As standards become more and more complex, there tend to be numerous options included which makes one wonder whether or a not a standard is really a standard.
Take the controversial IEEE P802.11n/D2.00 Draft for instance, which was recently questioned in an interesting blog at lovemytool.com. There are tons of options including the number of transmit and receive streams (i.e. MIMO operation), single or dual channel operation, various new data unit types, new ACKs, the list goes on.
Luckily, there are mandatory requirements as well as options. In fact, to obtain Wi-Fi Alliance 802.11n Draft 2.0 Certification, a device must implement a minimum set of mandatory capabilities specified in the IEEE draft. Specifically, a device must implement 2 spatial streams in transmit mode, 2 spatial streams in receive mode, the A-MPDU and A-MSDU, and block ACK. This simplifies things in that only a single 20 MHz channel in the 2.4 GHz band is required. These minimum mandatory requirements roughly double the raw data rate over 802.11g in a single channel. To gain the full benefit of 802.11n, a device may also implement the optional 40 MHz operational mode (that requires using the 5 GHz band in order to minimize interference with legacy b/g devices) as well as utilize additional spatial streams to boost throughput.
I would venture to say that a goal of the IEEE was to provide a minimal must-do set of requirements to gain at least some benefit over 802.11 b/g. Beyond the minimal requirements, options allow vendors and customers to boost throughput depending on their environmental and legacy requirements. This includes co-existence with2.4 GHz devices as well as optional deployment in the less-interference prone, albeit shorter-range 5 GHz band. The Wi-Fi Alliance will test these options as well, ensuring interoperability for vendors that choose to implement them. In fact, the majority of 2.0-certified devices to date support at least 3 spatial steams. In rough numbers, this gives us 150 Mbps for single channel operation, 300 Mbps for dual. I think the dual channel controversy (see 802.11n Going Enterprise?) will be put to rest especially in light of Cisco’s recent 802.11n equipment rollout for dual channel support in the 5 GHz band – the first to be Wi-Fi Alliance certified for that option.
Thank goodness we have organizations like the Wi-Fi Alliance to keep us on the straight and narrow.