That should read does not do DSCP.... Darn keyboard errors... On Sat, Sep 10, 2016 at 2:22 PM, Chuck Macenski <[email protected]> wrote:
> AirFiber prioritizes traffic based on the 802.1 VLAN tag priority bits. > Each of the priorities is sorted into unique MAC queues with the highest > priority queues supplying data first to the over-the-air multiplexed data > stream. That stream is then sent using a selective repeat ARQ mechanism - > the RF symbols carrying this traffic are encoded using FEC coding. AirFiber > does look at the IP header and thus does not do DHCP. > On the decoding side, the multiplexed data stream will not skip a missing > fragment - no packets from a given VLAN priority are ever delivered > out-of-order. The mean latency adder for fragment re-transmission is > roughly 1 - 1.5ms for a 2ms frame. This number varies based on the radio > type, configured frame length, and whether the link is half or full duplex. > > Chuck > > On Sat, Sep 10, 2016 at 10:20 AM, Ken Hohhof <[email protected]> wrote: > >> Oops, I mistakenly thought that was an update of this article: >> https://help.ubnt.com/hc/en-us/articles/205231970-airFiber- >> How-does-airFiber-handle-QoS-and-frame-prioritization- >> >> If I take that at face value, airFiber uses 802.1p but not DSCP. >> >> >> *From:* Mike Hammett <[email protected]> >> *Sent:* Saturday, September 10, 2016 10:00 AM >> *To:* [email protected] >> *Subject:* Re: [AFMUG] airFiber error correction >> >> airMax != airFiber >> >> >> >> ----- >> Mike Hammett >> Intelligent Computing Solutions <http://www.ics-il.com/> >> <https://www.facebook.com/ICSIL> >> <https://plus.google.com/+IntelligentComputingSolutionsDeKalb> >> <https://www.linkedin.com/company/intelligent-computing-solutions> >> <https://twitter.com/ICSIL> >> Midwest Internet Exchange <http://www.midwest-ix.com/> >> <https://www.facebook.com/mdwestix> >> <https://www.linkedin.com/company/midwest-internet-exchange> >> <https://twitter.com/mdwestix> >> The Brothers WISP <http://www.thebrotherswisp.com/> >> <https://www.facebook.com/thebrotherswisp> >> >> >> <https://www.youtube.com/channel/UCXSdfxQv7SpoRQYNyLwntZg> >> ------------------------------ >> *From: *"Ken Hohhof" <[email protected]> >> *To: *[email protected] >> *Sent: *Saturday, September 10, 2016 9:50:50 AM >> *Subject: *Re: [AFMUG] airFiber error correction >> >> According to the chart here, airFiber does prioritize based on DSCP tags >> (which are visible at layer 1): >> https://help.ubnt.com/hc/en-us/articles/205231750-airMAX-How >> -is-QoS-and-prioritization-handled-by-airMAX- >> >> Typically VoIP equipment would set DSCP on outgoing packets, and border >> routers would set DSCP on packets inbound to our network based on criteria >> like src or dst IP address. Then switches and bridges can prioritize based >> on those tags. >> >> airFiber doesn’t appear to be as sophisticated as some other products, in >> that you can’t configure the priorities, and the stats (at least in the >> GUI) are kind of meager. >> >> I’m mainly trying to determine if airFiber has an ARQ mechanism, the spec >> sheet doesn’t seem to mention error correction at all. I’m assuming the >> OFDM implementation has some form of forward error correction to monitor >> the error rate and adjust modulation and also for the coding gain. Whether >> it has FEC block coding or ARQ, I don’t know. Licensed backhauls typically >> don’t use ARQ because SNR is determined more by background noise than >> interference, plus ARQ requires buffering data until errored packets can be >> retried (assuming you still want to deliver packets in order), which >> impacts latency. I just don’t know if the airFiber designers applied the >> same thinking, given that it operates in unlicensed spectrum. >> >> >> *From:* Josh Reynolds <[email protected]> >> *Sent:* Saturday, September 10, 2016 9:09 AM >> *To:* [email protected] >> *Subject:* Re: [AFMUG] airFiber error correction >> >> >> Fixed delay jitter buffers are amazing things. >> >> That said, airfibers have NO IDEA what data they are sending. The >> management interface is aware of packets destined for it, and that's it. >> >> On Sep 10, 2016 9:07 AM, "Ken Hohhof" <[email protected]> wrote: >> >>> VoIP is UDP. Also latency variation or out-of-order packets are bad so >>> there is no retry mechanism at transport or application layer. So the >>> packet gets one chance for delivery, otherwise it gets dropped, and there >>> goes 10 ms of voice. >>> >>> airFiber already prioritizes packets based on COS and DSCP values, so >>> VoIP packets would typically be prioritized for example if DSCP=46. Plus >>> it’s fairly common to send beacons and retries at a lower modulation. So >>> all the pieces of the puzzle would seem to already be there. >>> >>> >>> *From:* Josh Reynolds <[email protected]> >>> *Sent:* Saturday, September 10, 2016 4:05 AM >>> *To:* [email protected] >>> *Subject:* Re: [AFMUG] airFiber error correction >>> >>> >>> For you first part, I don't know. >>> >>> For your second part, I have never heard of a feature like this - >>> normally that would be handled by TCP for most use cases and not a layer1 >>> device. >>> >>> On Sep 9, 2016 11:35 PM, "Ken Hohhof" <[email protected]> wrote: >>> >>>> I am going to assume airFiber has some sort of FEC, but does anyone >>>> know if it has a retry mechanism (ARQ)? And if it does have ARQ, what is >>>> the impact on latency, and can retries result in out-of-order packets? >>>> >>>> And has anyone ever heard of a manufacturer offering the option of >>>> having high priority latency sensitive traffic sent at a reduced modulation >>>> rate to insure it gets there the first time? >>>> >>>> >> > >
