I'd add to Frank's list: - Wave 2 won't increase spectral efficiency as much as initially projected. Expect 2x once most of the client radios are wave-2 11ac rather than the 4x that was being tossed around a year ago.
- Most, if not all, ac client devices will be 2-stream. - There's insufficient spectrum available to leverage 80MHz channels. Even if more spectrum becomes available in the next couple years, it will be years after that before a large enough percentage of client devices support those new channels for them to be useful. Add all this up and it is likely to be at least 5 years before you achieve Gbit on the wire to 802.11ac APs, and it may never happen. If you agree with this assessment, then there's no reason to rush into proprietary multi-gig edge switching. It seems wise to wait for an IEEE standard. Chuck Enfield Manager, Wireless Systems & Engineering Telecommunications & Networking Services The Pennsylvania State University 110H, USB2, UP, PA 16802 ph: 814.863.8715 fx: 814.865.3988 -----Original Message----- From: The EDUCAUSE Wireless Issues Constituent Group Listserv [mailto:[email protected]] On Behalf Of Frank Sweetser Sent: Tuesday, March 24, 2015 11:06 AM To: [email protected] Subject: Re: [WIRELESS-LAN] 1GBE as a bottleneck to APs? Personally, I'm not too worried about it. While naively adding up the wireless marketing sheets gets you to > 1Gb numbers, especially when treated with Wave 2 pixie dust, I think there are a few factors which make this a low concern. - The wireless numbers are half duplex, while that 1Gb wired connection is full duplex. This means that while your client bandwidth is probably going to be biased download more than upload, the upload and download packets that are bottlenecked through the common air time each have their own contention-free 1Gb channel once they hit the wired network. - Wireless throughput is *very* picky at top speeds. I've seen estimates that those magic wave 2 numbers won't be reachable more than a few meters away from the AP. - It only takes a few legacy clients hopping onto your nice new 11ac AP to drag you back down to a fraction of your peak throughput. Given how many budget laptops are being sold today with 2 stream, 2.4GHz only 11n adapters, this problem will be with us for a long time. Even if you do end up in a situation that legitimately needs over 1Gb, I'd be careful before relying on the LACP based solutions. Unless you're terminating your user sessions locally, all of the traffic will be going through an encapsulated tunnel between the AP and controller, which can easily end up hashing all of the traffic down one link. There are tricks to work around this (I believe Aruba opens up multiple tunnels with different endpoint IP addresses, for example), but this it's still an imperfect solution where 1 + 1 != 2. So my guess is that we have a few years before it's a major concern, and I'm waiting on a decent answer for 2.5Gb switching before I do any real investment in a solution. Frank Sweetser fs at wpi.edu | For every problem, there is a solution that Manager of Network Operations | is simple, elegant, and wrong. Worcester Polytechnic Institute | - HL Mencken On 3/24/2015 10:37 AM, Hinson, Matthew P wrote: > I've seen a few articles here and there regarding possible solutions > for "the gigabit bottleneck" as it pertains to .11ac access points. > Said solutions include Cisco's forthcoming protocols for 2.5G and 5G > over CAT5 cabling as well as LACP'ing two gigabit ports per switch and AP as some vendors suggest... > > My question for the group is: Has anyone actually seen a throughput > issue using gigabit to the edge? Certainly your distribution layer > gear could be a limitation if it's not specced correctly, but I've > just never seen a situation where I've wished for more than 1000BASE-T > to an AP. Our fastest 802.11ac access points can "only" hit > 600-700mbit/s real TCP throughput, and that's in ideal, almost laboratory conditions. > > Thoughts? > > Thank you! > > Matthew Hinson > > Network Operations > > ********** Participation and subscription information for this > EDUCAUSE Constituent Group discussion list can be found at > http://www.educause.edu/groups/. > ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/. ********** Participation and subscription information for this EDUCAUSE Constituent Group discussion list can be found at http://www.educause.edu/groups/.
