Issue 92
October 2015
When VoIP Fails:
'Breaking Up' is Hard to Undo
by William Flanagan, Publisher
There was a time when troubleshooting a voice problem was tedious
but well-defined. For an outage or "noise on the line" there
were standard procedures for test and repair. The technician
needed an analog "butt set" or resistance meter, seldom more.
When a Voice over IP connection is 'breaking up,' what's a tech to
do, just call your network administrator?
Start Right
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.
Watch Closely
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.
Flanagan Consulting Can Help You
We understand not only the technology of
networks, but also
the surrounding business processes:
procurement, bid
preparation/analysis, statements of work,
financial analysis,
consensus building around a solution, white
papers, and product
literature.
Find out more: call +1.703.242.8381
or email
Flanagan Consulting Supports Litigation Professionals
Several associates are experienced in analysis of
patents, trademarks,
contracts, and other intellectual property
related to IT and communications.
We have assisted attorneys preparing claims,
depositions, and testimony.
Queries to +1.703.855.0191.
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"Beware of
false knowledge; it is more dangerous than ignorance."
--George Bernard Shaw