Welcome to our new
WiFi Ninjas Podcast episode!
We’re lucky again to get a chance to speak with a true legend! This time around we chat with Andrew McHale discussing some juicy voice design tips.
A
bit about Andy:
- Worked for Vocera for 8 years as an implementation engineer
- Assess Vocera Badge and smartphone performance on customer WLAN’s
- Part of Vocera’s internal Wireless Council
- Assessed hospitals, libraries, hotels, schools,
offices, and a superyacht for VoWLAN quality
- Assessed in Asia, Middle East, Europe, UK and
North America
Coverage:
- At least 1 access point at a minimum of -67dBm
everywhere.
- Ideally 2 access points greater than -67dBm
everywhere.
- Access points in corridors… Bad?
Avoid
DFS Channels:
- DFS channels add a LOT of time to scanning
Advertise
SSID in Beacons!
Channel
Plan:
- We used to cope with 3 – 4 channels in a very
crowded band
- 5GHz is a cleaner band
- Voice devices often scan all configured channels
- Europe/UK only has 4 non-DFS channels
- 36-64 if indoor only, 36-48 + 100-112 if
supporting outdoors
- Sharing is Caring – use 11k.
Channel
Widths:
- Use 20MHz Wide Channels
- Only using 8 channels (right…!), we can’t afford
to bond them.
- Voice doesn’t need 20MHz, let alone 40MHz.
- 5 SNR everywhere is challenging, why take a
3-6dBm Noise hit because you’re bonding channels.
PSK,
OKC or 11r:
- What do we want? FAST ROAMS! When do we want
them? EVERYTIME!
- Pre-shared key 4 way handshake is quick and
consistent
- What is quicker than PSK exchanges? No
exchanges!
- OKC/11r can save the client performing the full
re-auth
- DO NOT make a voice client perform RADIUS
authentication every time.
No
subnet roaming:
- 400ms is a quick DHCP exchange. No biggie right?
- Voice needs delay below 150ms.
- 400-800ms (DHCP) + 100-200ms (Roam) = sad faces!
- Ensure voice clients only perform DHCP at
Association
- Set lease renewal to an entire shift (8hr in
business, 12hr in Hospitality/Healthcare)
QoS
End-to-End:
- End-to-End QoS is hard.
- Suck it up buttercup, this is why you get the
big bucks!
- Peer-to-peer voice clients need it to avoid
downstream voice packets casually skipping along holding hands with Facebook
status updates…
AP
Power Levels:
- 2011 – “Please turn your AP’s Down,
they’re on Max power”
- Too much CCI
- 2019 – “Please turn your AP’s Up, they’re on Min
power”
- Too much roaming
- Put a leash on RRM.
- Don’t leave -125dBm/30dBm defaults, we’re better
than that.
Thanks
for listening and please don’t hesitate to leave a comment, feedback, subscribe
or follow us on social media.
Amazing interview. I’ve often thought much the same about DFS in certain situations!
Really good job guys, thanks for starting this adventure.
I think you should also upload these podcasts same time to youtube as well so your voice is not limited to WiFi guys.