Practicing Safe RX-SOP By Jacob Snyder (Holy Grail Edition)
About Jake Mobility Solutions Architect at Velaspan CCIE-W #43153 CWNE #161 ACMP/ACCP W7SNY @jsnyder81 www.todsfromds.com
What is RX-SOP? How does it... um... how does it work?
Receiver Start of Packet To receive a frame, or not receive a frame, that is the question. This decision is made during the preamble, decision is made on a single criteria (RSSI or SNR) Receiving frame: Frame is decoded and AP defers to incoming frame Not receiving frame: frame is discarded, and AP behaves as if it never heard the preamble. Frame becomes noise on channel and subject to the contention process
RX-SOP Analogy
RX-SOP Analogy
A Better Analogy
AP Cell AP Chan1 AP Chan6 AP Chan11 AP Chan1 How AP hears Client Other AP Signal AP Differs (CCI) -82 Default RX-SOP threshold
AP Cell AP Chan1 AP Chan6 AP Chan11 AP Chan1 How AP hears Client Other AP Signal No differing to Green -78 RX-SOP threshold -82 Default RX-SOP threshold
AP Cell AP Chan1 AP Chan6 AP Chan11 AP Chan1 How AP hears Client No differing to Green Other AP Signal SNR -78 RX-SOP threshold -82 Default RX-SOP threshold
Contention to Noise Interchange RX-SOP is the effect of trading contention on the channel into noise on the channel. Or the effect of trading contention for reduced SINR
RX-SOP Pro vs Con Pro Reduce congestion between cells Increase aggregate throughput Overcomes increased AP RX Sensitivity Con Raises noise floor Can be disruptive to clients Unidirectional, doesn t affect clients RX No differentiation between wanted and unwanted frames (Yet)
Types of RX-SOP 1. Cisco RX-SOP: RSSI Based 2. Cisco Meraki RX-SOP: RSSI Based 3. Aruba Cell Size Reduction: SNR based
Guidelines for RX-SOP Use RX-SOP to tune out adjacent cells on the same channel Do not attempt to affect clients connected to your cell with RX-SOP. Do not attempt to alter the effective cell size of an AP with RX- SOP. When in doubt, use less RX-SOP. It s a wall. A giant, brick wall. I ll do you for that
The RX-SOP Wall https://giphy.com/gifs/monty-python-holy-grail-cinematics-bt10ktczgwafg
Hitting the wall
Bring out your dead
Be wary of marketing https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-0/hdx_final/b_hdx_dg_final/ high_density_experience_features_added_in_release_8_0.html
RX-SOP Myth Myth: RX-SOP creates channel reuse Truth: RX-SOP converts contention to Noise
RX-SOP Myth Myth: RX-SOP Reduces how an AP hears Truth: RX-SOP changes at what level the AP that will decode something
RX-SOP Myth Myth: RX-SOP only impacts Data frames Truth: RX-SOP affects every frame an AP hears
RX-SOP Myth Myth: RX-SOP reduces cell size Truth: RX-SOP just limits how far the AP will decode frames.
Where RX-SOP Fits Channels Course Tuning Power Data Rates RX-SOP Fine Tuning
Working with RX-SOP Design, Design, Design Evaluate environment, before/after Test with actual devices.
Design Principals External Antennas: The single best thing you can do to enable safer use of RX-SOP. Good channel planning Reasonable TX power Understand how RRM/ARM methods are affected. (NDP Packets are affected by RX-SOP)
Delta between Clients/Neighbors Delta between Clients/Neighbors Slicing clients from Neighbors My Clients RSSI Adjacent Cell RSSI
Determine how much RX-SOP Determine how well APs hear clients (Debugs, pcaps, polling, telemetry) Determine how well APs heard neighbors (Debugs, pcaps, polling) Determine average MCS, Retry % and channel utilization Did you design for it?
Finding the sweet spot
Quantify RX-SOP impact Reduce static channel utilization Without increasing client retry rates (OTA Packet Capture) Without dramatic decrease client MCS rates (OTA Packet Capture, NMS) Without impacting client roaming times You are unable to see info on frames you aren t decoding
Moving Forward Today, RX-SOP is a single dimension (RSSI/SNR) Tomorrow 11ax, will use BSS color to add a second dimension
Thank you https://www.imdb.com/title/tt0071853/mediaviewer/rm1599872256