Empirix Checks VOIP Call Quality Over Time

Hammer Call Analyzer IDs voice-specific problems.

Companies that have already taken the plunge and deployed voice over IP cannot depend solely on an upfront network assessment or prequalification for voice readiness throughout the life span of the voice deployment. Voice-analysis tools such as Empirix Inc.s Hammer Call Analyzer 1.6 will help organizations ensure call quality over time by identifying voice-specific problems throughout the network and by providing on-the-spot voice-quality assessments.

eWEEK Labs tested the software IP-only version of Hammer Call Analyzer 1.6, which started shipping this summer. Prices start at $9,900 for the software or $1,950 for a one-year subscription. Empirix also offers hardware-software solutions that support hybrid TDM (time-division multiplexing) and IP voice networks, albeit at substantially higher prices.

We used Hammer Call Analyzer 1.6 vigorously during our tests of ShoreTel Inc.s ShoreTel 6 VOIP solution , leveraging the tool to help isolate any signaling or call-quality issues we encountered as we deployed the ShoreTel network.

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We captured traffic in Normal mode, which shows live decode traffic during the capture, but we could also select Capture-Only mode for offline analysis, which is better for heavily congested network links.

It was a snap to set up capture triggers that started a capture upon detecting a certain event. We were impressed with the wide array of options to trigger on: We could select IP or MAC (media access control) addresses, different types of UDP (User Datagram Protocol) or TCP traffic, or various components of different call control standards, including SIP (Session Initiation Protocol), H.323 and MGCP (Media Gateway Control Protocol). Boolean command strings allowed us to set up complex multiexpression commands to trigger a capture event.

Like a standard network traffic analyzer, Hammer Call Analyzer 1.6s main console page displays a list of captured packets, allowing administrators to read the packet headers and payload content. Hammer Call Analyzer 1.6 leverages the WinPcap 3.0 Windows packet library for packet capture, so we could also import data culled from the WinPcap-based Ethereal network protocol analyzer tool.

From the Hammer Call Analyzer 1.6 console, we easily identified all VOIP calls found during a capture. From the call list, we could drill down to see a graphical representation of each data transaction throughout the entire flow, with each transaction time-stamped and diagrammed to help us understand its role in the call.

We could further drill down for media information particular to each call, including the codec used and detected jitter and packet loss. Based on these findings, Hammer Call Analyzer 1.6 presents a MOS (Mean Opinion Score) and R Factor (a component of the E Model of voice assessment) to provide call-quality assessment scores.

Administrators will find it easy to bring up the waveform screen to isolate and play back either or both sides of a call so that network technicians can experience the call as the original users did .

During testing with Hammer Call Analyzer 1.6, we noticed we could not gain a proper voice-quality assessment of calls within our ShoreTel network.

After some investigation, we discovered that we were using a 256K-bps codec that Hammer Call Analyzer 1.6 did not support. Nonetheless, Hammer Call Analyzer 1.6 was able to generate jitter and packet loss measurements. Hammer Call Analyzer 1.6 supports the G.711 A-law and u-law, G.729, G.723.1, and G.726 codecs.

Even when we enabled encryption on the ShoreTel system, we were able to cull important statistics on a monitored call from Hammer Call Analyzer 1.6, as well as retrieve a call-quality assessment score.

However, as expected, we were not able to play back the conversation; we were treated instead to an earful of static.

Technical Analyst Andrew Garcia can be reached at andrew_garcia@ziffdavis.com.

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