Hardware vs. software: does it matter?
I posed a number of questions last week about various attributes of spectrum analyzers and their relevance to how well your Wi-Fi network ultimately performs. In this sequel, I’ll address the first question and share some other folks’ views on the subject.
Does it matter if SA is hardware- or software-based?
Well, the answer can be indicative of the resolution/accuracy of the SA and how quickly it can detect and identify interference sources. It can also indicate whether SA causes a performance hit in APs that simultaneously serve traffic and monitor for interference sources. The implementation also affects the price and flexibility of the capabilities.
BACKGROUND: Are all spectrum analyzers created equal?
There are basically two camps here with Cisco on the hardware side and most others on the software side. Both groups make valid points.
In 2010, Qualcomm Atheros released chipsets to Wi-Fi makers that bundled the SA feature into them, thus the rush of SA support with software-based value-added features. Cisco, though, doesn’t use Atheros Wi-Fi chipsets as most of its competitors do. Rather, it embedded a custom digital signal processor (DSP) into its hardware and added another processor for each AP radio (one in the 2.4GHz band and on in the 5GHz band) along with 16MB of capture memory per radio to handle the SA function. Its SA implementation is called CleanAir, which runs in Cisco’s Aironet 3500 series of 802.11n APs.
Neil Deiner, technical leader for the office of the CTO in Cisco’s wireless networking business unit, indicates that the added horsepower afforded by hardware is necessary for the AP to avoid taking a performance hit when it is both serving traffic and running SA at the same time. When you enable competing software solutions, he says, “it fundamentally impacts baseline performance.”
Indeed, Aruba product manager Peter Lane acknowledged about a 5% throughput drop in cases “where you’re maxing out the throughput of the APs already.” Aerohive’s Matt Gast, director of product management, estimated the performance hit as closer to 30%; however, he recommends turning it on only when there’s a problem.
Nathan Rowe, senior manager of product planning at AirDefense, a part of Motorola Solutions, lauds Atheros for bringing the capability to commodity hardware.
“The value that you then bring is in the software for running SA everywhere. Users don’t have to make the decision upfront” as to whether to invest in the SA capabilities, as they do when they decide to pay a premium for Cisco’s 3500 APs or to buy Cisco APs without CleanAir.
Instead, with the software approach, “SA’s a capability they can turn on later. Higher resolution of spectrum data comes at quite a cost premium, and the market is very price sensitive right now,” Rowe says.
