There's seldom an easy answer for a VoIP sound quality problem. Here an ounce of prevention is worth a lot more than a pound of troubleshooting. In short, before putting VoIP on a network make sure that network can carry voice traffic properly.
Adequate Bandwidth. Local area networks running at 100 Mbit/s or a gigabit can carry dozens of voice calls. Even a 10 Mbit/s Ethernet is ample capacity for a small office. Access speed to the wide area network may present a bottleneck, particularly when shared with data-intensive applications.
Top Priority. A high quality VoIP connection depends
strongly on low latency and little if any packet loss. Short
voice packets get delayed if queued behind multiple long data
packets. Most routers can prioritize packets based on
criteria like subnet, vLAN, protocol, and application. Best
practice is to apply the top priority to voice for minimum delay
through all your internal networks.
Minimum Packet Loss. Voice packets sent quickly also face less chance of being discarded during congestion. Lost packets are a common cause of the 'breaking up' effect, starting at about 1% loss ratio. Missing information is not replaced by a retransmission because there is no time, which is why voice almost always travels on UDP and not TCP (which could retransmit a missing packet, but too late to be of use). So we fall back to the Human Understanding Helper protocol (Huh?).
When voice is sent to the WAN as IP packets, priority is
particularly important at the gateway router where the LAN speed
drops to a much lower rate. If your carrier supports class
of service markings, and your router is capable, mark voice
packets for better service than data (such as email and web
browsing) for the best end-to-end quality of service.
Network monitoring for voice quality can spot problems before they become user complaints. Several software products pull together information from routers, hardware probes, software agents, and applications on servers to estimate the user's perception of voice quality. There are standards to translate empirical measures (latency and packet loss) into approximate Mean Opinion Scores (MOS, the judgment of trained listeners).
When the quality measure falls below a threshold the alarm sounds and statistics point to possible causes. Don't have a dedicated voice quality monitor? Then the hunt gets harder.
Within an enterprise, the statistics on utilization, for example,
and logs of routers can point to sources of latency and places
where packets are dropped. Many vendors offer monitoring
software to simplify the job of keeping VoIP quality high.
The following table describes some examples.
Other names in management and monitoring for enterprise VoIP include Arbor Networks, Agilent Technologies, Dorado Software, eG Innovations, Fluke Networks, H-P, IBM, InfoVista, NetIQ, Opnet, Riverbed Technology, Savvius, SevOne, Viavi Solutions, and Zenoss. Carrier monitoring is a market segment which overlaps enterprises but isn't identical.When you're in a bind, there's always WireShark, the very sophisticated sniffer that can show what the traffic is doing (filtered for VoIP if desired) and decode most content.
All these monitoring tools typically fit the needs of network administrators and business managers. Alcatel-Lucent has an approach to push the first level of troubleshooting out to the consumer for self service. The Motive Customer Experience Manager, on a smart phone, detects and lists Wi-Fi access points and cell towers in the area, recommends radio channels to use, and alerts the user to problems like interference.
Every generation is comfortable with the latest technology. With 'friendlier' front ends on tools that monitor and manage the network, there will be less need to "Call your Network Administrator." We have seen the new NA, and he is us.
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