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.

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