WN Podcast 011 – Voice over WiFi with Andrew McHale

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.

2 comments on WN Podcast 011 – Voice over WiFi with Andrew McHale

  1. Aaron Lamey says:

    Amazing interview. I’ve often thought much the same about DFS in certain situations!

  2. 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.

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