Mobility Loop


Originally published by Mobility Loop.

Reposted with permission.

Copyright 2006 Core Competence Inc.

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VoWiFi: Can You Hear Me Now?




Friday, September 30, 2005

Written by Lisa Phifer   

PhiferI recently interviewed several IS and network administrators responsible for voice-over-WiFi (VoWiFi) deployments. Adjusting WLAN footprint to meet voice needs was an issue for all -- no surprise there. But some mentioned that user expectations for VoWiFi are more comparable to cellular than landline telephony. In other words, we've all struggled with cellular blind spots, dropped calls, and less than "you can hear a pin drop" clarity. Should we simply expect more of the same from VoWiFi?

I hope not. I'm tired of spotty, noisy cellular. I'd like to see VoWiFi do better, particularly if the end game is one 3G/Wi-Fi handset that replaces all of my other phones. In my view, landline telephone network operators set the bar correctly for voice. I wouldn't settle for an office or home phone that was less than 99.9% reliable. Why should mobility make me lower that bar?

Sure, VoIP and Wi-Fi are both far less mature than telephone circuit-switching and transmission technologies. QoS capabilities like priority queuing and scheduled access (both defined by 802.11e) are still in their infancy. But end users don't care WHY call quality is poor. In the long run, for enterprise-scale VoWiFi to be truly successful, administrators will need to find coverage and performance problems BEFORE frustrated users lob their new-fangled Wi-Fi phones at helpdesk staff.

To be fair, many early VoWiFi adopters have delivered surprisingly good results to a handful of users. But low user density and absence of serious contention are common today. As VoWiFi deployments move from small trial to large-scale production mode, administrators will require insight into call performance to diagnose user complaints.

Wi-Fi phones, VoIP proxies/gateways, APs and wireless switches are all invaluable sources of diagnostic information. But LAN administrators long ago learned the importance of over-the-wire traffic analysis. Most carry an Ethernet analyzer in their toolbox to examine packets at points along the path between troubled systems.

WLAN administrators rely on similar tools for 802.11 trouble-shooting. Those portable tools capture Wi-Fi frames, helping to answer questions like "Why is this user not associating with that AP?" or "Is there RF interference in this spot?" Some WLAN analyzers can also generate 802.11 packets and/or associate with specific APs. But VoWiFi administrators will need more. They'll need to assemble 802.11 packets into VoIP streams to see Wi-Fi impact on call setup and real-time multi-media delivery.

Which brings me to WildPackets' release of AiroPeek VX, a VoIP-capable WLAN analyzer. I have used AiroPeek NX for several years and look forward to getting my hands on VX. VX is an upgrade to the AiroPeek platform. In VX, AiroPeek (NX) users will find many familiar capabilities, like WLAN network monitoring; 802.11 (RFMON) capture; 7-layer decodes; expert analysis of packet retries, errors, response time, throughput, and latency; TCP session and payload reconstruction; channel, signal, and node-level statistics; and graphs that can help visualize trends and relationships.

VX adds a new VoIP tab containing a slew of features for those running SIP, H.323, MGCP, MEGACO, SCCP, RTP, and/or RTCP VoIP protocols. VX can capture VoWiFi calls, providing drill-down analysis of each call and all associated media channels. Available quality metrics include bandwidth, jitter, loss, post dialing delay, answering delay, passive mean opinion score (PMOS), and R-Factor. Active calls can be viewed in real-time, and finished calls can be played back to assess jitter buffer impact on audio quality. Because call recording and decoding is resource-intensive, filters can be used to record only calls involving specific dialing/dialed numbers or to/from addresses.

Over-the-air VoWiFi analysis depends heavily (but not exclusively) on ability to "see" the VoIP protocols carried as 802.11 data frame payload. VoIP endpoints always have access to this payload, but data captured in transit may be obscured by encryption. AiroPeek VX can analyze WEP or TKIP/WPA-PSK encrypted data payloads when WEP keys or WPA Preshared Secrets are known. But those using AES/WPA2 encryption, 802.1X key delivery, or a secure tunneling protocol like IPsec will need to temporarily disable encryption to decode VoWiFi protocols, or analyze VoIP protocols after they are converted to cleartext on the wired network.

An 802.11/VoIP analysis and expert diagnostic tool like AiroPeek VX isn't going to solve VoWiFi problems. But I believe that such products will be needed to get a handle on call behavior and quality over the air. After all, it's not enough to know that you CAN'T hear me now -- tools that explain WHY will be essential to those who want to create robust VoWiFi networks.