or retail outlet could be that misinformed about the 802.11n standard and how the equipment they are selling and promoting should perform. Set me straight on what to expect from a piece of equipment that says it conforms to the 802.11n Standard. Thanks for your response,
Who wrote this article? I need to reference it in a research paper i’m working on ,thanks