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.

Comments are closed.

Stay up to date with the WiFi Ninjas
Never miss a blog or podcast again!